Lecture 5 -7 (Set A)
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Questions and Answers

What is the characteristic of blastulation in mammals?

  • Development of the primitive gut
  • Establishment of body polarity
  • Generation of ICM and tropoblast (correct)
  • Formation of three germ layers
  • During gastrulation, what is the main goal of establishing the dorsal lip of the blastopore?

  • To establish body polarity
  • To lay down the primitive gut (correct)
  • To initiate cell movements
  • To form the three primary germ layers
  • What is the significance of the blastocoel in mammalian blastulation?

  • It marks the future posterior end of the embryo
  • It forms the primitive gut
  • It is the space between the epiblast and hypoblast (correct)
  • It is the space that will give rise to the ICM
  • What is the characteristic of the ectoderm and endoderm?

    <p>Epithelial type with a flat sheet of cells</p> Signup and view all the answers

    What is the significance of cell movements during gastrulation?

    <p>To acquire positional information</p> Signup and view all the answers

    What is the characteristic of the mesoderm?

    <p>Mesenchymal type with plenty of ECM</p> Signup and view all the answers

    What is the significance of the archenteron?

    <p>It is the precursor of the digestive gut</p> Signup and view all the answers

    During gastrulation, what is the significance of the formation of the blastopore?

    <p>It initiates the formation of the primitive gut</p> Signup and view all the answers

    What is the characteristic of the behavior of ectoderm and endoderm?

    <p>They can spread, roll, fold, buckle, and bend</p> Signup and view all the answers

    What is the characteristic of the behavior of mesoderm?

    <p>They migrate individually</p> Signup and view all the answers

    What is the resulting embryonic phase at the end of the blastulation process in amphibians?

    <p>A hollow ball of cells with a cavity</p> Signup and view all the answers

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

    <p>At the marginal zone (MZ)</p> Signup and view all the answers

    What is the term for the cavity found in the avian embryo at the end of blastulation?

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

    What is the resulting structure formed at the end of blastulation in avians?

    <p>A stack of cell layers</p> Signup and view all the answers

    What is the term for the layer of cells that forms underneath the blastoderm in avian blastulation?

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

    What is the process by which the blastoderm cells absorb the fluid in the yolk underneath to form the subgerminal cavity?

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

    What is the relationship between the end of blastulation and the start of gastrulation in avians?

    <p>There is a swift transition from the last part of blastulation to early gastrulation</p> Signup and view all the answers

    What is the term for the cavity formed underneath the blastoderm in avian blastulation?

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

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

    <p>Regulating cell division by controlling the rate of mitosis</p> Signup and view all the answers

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

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

    What is the term for the process by which cells spread out and thin, resulting in an increase in surface area?

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

    Which type of morphogenetic movement involves the migration of cells?

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

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

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

    What is the term for the process by which cells undergo a change in shape?

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

    Which type of gene is responsible for regulating the expression of other genes?

    <p>Regulatory gene</p> Signup and view all the answers

    What is the term for the process by which cells move from a layer of flat cells to a cavity?

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

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

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

    Which type of morphogenetic movement involves the inpocketing of cells to form a cavity?

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

    What is the process by which a double-layered epithelium becomes monolayered?

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

    What is the term for the movement of cells that results in a change in the dimensions of a sheet of cells?

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

    What is the result of intercalation of cells in a highly directional manner?

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

    What is the type of cell migration that occurs in primordial germ cells?

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

    What is the process by which tissue becomes 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 is the result of the process of involution in the development of an amphibian oocyte?

    <p>Formation of the blastopore</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 reason for the slower rate of cell division in the vegetal pole?

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

    What is the term for the movement of cells that results in a change in the shape of individual cells?

    <p>Change in shape of individual cells</p> Signup and view all the answers

    What is the correct sequence of migration of primordial germ cells in the embryo?

    <p>From the yolk sac endoderm to the dorsal mesentery, then to the genital ridges</p> Signup and view all the answers

    Which type of migration involves the movement of neural crest cells and the head mesenchyme?

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

    What is the primary role of genes in morphogenetic movements?

    <p>To regulate the expression of CAMs and SAMs</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 is the term for the process by which cells leave an epithelial sheet to form a cavity?

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

    What is the term for the programmed cell death that occurs during embryonic development?

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

    What is the result of change in cell shape and position during the 16-cell stage of the mammalian embryo?

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

    What is the role of cadherin and the actomyosin cortex in cellular adhesion?

    <p>To determine the shape and strength of the adhesion contact between two cells</p> Signup and view all the answers

    What is the term for the process by which cells acquire different degrees of adhesiveness from the cellular level to the tissue level?

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

    What is the term for the process by which cells undergo a change in shape and position, resulting in the formation of a cavity?

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

    At what stage of development do transcription factors control the expression of CAMs and SAMs?

    <p>During embryonic stage</p> Signup and view all the answers

    What is the result of cell-to-cell adhesion interactions between CAMs and SAMs and other cells?

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

    What is the role of feedback on selector genes during morphogenesis?

    <p>To activate more CAMs/SAMs genes</p> Signup and view all the answers

    What is the significance of the gray crescent region in amphibian gastrulation?

    <p>It determines the site of the dorsal lip of the blastopore</p> Signup and view all the answers

    What is the outcome of invagination during amphibian gastrulation?

    <p>Formation of the dorsal lip of the blastopore</p> Signup and view all the answers

    What is the role of fibronectin in amphibian gastrulation?

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

    What is the significance of the chordamesoderm in amphibian gastrulation?

    <p>It has a powerful influence on neurulation</p> Signup and view all the answers

    What is the difference between the area pellucida and the area opaca in avian gastrulation?

    <p>The area pellucida is lighter, while the area opaca is darker</p> Signup and view all the answers

    What is the significance of the blastoderm in avian gastrulation?

    <p>It undergoes cleavage division</p> Signup and view all the answers

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

    <p>They are involved in cell adhesion and intercellular signaling</p> Signup and view all the answers

    What is the primary factor that determines the shape of multicellular aggregates and the sorting order in heterotypic aggregates?

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

    Which of the following CAMs is highly expressed in prospective epidermis?

    <p>E-cadherin</p> Signup and view all the answers

    What is the primary function of SAMs?

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

    What is the characteristic of CAMs and SAMs in terms of adhesion?

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

    What is the term for the process of regulating morphogenesis during development, adaptation, and regeneration?

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

    What is the primary role of selector genes?

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

    What is the significance of spatio-temporal gene expression in embryonic development?

    <p>Ensures that gene products are present at the right time and place</p> Signup and view all the answers

    What is the region where cells undergo ingression during avian gastrulation?

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

    Which of the following molecules is NOT a type of morphoregulatory molecule?

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

    Which structure is formed by the migratory cells that move ventrally during avian gastrulation?

    <p>Foregut endoderm</p> Signup and view all the answers

    What is the term for the molecules that facilitate cell-cell contact and cell-ECM contact?

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

    What is the role of fibronectin in avian gastrulation?

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

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

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

    What is the destination of the cells that move sideways during avian gastrulation?

    <p>Lateral mesoderm and axial mesoderm</p> Signup and view all the answers

    What is the result of the migration of cells into the blastocoel during avian gastrulation?

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

    What is the direction of movement of the primitive streak during avian gastrulation?

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

    What is the role of hyaluronic acid in avian gastrulation?

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

    What is the term for the process by which epiblastic cells form mesenchyme cells during avian gastrulation?

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

    What is the significance of the area pellucida?

    <p>It is a translucent region occupied by the blastoderm and the subgerminal space.</p> Signup and view all the answers

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

    <p>Delamination</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>The thickening of the area opaca</p> Signup and view all the answers

    What is the significance of the blastocoel in avian gastrulation?

    <p>It is a cavity that forms between the epiblast and hypoblast.</p> Signup and view all the answers

    What is the process by which cells from the posterior margin migrate towards the midline?

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

    What is the term for the knot formed at the anterior end of the primitive groove?

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

    What is the significance of the formation of the primitive streak?

    <p>It designates the future posterior end of the embryo.</p> Signup and view all the answers

    What is the relationship between the epiblast and hypoblast?

    <p>The epiblast forms the embryo proper, while the hypoblast forms the extraembryonic membranes.</p> Signup and view all the answers

    What is the term for the depression that forms within the primitive streak?

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

    Study Notes

    Blastulation

    • In amphibian development, 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
    • The site where the first falling off cells to form the hypoblast represents the future posterior end of the embryo

    Avian Blastulation

    • The resulting stack of cell layers at the end of blastulation consists of the epiblast and hypoblast
    • The blastoderm forms when the blastodisc starts cleaving
    • The formation of the epiblast and hypoblast marks the start of the early phase of gastrulation
    • The blastoderm cells underneath the hypoblast fall off and coalesce to form the hypoblast
    • The blastocoel is the cavity between the epiblast and hypoblast

    Mammalian Blastulation

    • The end of blastulation results in 2 distinct populations of cells: the ICM (inner cell mass) and the tropoblast or trophectoderm, with the blastocoel
    • Polarity is not yet established in mammalian development
    • The embryo proper has yet to form in the ICM

    Gastrulation

    • The most distinguishing feature of gastrulation is the formation of the dorsal lip of the blastopore
    • Gastrulation establishes the precursor of the digestive gut, called the primitive gut or archenteron
    • The main goals of gastrulation are:
      • Laying down the primitive gut
      • Cell movements and rearrangements (morphogenetic movements)
      • Starting to acquire positional formation
      • Forming the three germ layers (ectoderm, endoderm, and mesoderm)

    The Three Germ Layers

    • Ectoderm and endoderm are epithelial type (flat sheet; closely-packed cells; little ECM)
    • Mesoderm is mesenchymal type (loosely-arranged; plenty of ECM)
    • Each germ layer has distinct characteristics and behaviors

    Morphogenetic Movements

    • Examples of morphogenetic movements include:
      • Invagination (inpocketing of cells)
      • Epiboly (spreading of cells)
      • Involution (mass movement of cells rolling inward)
      • Convergent extension (intercalation of cells in a specific direction)
      • Delamination (splitting of a layer of cells)
      • Passive movement of cells and migration of cells

    Regulation of Morphogenetic Movements

    • Morphogenetic movements are regulated by gene activity

    • Genes are activated to form gene products that facilitate morphogenetic movements

    • CAMs (cell adhesion molecules) and SAMs (substrate adhesion molecules) are morphoregulatory molecules that regulate morphogenesis during development

    • Spatio-temporal gene expression ensures that gene products are present at the right time and place during development### Cell-to-Cell Adhesion Interactions

    • Cell-to-cell adhesion interactions cause various cell movements, including changes in cell shape, movements, ingression, and involution.

    • These movements drive morphogenesis, and cells move, change shape, and interact with other cells or new neighboring cells.

    • This leads to new cell-to-cell interactions and new intercellular signaling, which can have feedback on selector genes.

    Amphibian Gastrulation

    • The gray crescent region determines the site of the dorsal lip of the blastopore (DLB).
    • The dorsal lip of the blastopore forms through invagination, and the bottle-shaped cells cause invagination.
    • Epiboly occurs when cells in the animal hemisphere undergo mitotic division, spreading, and thinning.
    • Involution occurs when cells move inward due to a depression, and they can intercalate with the ectoderm and endoderm.
    • The three morphogenetic movements - invagination, epiboly, and involution - occur simultaneously in amphibian gastrulation.
    • The dorsal lip of the blastopore is the site of cell turnover, and the involute cells migrate from the dorsal lip to the other side, guided by fibronectin.

    Avian Gastrulation

    • The blastoderm is the black structure on top of the yellow yolk, and it undergoes cleavage division.
    • The blastoderm is divided into the area pellucida (translucent region) and the area opaca (opaque region).
    • The primitive streak forms at the epiblast and designates the future posterior end of the embryo.
    • The blastoderm eventually delaminates, forming the epiblast and the primary hypoblast, and the blastocoel forms at the expense of the subgerminal cavity.
    • The formation of the primitive streak involves the delamination of cells from the epiblast, which ingress into the subgerminal cavity, forming the primary hypoblast.
    • The cells from the posterior margin migrate anteriorly and join the primary hypoblast, forming the secondary hypoblast.
    • The primary hypoblast with secondary hypoblast interdigitating results in the elongation of the hypoblast.
    • The epiblast and hypoblast converge at the margins of the area opaca, forming a thickening, which is the Koller's sickle.
    • The Koller's sickle induces the formation of the primitive streak in avian gastrulation.

    Formation of the Primitive Streak

    • Cells from the lateral region of the posterior epiblast migrate towards the midline, inducing the formation of the primitive streak.
    • The primitive streak lengthens and narrows as more cells converge.
    • A depression forms within the streak, the primitive groove, surrounded by primitive folds.
    • A thickening of cells forms into a knot at the anterior end of the primitive groove, the Hensen's node (primitive knot).
    • The Hensen's node is homologous to the dorsal lip of the blastopore.
    • The primitive groove is homologous to the blastopore.

    Gastrulation and Morphogenesis

    • Cells from the epiblast move into the blastocoel, migrating over the lips of the primitive streak and into the blastocoel.
    • Cells move towards the midline, ingressing through the primitive groove.
    • The blastocoel cells migrate to form the endoderm, mesoderm, and ectoderm.
    • Fibronectin guides the migratory behavior of cells from the epiblast, and hyaluronic acid coats the ingressing cells, changing their adhesive behavior.
    • The first migrating cells move ventrally to form the foregut endoderm, displacing the hypoblastic cells.
    • The other cells move anteriorly and form the head process, overlying the Hensen's node.
    • The cells move sideways in the blastocoel to form the head mesoderm and lateral mesoderm.
    • The axial mesoderm forms the chordamesoderm.
    • Avian gastrulation is an ingression of epiblastic cells that form mesenchyme cells.
    • The primitive streak regresses, and the neural structures are pushed anteriorly.
    • The posterior portions of the embryo are still undergoing late gastrulation.
    • The Hensen's Node moves posteriorly, leaving the head process and the notochord in its wake.

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