Embryonic Development: Gastrulation Processes
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Questions and Answers

What role does the notochord play during embryonic development?

  • Inhibits the development of skeletal structures
  • Acts as the original longitudinal support of the body and induces neural tissue formation (correct)
  • Facilitates the division of mesodermal somites into muscle membranes
  • Promotes the growth of ectoderm into muscle tissue

    • Which signaling molecule is crucial for establishing the dorsal-ventral axis during gastrulation?

  • Nanog
  • WNT3 (correct)
  • Gata-6
  • Sonic hedgehog

    • How does the notochord influence the development of the nervous system?

  • By providing structural support to the developing brain
  • By directly forming neural tissues in the ectoderm
  • Through inductive signals that specify cells in the early nervous system (correct)
  • By transforming endodermal tissues into neural structures

    • What function does Sonic hedgehog serve in embryonic development?

    <p>Facilitates cell differentiation and patterning (D)</p> Signup and view all the answers

    What is the primary role of Nanog in embryonic development?

    <p>Maintains the pluripotency of embryonic stem cells (A)</p> Signup and view all the answers

    Which process allows the formation of different layers during embryonic development?

    <p>Delamination (A)</p> Signup and view all the answers

    What role do the epiblast and hypoblast serve in the inner cell mass?

    <p>Form the yolk sac and the embryo proper (D)</p> Signup and view all the answers

    What process involves cells interlacing with one another and splitting a cell sheet?

    <p>Intercalation (A)</p> Signup and view all the answers

    Which cell type is associated with pluripotency in the inner cell mass?

    <p>Epiblast (C)</p> Signup and view all the answers

    During which week of development does gastrulation primarily occur in humans?

    <p>Third week (D)</p> Signup and view all the answers

    What is the outcome of the convergent extension process?

    <p>Cells extending and forming fewer layers (B)</p> Signup and view all the answers

    What factor do early cells in the inner cell mass secrete to induce later cells to express GATA-6?

    <p>FGF4 (D)</p> Signup and view all the answers

    Why is gastrulation considered a pivotal stage in embryonic development?

    <p>It leads to the establishment of three primary germ layers (B)</p> Signup and view all the answers

    Which germ layer is primarily responsible for the development of skin and the nervous system?

    <p>Ectoderm (D)</p> Signup and view all the answers

    What structure forms at the anterior end of the primitive streak during gastrulation?

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

    What is the function of the primitive pit during the gastrulation process?

    <p>Serve as an entrance for epiblast cells (A)</p> Signup and view all the answers

    Which of the following cell types develops from the mesoderm?

    <p>Cardiac muscle cells (C)</p> Signup and view all the answers

    Which signaling molecule is crucial for initiating gastrulation?

    <p>Nodal (B)</p> Signup and view all the answers

    Which transcription factor is involved in the development of the anterior visceral endoderm (AVE)?

    <p>Hesx-1 (B)</p> Signup and view all the answers

    What occurs at the start of gastrulation regarding the epiblast cells?

    <p>They start to move and internalize. (D)</p> Signup and view all the answers

    What is the primary role of fibroblast growth factor (FGF) during gastrulation?

    <p>To control cell movement and EMT (A)</p> Signup and view all the answers

    What is the ultimate fate of the cells that pass through the primitive streak?

    <p>They become mesodermal cells. (C)</p> Signup and view all the answers

    Which of the following factors is NOT involved in the induction of the primitive streak?

    <p>Histone modification (C)</p> Signup and view all the answers

    What transformation occurs in cells during the epithelial-mesenchymal transition (EMT)?

    <p>Cells become more mobile and lose shape (B)</p> Signup and view all the answers

    Which germ layer gives rise to the organs such as the lungs, liver, and pancreas?

    <p>Endoderm (D)</p> Signup and view all the answers

    Which component of the embryo is primarily responsible for establishing the left-right body axis?

    <p>Nodal (D)</p> Signup and view all the answers

    Flashcards

    Notochord

    A structure formed during development that provides support and induces tissue formation.

    Inductive signals

    Signals from the notochord that influence surrounding tissues to change fate.

    WNT3

    A signaling molecule important for establishing body axis during gastrulation.

    Sonic hedgehog (Shh)

    A signaling molecule that guides cell differentiation and organ formation.

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    Nanog

    A transcription factor that maintains the pluripotent state of embryonic stem cells.

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    Delamination

    The process that allows formation of different layers before implantation.

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    Intercalation

    Two cell layers interlace, splitting a cell sheet into multiple layers.

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    Epiboly

    Cell spreading that allows a layer to cover more surface area.

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    Invagination

    A tissue layer folds inward, crucial for structures like the optic vesicle.

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    Convergent extension

    Cells extend out while forming fewer layers, seen in notochordal processes.

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    Epiblast

    Columnar cells that form the embryo proper as part of the inner cell mass.

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    Gastrulation

    The process where three primary germ layers form from the epiblast.

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    Time inside - Time outside Hypothesis

    Early entering cells express Nanog and induce later cells to form hypoblast through GATA-6.

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    Germ Layers

    Three primary layers in early embryos: ectoderm, mesoderm, endoderm.

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    Ectoderm

    The outer germ layer that forms skin and nervous system.

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    Mesoderm

    The middle germ layer that develops into muscles and organs.

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    Endoderm

    The innermost germ layer that forms hollow organs like lungs and liver.

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    Anterior and Posterior

    Refers to the front (anterior) and back (posterior) of the embryo.

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    Primitive Streak

    Structure that forms during gastrulation marking the future body axes.

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    Hensen's Node

    Thickening at the anterior part of the primitive groove in developing embryos.

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    Induction

    The process where one tissue influences another during development.

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    Epithelial-Mesenchymal Transformation (EMT)

    Process where epithelial cells gain migratory properties and lose adhesions.

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    Nodal

    A signaling molecule that initiates gastrulation and axis formation.

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    Fibroblast Growth Factor (FGF)

    A protein that regulates cell movement during gastrulation.

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    Mesoderm Formation

    Event where cells spread out and differentiate into various mesodermal regions.

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    Paraxial Mesoderm

    Region of mesoderm that forms somites, leading to vertebrates and muscles.

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    Lefty-1

    A protein involved in the determination of left-right asymmetry in embryos.

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    Otx-2

    A transcription factor essential for head and forebrain development.

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    Study Notes

    Embryonic Development: Before and During Gastrulation

    • Pre-Gastrulation Processes:
      • Delamination: Cells split into layers, forming different cell types.
      • Intercalation: Cell layers intermix, forming complex structures.
      • Epiboly: Cells spread and flatten, covering more surface area. Crucial for embryo growth.
      • Invagination/Evagination: Inward or outward folding of tissues (e.g., optic vesicle).
      • Involution: Tissue lip folds inward.
      • Convergent Extension: Cells form fewer layers and extend outward (e.g., notochord).
    • Inner Cell Mass (ICM) Differentiation:
      • Epiblast: Columnar cells forming the embryo. Expresses Nanog for pluripotency.
      • Hypoblast (Primitive Endoderm): Cuboidal cells, underlying epiblast, forming the yolk sac. Expresses GATA-6.
      • Bilaminar Germ Disc: Two-layered structure (epiblast and hypoblast) formed from ICM.
    • Time Inside/Time Outside Hypothesis:
      • Cells entering ICM early have Nanog expression for pluripotency.
      • Secrete FGF4, inducing GATA-6 expression in later arriving cells.
      • GATA-6 positive cells exhibit increased adhesion and mobility, migrating to form hypoblast.
    • Gastrulation:
      • Process forming three primary germ layers (ectoderm, mesoderm, endoderm) from epiblast.
      • Forms trilaminar embryo, called gastrula.
      • Occurs around week three in humans.
      • Importance: Establishes germ layers, basic body plan, and body axes(anterior/posterior, dorsal/ventral, left/right).
    • Germ Layers:
      • Ectoderm: Forms outer layer; includes neural tissue and skin.
      • Mesoderm: Middle layer; forms heart, blood, muscle, skeletal systems.
      • Endoderm: Innermost layer; forms organs (lungs, liver, pancreas).
    • Gastrulation Initiation:
      • Primitive Streak: Structure initiating germ layer formation in epiblast, appearing posteriorly and growing anteriorly.
      • Defines anteroposterior (craniocaudal), right-left body axes.
      • Primitive Node: Anterior thickening of primitive streak.
      • Primitive Pit: Depression within primitive node.
      • Primitive Groove: Groove created by the moving primitive streak.
      • Hensen's Node: Thickening at primitive streak's anterior end.
    • Induction:
      • Influence of one tissue (inducer) on another (responder), altering their cell fate.
      • Signals cause responder differentiation (changes gene expression).
    • Primitive Streak Induction Signals:
      • Posterior Wnt activity induces Nodal expression.
      • AVE cells produce nodal inhibitors Lefty-1 & Cer-1.
      • Node expresses Noggin & Chordin genes, influencing head development.
      • AVE cells express Lim-1, Hesx-1, Otx-2 genes crucial for head development.
    • Significance of Nodal, Lefty-1, Cer-1, etc: These proteins are key signaling molecules and transcription factors regulating gastrulation and axis formation.
    • Cell Movements & Rearrangements:
      • Epiblast cells converge in defined steps forming primitive node, groove.
      • Cells internalize, moving into the embryo to form mesoderm & endoderm from epiblast.
    • Epithelial-Mesenchymal Transition (EMT):
      • Epiblast cells change shape, losing basal lamina connections (epithelial) becoming mesenchymal cells for migration. -> Crucial for layer formation.
    • EMT-related Markers:
      • Epiblast cells respond to signals, influencing mesoderm formation.
      • Synthesis of FGFs.
      • FGFs regulate cell movements, downregulating E-cadherin (promotes EMT); activating snail gene.
      • Switching to N-cadherin loosens cell adhesion facilitating movement.
    • Mesoderm Formation: Lateral spreading of mesodermal cells into three regions:
      • Paraxial: Somites (vertebrae, ribs, muscles).
      • Intermediate: Urogenital system.
      • Lateral plate: Circulatory system, body cavities, limb connective tissue.
    • Notochord:
      • Formed ventrally to the CNS, initially caudal then regresses cranially.
      • Important for body support and inducing neural tissue from overlying ectoderm.
      • Influences mesodermal cells into vertebral structures.
    • Signaling Molecules: Examples of crucial signaling molecules during this process.
      • Nodal, WNT3, Nanog, Shh, Gata-6 (and various other example transcription factors not in text)

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    Description

    Explore the intricate processes of embryonic development before and during gastrulation. This quiz covers key concepts such as delamination, intercalation, and differentiation of the inner cell mass. Test your knowledge on how these processes contribute to the formation of the embryo.

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