255 Questions
What is the resulting embryonic phase at the end of blastulation in amphibian development?
A hollow ball of cells with a cavity
Where is the future dorsal side of the embryo located at the end of blastulation?
In the marginal zone (MZ)
What is formed before the epiblast and hypoblast in avian blastulation?
Massive cells that replace the blastodisc
What is the cavity between the epiblast and hypoblast called?
Blastocoel
What happens to the blastoderm cells underneath?
They coalesce to form the hypoblast
What is formed when the blastoderm cells absorb the fluid in the yolk underneath?
Subgerminal cavity
What is the process that quickly transitions into gastrulation after avian blastulation?
Early gastrulation
What is the term for the yellow part of the oocyte?
Yolk
What is the primary function of cyclins and cyclin-dependent kinases in the cell cycle?
Regulation of cell division
What is the term for the transition of cells from a layer of flat sheet cells to a cavity?
Ingression
What is the function of selector genes in embryonic development?
Activation of morphoregulatory molecules
What is the term for the spreading of cells caused by rapid cell division?
Epiboly
What is the term for the in-pocketing of cells, resulting in the formation of a dorsal lip of blastopore?
Invagination
What is the role of transcription factors in regulating gene expression?
Up-regulation or down-regulation of gene activity
What is the term for the mass movement of cells, resulting in the formation of a new layer?
Involution
What is the function of CAMs and SAMs in embryonic development?
Morphoregulatory molecules
What is the term for the change in cell behavior, resulting in the formation of a new shape?
Change in cell shape
What is the primary function of regulatory genes in embryonic development?
Regulation of gene expression
What occurs if a cell is double layered?
It becomes single layered
What is the term for the process where cells move inward to form an underlying layer?
Involution
What is the direction of intercalation in convergent extension?
Perpendicular to the axis of extension
What is the result of convergent extension on the dimensions of a sheet of cells?
Increase in one dimension and decrease in another
What is the term for the process of tissue becoming thicker in the direction at right angles to the convergent extension?
Convergent thickening
What is the term for the formation of the epiblast and hypoblast?
Delamination
What type of migration strategy is used by primordial germ cells?
Ameboid migration
What is the term for the movement of cells inward to form an underlying layer via bulk movement of cells?
Invagination
What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?
Convergent extension
What is the term for the splitting of a layer of cells, but not a literal split?
Delamination
What is the primary difference between the blastocoel and the subgerminal cavity?
The blastocoel is formed by the splitting of the blastoderm, while the subgerminal cavity is not
In which stage of development is polarity established in avians?
Early in development, before blastulation
What is the main goal of gastrulation?
To establish the precursor of the digestive gut
What is the term for the cells acquiring molecular cues that tell them where they are relative to the body axis?
Positional information
What is the characteristic of the ectoderm and endoderm?
They are epithelial type with closely-packed cells and little ECM
What is the term for the process of cells moving individually one after the other with a mass movement?
Migration
What is the term for the precursor of the digestive gut?
Archenteron
What is the characteristic of the blastopore?
It is the opening of the primitive gut
What is the term for the process of laying down the three primary germ layers?
Gastrulation
What is the term for the movement of cells during gastrulation that helps establish the precursor of the digestive gut?
Morphogenetic movements
What type of migration involves neural crest cells and head mesenchyme?
Mesenchymal migration
What regulates morphogenetic movements during embryonic development?
Gene activity
What is the result of intercalation during embryonic development?
Convergent extension and convergent thickening
What type of cells undergo change in cell shape and position during embryonic development?
Epithelial cells
What is the process of programmed cell death during embryonic development?
Apoptosis
What is the result of change in cell adhesiveness during embryonic development?
Cell sorting and tissue formation
What is the type of migration that involves gastrulating cells moving inward?
Collective migration
What is the function of CAMs and SAMs during embryonic development?
Cell adhesion and migration
What is the process of cells leaving an epithelial sheet to become freely migrating mesenchyme cells?
Ingression
What is the result of change in cell shape during embryonic development?
Formation of cavities
What determines the shape of multicellular aggregates and the sorting order in heterotypic aggregates?
Cell-cell adhesion and cortex tension
What is the function of SAMs (substrate adhesion molecules)?
Establishes structural integrity of cells with the surrounding matrix
What is the characteristic of CAMs and SAMs?
Reversible adhesion, quick attachment/detachment
What is the purpose of spatio-temporal gene expression of CAMs and SAMs?
To ensure gene products are available at the right time and place
What is the process that regulates morphogenesis during development, adaptation, and regeneration?
Morphoregulation
What is the function of E-cadherin?
Facilitate cell-cell adhesion in prospective epidermis
What is the function of N-cadherin?
Facilitate cell-cell adhesion in prospective neural plate
What is the term for morphoregulatory molecules that facilitate cell to cell contact?
CAMs (cell adhesion molecules)
What is the result of the coordinated expression and function of CAMs, SAMs, and JAMs?
Activation of intracellular signaling cascades
What is the role of CAMs, SAMs, and JAMs in development?
Provide an essential link between genetic and epigenetic mechanisms
What is the main difference between the area opaca and area pellucida?
Area opaca is dark, while area pellucida is light in color
What is the process by which cells fall off from the epiblast and enter the subgerminal cavity?
Ingression
What is the structure formed by the thickening of cells at the posterior margin of the area pellucida?
Koller's sickle
What is the term for the cavity formed between the epiblast and hypoblast?
Blastocoel
What is the fate of the epiblast and hypoblast in avian development?
Epiblast forms the embryo proper, hypoblast forms extraembryonic membranes
What is the term for the process by which the blastoderm cleaves to form the blastoderm?
Blastulation
What is the significance of the primitive streak in avian development?
It forms the posterior end of the embryo
What is the cavity that forms underneath the blastoderm?
Subgerminal cavity
What is the term for the translucent region occupied by the blastoderm and subgerminal space?
Area pellucida
What is the process by which cells from the lateral region of the posterior epiblast migrate towards the midline?
Formation of the primitive streak
What is the primary function of CAMs and SAMs in embryonic development?
To control cell-to-cell adhesion and interaction
What is the term for the process by which cells move inward due to lack of space?
Involution
What is the role of the dorsal lip of the blastopore in amphibian gastrulation?
Site of cell turnover and migration
What is the term for the interaction between cells and the extracellular matrix?
Cell-to-matrix adhesion
What is the function of selector genes in embryonic development?
To code for transcription factors
What is the term for the process by which cells change shape and move to form new structures?
Morphogenesis
What is the role of fibronectin in amphibian gastrulation?
Providing contact guidance to migrating cells
What is the term for the process by which cells spread and thin out?
Epiboly
What is the function of the chordamesoderm in embryonic development?
Influence on neurulation
What is the term for the cavity between the epiblast and hypoblast in avian blastulation?
Subgerminal cavity
What is the function of fibronectin in avian gastrulation?
Guiding migratory behavior of cells from the epiblast
What forms when the blastoderm cells migrate over the lips of the primitive streak and into the blastocoel?
Endoderm and mesoderm
What is homologous to the dorsal lip of the blastopore?
Hensen's node
What is the term for the movement of cells inward to form an underlying layer in avian gastrulation?
Ingression
What is the result of the movement of cells towards the midline in avian gastrulation?
Formation of the primitive streak
What is the function of hyaluronic acid in avian gastrulation?
Coating the ingressing cells and changing adhesive behavior
What is the term for the cavity that forms between the epiblast and hypoblast?
Blastocoel
What is the result of the regression of the primitive streak?
Formation of the head process
What happens to the cells during the process of involution?
They undergo a change in shape and move inward
What is the result of convergent extension on the dimensions of a sheet of cells?
It becomes narrower and longer
What type of migration strategy is used by primordial germ cells?
Ameboid migration
What is the term for the process of tissue becoming thicker in the direction at right angles to the convergent extension?
Convergent thickening
What is the result of intercalation during embryonic development?
Convergent extension
What is the process by which tissue elongates along the anterior-posterior (AP) axis and becomes narrower along the medio-lateral (ML) axis?
Convergent extension
What is the term for the formation of the epiblast and hypoblast?
Delamination
What type of cells undergo change in cell shape and position during embryonic development?
All of the above
What is the term for the mass movement of cells rolling inward to form an underlying layer via bulk movement of cells?
Involution
What is the direction of intercalation in convergent extension?
Perpendicular to the axis of extension
What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?
Convergent extension
What is the primary function of the main goal of gastrulation?
To establish the precursor of the digestive gut
What is the characteristic of the ectoderm and endoderm germ layers?
They are epithelial type with closely-packed cells
What is the term for the process of cells acquiring molecular cues that tell them where they are relative to the body axis?
Positional information
What is the result of the movement of cells during gastrulation that helps establish the precursor of the digestive gut?
Formation of the primitive gut
What is the characteristic of the mesoderm germ layer?
It is mesenchymal type with loosely-arranged cells
What is the term for the process of cells moving individually one after the other with a mass movement?
Migration
What is the primary function of the blastopore?
To form the opening of the primitive gut
What is the term for the process of laying down the three primary germ layers?
Gastrulation
What is the primary function of cell adhesion molecules (CAMs) during embryonic development?
To facilitate cell-to-cell contact and adhesion
What is the main function of substrate adhesion molecules (SAMs) during embryonic development?
To facilitate cell-to-ECM contact and adhesion
What is the term for the dynamic expression patterns of CAMs and SAMs correlated with cell fates during embryonic development?
Spatio-temporal gene expression
What is the term for the process of morphogenesis during embryonic development regulated by CAMs, SAMs, and JAMs?
Morphoregulation
What is the result of the coordinated expression and function of CAMs, SAMs, and JAMs during embryonic development?
Pattern formation and morphogenesis
What is the role of CAMs and SAMs in regulating morphogenetic movements during embryonic development?
To facilitate cell-to-cell and cell-to-ECM adhesion
What is the result of the dynamic expression of CAMs and SAMs during embryonic development?
Regulation of morphogenetic movements and pattern formation
What is the function of CAMs in regulating cell behavior during embryonic development?
Facilitation of cell-to-cell adhesion and contact
What is the result of the interaction between CAMs and SAMs during embryonic development?
Regulation of morphogenetic movements and pattern formation
What is the primary mechanism by which CAMs and SAMs regulate morphogenetic movements during embryonic development?
Activation of intracellular signaling cascades
What is the primary function of CAMs and SAMs in regulating morphogenetic movements during embryonic development?
To facilitate cell adhesion and migration
What type of migration involves the movement of cells in a collective manner, often seen in gastrulating cells?
Collective migration
What is the result of convergent extension on the dimensions of a sheet of cells?
The sheet becomes narrower in the direction perpendicular to extension
What is the primary difference between the process of ingression and the process of intercalation?
Ingression involves the transformation of epithelial cells into mesenchyme cells, while intercalation involves the movement of cells between existing layers
What is the role of genes in regulating morphogenetic movements during embryonic development?
They regulate the expression of CAMs and SAMs
What is the characteristic of the cells that undergo change in cell shape and position during embryonic development?
They are epithelial cells
What is the process of programmed cell death during embryonic development?
Apoptosis
What is the result of change in cell adhesiveness during embryonic development?
Cells become more aggregated
What is the type of migration that involves the movement of primordial germ cells?
Mesenchymal migration
What is the role of neural crest cells in embryonic development?
They form the different ganglia of the body
What is the primary function of genes coding for cyclins and cyclin-dependent kinases in the cell cycle?
To change the rate of cell division
What is the result of the combination of epithelial-mesenchymal transition and the activation of genes coding for cyclins and cyclin-dependent kinases?
Epiboly
What is the role of selector genes in regulating the expression of CAMs and SAMs during embryonic development?
To activate the expression of CAMs and SAMs
What is the primary difference between the epithelial type and mesenchymal type of cells during embryonic development?
Epithelial cells undertake major morphogenetic movements, while mesenchymal cells undergo changes in cell behavior
What is the result of the migration of cells during gastrulation?
The formation of the precursor of the digestive gut
What is the function of transcription factors in regulating gene expression during embryonic development?
To regulate the activity of other genes
What is the result of the change in cell adhesiveness during embryonic development?
Change in the ability of cells to migrate
What is the function of CAMs and SAMs during embryonic development?
To regulate cell-cell and cell-substrate interactions
What is the result of the epithelial-mesenchymal transition during embryonic development?
The change in cell behavior and cell shape
What regulates morphogenetic movements during embryonic development?
Gene activity
What is the primary function of CAMs and SAMs in morphoregulatory cycles?
To control cell-to-cell adhesion and interaction
What is the result of changes in cell shape and movement during morphogenesis?
Changes in cell shape and movement drive morphogenesis
What is the role of selector genes in morphoregulatory cycles?
To code for transcription factors that control CAMs and SAMs
What is the function of fibronectin in amphibian gastrulation?
To provide contact guidance to migrating cells
What is the result of involution in amphibian gastrulation?
Elongation of the embryo
What is the term for the process of cells moving inward to form an underlying layer?
Involution
What is the role of CAMs and SAMs in embryonic cell positioning?
To control cell-to-cell adhesion and interaction
What is the outcome of the orchestration of the three morphogenetic movements in amphibian gastrulation?
Establishment of the body axis
What is the function of the dorsal lip of the blastopore in amphibian gastrulation?
To provide a site for cell turnover
What is the term for the mass movement of cells resulting in the formation of a new layer?
Epiboly
What is the term for the site of cell turnover, which is a knot at the anterior end of the primitive groove?
Hensen's node
What is the role of fibronectin in avian gastrulation?
Guides migratory behavior of cells from the epiblast
What is the term for the cavity between the epiblast and hypoblast?
Blastocoel
What is the process by which cells move inward to form an underlying layer during gastrulation?
Ingression
What is the term for the structure that forms the scaffold for the formation of the CNS?
Notochord
What is the term for the movement of cells towards the midline, resulting in the formation of the head process?
Convergent extension
What is the term for the region occupied by the embryo?
Area pellucida
What is the term for the process by which the blastoderm cells migrate over the lips of the primitive streak and into the blastocoel?
Ingression
What is the term for the cells that move ventrally to form the foregut endoderm?
First migrating cells
What is the term for the process by which the hypoblast is pushed to the sides and replaced by the ingressing cells?
Colonization
What is the process by which the three primary germ layers are formed?
Trilaminar disc formation
What is the role of the notochordal process in embryonic development?
Pick up point for neurulation
What is the term for the translucent region occupied by the blastoderm and the subgerminal space?
Area pellucida
Which structure forms at the expense of the subgerminal cavity?
Blastocoel
What is the fate of the amniotic ectoderm and the rest of the hypoblast and trophoblast?
They contribute to the formation of the placenta
What is the process that involves the falling off of cells from the epiblast into the subgerminal cavity?
Ingression
What is the process by which the epiblast and hypoblast are formed?
Bilaminar germ disc formation
What is the result of ingression of cells during trilaminar disc formation?
Formation of the embryonic endoderm and mesoderm
What is the term for the dark region of the yolk that is still in close contact with the underlying yolk?
Area opaca
What is the structure that forms from the thickening of cells at the posterior margin of the area pellucida?
Koller's sickle
What is the relationship between the notochordal process and the axial mesoderm?
The notochordal process is the same as the axial mesoderm
What is the direction of cell migration during the formation of the primitive streak?
From the lateral region towards the midline
What is the result of the convergence of the epiblast and hypoblast at the margins of the area opaca?
Formation of the primitive streak
What is the term for the process of cells sticking together to form the primary hypoblast?
Aggregation
What is the role of the hypoblast during avian gastrulation?
Formation of the extraembryonic membranes
What is the stage of development during which the primitive streak forms?
Gastrulation
What is the primary goal of gastrulation?
To lay down the primitive gut
What type of cells are ectoderm and endoderm?
Epithelial type
What do cells acquire during gastrulation?
Positional information
What is the characteristic of mesoderm cells?
They are loosely-arranged cells
What is the term for the process of laying down the three primary germ layers?
Gastrulation
What is the type of migration that involves neural crest cells and head mesenchyme?
Individually one after the other with a mass movement
What is the result of intercalation during embryonic development?
Formation of a new layer
What is the term for the precursor of the digestive gut?
Archenteron
What is the primary mechanism of mesenchymal migration?
Amoeboid motion
What is the result of convergent extension?
Convergent thickening
What type of cells undergo change in cell shape and position during embryonic development?
Epithelial cells
What is the process of programmed cell death during embryonic development?
Apoptosis
What regulates morphogenetic movements during embryonic development?
Gene activity
What is the result of change in cell adhesiveness during embryonic development?
Tissue formation
What is the type of migration that involves neural crest cells and head mesenchyme?
Mesenchymal migration
What is the function of SAMs (substrate adhesion molecules) during embryonic development?
Cell adhesion
What is the process of cells leaving an epithelial sheet to become freely migrating mesenchyme cells?
Ingression
What determines the shape of multicellular aggregates and the sorting order in heterotypic aggregates?
Cell adhesion molecules
What is the primary function of CAMs and SAMs in morphogenetic cycles?
To control cell-to-cell adhesion and intercellular signaling
What is the role of selector genes in embryonic development?
To specify cell fate and pattern formation
What is the outcome of changes in cell shape and adhesiveness during embryonic development?
Cell migration and tissue formation
What is the function of fibronectin in amphibian gastrulation?
To provide contact guidance to migrating cells
What is the result of intercalation during embryonic development?
Cell elongation and shape change
What is the role of the dorsal lip of the blastopore in amphibian gastrulation?
To guide cell movement and establish the anterior-posterior axis
What is the primary reason for the difference in cell size between the animal hemisphere and the vegetal pole?
Impeded cell division due to the thick yolk in the vegetal pole
What is the term for the mass movement of cells rolling inward to form an underlying layer?
Involution
What is the function of the chordamesoderm in embryonic development?
To form the neural tube
What is the result of convergent extension on the dimensions of a sheet of cells?
Decrease in width and increase in length
What is the outcome of epiboly during amphibian gastrulation?
Cell spreading and thinning
What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?
Convergent extension
What is the function of CAMs and SAMs in cell-to-cell adhesion?
To facilitate cell-to-cell adhesion and intercellular signaling
What is the primary difference between convergent extension and convergent thickening?
Direction of cell movement
What is the result of involution during amphibian gastrulation?
Cell intercalation and rearrangement
What is the term for the splitting of a layer of cells, but not a literal split?
Delamination
What is the migration strategy used by primordial germ cells?
Ameboid migration
What is the result of intercalation during convergent extension?
Change in cell shape and position
What is the direction of intercalation in convergent extension?
Perpendicular to the axis of extension
What is the primary function of convergent extension during embryonic development?
Shaping of the embryo
What is the main function of cortex tension in multicellular aggregates?
To determine the shape of multicellular aggregates
What is the function of CAMs (cell adhesion molecules) in embryonic development?
To facilitate cell-to-cell contact and adhesion
What is the term for the process of cells acquiring molecular cues that tell them where they are relative to the body axis?
Pattern formation
What is the role of SAMs (substrate adhesion molecules) in embryonic development?
To establish cell-to-ECM contact and adhesion
What is the term for the process of cells moving inward to form an underlying layer via bulk movement of cells?
Invagination
What is the function of morphoregulatory molecules in embryonic development?
To regulate morphogenesis during development
What is the term for the process of cells converging by intercalating perpendicular to the axis of extension?
Convergent extension
What is the result of change in cell adhesiveness during embryonic development?
Change in tissue shape
What is the function of E-cadherin in embryonic development?
To facilitate cell-to-cell contact and adhesion in prospective epidermis
What is the term for the process of cells undergoing dynamic expression patterns correlated with cell fates?
Spatio-temporal gene expression
What is the primary mechanism that drives epiboly?
Cell division and thinning of the epithelial sheet
Which type of cells can undergo epithelial-mesenchymal transition during embryonic development?
Ectoderm, endoderm, and mesoderm cells
What is the role of transcription factors in regulating gene expression during embryonic development?
To activate or deactivate gene expression
What is the result of a change in cell adhesiveness during embryonic development?
Change in cell-cell interaction
Which genes are responsible for regulating the expression of CAMs and SAMs during embryonic development?
Selector genes
What is the term for the process of cells moving inward to form an underlying layer via bulk movement of cells?
Involution
What regulates morphogenetic movements during embryonic development?
Gene activity
What is the result of convergent extension during embryonic development?
Change in tissue dimensions
What is the term for the process of cells leaving an epithelial sheet to become freely migrating mesenchyme cells?
Epithelial-mesenchymal transition
What is the role of CAMs and SAMs during embryonic development?
To facilitate morphogenetic movements
What is the term for the light area occupied by the blastoderm?
Area pellucida
What is the process that occurs between the formation of the epiblast and the primary hypoblast?
Formation of the blastocoel
What is the term for the dark area in close contact with the underlying yolk?
Area opaca
What is the structure that forms at the posterior margin of the area pellucida?
Koller's sickle
What is the term for the thickening of cells at the posterior margin of the area pellucida?
Koller's sickle
What is the result of the convergence of the epiblast and hypoblast at the margins of the area opaca?
Thickening of cells
What is the term for the process of cells falling off from the epiblast into the subgerminal cavity?
Ingression
What is the term for the cavity that forms underneath the blastoderm?
Subgerminal cavity
What is the result of the formation of the primary hypoblast and the secondary hypoblast?
Elongation of the hypoblast
What is the term for the structure that designates the future posterior end of the embryo?
Primitive streak
What is the purpose of Fibronectin in avian gastrulation?
Guiding migratory behavior of cells from the epiblast
What is the outcome of cells moving anteriorly and forming the head process?
Overlying of the Hensen's node
What is the significance of the primitive pit?
It is homologous to the blastopore
What is the primary function of the epiblast in embryonic development?
To give rise to the embryonic ectoderm, endoderm, and mesoderm
What happens to the hypoblast during avian gastrulation?
It gets pushed to the sides
During trilaminar disc formation, what happens to the cells that ingress?
They form the embryonic endoderm and mesoderm
What is the role of the notochordal process in embryonic development?
It is the pick-up point for neurulation
What is the function of the notochord?
To provide an axial skeleton for the formation of the CNS
What is the outcome of cells moving ventrally?
Formation of the foregut endoderm
What is the result of bilaminar germ disc formation?
The formation of the epiblast and hypoblast
What is the term for the area occupied by the embryo?
Area pellucida
What is the fate of the amniotic ectoderm and the rest of the hypoblast and trophoblast?
They contribute to the formation of the placenta
What is the significance of the primitive streak in embryonic development?
It is where the ingression of cells will occur
What is the role of Hyaluronic acid in avian gastrulation?
Coating the ingressing cells and changing adhesive behavior
What is the characteristic of the proamnion?
It is devoid of mesenchyme
What happens to the Hensen's node during avian gastrulation?
It moves posteriorly
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.
Lecture 5
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