82 Questions
What is the process called when the epiblast and hypoblast form from the inner cell mass?
Bilaminar germ disc formation
Which of the following is NOT a germ layer formed during trilaminar disc formation?
Hypoblast
What is the fate of the cells that ingress during trilaminar disc formation?
They form the embryonic endoderm and mesoderm
What is the name of the structure that forms in the epiblast and gives rise to the notochordal process?
Primitive streak
Which of the following is NOT a derivative of the epiblast?
Embryonic endoderm
What is the fate of the amniotic ectoderm and the rest of the hypoblast and trophoblast?
They contribute to the large part of the placenta
What is the primary function of the notochordal process in gastrulation?
To induce neural induction
What is the outcome of neural induction?
Transformation of dorsal ectoderm to neural plate
What is the characteristic of presumptive neural plate cells?
They are low columnar cells that transform into tall columnar cells
What is the role of CAMs (cell adhesion molecules) in neural plate formation?
To facilitate cell-to-cell contact and detachment of neural plate cells from epidermal cells
What is the outcome of the first phase of neurulation?
Thickening of the epithelial cells
What is the characteristic of neural plate cells?
They are tall columnar cells
What is the role of the axial mesoderm in gastrulation?
To facilitate neural induction
What is the process of transformation of low columnar cells into tall columnar cells?
Columnarization
What is the outcome of neurulation?
Laying down the rudiments of the CNS
What is the characteristic of presumptive epidermal cells?
They are flat and squamous
What is the result of different concentration gradients of signalling factors?
Activation of different sets of genes
Where are motor neurons expressed?
Ventral side
What happens to the notochord after sending signals?
It degenerates and is incorporated into the vertebral discs
What is the name of the opening at the head end of the neural tube?
Anterior neuropore
What forms the ventricles of the central nervous system?
Cavity of the neural tube
What is the result of the failure of the anterior neuropore to close?
Anencephaly
What is the mild form of Spina Bifida?
Spina Bifida Occulta
What induces the formation of the neural tube?
Notochord and mesoderm
Where does secondary neurulation occur?
Lumbar region
What is the result of epithelialization in secondary neurulation?
Formation of a cavity
What is the primary difference between the neural plate cells and the epidermal cells during the neural plate stage?
N-cadherin is seen on the neural plate cells, while E-cadherin is seen on the presumptive epidermis
What is the result of the neural plate deepening and the neural folds converging towards the midline?
Formation of the neural groove
What type of movement do the neural crest cells undergo during mesenchymal migration?
Amoeboid movement
What is the primary function of the dorsal mesoderm?
Formation of the somites
What is the primary signaling molecule produced by the notochordal cells?
Sonic hedgehog protein
What is the outcome of the convergence of the neural folds towards the midline?
Formation of the neural tube
What is the characteristic of neural crest cells that distinguishes them from epidermal cells and neural plate cells?
They do not have cell adhesion proteins
What is the primary function of the ectodermal cells of the epidermis?
Production of BMP4 and BMP7
What is the result of the exposure of the floor plate to Sonic hedgehog protein?
Formation of the secondary signaling centers
What is the outcome of the migration of neural crest cells?
Formation of the somites
What is the primary function of the neural crest cells in the development of the human brain?
To form the ganglia of the cranial nerves
What is the outcome of the fusion of the neural folds in the cervical region?
Formation of the neural tube
What is the characteristic of the rhombencephalon at a later stage of development?
It subdivides into rhombomeres
What is the role of the neural plate in the development of the human brain?
It develops into the neural plate cells
What is the characteristic of the 20D embryo?
The neural groove and fold are formed
What is the function of the neural crest cells in determining the position of the cranial nerves?
They determine the position of the cranial nerves
What is the characteristic of the 23D embryo?
The pericardial bulge is visible
What is the role of the gray crescent region in neural induction?
It determines the dorsal side of the embryo
What is the characteristic of the 25D embryo?
The pharyngeal arches are formed
What is the outcome of the closure of the anterior neuropore?
Formation of the neural tube
What is the primary location of neural tube formation in avians?
Anterior region of the neural tube
Which class of vertebrates exhibits exclusively secondary neurulation?
Fishes
What is the function of hinge point cells in neural tube formation?
To serve as anchors for cell shape change
At which stage of avian primary neurulation do the neural folds converge?
C3
What is the characteristic of neural tube formation in the cephalic end of the embryo?
It is well advanced
What is the fate of the neural crest cells during neural tube formation?
They disperse and leave the neural tube separate from the epidermis
How many ways does differentiation of the neural tube occur simultaneously?
3
What is the level of the embryo where secondary neurulation takes place in humans?
Around the 35th somite
What is the role of the B-Catenin-Tcf-3 complex in establishing the dorsal-ventral axis of the embryo?
To regulate the expression of genes involved in establishing the dorsal-ventral axis, such as siamois and twin genes
What is the function of the Goosecoid gene in the development of the embryo?
To regulate the expression of genes involved in establishing the dorsal-ventral axis, such as chordin and noggin
What is the role of the Anterior Visceral Endoderm (AVE) in embryonic development?
To organize the anterior-posterior axis and specify the neural pattern
What is the outcome of the inactivation of the Goosecoid gene?
The development of ventral structures is promoted
What is the role of the Beta-Catenin protein in establishing the dorsal-ventral axis?
To accumulate in the gray crescent region and regulate the expression of dorsal genes
What is the function of the chordin and noggin genes in establishing the dorsal-ventral axis?
To inhibit the activity of BMP4 and promote dorsal development
What is the role of the organizer in embryonic development?
To pattern the dorsal-ventral axis and regulate the expression of genes involved in neural induction
What is the outcome of the activation of the Goosecoid gene?
Neural induction is promoted
What is the role of the TGF-Beta signaling pathway in establishing the dorsal-ventral axis?
To regulate the expression of genes involved in establishing the dorsal-ventral axis, such as Goosecoid
What is the outcome of the inhibition of BMP4 activity?
Neural induction is promoted
What is the primary function of the molecular cues or signals during embryonic development?
To determine the position of embryonic cells relative to the embryo's body axis
What is the result of the cytoplasmic rearrangement that occurs during fertilization?
The depletion of particle granules and cytoplasm on the opposite side of sperm entry
What is the role of VegT and Vg1 molecules during embryonic development?
To control the expression of genes involved in dorsal fate
What is the characteristic of the gray crescent area formed during fertilization?
It is devoid of particle granules and cytoplasm
What is the outcome of the accumulation of beta catenin on the future dorsal side of the embryo?
The marking of cells as the future dorsal side of the embryo
What is the role of cytoplasmic rearrangement during embryonic development?
To move molecules that specify dorsal fate towards the gray crescent region
What is the function of the molecules dragged along with the cytoplasmic rearrangement during fertilization?
To specify the future dorsal side of the embryo
What is the significance of the region opposite to the site of sperm entry during fertilization?
It is the site of gray crescent area formation
What is the role of the Goosecoid gene in the dorsal development of the embryo?
It codes for the transcription factor that regulates the activity of chordin and noggin.
What is the outcome of the inhibition of BMP4 activity during gastrulation?
It favors dorsal development.
What is the characteristic of the embryonic cells after the midblastula transition?
They develop dorsal organ rudiments unless they are told differently.
What is the role of the dorsal mesoderm during the formation of the body axes?
It sends planar induction signals to the overlying prospective neuroectoderm.
What is the name of the process that establishes the spatial information within the embryo?
Body plan formation.
What is the relationship between the dorsal-ventral patterning of the neural tube and the BMP4 activity?
BMP4 activity inhibition favors dorsal development, while its activation favors ventral development.
What is the nature of the inductive signal sent by the dorsal mesoderm during the formation of the body axes?
Planar signal.
What is the role of the notochordal process during the formation of the body axes?
It is part of the axial mesoderm.
What is the outcome of the gastrulation process?
The establishment of the chorda-mesodermal cells at the dorsal lip of the blastopore.
What is the characteristic of the neuroectoderm after receiving the inductive signal?
It is primed to respond to signal stimuli.
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
Learn about the process of mammalian gastrulation, including the formation of the primitive streak, epiblast, and hypoblast, and their roles in embryonic development.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
