Lecture 5
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Questions and Answers

What is the resulting embryonic phase at the end of blastulation in amphibian development?

  • A hollow ball of cells with a cavity (correct)
  • A stack of cell layers
  • A compact cluster of cells
  • A solid ball of cells

    • Where is the future dorsal side of the embryo located at the end of blastulation?

  • In the subgerminal cavity
  • In the gray crescent area
  • In the blastocoel
  • In the marginal zone (MZ) (correct)

    • What is formed before the epiblast and hypoblast in avian blastulation?

  • Epiblast and hypoblast
  • Massive cells that replace the blastodisc (correct)
  • Gastrula
  • Blastoderm and subgerminal cavity

    • What is the cavity between the epiblast and hypoblast called?

    <p>Blastocoel</p> Signup and view all the answers

    What happens to the blastoderm cells underneath?

    <p>They coalesce to form the hypoblast</p> Signup and view all the answers

    What is formed when the blastoderm cells absorb the fluid in the yolk underneath?

    <p>Subgerminal cavity</p> Signup and view all the answers

    What is the process that quickly transitions into gastrulation after avian blastulation?

    <p>Early gastrulation</p> Signup and view all the answers

    What is the term for the yellow part of the oocyte?

    <p>Yolk</p> Signup and view all the answers

    What is the primary function of cyclins and cyclin-dependent kinases in the cell cycle?

    <p>Regulation of cell division</p> Signup and view all the answers

    What is the term for the transition of cells from a layer of flat sheet cells to a cavity?

    <p>Ingression</p> Signup and view all the answers

    What is the function of selector genes in embryonic development?

    <p>Activation of morphoregulatory molecules</p> Signup and view all the answers

    What is the term for the spreading of cells caused by rapid cell division?

    <p>Epiboly</p> Signup and view all the answers

    What is the term for the in-pocketing of cells, resulting in the formation of a dorsal lip of blastopore?

    <p>Invagination</p> Signup and view all the answers

    What is the role of transcription factors in regulating gene expression?

    <p>Up-regulation or down-regulation of gene activity</p> Signup and view all the answers

    What is the term for the mass movement of cells, resulting in the formation of a new layer?

    <p>Involution</p> Signup and view all the answers

    What is the function of CAMs and SAMs in embryonic development?

    <p>Morphoregulatory molecules</p> Signup and view all the answers

    What is the term for the change in cell behavior, resulting in the formation of a new shape?

    <p>Change in cell shape</p> Signup and view all the answers

    What is the primary function of regulatory genes in embryonic development?

    <p>Regulation of gene expression</p> Signup and view all the answers

    What occurs if a cell is double layered?

    <p>It becomes single layered</p> Signup and view all the answers

    What is the term for the process where cells move inward to form an underlying layer?

    <p>Involution</p> Signup and view all the answers

    What is the direction of intercalation in convergent extension?

    <p>Perpendicular to the axis of extension</p> Signup and view all the answers

    What is the result of convergent extension on the dimensions of a sheet of cells?

    <p>Increase in one dimension and decrease in another</p> Signup and view all the answers

    What is the term for the process of tissue becoming thicker in the direction at right angles to the convergent extension?

    <p>Convergent thickening</p> Signup and view all the answers

    What is the term for the formation of the epiblast and hypoblast?

    <p>Delamination</p> Signup and view all the answers

    What type of migration strategy is used by primordial germ cells?

    <p>Ameboid migration</p> Signup and view all the answers

    What is the term for the movement of cells inward to form an underlying layer via bulk movement of cells?

    <p>Invagination</p> Signup and view all the answers

    What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?

    <p>Convergent extension</p> Signup and view all the answers

    What is the term for the splitting of a layer of cells, but not a literal split?

    <p>Delamination</p> Signup and view all the answers

    What is the primary difference between the blastocoel and the subgerminal cavity?

    <p>The blastocoel is formed by the splitting of the blastoderm, while the subgerminal cavity is not</p> Signup and view all the answers

    In which stage of development is polarity established in avians?

    <p>Early in development, before blastulation</p> Signup and view all the answers

    What is the main goal of gastrulation?

    <p>To establish the precursor of the digestive gut</p> Signup and view all the answers

    What is the term for the cells acquiring molecular cues that tell them where they are relative to the body axis?

    <p>Positional information</p> Signup and view all the answers

    What is the characteristic of the ectoderm and endoderm?

    <p>They are epithelial type with closely-packed cells and little ECM</p> Signup and view all the answers

    What is the term for the process of cells moving individually one after the other with a mass movement?

    <p>Migration</p> Signup and view all the answers

    What is the term for the precursor of the digestive gut?

    <p>Archenteron</p> Signup and view all the answers

    What is the characteristic of the blastopore?

    <p>It is the opening of the primitive gut</p> Signup and view all the answers

    What is the term for the process of laying down the three primary germ layers?

    <p>Gastrulation</p> Signup and view all the answers

    What is the term for the movement of cells during gastrulation that helps establish the precursor of the digestive gut?

    <p>Morphogenetic movements</p> Signup and view all the answers

    What type of migration involves neural crest cells and head mesenchyme?

    <p>Mesenchymal migration</p> Signup and view all the answers

    What regulates morphogenetic movements during embryonic development?

    <p>Gene activity</p> Signup and view all the answers

    What is the result of intercalation during embryonic development?

    <p>Convergent extension and convergent thickening</p> Signup and view all the answers

    What type of cells undergo change in cell shape and position during embryonic development?

    <p>Epithelial cells</p> Signup and view all the answers

    What is the process of programmed cell death during embryonic development?

    <p>Apoptosis</p> Signup and view all the answers

    What is the result of change in cell adhesiveness during embryonic development?

    <p>Cell sorting and tissue formation</p> Signup and view all the answers

    What is the type of migration that involves gastrulating cells moving inward?

    <p>Collective migration</p> Signup and view all the answers

    What is the function of CAMs and SAMs during embryonic development?

    <p>Cell adhesion and migration</p> Signup and view all the answers

    What is the process of cells leaving an epithelial sheet to become freely migrating mesenchyme cells?

    <p>Ingression</p> Signup and view all the answers

    What is the result of change in cell shape during embryonic development?

    <p>Formation of cavities</p> Signup and view all the answers

    What determines the shape of multicellular aggregates and the sorting order in heterotypic aggregates?

    <p>Cell-cell adhesion and cortex tension</p> Signup and view all the answers

    What is the function of SAMs (substrate adhesion molecules)?

    <p>Establishes structural integrity of cells with the surrounding matrix</p> Signup and view all the answers

    What is the characteristic of CAMs and SAMs?

    <p>Reversible adhesion, quick attachment/detachment</p> Signup and view all the answers

    What is the purpose of spatio-temporal gene expression of CAMs and SAMs?

    <p>To ensure gene products are available at the right time and place</p> Signup and view all the answers

    What is the process that regulates morphogenesis during development, adaptation, and regeneration?

    <p>Morphoregulation</p> Signup and view all the answers

    What is the function of E-cadherin?

    <p>Facilitate cell-cell adhesion in prospective epidermis</p> Signup and view all the answers

    What is the function of N-cadherin?

    <p>Facilitate cell-cell adhesion in prospective neural plate</p> Signup and view all the answers

    What is the term for morphoregulatory molecules that facilitate cell to cell contact?

    <p>CAMs (cell adhesion molecules)</p> Signup and view all the answers

    What is the result of the coordinated expression and function of CAMs, SAMs, and JAMs?

    <p>Activation of intracellular signaling cascades</p> Signup and view all the answers

    What is the role of CAMs, SAMs, and JAMs in development?

    <p>Provide an essential link between genetic and epigenetic mechanisms</p> Signup and view all the answers

    What is the main difference between the area opaca and area pellucida?

    <p>Area opaca is dark, while area pellucida is light in color</p> Signup and view all the answers

    What is the process by which cells fall off from the epiblast and enter the subgerminal cavity?

    <p>Ingression</p> Signup and view all the answers

    What is the structure formed by the thickening of cells at the posterior margin of the area pellucida?

    <p>Koller's sickle</p> Signup and view all the answers

    What is the term for the cavity formed between the epiblast and hypoblast?

    <p>Blastocoel</p> Signup and view all the answers

    What is the fate of the epiblast and hypoblast in avian development?

    <p>Epiblast forms the embryo proper, hypoblast forms extraembryonic membranes</p> Signup and view all the answers

    What is the term for the process by which the blastoderm cleaves to form the blastoderm?

    <p>Blastulation</p> Signup and view all the answers

    What is the significance of the primitive streak in avian development?

    <p>It forms the posterior end of the embryo</p> Signup and view all the answers

    What is the cavity that forms underneath the blastoderm?

    <p>Subgerminal cavity</p> Signup and view all the answers

    What is the term for the translucent region occupied by the blastoderm and subgerminal space?

    <p>Area pellucida</p> Signup and view all the answers

    What is the process by which cells from the lateral region of the posterior epiblast migrate towards the midline?

    <p>Formation of the primitive streak</p> Signup and view all the answers

    What is the primary function of CAMs and SAMs in embryonic development?

    <p>To control cell-to-cell adhesion and interaction</p> Signup and view all the answers

    What is the term for the process by which cells move inward due to lack of space?

    <p>Involution</p> Signup and view all the answers

    What is the role of the dorsal lip of the blastopore in amphibian gastrulation?

    <p>Site of cell turnover and migration</p> Signup and view all the answers

    What is the term for the interaction between cells and the extracellular matrix?

    <p>Cell-to-matrix adhesion</p> Signup and view all the answers

    What is the function of selector genes in embryonic development?

    <p>To code for transcription factors</p> Signup and view all the answers

    What is the term for the process by which cells change shape and move to form new structures?

    <p>Morphogenesis</p> Signup and view all the answers

    What is the role of fibronectin in amphibian gastrulation?

    <p>Providing contact guidance to migrating cells</p> Signup and view all the answers

    What is the term for the process by which cells spread and thin out?

    <p>Epiboly</p> Signup and view all the answers

    What is the function of the chordamesoderm in embryonic development?

    <p>Influence on neurulation</p> Signup and view all the answers

    What is the term for the cavity between the epiblast and hypoblast in avian blastulation?

    <p>Subgerminal cavity</p> Signup and view all the answers

    What is the function of fibronectin in avian gastrulation?

    <p>Guiding migratory behavior of cells from the epiblast</p> Signup and view all the answers

    What forms when the blastoderm cells migrate over the lips of the primitive streak and into the blastocoel?

    <p>Endoderm and mesoderm</p> Signup and view all the answers

    What is homologous to the dorsal lip of the blastopore?

    <p>Hensen's node</p> Signup and view all the answers

    What is the term for the movement of cells inward to form an underlying layer in avian gastrulation?

    <p>Ingression</p> Signup and view all the answers

    What is the result of the movement of cells towards the midline in avian gastrulation?

    <p>Formation of the primitive streak</p> Signup and view all the answers

    What is the function of hyaluronic acid in avian gastrulation?

    <p>Coating the ingressing cells and changing adhesive behavior</p> Signup and view all the answers

    What is the term for the cavity that forms between the epiblast and hypoblast?

    <p>Blastocoel</p> Signup and view all the answers

    What is the result of the regression of the primitive streak?

    <p>Formation of the head process</p> Signup and view all the answers

    What happens to the cells during the process of involution?

    <p>They undergo a change in shape and move inward</p> Signup and view all the answers

    What is the result of convergent extension on the dimensions of a sheet of cells?

    <p>It becomes narrower and longer</p> Signup and view all the answers

    What type of migration strategy is used by primordial germ cells?

    <p>Ameboid migration</p> Signup and view all the answers

    What is the term for the process of tissue becoming thicker in the direction at right angles to the convergent extension?

    <p>Convergent thickening</p> Signup and view all the answers

    What is the result of intercalation during embryonic development?

    <p>Convergent extension</p> Signup and view all the answers

    What is the process by which tissue elongates along the anterior-posterior (AP) axis and becomes narrower along the medio-lateral (ML) axis?

    <p>Convergent extension</p> Signup and view all the answers

    What is the term for the formation of the epiblast and hypoblast?

    <p>Delamination</p> Signup and view all the answers

    What type of cells undergo change in cell shape and position during embryonic development?

    <p>All of the above</p> Signup and view all the answers

    What is the term for the mass movement of cells rolling inward to form an underlying layer via bulk movement of cells?

    <p>Involution</p> Signup and view all the answers

    What is the direction of intercalation in convergent extension?

    <p>Perpendicular to the axis of extension</p> Signup and view all the answers

    What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?

    <p>Convergent extension</p> Signup and view all the answers

    What is the primary function of the main goal of gastrulation?

    <p>To establish the precursor of the digestive gut</p> Signup and view all the answers

    What is the characteristic of the ectoderm and endoderm germ layers?

    <p>They are epithelial type with closely-packed cells</p> Signup and view all the answers

    What is the term for the process of cells acquiring molecular cues that tell them where they are relative to the body axis?

    <p>Positional information</p> Signup and view all the answers

    What is the result of the movement of cells during gastrulation that helps establish the precursor of the digestive gut?

    <p>Formation of the primitive gut</p> Signup and view all the answers

    What is the characteristic of the mesoderm germ layer?

    <p>It is mesenchymal type with loosely-arranged cells</p> Signup and view all the answers

    What is the term for the process of cells moving individually one after the other with a mass movement?

    <p>Migration</p> Signup and view all the answers

    What is the primary function of the blastopore?

    <p>To form the opening of the primitive gut</p> Signup and view all the answers

    What is the term for the process of laying down the three primary germ layers?

    <p>Gastrulation</p> Signup and view all the answers

    What is the primary function of cell adhesion molecules (CAMs) during embryonic development?

    <p>To facilitate cell-to-cell contact and adhesion</p> Signup and view all the answers

    What is the main function of substrate adhesion molecules (SAMs) during embryonic development?

    <p>To facilitate cell-to-ECM contact and adhesion</p> Signup and view all the answers

    What is the term for the dynamic expression patterns of CAMs and SAMs correlated with cell fates during embryonic development?

    <p>Spatio-temporal gene expression</p> Signup and view all the answers

    What is the term for the process of morphogenesis during embryonic development regulated by CAMs, SAMs, and JAMs?

    <p>Morphoregulation</p> Signup and view all the answers

    What is the result of the coordinated expression and function of CAMs, SAMs, and JAMs during embryonic development?

    <p>Pattern formation and morphogenesis</p> Signup and view all the answers

    What is the role of CAMs and SAMs in regulating morphogenetic movements during embryonic development?

    <p>To facilitate cell-to-cell and cell-to-ECM adhesion</p> Signup and view all the answers

    What is the result of the dynamic expression of CAMs and SAMs during embryonic development?

    <p>Regulation of morphogenetic movements and pattern formation</p> Signup and view all the answers

    What is the function of CAMs in regulating cell behavior during embryonic development?

    <p>Facilitation of cell-to-cell adhesion and contact</p> Signup and view all the answers

    What is the result of the interaction between CAMs and SAMs during embryonic development?

    <p>Regulation of morphogenetic movements and pattern formation</p> Signup and view all the answers

    What is the primary mechanism by which CAMs and SAMs regulate morphogenetic movements during embryonic development?

    <p>Activation of intracellular signaling cascades</p> Signup and view all the answers

    What is the primary function of CAMs and SAMs in regulating morphogenetic movements during embryonic development?

    <p>To facilitate cell adhesion and migration</p> Signup and view all the answers

    What type of migration involves the movement of cells in a collective manner, often seen in gastrulating cells?

    <p>Collective migration</p> Signup and view all the answers

    What is the result of convergent extension on the dimensions of a sheet of cells?

    <p>The sheet becomes narrower in the direction perpendicular to extension</p> Signup and view all the answers

    What is the primary difference between the process of ingression and the process of intercalation?

    <p>Ingression involves the transformation of epithelial cells into mesenchyme cells, while intercalation involves the movement of cells between existing layers</p> Signup and view all the answers

    What is the role of genes in regulating morphogenetic movements during embryonic development?

    <p>They regulate the expression of CAMs and SAMs</p> Signup and view all the answers

    What is the characteristic of the cells that undergo change in cell shape and position during embryonic development?

    <p>They are epithelial cells</p> Signup and view all the answers

    What is the process of programmed cell death during embryonic development?

    <p>Apoptosis</p> Signup and view all the answers

    What is the result of change in cell adhesiveness during embryonic development?

    <p>Cells become more aggregated</p> Signup and view all the answers

    What is the type of migration that involves the movement of primordial germ cells?

    <p>Mesenchymal migration</p> Signup and view all the answers

    What is the role of neural crest cells in embryonic development?

    <p>They form the different ganglia of the body</p> Signup and view all the answers

    What is the primary function of genes coding for cyclins and cyclin-dependent kinases in the cell cycle?

    <p>To change the rate of cell division</p> Signup and view all the answers

    What is the result of the combination of epithelial-mesenchymal transition and the activation of genes coding for cyclins and cyclin-dependent kinases?

    <p>Epiboly</p> Signup and view all the answers

    What is the role of selector genes in regulating the expression of CAMs and SAMs during embryonic development?

    <p>To activate the expression of CAMs and SAMs</p> Signup and view all the answers

    What is the primary difference between the epithelial type and mesenchymal type of cells during embryonic development?

    <p>Epithelial cells undertake major morphogenetic movements, while mesenchymal cells undergo changes in cell behavior</p> Signup and view all the answers

    What is the result of the migration of cells during gastrulation?

    <p>The formation of the precursor of the digestive gut</p> Signup and view all the answers

    What is the function of transcription factors in regulating gene expression during embryonic development?

    <p>To regulate the activity of other genes</p> Signup and view all the answers

    What is the result of the change in cell adhesiveness during embryonic development?

    <p>Change in the ability of cells to migrate</p> Signup and view all the answers

    What is the function of CAMs and SAMs during embryonic development?

    <p>To regulate cell-cell and cell-substrate interactions</p> Signup and view all the answers

    What is the result of the epithelial-mesenchymal transition during embryonic development?

    <p>The change in cell behavior and cell shape</p> Signup and view all the answers

    What regulates morphogenetic movements during embryonic development?

    <p>Gene activity</p> Signup and view all the answers

    What is the primary function of CAMs and SAMs in morphoregulatory cycles?

    <p>To control cell-to-cell adhesion and interaction</p> Signup and view all the answers

    What is the result of changes in cell shape and movement during morphogenesis?

    <p>Changes in cell shape and movement drive morphogenesis</p> Signup and view all the answers

    What is the role of selector genes in morphoregulatory cycles?

    <p>To code for transcription factors that control CAMs and SAMs</p> Signup and view all the answers

    What is the function of fibronectin in amphibian gastrulation?

    <p>To provide contact guidance to migrating cells</p> Signup and view all the answers

    What is the result of involution in amphibian gastrulation?

    <p>Elongation of the embryo</p> Signup and view all the answers

    What is the term for the process of cells moving inward to form an underlying layer?

    <p>Involution</p> Signup and view all the answers

    What is the role of CAMs and SAMs in embryonic cell positioning?

    <p>To control cell-to-cell adhesion and interaction</p> Signup and view all the answers

    What is the outcome of the orchestration of the three morphogenetic movements in amphibian gastrulation?

    <p>Establishment of the body axis</p> Signup and view all the answers

    What is the function of the dorsal lip of the blastopore in amphibian gastrulation?

    <p>To provide a site for cell turnover</p> Signup and view all the answers

    What is the term for the mass movement of cells resulting in the formation of a new layer?

    <p>Epiboly</p> Signup and view all the answers

    What is the term for the site of cell turnover, which is a knot at the anterior end of the primitive groove?

    <p>Hensen's node</p> Signup and view all the answers

    What is the role of fibronectin in avian gastrulation?

    <p>Guides migratory behavior of cells from the epiblast</p> Signup and view all the answers

    What is the term for the cavity between the epiblast and hypoblast?

    <p>Blastocoel</p> Signup and view all the answers

    What is the process by which cells move inward to form an underlying layer during gastrulation?

    <p>Ingression</p> Signup and view all the answers

    What is the term for the structure that forms the scaffold for the formation of the CNS?

    <p>Notochord</p> Signup and view all the answers

    What is the term for the movement of cells towards the midline, resulting in the formation of the head process?

    <p>Convergent extension</p> Signup and view all the answers

    What is the term for the region occupied by the embryo?

    <p>Area pellucida</p> Signup and view all the answers

    What is the term for the process by which the blastoderm cells migrate over the lips of the primitive streak and into the blastocoel?

    <p>Ingression</p> Signup and view all the answers

    What is the term for the cells that move ventrally to form the foregut endoderm?

    <p>First migrating cells</p> Signup and view all the answers

    What is the term for the process by which the hypoblast is pushed to the sides and replaced by the ingressing cells?

    <p>Colonization</p> Signup and view all the answers

    What is the process by which the three primary germ layers are formed?

    <p>Trilaminar disc formation</p> Signup and view all the answers

    What is the role of the notochordal process in embryonic development?

    <p>Pick up point for neurulation</p> Signup and view all the answers

    What is the term for the translucent region occupied by the blastoderm and the subgerminal space?

    <p>Area pellucida</p> Signup and view all the answers

    Which structure forms at the expense of the subgerminal cavity?

    <p>Blastocoel</p> Signup and view all the answers

    What is the fate of the amniotic ectoderm and the rest of the hypoblast and trophoblast?

    <p>They contribute to the formation of the placenta</p> Signup and view all the answers

    What is the process that involves the falling off of cells from the epiblast into the subgerminal cavity?

    <p>Ingression</p> Signup and view all the answers

    What is the process by which the epiblast and hypoblast are formed?

    <p>Bilaminar germ disc formation</p> Signup and view all the answers

    What is the result of ingression of cells during trilaminar disc formation?

    <p>Formation of the embryonic endoderm and mesoderm</p> Signup and view all the answers

    What is the term for the dark region of the yolk that is still in close contact with the underlying yolk?

    <p>Area opaca</p> Signup and view all the answers

    What is the structure that forms from the thickening of cells at the posterior margin of the area pellucida?

    <p>Koller's sickle</p> Signup and view all the answers

    What is the relationship between the notochordal process and the axial mesoderm?

    <p>The notochordal process is the same as the axial mesoderm</p> Signup and view all the answers

    What is the direction of cell migration during the formation of the primitive streak?

    <p>From the lateral region towards the midline</p> Signup and view all the answers

    What is the result of the convergence of the epiblast and hypoblast at the margins of the area opaca?

    <p>Formation of the primitive streak</p> Signup and view all the answers

    What is the term for the process of cells sticking together to form the primary hypoblast?

    <p>Aggregation</p> Signup and view all the answers

    What is the role of the hypoblast during avian gastrulation?

    <p>Formation of the extraembryonic membranes</p> Signup and view all the answers

    What is the stage of development during which the primitive streak forms?

    <p>Gastrulation</p> Signup and view all the answers

    What is the primary goal of gastrulation?

    <p>To lay down the primitive gut</p> Signup and view all the answers

    What type of cells are ectoderm and endoderm?

    <p>Epithelial type</p> Signup and view all the answers

    What do cells acquire during gastrulation?

    <p>Positional information</p> Signup and view all the answers

    What is the characteristic of mesoderm cells?

    <p>They are loosely-arranged cells</p> Signup and view all the answers

    What is the term for the process of laying down the three primary germ layers?

    <p>Gastrulation</p> Signup and view all the answers

    What is the type of migration that involves neural crest cells and head mesenchyme?

    <p>Individually one after the other with a mass movement</p> Signup and view all the answers

    What is the result of intercalation during embryonic development?

    <p>Formation of a new layer</p> Signup and view all the answers

    What is the term for the precursor of the digestive gut?

    <p>Archenteron</p> Signup and view all the answers

    What is the primary mechanism of mesenchymal migration?

    <p>Amoeboid motion</p> Signup and view all the answers

    What is the result of convergent extension?

    <p>Convergent thickening</p> Signup and view all the answers

    What type of cells undergo change in cell shape and position during embryonic development?

    <p>Epithelial cells</p> Signup and view all the answers

    What is the process of programmed cell death during embryonic development?

    <p>Apoptosis</p> Signup and view all the answers

    What regulates morphogenetic movements during embryonic development?

    <p>Gene activity</p> Signup and view all the answers

    What is the result of change in cell adhesiveness during embryonic development?

    <p>Tissue formation</p> Signup and view all the answers

    What is the type of migration that involves neural crest cells and head mesenchyme?

    <p>Mesenchymal migration</p> Signup and view all the answers

    What is the function of SAMs (substrate adhesion molecules) during embryonic development?

    <p>Cell adhesion</p> Signup and view all the answers

    What is the process of cells leaving an epithelial sheet to become freely migrating mesenchyme cells?

    <p>Ingression</p> Signup and view all the answers

    What determines the shape of multicellular aggregates and the sorting order in heterotypic aggregates?

    <p>Cell adhesion molecules</p> Signup and view all the answers

    What is the primary function of CAMs and SAMs in morphogenetic cycles?

    <p>To control cell-to-cell adhesion and intercellular signaling</p> Signup and view all the answers

    What is the role of selector genes in embryonic development?

    <p>To specify cell fate and pattern formation</p> Signup and view all the answers

    What is the outcome of changes in cell shape and adhesiveness during embryonic development?

    <p>Cell migration and tissue formation</p> Signup and view all the answers

    What is the function of fibronectin in amphibian gastrulation?

    <p>To provide contact guidance to migrating cells</p> Signup and view all the answers

    What is the result of intercalation during embryonic development?

    <p>Cell elongation and shape change</p> Signup and view all the answers

    What is the role of the dorsal lip of the blastopore in amphibian gastrulation?

    <p>To guide cell movement and establish the anterior-posterior axis</p> Signup and view all the answers

    What is the primary reason for the difference in cell size between the animal hemisphere and the vegetal pole?

    <p>Impeded cell division due to the thick yolk in the vegetal pole</p> Signup and view all the answers

    What is the term for the mass movement of cells rolling inward to form an underlying layer?

    <p>Involution</p> Signup and view all the answers

    What is the function of the chordamesoderm in embryonic development?

    <p>To form the neural tube</p> Signup and view all the answers

    What is the result of convergent extension on the dimensions of a sheet of cells?

    <p>Decrease in width and increase in length</p> Signup and view all the answers

    What is the outcome of epiboly during amphibian gastrulation?

    <p>Cell spreading and thinning</p> Signup and view all the answers

    What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?

    <p>Convergent extension</p> Signup and view all the answers

    What is the function of CAMs and SAMs in cell-to-cell adhesion?

    <p>To facilitate cell-to-cell adhesion and intercellular signaling</p> Signup and view all the answers

    What is the primary difference between convergent extension and convergent thickening?

    <p>Direction of cell movement</p> Signup and view all the answers

    What is the result of involution during amphibian gastrulation?

    <p>Cell intercalation and rearrangement</p> Signup and view all the answers

    What is the term for the splitting of a layer of cells, but not a literal split?

    <p>Delamination</p> Signup and view all the answers

    What is the migration strategy used by primordial germ cells?

    <p>Ameboid migration</p> Signup and view all the answers

    What is the result of intercalation during convergent extension?

    <p>Change in cell shape and position</p> Signup and view all the answers

    What is the direction of intercalation in convergent extension?

    <p>Perpendicular to the axis of extension</p> Signup and view all the answers

    What is the primary function of convergent extension during embryonic development?

    <p>Shaping of the embryo</p> Signup and view all the answers

    What is the main function of cortex tension in multicellular aggregates?

    <p>To determine the shape of multicellular aggregates</p> Signup and view all the answers

    What is the function of CAMs (cell adhesion molecules) in embryonic development?

    <p>To facilitate cell-to-cell contact and adhesion</p> Signup and view all the answers

    What is the term for the process of cells acquiring molecular cues that tell them where they are relative to the body axis?

    <p>Pattern formation</p> Signup and view all the answers

    What is the role of SAMs (substrate adhesion molecules) in embryonic development?

    <p>To establish cell-to-ECM contact and adhesion</p> Signup and view all the answers

    What is the term for the process of cells moving inward to form an underlying layer via bulk movement of cells?

    <p>Invagination</p> Signup and view all the answers

    What is the function of morphoregulatory molecules in embryonic development?

    <p>To regulate morphogenesis during development</p> Signup and view all the answers

    What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?

    <p>Convergent extension</p> Signup and view all the answers

    What is the result of change in cell adhesiveness during embryonic development?

    <p>Change in tissue shape</p> Signup and view all the answers

    What is the function of E-cadherin in embryonic development?

    <p>To facilitate cell-to-cell contact and adhesion in prospective epidermis</p> Signup and view all the answers

    What is the term for the process of cells undergoing dynamic expression patterns correlated with cell fates?

    <p>Spatio-temporal gene expression</p> Signup and view all the answers

    What is the primary mechanism that drives epiboly?

    <p>Cell division and thinning of the epithelial sheet</p> Signup and view all the answers

    Which type of cells can undergo epithelial-mesenchymal transition during embryonic development?

    <p>Ectoderm, endoderm, and mesoderm cells</p> Signup and view all the answers

    What is the role of transcription factors in regulating gene expression during embryonic development?

    <p>To activate or deactivate gene expression</p> Signup and view all the answers

    What is the result of a change in cell adhesiveness during embryonic development?

    <p>Change in cell-cell interaction</p> Signup and view all the answers

    Which genes are responsible for regulating the expression of CAMs and SAMs during embryonic development?

    <p>Selector genes</p> Signup and view all the answers

    What is the term for the process of cells moving inward to form an underlying layer via bulk movement of cells?

    <p>Involution</p> Signup and view all the answers

    What regulates morphogenetic movements during embryonic development?

    <p>Gene activity</p> Signup and view all the answers

    What is the result of convergent extension during embryonic development?

    <p>Change in tissue dimensions</p> Signup and view all the answers

    What is the term for the process of cells leaving an epithelial sheet to become freely migrating mesenchyme cells?

    <p>Epithelial-mesenchymal transition</p> Signup and view all the answers

    What is the role of CAMs and SAMs during embryonic development?

    <p>To facilitate morphogenetic movements</p> Signup and view all the answers

    What is the term for the light area occupied by the blastoderm?

    <p>Area pellucida</p> Signup and view all the answers

    What is the process that occurs between the formation of the epiblast and the primary hypoblast?

    <p>Formation of the blastocoel</p> Signup and view all the answers

    What is the term for the dark area in close contact with the underlying yolk?

    <p>Area opaca</p> Signup and view all the answers

    What is the structure that forms at the posterior margin of the area pellucida?

    <p>Koller's sickle</p> Signup and view all the answers

    What is the term for the thickening of cells at the posterior margin of the area pellucida?

    <p>Koller's sickle</p> Signup and view all the answers

    What is the result of the convergence of the epiblast and hypoblast at the margins of the area opaca?

    <p>Thickening of cells</p> Signup and view all the answers

    What is the term for the process of cells falling off from the epiblast into the subgerminal cavity?

    <p>Ingression</p> Signup and view all the answers

    What is the term for the cavity that forms underneath the blastoderm?

    <p>Subgerminal cavity</p> Signup and view all the answers

    What is the result of the formation of the primary hypoblast and the secondary hypoblast?

    <p>Elongation of the hypoblast</p> Signup and view all the answers

    What is the term for the structure that designates the future posterior end of the embryo?

    <p>Primitive streak</p> Signup and view all the answers

    What is the purpose of Fibronectin in avian gastrulation?

    <p>Guiding migratory behavior of cells from the epiblast</p> Signup and view all the answers

    What is the outcome of cells moving anteriorly and forming the head process?

    <p>Overlying of the Hensen's node</p> Signup and view all the answers

    What is the significance of the primitive pit?

    <p>It is homologous to the blastopore</p> Signup and view all the answers

    What is the primary function of the epiblast in embryonic development?

    <p>To give rise to the embryonic ectoderm, endoderm, and mesoderm</p> Signup and view all the answers

    What happens to the hypoblast during avian gastrulation?

    <p>It gets pushed to the sides</p> Signup and view all the answers

    During trilaminar disc formation, what happens to the cells that ingress?

    <p>They form the embryonic endoderm and mesoderm</p> Signup and view all the answers

    What is the role of the notochordal process in embryonic development?

    <p>It is the pick-up point for neurulation</p> Signup and view all the answers

    What is the function of the notochord?

    <p>To provide an axial skeleton for the formation of the CNS</p> Signup and view all the answers

    What is the outcome of cells moving ventrally?

    <p>Formation of the foregut endoderm</p> Signup and view all the answers

    What is the result of bilaminar germ disc formation?

    <p>The formation of the epiblast and hypoblast</p> Signup and view all the answers

    What is the term for the area occupied by the embryo?

    <p>Area pellucida</p> Signup and view all the answers

    What is the fate of the amniotic ectoderm and the rest of the hypoblast and trophoblast?

    <p>They contribute to the formation of the placenta</p> Signup and view all the answers

    What is the significance of the primitive streak in embryonic development?

    <p>It is where the ingression of cells will occur</p> Signup and view all the answers

    What is the role of Hyaluronic acid in avian gastrulation?

    <p>Coating the ingressing cells and changing adhesive behavior</p> Signup and view all the answers

    What is the characteristic of the proamnion?

    <p>It is devoid of mesenchyme</p> Signup and view all the answers

    What happens to the Hensen's node during avian gastrulation?

    <p>It moves posteriorly</p> Signup and view all the answers

    Study Notes

    Amphibian Blastulation

    • At the end of blastulation, the resulting embryonic phase is a hollow ball of cells with a cavity called the blastocoel.
    • The future dorsal side of the embryo is established at the end of blastulation, residing in the previous position occupied by the gray crescent area.

    Avian Blastulation

    • At the end of blastulation, a resulting stack of cell layers is formed: the epiblast and hypoblast.
    • The blastoderm is formed from the cleaving blastodisc, which eventually splits into the epiblast and hypoblast.
    • This marks the start of the early phase of gastrulation.

    Blastulation Components

    • Blastoderm: a layer of cells that looks like a black spider.
    • Hypoblast: a layer of cells that forms when blastoderm cells underneath fall off and coalesce.
    • Epiblast: a layer of cells that forms when the hypoblast splits.
    • Blastocoel: the cavity between the epiblast and hypoblast.
    • Subgerminal cavity: the cavity underneath the blastoderm, formed when the blastoderm cells absorb the fluid in the yolk.

    Mammalian Blastulation

    • At the end of blastulation, two distinct populations of cells are generated: the inner cell mass (ICM) and the tropoblast or trophectoderm, along with the blastocoel.
    • The embryo proper has not yet formed in the ICM, and polarity is not yet established in mammalian development.

    Gastrulation

    • The most remarkable developmental landmark of early gastrula is the formation of the dorsal lip of the blastopore.
    • Gastrulation involves the laying down of the three primary germ layers: ectoderm, endoderm, and mesoderm.
    • The main goal of gastrulation is to establish the precursor of the digestive gut, called the primitive gut or archenteron.

    Morphogenetic Movements

    • Invagination: the inpocketing of cells to form a blastopore.
    • Epiboly: the spreading of cells, driven by mitosis.
    • Involution: the mass movement of cells rolling inward to form an underlying layer.
    • Convergent extension: the intercalation of cells, resulting in the elongation of a tissue in a preferred direction.
    • Delamination: the splitting of a layer of cells, such as the formation of the epiblast and hypoblast.
    • Passive movement of cells: the movement of cells without any change in their shape or position.
    • Migration: the movement of cells from one location to another.

    Cell Behaviors

    • Epithelial type: cells that can undertake major morphogenetic movements, such as invagination, epiboly, and involution.
    • Mesenchymal type: cells that can undertake changes in cell behavior or activities, such as migration, intercalation, and change in cell shape.

    Gene Regulation

    • Genes are activated to regulate morphogenetic movements and cellular activities.
    • Gene products, such as proteins, facilitate the onset of morphogenetic movements and cellular activities.
    • Examples of gene products involved in morphogenetic movements include actin cytoskeleton, integrins, and adherins junctions.

    Morphoregulatory Molecules

    • CAMs (cell adhesion molecules): facilitate cell-to-cell contact.
    • SAMs (substrate adhesion molecules): facilitate cell-to-ECM contact.
    • JAMs (cell junctional molecules): facilitate cell-to-cell contact.
    • These molecules are involved in the regulation of morphogenesis during development, adaptation, and regeneration.### Cell Adhesion and Morphogenesis
    • Cell-to-cell adhesion interactions involve CAMs and SAMs, leading to various cell movements and changes in cell shape, which are drivers for morphogenesis.
    • These interactions can have feedback on selector genes, influencing the activation of CAMs and SAMs genes.

    Amphibian Gastrulation

    • The process involves the orchestration of three morphogenetic movements: invagination, epiboly, and involution.
    • Invagination: the formation of the dorsal lip of the blastopore (DLB) due to the formation of bottle-shaped cells.
    • Epiboly: cells in the animal hemisphere undergo mitotic division, spreading and thinning.
    • Involution: cells moving inward, intercalating with the ectoderm and endoderm, causing the elongation of the embryo in late gastrula.
    • The dorsal lip of the blastopore is the site of cell turnover, guided by fibronectin, a SAM.
    • The migrating cells will designate the posterior cell of the embryo, establishing the anterior axis.

    Avian Gastrulation

    • The process involves the formation of the blastoderm, which undergoes cleavage to form the epiblast and primary hypoblast.
    • The blastocoel forms at the expense of the subgerminal cavity.
    • The primitive streak forms at the epiblast, designating the future posterior end of the embryo.
    • Cells delaminate and ingress from the epiblast into the subgerminal cavity, forming the primary hypoblast.
    • Cells from the posterior margin (secondary hypoblast) migrate anteriorly and join the primary hypoblast.
    • The thickening of cells forms the Koller's sickle, inducing the formation of the primitive streak.
    • Cells from the lateral region of the posterior epiblast migrate towards the midline, forming the primitive streak.

    Formation of the Primitive Streak

    • Cells at the anterior end of the primitive streak form a knot, the Hensen's node (primitive knot), which surrounds a pit, the primitive pit.
    • The primitive pit is continuous with the primitive groove, homologous to the blastopore.
    • Hensen's node becomes the site of cell turnover, with cells moving into the blastocoel between the epiblast and hypoblast.
    • Cells migrating through the primitive groove form the endoderm, mesoderm, and axial mesoderm.

    Guidance of Cell Migration

    • Fibronectin guides migratory behavior of cells from the epiblast.
    • Hyaluronic acid coats the ingressing cells, changing their adhesive behavior and allowing them to adhere to ECM molecules in the blastocoel.

    Gastrulation

    • The main goal of gastrulation is to establish the precursor of the digestive gut, called the primitive gut or archenteron.
    • The process of gastrulation involves the following main goals:
      • Laying down the primitive gut
      • Cell movements and rearrangements (morphogenetic movements)
      • Starting to acquire positional information
      • Forming the three germ layers (ectoderm, endoderm, and mesoderm)

    The Three Germ Layers

    • The three primary germ layers vary in characteristics:
      • Ectoderm and endoderm are epithelial type (flat sheet, closely-packed cells, little amount of ECM)
      • Mesoderm is mesenchymal type (loosely-arranged, plenty of ECM)
    • The behavior of these layers is influenced by their structure:
      • Ectoderm and endoderm can spread, roll, fold, buckle, and bend
      • Mesoderm can migrate, intercalate, change cell shape, and change adhesiveness

    Morphogenetic Movements

    • There are several types of morphogenetic movements:
      • Invagination: inpocketing of cells, forming an invagination
      • Epiboly: spreading of cells, thinning, and increasing surface area
      • Involution: mass movement of cells rolling inward to form an underlying layer
      • Convergent extension: intercalation of cells in a directional manner
      • Delamination: formation of the epiblast and hypoblast
      • Passive movement of cells and migration of cells
    • Intercalation can be lateral or radial and can result in convergent extension and convergent thickening

    Gene Regulation

    • Morphogenetic movements are regulated by gene activity
    • Genes are activated, resulting in gene products that are involved in these movements
    • Examples of gene products include:
      • Actin cytoskeleton
      • Integrins
      • Adherins junctions
      • CAMs (cell adhesion molecules) and SAMs (substrate adhesion molecules)

    Cell Adhesion Molecules (CAMs) and Substrate Adhesion Molecules (SAMs)

    • CAMs facilitate cell-to-cell contact
    • SAMs facilitate cell-to-ECM contact
    • Both CAMs and SAMs are morphoregulatory molecules
    • They are capable of reversible adhesion, allowing for quick attachment and detachment
    • Examples of CAMs and SAMs include:
      • E-cadherin (epidermal cell adhesion protein)
      • N-cadherin (neural cell adhesion protein)
      • Laminin
      • Fibronectin
      • Integrins

    Spatio-Temporal Gene Expression

    • Embryonic cells synthesize stage-dependent and region-specific ECM components
    • CAMs and SAMs are expressed at specific times and locations
    • This is an example of spatio-temporal gene expression

    Morphoregulatory Molecules

    • CAMs, SAMs, and JAMs (cell junctional molecules) provide an essential link between genetic and epigenetic mechanisms
    • They exert critical interactions at both the cell surface and the cytoskeleton
    • They mediate their effects through activation of intracellular signaling cascades

    Amphibian Gastrulation

    • The presence of the gray crescent region determines the site of the dorsal lip of the blastopore
    • Invagination, epiboly, and involution occur in a coordinated manner
    • The dorsal lip of the blastopore becomes the site of cell turnover
    • The involute cells migrate to the other side, guided by fibronectin
    • This establishes the body axis

    Avian Gastrulation

    • The fertilized egg has a blastoderm on top of the yellow yolk
    • The blastoderm undergoes cleavage division
    • The subgerminal cavity is visible under the microscope### Formation of Blastoderm
    • After fertilization, the blastodisk cleaves to form the blastoderm.
    • The blastoderm absorbs fluid underneath, creating the subgerminal cavity.
    • The blastoderm eventually delaminates, forming the epiblast and the primary hypoblast.
    • Blastocoel forms at the expense of the subgerminal cavity.

    Area Pellucida and Area Opaca

    • The area occupied by the blastoderm is called area pellucida, which is translucent.
    • The area opaca is opaque and darker due to its close contact with the underlying yolk.

    Gastrulation in Avian Embryos

    • The primitive streak forms at the epiblast, designating the future posterior end of the embryo.
    • Cells delaminate and ingress from the epiblast into the subgerminal cavity, forming the primary hypoblast.
    • Cells from the posterior margin migrate anteriorly and join the primary hypoblast, forming the secondary hypoblast.
    • The primary hypoblast and secondary hypoblast interdigitate, resulting in the elongation of the hypoblast.

    Formation of the Primitive Streak

    • Koller's sickle, a thickening of cells, induces the formation of the primitive streak.
    • Cells from the lateral region of the posterior epiblast migrate towards the midline, converging to form the primitive streak.
    • The primitive streak lengthens and narrows, and a depression forms within the streak, called the primitive groove.
    • A thickening of cells forms into a knot at the anterior end of the primitive groove, called Hensen's node.

    Formation of the Endoderm and Mesoderm

    • The blastoderm cells migrate over the lips of the primitive streak and into the blastocoel.
    • Some cells move directly downward and mix with the hypoblast, forming the endoderm.
    • Other cells move sideways, giving rise to the mesoderm (mesenchymal type).

    Avian Gastrulation

    • Avian gastrulation involves the ingression of epiblastic cells, which form mesenchyme cells.
    • Epiblastic cells move into the cavity, and cells at the anterior end start to form organs and undergo neurulation.

    Mammalian Gastrulation

    • Mammalian gastrulation involves the formation of a primitive streak similar to that of avian embryos.
    • The inner cell mass undergoes delamination, forming the epiblast and hypoblast (bilaminar germ disc formation).
    • The epiblast gives rise to the amniotic ectoderm, and the remainder of the embryonic epiblast, where the primitive streak forms.

    Trilaminar Disc Formation

    • The embryonic epiblast undergoes ingression, forming the embryonic endoderm and embryonic mesoderm.
    • The three germ layers (ectoderm, endoderm, and mesoderm) are formed in trilaminar disc formation.

    Gastrulation

    • The main goal of gastrulation is to establish the precursor of the digestive gut, called the primitive gut or archenteron.
    • The process of gastrulation involves the following main goals:
      • Laying down the primitive gut
      • Cell movements and rearrangements (morphogenetic movements)
      • Starting to acquire positional information
      • Forming the three germ layers (ectoderm, endoderm, and mesoderm)

    The Three Germ Layers

    • The three primary germ layers vary in characteristics:
      • Ectoderm and endoderm are epithelial type (flat sheet, closely-packed cells, little amount of ECM)
      • Mesoderm is mesenchymal type (loosely-arranged, plenty of ECM)
    • The behavior of these layers is influenced by their structure:
      • Ectoderm and endoderm can spread, roll, fold, buckle, and bend
      • Mesoderm can migrate, intercalate, change cell shape, and change adhesiveness

    Morphogenetic Movements

    • There are several types of morphogenetic movements:
      • Invagination: inpocketing of cells, forming an invagination
      • Epiboly: spreading of cells, thinning, and increasing surface area
      • Involution: mass movement of cells rolling inward to form an underlying layer
      • Convergent extension: intercalation of cells in a directional manner
      • Delamination: formation of the epiblast and hypoblast
      • Passive movement of cells and migration of cells
    • Intercalation can be lateral or radial and can result in convergent extension and convergent thickening

    Gene Regulation

    • Morphogenetic movements are regulated by gene activity
    • Genes are activated, resulting in gene products that are involved in these movements
    • Examples of gene products include:
      • Actin cytoskeleton
      • Integrins
      • Adherins junctions
      • CAMs (cell adhesion molecules) and SAMs (substrate adhesion molecules)

    Cell Adhesion Molecules (CAMs) and Substrate Adhesion Molecules (SAMs)

    • CAMs facilitate cell-to-cell contact
    • SAMs facilitate cell-to-ECM contact
    • Both CAMs and SAMs are morphoregulatory molecules
    • They are capable of reversible adhesion, allowing for quick attachment and detachment
    • Examples of CAMs and SAMs include:
      • E-cadherin (epidermal cell adhesion protein)
      • N-cadherin (neural cell adhesion protein)
      • Laminin
      • Fibronectin
      • Integrins

    Spatio-Temporal Gene Expression

    • Embryonic cells synthesize stage-dependent and region-specific ECM components
    • CAMs and SAMs are expressed at specific times and locations
    • This is an example of spatio-temporal gene expression

    Morphoregulatory Molecules

    • CAMs, SAMs, and JAMs (cell junctional molecules) provide an essential link between genetic and epigenetic mechanisms
    • They exert critical interactions at both the cell surface and the cytoskeleton
    • They mediate their effects through activation of intracellular signaling cascades

    Amphibian Gastrulation

    • The presence of the gray crescent region determines the site of the dorsal lip of the blastopore
    • Invagination, epiboly, and involution occur in a coordinated manner
    • The dorsal lip of the blastopore becomes the site of cell turnover
    • The involute cells migrate to the other side, guided by fibronectin
    • This establishes the body axis

    Avian Gastrulation

    • The fertilized egg has a blastoderm on top of the yellow yolk
    • The blastoderm undergoes cleavage division
    • The subgerminal cavity is visible under the microscope### Formation of Blastoderm
    • After fertilization, the blastodisk cleaves to form the blastoderm.
    • The blastoderm absorbs fluid underneath, creating the subgerminal cavity.
    • The blastoderm eventually delaminates, forming the epiblast and the primary hypoblast.
    • Blastocoel forms at the expense of the subgerminal cavity.

    Area Pellucida and Area Opaca

    • The area occupied by the blastoderm is called area pellucida, which is translucent.
    • The area opaca is opaque and darker due to its close contact with the underlying yolk.

    Gastrulation in Avian Embryos

    • The primitive streak forms at the epiblast, designating the future posterior end of the embryo.
    • Cells delaminate and ingress from the epiblast into the subgerminal cavity, forming the primary hypoblast.
    • Cells from the posterior margin migrate anteriorly and join the primary hypoblast, forming the secondary hypoblast.
    • The primary hypoblast and secondary hypoblast interdigitate, resulting in the elongation of the hypoblast.

    Formation of the Primitive Streak

    • Koller's sickle, a thickening of cells, induces the formation of the primitive streak.
    • Cells from the lateral region of the posterior epiblast migrate towards the midline, converging to form the primitive streak.
    • The primitive streak lengthens and narrows, and a depression forms within the streak, called the primitive groove.
    • A thickening of cells forms into a knot at the anterior end of the primitive groove, called Hensen's node.

    Formation of the Endoderm and Mesoderm

    • The blastoderm cells migrate over the lips of the primitive streak and into the blastocoel.
    • Some cells move directly downward and mix with the hypoblast, forming the endoderm.
    • Other cells move sideways, giving rise to the mesoderm (mesenchymal type).

    Avian Gastrulation

    • Avian gastrulation involves the ingression of epiblastic cells, which form mesenchyme cells.
    • Epiblastic cells move into the cavity, and cells at the anterior end start to form organs and undergo neurulation.

    Mammalian Gastrulation

    • Mammalian gastrulation involves the formation of a primitive streak similar to that of avian embryos.
    • The inner cell mass undergoes delamination, forming the epiblast and hypoblast (bilaminar germ disc formation).
    • The epiblast gives rise to the amniotic ectoderm, and the remainder of the embryonic epiblast, where the primitive streak forms.

    Trilaminar Disc Formation

    • The embryonic epiblast undergoes ingression, forming the embryonic endoderm and embryonic mesoderm.
    • The three germ layers (ectoderm, endoderm, and mesoderm) are formed in trilaminar disc formation.

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