Lecture 5 - 7 (Set B)
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Questions and Answers

What is the process called when the epiblast and hypoblast form from the inner cell mass?

  • Primitive steak formation
  • Trilaminar germ disc formation
  • Bilaminar germ disc formation (correct)
  • Gastrulation

    • Which of the following is NOT a germ layer formed during trilaminar disc formation?

  • Endoderm
  • Ectoderm
  • Mesoderm
  • Hypoblast (correct)

    • What is the fate of the cells that ingress during trilaminar disc formation?

  • They form the embryonic endoderm and mesoderm (correct)
  • They contribute to the formation of the placenta
  • They differentiate into the notochordal process
  • They give rise to the amniotic ectoderm

    • What is the name of the structure that forms in the epiblast and gives rise to the notochordal process?

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

    Which of the following is NOT a derivative of the epiblast?

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

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

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

    What is the primary function of the notochordal process in gastrulation?

    <p>To induce neural induction</p> Signup and view all the answers

    What is the outcome of neural induction?

    <p>Transformation of dorsal ectoderm to neural plate</p> Signup and view all the answers

    What is the characteristic of presumptive neural plate cells?

    <p>They are low columnar cells that transform into tall columnar cells</p> Signup and view all the answers

    What is the role of CAMs (cell adhesion molecules) in neural plate formation?

    <p>To facilitate cell-to-cell contact and detachment of neural plate cells from epidermal cells</p> Signup and view all the answers

    What is the outcome of the first phase of neurulation?

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

    What is the characteristic of neural plate cells?

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

    What is the role of the axial mesoderm in gastrulation?

    <p>To facilitate neural induction</p> Signup and view all the answers

    What is the process of transformation of low columnar cells into tall columnar cells?

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

    What is the outcome of neurulation?

    <p>Laying down the rudiments of the CNS</p> Signup and view all the answers

    What is the characteristic of presumptive epidermal cells?

    <p>They are flat and squamous</p> Signup and view all the answers

    What is the result of different concentration gradients of signalling factors?

    <p>Activation of different sets of genes</p> Signup and view all the answers

    Where are motor neurons expressed?

    <p>Ventral side</p> Signup and view all the answers

    What happens to the notochord after sending signals?

    <p>It degenerates and is incorporated into the vertebral discs</p> Signup and view all the answers

    What is the name of the opening at the head end of the neural tube?

    <p>Anterior neuropore</p> Signup and view all the answers

    What forms the ventricles of the central nervous system?

    <p>Cavity of the neural tube</p> Signup and view all the answers

    What is the result of the failure of the anterior neuropore to close?

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

    What is the mild form of Spina Bifida?

    <p>Spina Bifida Occulta</p> Signup and view all the answers

    What induces the formation of the neural tube?

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

    Where does secondary neurulation occur?

    <p>Lumbar region</p> Signup and view all the answers

    What is the result of epithelialization in secondary neurulation?

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

    What is the primary difference between the neural plate cells and the epidermal cells during the neural plate stage?

    <p>N-cadherin is seen on the neural plate cells, while E-cadherin is seen on the presumptive epidermis</p> Signup and view all the answers

    What is the result of the neural plate deepening and the neural folds converging towards the midline?

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

    What type of movement do the neural crest cells undergo during mesenchymal migration?

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

    What is the primary function of the dorsal mesoderm?

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

    What is the primary signaling molecule produced by the notochordal cells?

    <p>Sonic hedgehog protein</p> Signup and view all the answers

    What is the outcome of the convergence of the neural folds towards the midline?

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

    What is the characteristic of neural crest cells that distinguishes them from epidermal cells and neural plate cells?

    <p>They do not have cell adhesion proteins</p> Signup and view all the answers

    What is the primary function of the ectodermal cells of the epidermis?

    <p>Production of BMP4 and BMP7</p> Signup and view all the answers

    What is the result of the exposure of the floor plate to Sonic hedgehog protein?

    <p>Formation of the secondary signaling centers</p> Signup and view all the answers

    What is the outcome of the migration of neural crest cells?

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

    What is the primary function of the neural crest cells in the development of the human brain?

    <p>To form the ganglia of the cranial nerves</p> Signup and view all the answers

    What is the outcome of the fusion of the neural folds in the cervical region?

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

    What is the characteristic of the rhombencephalon at a later stage of development?

    <p>It subdivides into rhombomeres</p> Signup and view all the answers

    What is the role of the neural plate in the development of the human brain?

    <p>It develops into the neural plate cells</p> Signup and view all the answers

    What is the characteristic of the 20D embryo?

    <p>The neural groove and fold are formed</p> Signup and view all the answers

    What is the function of the neural crest cells in determining the position of the cranial nerves?

    <p>They determine the position of the cranial nerves</p> Signup and view all the answers

    What is the characteristic of the 23D embryo?

    <p>The pericardial bulge is visible</p> Signup and view all the answers

    What is the role of the gray crescent region in neural induction?

    <p>It determines the dorsal side of the embryo</p> Signup and view all the answers

    What is the characteristic of the 25D embryo?

    <p>The pharyngeal arches are formed</p> Signup and view all the answers

    What is the outcome of the closure of the anterior neuropore?

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

    What is the primary location of neural tube formation in avians?

    <p>Anterior region of the neural tube</p> Signup and view all the answers

    Which class of vertebrates exhibits exclusively secondary neurulation?

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

    What is the function of hinge point cells in neural tube formation?

    <p>To serve as anchors for cell shape change</p> Signup and view all the answers

    At which stage of avian primary neurulation do the neural folds converge?

    <p>C3</p> Signup and view all the answers

    What is the characteristic of neural tube formation in the cephalic end of the embryo?

    <p>It is well advanced</p> Signup and view all the answers

    What is the fate of the neural crest cells during neural tube formation?

    <p>They disperse and leave the neural tube separate from the epidermis</p> Signup and view all the answers

    How many ways does differentiation of the neural tube occur simultaneously?

    <p>3</p> Signup and view all the answers

    What is the level of the embryo where secondary neurulation takes place in humans?

    <p>Around the 35th somite</p> Signup and view all the answers

    What is the role of the B-Catenin-Tcf-3 complex in establishing the dorsal-ventral axis of the embryo?

    <p>To regulate the expression of genes involved in establishing the dorsal-ventral axis, such as siamois and twin genes</p> Signup and view all the answers

    What is the function of the Goosecoid gene in the development of the embryo?

    <p>To regulate the expression of genes involved in establishing the dorsal-ventral axis, such as chordin and noggin</p> Signup and view all the answers

    What is the role of the Anterior Visceral Endoderm (AVE) in embryonic development?

    <p>To organize the anterior-posterior axis and specify the neural pattern</p> Signup and view all the answers

    What is the outcome of the inactivation of the Goosecoid gene?

    <p>The development of ventral structures is promoted</p> Signup and view all the answers

    What is the role of the Beta-Catenin protein in establishing the dorsal-ventral axis?

    <p>To accumulate in the gray crescent region and regulate the expression of dorsal genes</p> Signup and view all the answers

    What is the function of the chordin and noggin genes in establishing the dorsal-ventral axis?

    <p>To inhibit the activity of BMP4 and promote dorsal development</p> Signup and view all the answers

    What is the role of the organizer in embryonic development?

    <p>To pattern the dorsal-ventral axis and regulate the expression of genes involved in neural induction</p> Signup and view all the answers

    What is the outcome of the activation of the Goosecoid gene?

    <p>Neural induction is promoted</p> Signup and view all the answers

    What is the role of the TGF-Beta signaling pathway in establishing the dorsal-ventral axis?

    <p>To regulate the expression of genes involved in establishing the dorsal-ventral axis, such as Goosecoid</p> Signup and view all the answers

    What is the outcome of the inhibition of BMP4 activity?

    <p>Neural induction is promoted</p> Signup and view all the answers

    What is the primary function of the molecular cues or signals during embryonic development?

    <p>To determine the position of embryonic cells relative to the embryo's body axis</p> Signup and view all the answers

    What is the result of the cytoplasmic rearrangement that occurs during fertilization?

    <p>The depletion of particle granules and cytoplasm on the opposite side of sperm entry</p> Signup and view all the answers

    What is the role of VegT and Vg1 molecules during embryonic development?

    <p>To control the expression of genes involved in dorsal fate</p> Signup and view all the answers

    What is the characteristic of the gray crescent area formed during fertilization?

    <p>It is devoid of particle granules and cytoplasm</p> Signup and view all the answers

    What is the outcome of the accumulation of beta catenin on the future dorsal side of the embryo?

    <p>The marking of cells as the future dorsal side of the embryo</p> Signup and view all the answers

    What is the role of cytoplasmic rearrangement during embryonic development?

    <p>To move molecules that specify dorsal fate towards the gray crescent region</p> Signup and view all the answers

    What is the function of the molecules dragged along with the cytoplasmic rearrangement during fertilization?

    <p>To specify the future dorsal side of the embryo</p> Signup and view all the answers

    What is the significance of the region opposite to the site of sperm entry during fertilization?

    <p>It is the site of gray crescent area formation</p> Signup and view all the answers

    What is the role of the Goosecoid gene in the dorsal development of the embryo?

    <p>It codes for the transcription factor that regulates the activity of chordin and noggin.</p> Signup and view all the answers

    What is the outcome of the inhibition of BMP4 activity during gastrulation?

    <p>It favors dorsal development.</p> Signup and view all the answers

    What is the characteristic of the embryonic cells after the midblastula transition?

    <p>They develop dorsal organ rudiments unless they are told differently.</p> Signup and view all the answers

    What is the role of the dorsal mesoderm during the formation of the body axes?

    <p>It sends planar induction signals to the overlying prospective neuroectoderm.</p> Signup and view all the answers

    What is the name of the process that establishes the spatial information within the embryo?

    <p>Body plan formation.</p> Signup and view all the answers

    What is the relationship between the dorsal-ventral patterning of the neural tube and the BMP4 activity?

    <p>BMP4 activity inhibition favors dorsal development, while its activation favors ventral development.</p> Signup and view all the answers

    What is the nature of the inductive signal sent by the dorsal mesoderm during the formation of the body axes?

    <p>Planar signal.</p> Signup and view all the answers

    What is the role of the notochordal process during the formation of the body axes?

    <p>It is part of the axial mesoderm.</p> Signup and view all the answers

    What is the outcome of the gastrulation process?

    <p>The establishment of the chorda-mesodermal cells at the dorsal lip of the blastopore.</p> Signup and view all the answers

    What is the characteristic of the neuroectoderm after receiving the inductive signal?

    <p>It is primed to respond to signal stimuli.</p> Signup and view all the answers

    Study Notes

    Mammalian Gastrulation

    • Formation of primitive streak similar to avian embryo
    • Inner cell mass undergoes delamination to form epiblast and hypoblast
    • Epiblast forms amniotic ectoderm and embryonic epiblast, where the primitive streak will form
    • Formation of epiblast and hypoblast is called bilaminar germ disc formation

    Formation of Germ Layers

    • Ingression of cells to form embryonic endoderm and mesoderm
    • Left on top (outermost) will form embryonic ectoderm
    • Formation of three germ layers: ectoderm, endoderm, and mesoderm (trilaminar disc formation)

    Neural Induction

    • Process where mesodermal cells (notochordal process) act on overlying ectoderm to transform dorsal ectoderm to neural plate
    • Chordamesoderm/notochordal process has an inductive effect, enhancing neural induction
    • Neural plate formation involves epithelial cell behaviors (bending, folding) and cellular activities (change in cell shape)

    Neurulation

    • Formation of neural plate, neural groove, and neural folds
    • Neural groove deepens and neural folds converge towards the midline, forming a V-shaped cavity
    • Neural tube formation through closure of the neuropore
    • Two primary signaling centers: ectodermal cells of the epidermis produce BMP4 and BMP7, and notochordal cells produce Sonic hedgehog protein
    • Secondary signaling centers established within the neural tube, determining dorsal-ventral specification

    Development of the Neural Tube

    • Open anterior and posterior neuropores
    • Anterior neuropore closes around 24th-26th day, and posterior neuropore closes around 28th day
    • Cavity of the neural tube forms the ventricles of the central nervous system
    • Neurocoel (cavity of the neural tube) allows passage of anionic fluid

    Neural Tube Defects (NTDs)

    • Failure of anterior neuropore closure: anencephaly
    • Failure of posterior neuropore closure: spina bifida
    • Spina bifida occulta: mild form, no pain, no neurological disorder
    • Spina bifida cystica: more severe, spinal cord bulges out dorsally, with neurological disorder### Dorsal-Ventral Axis Establishment
    • Dorsal development is allowed when Chordin and Noggin inhibit BMP4 activity
    • Dorsal development leads to the establishment of dorsal mesoderm
    • Dorsal mesoderm consists of notochordal process/axial mesoderm, paraxial mesoderm/somites, and lateral plate mesoderm

    Body Axes Formation

    • Body axes formation occurs after gastrulation
    • Body axes formation involves the establishment of spatial information (positional information)
    • Positional information is supplied by molecular cues or molecular signals
    • Body axes include dorso-ventral axis, anterior-posterior axis (cranio-caudal axis), and left-right axis

    Dorsal-Ventral Axis Establishment (Continued)

    • In amphibian oocyte, cortical reaction occurs at fertilization, leading to cytoplasmic rearrangement
    • Cytoplasmic rearrangement results in the movement of cytoplasm towards the point of sperm entry, creating a gray crescent area
    • Molecules that specify dorsal fate, such as VegT and Vg1, are dragged towards the gray crescent region, marking the future dorsal side of the embryo
    • Beta-catenin accumulates in the gray crescent region, participating in establishing the cordo-mesodermal cells

    Molecular Mechanism

    • Beta-catenin undergoes gradual accumulation in the gray crescent region
    • Beta-catenin forms a complex with Tcf-3, which translocates into the nuclei of cells in the gray crescent region
    • The complex regulates the expression of genes involved in establishing the ventral and dorsal sides of the embryo
    • Siamois and twin genes are activated, which in turn activate the goosecoid gene
    • Goosecoid gene codes for a transcription factor that regulates the chordamesodermal cells
    • Chordin and Noggin, inhibitors of BMP4, are activated, allowing dorsal development to proceed

    Neurulation

    • Neurulation occurs when dorsal development is allowed
    • Neurulation involves the formation of notochord (midline), paraxial mesoderm (lateral to the notochord), and dorsal ectoderm/epidermis (overlaying paraxial mesoderm)

    Anterior-Posterior (A-P) Axis/Cranio-Caudal Axis

    • In mammalian development, A-P polarity is specified by Hox genes during gastrulation
    • Anterior Visceral Endoderm (AVE) is an organizing center for the embryo
    • AVE expresses genes coding for transcription factors, such as OTX2, LIM1, and HESX1, and secreted factors, such as Cerberus and Lefty
    • AVE specifies the neural pattern by inhibiting primitive streak formation anteriorly

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    Description

    Learn about the process of mammalian gastrulation, including the formation of the primitive streak, epiblast, and hypoblast, and their roles in embryonic development.

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