Zebrafish Development and Axis Formation
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Questions and Answers

What role do the deep cells in a zebrafish egg play during development?

  • They will slough off during cleavage.
  • They will form the yolk sac.
  • They will form the embryo. (correct)
  • They will direct cell movements during fertilization.

    • Which component is primarily involved in moving maternally deposited determinants in zebrafish eggs?

  • Actin filaments
  • Cytoskeletons
  • Centrioles
  • Microtubules (correct)

    • In the context of dorsalizing activity in zebrafish, which factor contributes to establishing the dorsal-ventral axis?

  • Activation of squint
  • Inhibitors of β-catenin degradation (correct)
  • Synthesis of yolk proteins
  • Localization of YSL nuclei

    • What is the function of the YSL in zebrafish development?

    <p>To direct cell movements during gastrulation</p> Signup and view all the answers

    Which of the following pairs indicates a similarity in mechanisms for mesoderm induction between zebrafish and Xenopus?

    <p>Zebrafish squint and Xenopus Xnr</p> Signup and view all the answers

    What role does Cyp26 play in anterior-posterior axis specification?

    <p>Hydroxylates retinoic acid in the anterior end</p> Signup and view all the answers

    Which of the following embryos were activated with Nodal ligands in the experiment?

    <p>GFP+/cas+ and RFP+/cas-</p> Signup and view all the answers

    What is the zebrafish equivalent of mammalian brachyury?

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

    During zebrafish gastrulation, what are the two primary mechanisms of cell rearrangement?

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

    Which signaling pathways repress the expression of anterior genes in zebrafish?

    <p>Wnt and Fgf</p> Signup and view all the answers

    What is the primary role of E-Cadherin during zebrafish gastrulation?

    <p>Attaches the EVL to deep cells</p> Signup and view all the answers

    Which factor is known to specify mesoderm in zebrafish?

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

    What indicates a dorsal to ventral BMP signaling gradient in zebrafish?

    <p>Nodal production</p> Signup and view all the answers

    What migratory behavior do endodermal cells exhibit in fish during development?

    <p>Nodal &amp; Casanova-dependent random walk</p> Signup and view all the answers

    What is the significance of latrunculin and nocodazole in mesoderm specification?

    <p>They activate mesoderm specifiers</p> Signup and view all the answers

    Which of the following pairs is likely responsible for endodermal specification in frogs and fish?

    <p>Sox17 and VegT</p> Signup and view all the answers

    How do cell movements during gastrulation primarily occur in zebrafish?

    <p>Via coordinated cell movements</p> Signup and view all the answers

    What is a major outcome of involution during zebrafish development?

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

    What is the function of Cyp26 during zebrafish development?

    <p>Represses expression of anterior genes</p> Signup and view all the answers

    What is the outcome of activating GFP+/cas+ and RFP+/cas- embryos with Nodal ligands?

    <p>Endodermal specification involvement</p> Signup and view all the answers

    Which of the following is a key aspect of the random walk migration of endodermal cells?

    <p>It depends on Nodal and Casanova activity</p> Signup and view all the answers

    What significant role does Notail play in zebrafish development?

    <p>Serving as the equivalent of mammalian brachyury</p> Signup and view all the answers

    In the context of zebrafish gastrulation, which processes describe cell rearrangements?

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

    What is the primary function of the EVL in a zebrafish egg?

    <p>Be sloughed off during development</p> Signup and view all the answers

    In zebrafish development, what does the localization of β-catenin to the presumptive dorsal pole primarily indicate?

    <p>Determination of the dorsal-ventral axis</p> Signup and view all the answers

    How are squint and Xnr related in the context of mesoderm induction?

    <p>They serve as inducers of mesoderm in their respective species</p> Signup and view all the answers

    What does the term 'discoidal meroblastic cleavage' refer to in the context of zebrafish eggs?

    <p>Division where only a small disc of the egg undergoes cleavage</p> Signup and view all the answers

    What role does the YSL play during zebrafish gastrulation?

    <p>Directs cell movements</p> Signup and view all the answers

    What is the primary function of E-Cadherin during zebrafish epiboly?

    <p>Attaches the EVL to deep cells</p> Signup and view all the answers

    Which of the following correctly describes the role of BMP signaling in zebrafish development?

    <p>Establishes a dorsal-ventral signaling gradient</p> Signup and view all the answers

    What mechanism is involved in cell migration for endodermal cells in zebrafish?

    <p>Random walk over the yolk surface</p> Signup and view all the answers

    Which factors are essential for mesoderm specification in both frogs and zebrafish?

    <p>Nodal and Eomesodermin</p> Signup and view all the answers

    During gastrulation, what is the significance of involution in zebrafish development?

    <p>Facilitates the inward movement of cells</p> Signup and view all the answers

    What occurs when Brachyury is absent in zebrafish?

    <p>Inhibition of involution</p> Signup and view all the answers

    How do zebrafish and frogs utilize Sox17 in their development?

    <p>For endoderm specification</p> Signup and view all the answers

    What is the role of mechanical forces such as latrunculin and nocodazole in zebrafish development?

    <p>Activate mesoderm specifiers</p> Signup and view all the answers

    Study Notes

    Early Development in Zebrafish

    • Discoidal meroblastic cleavage: Zebrafish eggs undergo discoidal meroblastic cleavage, where the yolk is not cleaved.
    • Epithelial cells (EVL): An outermost layer of epithelial cells will be sloughed off.
    • Deep cells: Interior cells will form the embryo.
    • YSL: The yolk syncytial layer will direct cell movements during gastrulation.
    • Microtubules: Microtubules move maternally deposited determinants, contributing to the establishment of the dorsoventral axis.

    Dorsoventral Axis Formation

    • Maternal determinants: Maternal determinants establish the dorsoventral axis in a manner similar to Xenopus.
    • Dorsalizing activity: Factors like inhibitors of β-catenin degradation contribute to dorsalizing activity.
    • β-catenin localization: β-catenin localizes to the presumptive dorsal pole.
    • Squint activation: β-catenin activation leads to the activation of the squint gene.

    Endoderm and Mesoderm Specification

    • Similar mechanisms: Zebrafish and Xenopus use similar molecular mechanisms to specify endoderm and mesoderm.
    • Xnr (Xenopus) and Squint (Zebrafish): Both are Nodal-related genes crucial for mesoderm induction.
    • Squint and Cyclops: Zebrafish squint and cyclops genes are similar to Xnr in Xenopus and induce mesoderm formation.

    E-Cadherin and Epiboly

    • Epiboly: A key cell movement during gastrulation in zebrafish, where the outer epithelial layer spreads over the yolk.
    • E-Cadherin role: E-cadherin is essential for epiboly, attaching the EVL to the deep cells, and driving this cell movement.

    Zebrafish Germ Ring

    • Source of mesoderm and endoderm: The germ ring is the source of mesoderm and endoderm in zebrafish.
    • Delamination and Ingression: These processes involve specific migration and movement of cells.

    BMP Gradients and Neuroectoderm/Mesoderm Patterning

    • Gradients: A dorsal-ventral (low-high) BMP signaling gradient is established during zebrafish development.
    • Pattern formation: This gradient influences the patterning of neuroectoderm and mesoderm along the DV axis.

    Endomesoderm Specification in the Frog

    • Model for mesoderm specification in Xenopus:
      • VegT (a transcription factor) activates Xnr (Nodal).
      • Xnr activates specific genes for mesoderm formation: Brachyury and Eomesodermin.
    • Endoderm factors: Transcription factors in the endoderm, such as Sox17, likely contribute to mesoderm specification.

    Mechanical Forces and Mesoderm Specification in Zebrafish

    • Latrunculin A and Nocodazole: These drugs disrupt the actin cytoskeleton and microtubule function, respectively.
    • Effects on Brachyury expression: Disrupting cytoskeletal function affects the expression of Brachyury (aka notail) gene, which is crucial for mesoderm formation.

    Endodermal Markers and Cell Migration

    • Casanova (sox32) and Sox17: These genes are markers of endoderm in zebrafish.
    • Endodermal cell migration: Zebrafish endodermal cells migrate randomly over the surface of the yolk.
    • Nodal and Casanova: These factors are crucial for endodermal cell migration.

    Zebrafish AP Axis Formation

    • Notail: Notail is the zebrafish homologue of mammalian brachyury and Xenopus Xbra.
    • Evolutionary conservation: Notail, brachyury, and Xbra are part of a conserved pathway across evolution, dating back over 450 million years.

    Recap of Zebrafish Gastrulation

    • Key events: Gastrulation in zebrafish involves involution and ingression of cells from the germ ring.

    Anterior-Posterior Axis Formation

    • Cyp26: This gene encodes a retinoic acid hydroxylase that degrades retinoic acid (RA), a key player in anterior-posterior patterning.
    • Anterior-posterior gradient: A gradient of RA is established, with higher levels in the posterior and lower levels in the anterior.
    • Cyp26 localization: High levels of Cyp26 expression in the anterior region contribute to an anterior-posterior gradient in RA signaling.
    • FGF and Wnt: Signaling pathways involving FGF and Wnt repress expression of anterior genes.
    • Otx2: An anterior gene regulated by Cyp26 and FGF/Wnt signaling.

    Zebrafish Development

    • Discoidal Meroblastic Cleavage: The zebrafish egg undergoes discoidal meroblastic cleavage, with a yolk mass and a blastodisc.
    • Epithelial (EVL) Cells: The epithelial cells will eventually be sloughed off.
    • Deep Cells: Deep cells differentiate into the embryo.
    • YSL (Yolk Syncytial Layer): Provides structure and directs cell movements during gastrulation.
    • Microtubules: Transport maternally deposited determinants during development.

    Dorsal-Ventral Axis Formation

    • Maternal determinants: Establish the dorsal-ventral (DV) axis in zebrafish.
    • Dorsalizing Activity: Dorsalizing activity, like inhibitors of β-catenin degradation, leads to β-catenin localization to the presumptive dorsal pole.
    • Squint: Squint is a Nodal-related protein that is activated in the dorsal region.

    Endoderm and Mesoderm Specification

    • Squint and Xnr: Squint and Xnr are similar in function and play roles in the induction of mesoderm in zebrafish and Xenopus, respectively.
    • β-catenin Localization: β-catenin is localized in YSL nuclei, which are analogous to the Xnr expressing cells in Xenopus.

    Gastrulation in Zebrafish

    • E-cadherin: Essential for epiboly, the process of cell movement during gastrulation in zebrafish. E-cadherin attaches the EVL cells to the deep cells.
    • Germ Ring: The source of mesoderm and endoderm in zebrafish.
    • Involution and Ingression: Cell movements that occur at the 6-hour post-fertilization (hpf) mark.
    • BMP Signaling: A dorsal-ventral gradient of BMP signaling patterns the neuroectoderm and mesoderm along the DV axis.

    Endomesoderm Specification in Fish

    • Endoderm: Endodermal factors contribute to mesoderm specification in fish.
    • Sox17, VegT, Xnr, Brachyury: These are key factors involved in endoderm and mesoderm specification in fish, with similarities to processes observed in Xenopus.
    • Brachyury: A transcription factor required for mesoderm formation.
    • Mechanical Forces: Mechanical forces, like those generated by cytoskeletal elements or changes in cell shape, contribute to mesoderm development in fish.

    Endoderm Cell Migration in Zebrafish

    • Casanova (sox32) and sox17: Endodermal markers in zebrafish.
    • Nodal and Casanova: Work together to enable endodermal cell migration, which occurs as a random walk on the yolk surface.

    Anterior-Posterior (AP) Axis Formation in Zebrafish

    • Notail: A zebrafish gene equivalent to mammalian brachyury and Xenopus Xbra, involved in AP axis formation.
    • Cyp26: A retinoic acid hydroxylase that breaks down retinoic acid (RA) in the anterior region, preventing its accumulation and allowing for correct anterior development.
    • Wnt and FGF: These signaling pathways repress expression of anterior genes, contributing to establishing the AP axis.
    • Otx2: An anterior gene that is repressed by Wnt and FGF signaling and promoted where Cyp26 is expressed.

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    Description

    This quiz covers the early developmental processes in zebrafish, focusing on discoidal meroblastic cleavage, the formation of the dorsoventral axis, and the role of maternal determinants. It includes key concepts such as the roles of epithelial cells, deep cells, and the yolk syncytial layer in embryogenesis.

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