Leccture 6

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Questions and Answers

During the neural plate stage, which type of cells is characterized by the presence of E-cadherin?

Neural cells

Epidermal cells (correct)

Neural crest cells

Mesenchymal cells

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

Formation of the neural folds

Formation of the neural crest

Formation of the neural tube

Formation of the neural groove (correct)

Which of the following is NOT a characteristic of neural crest cells?

They are of mesenchymal type

They express N-cadherin

They do not have cell adhesion proteins

They express E-cadherin (correct)

What is the result of the closure of the neuromere?

The neural tube pinches off from the epidermal layer Signup and view all the answers

Which of the following is a primary signaling center in the neural tube?

Ectodermal cells of the epidermis Signup and view all the answers

What is the role of Sonic hedgehog protein in the neural tube?

It determines the dorsal-ventral specification of the neural tube Signup and view all the answers

What is the result of the convergent elongation and convergent thickening of the neural plate?

Formation of the neural folds Signup and view all the answers

Which of the following is a characteristic of the neural crest cells?

They are of mesenchymal type Signup and view all the answers

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

Differentiation into the dorsal mesoderm Signup and view all the answers

Which of the following is a secondary signaling center in the neural tube?

Floor plate cells Signup and view all the answers

What is the significance of neurulation in organogenesis?

It marks the start of organogenesis Signup and view all the answers

What is the role of the axial mesoderm in neurulation?

It facilitates neural induction Signup and view all the answers

What is the outcome of neural induction?

The transformation of dorsal ectoderm into neural plate Signup and view all the answers

What is the function of N-cadherin in neural plate formation?

It facilitates the formation of neural plate cells Signup and view all the answers

What is the role of CAMs in neural plate formation?

They facilitate the clumping of neural plate cells and epidermal cells Signup and view all the answers

What is the characteristic of presumptive neural plate cells?

They are tall columnar cells Signup and view all the answers

What is the outcome of the first phase of neurulation?

The compression and thickening of epithelial cells Signup and view all the answers

What is the role of neural crest cells in neurulation?

They give rise to ganglia Signup and view all the answers

What is the characteristic of the neural plate during neurulation?

It is a plate of tall columnar cells Signup and view all the answers

What is the significance of the dorsal-ventral axis in neurulation?

It is established during the gastrula stage Signup and view all the answers

What is the primary function of the concentration gradients in the development of the neural tube?

To activate the expression of different sets of genes Signup and view all the answers

What is the fate of the notochord in the vertebral column?

It degenerates and forms the nucleus pulposus Signup and view all the answers

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

Anencephaly Signup and view all the answers

What is the difference between primary and secondary neurulation?

Primary neurulation occurs in the cephalic region, while secondary neurulation occurs in the lumbar region Signup and view all the answers

What is the role of the mesoderm in primary neurulation?

To induce the formation of the neural tube Signup and view all the answers

What is the name of the cavity that forms within the neural tube?

Neurocoel Signup and view all the answers

What is the term for the mild form of Spina Bifida?

Spina Bifida Occulta Signup and view all the answers

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

Spina Bifida Signup and view all the answers

What is the term for the process by which the medullary cord undergoes epithelialization?

Epithelialization Signup and view all the answers

What is the stage at which primary neurulation ends in human embryonic development?

4th week Signup and view all the answers

Where does the neural tube form in avians during secondary neurulation?

Caudal region at about the level of the 25th somite Signup and view all the answers

What is the major difference between primary and secondary neurulation in terms of location?

Primary neurulation occurs in the anterior region, while secondary neurulation occurs in the posterior region Signup and view all the answers

What is the role of the hinge point cells in neurulation?

They change shape, wedging, and pull the epidermal cells to the midline Signup and view all the answers

In which class of vertebrates does secondary neurulation occur exclusively?

Fishes Signup and view all the answers

What is the order of neurulation in the chick embryo?

A1, B2, C3, D4 Signup and view all the answers

What is the result of the convergence of the neural folds during neurulation?

The neural tube becomes separate from the epidermis Signup and view all the answers

What is the level at which secondary neurulation occurs in humans?

Around the level of the 35th somite Signup and view all the answers

What is the result of the formation of dorsolateral hinge point cells during neurulation?

The epidermal cells are pulled towards the midline Signup and view all the answers

What is the primary function of neural crest cells in rhombencephalon?

Determining the location of cranial nerves Signup and view all the answers

What is the term for the periodic swellings on the rhombencephalon?

Rhombomeres Signup and view all the answers

At what stage of embryonic development does the neural plate become visible?

19D embryo Signup and view all the answers

What is the term for the aggregate of nerve cell bodies?

Ganglion Signup and view all the answers

What is the process by which the neural folds close in the cervical region?

Fusion Signup and view all the answers

At what stage of embryonic development does the pericardial bulge form?

23D embryo Signup and view all the answers

What is the term for the gray crescent region formed in the fertilized egg?

Dorsal side Signup and view all the answers

What is the function of the cortical movement in the fertilized egg?

Determining the dorsal side of the embryo Signup and view all the answers

What is the term for the molecular marker expressed in ventral cells?

Epi 1 Signup and view all the answers

What is the process by which the neural induction occurs?

Multistep process Signup and view all the answers

What is the primary function of the dorsal mesoderm during the gastrula stage?

Sending planar induction signals to the organizer Signup and view all the answers

What is the role of Bone Morphogenetic Protein 4 (BMP4) in dorsal axis formation?

Natural inhibitor of dorsal axis formation Signup and view all the answers

During gastrulation, what is established at the dorsal lip of the blastopore?

The dorsal lip of the blastopore and the chorda-mesodermal cells Signup and view all the answers

What is the purpose of the goosecoid gene in dorsal development?

To regulate the activity of chordin and noggin Signup and view all the answers

What is the outcome of BMP4 inactivation during axis formation?

Favors dorsal development Signup and view all the answers

What is the significance of the Hensen’s node in avian and mammalian development?

Establishes the presence of nodal cells Signup and view all the answers

What is the relationship between the cranio-caudal axis and the dorsal-ventral patterning of the neural tube?

The dorsal-ventral patterning of the neural tube determines the cranio-caudal axis Signup and view all the answers

What is the process by which the body axes are formed after neurulation?

Body axes formation Signup and view all the answers

What is the term for the spatial and temporal expression of genes during axis formation?

Spatial temporal expression Signup and view all the answers

What is the primary outcome of the dorsal mesoderm sending vertical signals to the overlying prospective neuroectoderm/dorsal ectoderm?

Formation of the neural tube Signup and view all the answers

During the neural plate stage, what is the primary function of N-cadherin?

To separate neural cells from epidermal cells Signup and view all the answers

What is the primary signaling molecule involved in the specification of the dorsal-ventral axis of the neural tube?

Sonic hedgehog protein Signup and view all the answers

What is the characteristic of neural crest cells that allows them to migrate and disperse?

Absence of cell adhesion proteins Signup and view all the answers

During the formation of the neural tube, what is the role of convergent extension?

To converge the neural folds towards the midline Signup and view all the answers

What is the primary function of the notochordal process during neurulation?

To pattern the dorsal-ventral axis of the neural tube Signup and view all the answers

What is the result of the closure of the neural tube?

Separation of the neural crest cells from the epidermis Signup and view all the answers

What is the characteristic of the roof plate cells of the neural tube?

They secrete BMP4 Signup and view all the answers

What is the primary function of the neural crest cells during development?

To migrate and differentiate into various cell types Signup and view all the answers

During the formation of the neural tube, what is the role of the neural folds?

To converge towards the midline Signup and view all the answers

What is the primary function of the axial mesoderm during neurulation?

To form the notochordal process Signup and view all the answers

In which region of the embryo does secondary neurulation occur in avians?

Caudal end Signup and view all the answers

What is the level at which secondary neurulation occurs in humans?

35th somite Signup and view all the answers

What is the difference between primary and secondary neurulation in terms of location?

Primary occurs in the anterior, secondary in the posterior Signup and view all the answers

In which class of vertebrates does secondary neurulation occur exclusively?

Fishes Signup and view all the answers

What is the role of dorsolateral hinge point cells in neurulation?

To change cell shape and pull epidermal cells to the midline Signup and view all the answers

What is the order of neurulation in the chick embryo?

A1, B2, C3, D4 Signup and view all the answers

What is the result of the convergence of the neural folds during neurulation?

Formation of the neural tube Signup and view all the answers

Where does the neural tube form in avians during secondary neurulation?

Caudal end Signup and view all the answers

What is the result of the different concentrations of the signalling factors in the neural tube?

Different sets of genes are activated in response to the different concentrations of the signalling factors. Signup and view all the answers

What is the fate of the notochord in the vertebral column?

It eventually degenerates and is incorporated as components of the vertebral discs. Signup and view all the answers

What is the difference between primary and secondary neurulation?

Primary neurulation occurs in the cephalic region, while secondary neurulation occurs in the lumbar region. Signup and view all the answers

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

Spina Bifida, which has different degrees of severity. Signup and view all the answers

What is the term for the mild form of Spina Bifida?

Spina Bifida Occulta Signup and view all the answers

What is the process by which the medullary cord undergoes epithelialization?

Epithelialization Signup and view all the answers

What is the stage at which primary neurulation ends in human embryonic development?

4th week of embryonic development Signup and view all the answers

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

The formation of the brain Signup and view all the answers

What is the term for the cavity that forms within the neural tube?

Neurocoel Signup and view all the answers

What is the role of the notochord and the mesoderm in primary neurulation?

They induce the formation of the neural tube. Signup and view all the answers

What is the name of the cavity that forms within the neural tube during embryonic development?

Neural cavity Signup and view all the answers

At what stage of embryonic development does the neural plate become visible?

19D embryo Signup and view all the answers

What is the term for the periodic swellings on the rhombencephalon?

Rhombomeres Signup and view all the answers

What is the term for the aggregate of nerve cell bodies?

Ganglion Signup and view all the answers

What is the process by which the neural folds close in the cervical region?

Neural closure Signup and view all the answers

At what stage of embryonic development does the pericardial bulge form?

23D embryo Signup and view all the answers

What is the term for the gray crescent region formed in the fertilized egg?

Gray crescent Signup and view all the answers

What is the function of the cortical movement in the fertilized egg?

Determines the dorsal side of the embryo Signup and view all the answers

What is the term for the molecular marker expressed in ventral cells?

Epi 1 Signup and view all the answers

What is the process by which the neural induction occurs?

Neural induction Signup and view all the answers

What is the primary function of the neural crest cells in the development of the central nervous system?

To differentiate into various neural structures and migrate to different parts of the body Signup and view all the answers

During which stage of embryonic development is the dorsal-ventral axis established?

Gastrula stage Signup and view all the answers

What is the role of the notochordal process in the development of the central nervous system?

To facilitate neural induction and form the neural plate Signup and view all the answers

What is the outcome of the neural induction process?

The transformation of the dorsal ectoderm into the neural plate Signup and view all the answers

What is the characteristic of the presumptive neural plate cells?

They are tall columnar and express N-cadherin Signup and view all the answers

What is the role of the cell adhesion molecules (CAMs) during neurulation?

To make the cells of the presumptive epidermis clump together, and the neural plate cells clump together Signup and view all the answers

What is the significance of neurulation in organogenesis?

It marks the start of organogenesis Signup and view all the answers

What is the outcome of the first phase of neurulation?

The compression and thickening of the epithelial cells Signup and view all the answers

What is the role of the axial mesoderm in neurulation?

To facilitate neural induction and form the neural plate Signup and view all the answers

What is the characteristic of the neural plate during neurulation?

It is a plate of tall columnar cells Signup and view all the answers

What is the primary function of the goosecoid gene during the gastrula stage?

To regulate the activity of chordin and noggin Signup and view all the answers

What is the significance of the dorsal-ventral axis in body axes formation?

It governs the establishment of axis formation Signup and view all the answers

During gastrulation, what is the role of the dorsal lip of the blastopore?

It establishes the chorda-mesodermal cells Signup and view all the answers

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

It favors dorsal development Signup and view all the answers

What is the significance of the establishment of the primitive streak and Hensen's node during gastrulation?

It is unique to avian and mammalian development Signup and view all the answers

What is the role of chordin and noggin in dorsal axis formation?

They inhibit the activity of BMP4 Signup and view all the answers

What is the outcome of the process of axis induction during gastrulation?

It governs the establishment of axis formation Signup and view all the answers

What is the significance of the cranio-caudal axis in body axes formation?

It is established during gastrulation Signup and view all the answers

What is the role of the dorsal mesoderm in axis formation?

It governs the establishment of axis formation Signup and view all the answers

What is the significance of spatial-temporal expression of genes in body axes formation?

It governs the establishment of axis formation at specific times and locations Signup and view all the answers

What is the primary mechanism by which the neural folds converge towards the midline during neurulation?

Convergent extension Signup and view all the answers

Which type of cells is characterized by the lack of cell adhesion proteins?

Neural crest cells Signup and view all the answers

What is the role of Sonic hedgehog protein in the neural tube?

Dorsal-ventral patterning Signup and view all the answers

What is the outcome of the closure of the neuropore?

Formation of the neural tube Signup and view all the answers

Which of the following is NOT a primary signaling center in the neural tube?

Neural crest cells Signup and view all the answers

What is the role of BMP4 and BMP7 in the neural tube?

Dorsal-ventral patterning Signup and view all the answers

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

Dispersion and migration Signup and view all the answers

What is the primary function of the concentration gradients in the neural tube?

Dorsal-ventral patterning Signup and view all the answers

What is the outcome of the convergent thickening of the neural plate?

Formation of the neural folds Signup and view all the answers

What is the role of the dorsal mesoderm in primary neurulation?

Differentiation into somites Signup and view all the answers

What is the primary role of the axial mesoderm in neural induction?

To induce the transformation of the dorsal ectoderm into neural tissue Signup and view all the answers

What is the characteristic of the neural plate during neurulation?

A bending of the ectoderm due to changes in cell shape Signup and view all the answers

What is the outcome of the interaction between the axial mesoderm and the dorsal ectoderm?

The induction of the neural plate Signup and view all the answers

What is the function of N-cadherin in neural plate formation?

To facilitate the adhesion of neural plate cells Signup and view all the answers

What is the significance of the dorsal-ventral axis in neurulation?

It establishes the pattern of organogenesis Signup and view all the answers

What is the role of CAMs in neural plate formation?

To facilitate the adhesion of neural plate cells Signup and view all the answers

What is the outcome of neural induction?

The transformation of the dorsal ectoderm into neural tissue Signup and view all the answers

What is the significance of neurulation in organogenesis?

It generates the central nervous system Signup and view all the answers

What is the characteristic of the neural plate cells during neurulation?

They are tall and columnar Signup and view all the answers

What is the role of the notochord in neural induction?

To induce the expression of genes involved in neural induction Signup and view all the answers

What is the primary mechanism of neural tube formation in the caudal region of avian embryos?

Secondary neurulation Signup and view all the answers

At what level of the embryo does secondary neurulation occur in humans?

Around the 35th somite Signup and view all the answers

What is the role of the dorsolateral hinge point cells during neurulation?

They pull the epidermal cells towards the midline Signup and view all the answers

In which class of vertebrates does primary neurulation occur exclusively?

None of the above Signup and view all the answers

What is the outcome of the formation of the neural folds during neurulation?

The neural tube gets detached from the epidermis Signup and view all the answers

What is the characteristic of neural tube formation in amphibians?

It occurs mostly through primary neurulation, with secondary neurulation at the tail end Signup and view all the answers

What is the significance of the hinge point cells during neurulation?

They serve as anchors for the neural plate Signup and view all the answers

What is the difference between primary and secondary neurulation in terms of location?

Primary neurulation occurs in the anterior region, while secondary neurulation occurs in the posterior region Signup and view all the answers

What is the primary function of the concentration gradients in the development of the neural tube?

To activate the expression of different sets of genes Signup and view all the answers

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

Anencephaly Signup and view all the answers

What is the role of the notochord in the development of the neural tube?

To provide the inductive signal for the formation of the neural tube Signup and view all the answers

What is the difference between primary and secondary neurulation?

Primary neurulation occurs in the cephalic region, while secondary neurulation occurs in the lumbar region Signup and view all the answers

What is the term for the mild form of Spina Bifida?

Spina Bifida Occulta Signup and view all the answers

What is the outcome of the failure of the posterior neuropore to close?

Spina Bifida Cystica Signup and view all the answers

What is the role of the mesoderm in primary neurulation?

To provide the inductive signal for the formation of the neural tube Signup and view all the answers

What is the name of the cavity that forms within the neural tube?

Neurocoel Signup and view all the answers

What is the stage at which primary neurulation ends in human embryonic development?

4th week Signup and view all the answers

What is the process by which the medullary cord undergoes epithelialization?

Epithelialization Signup and view all the answers

What is the primary function of Goosecoid gene in dorsal axis formation?

Code for the transcription factor that regulates the activity of chordin and noggin Signup and view all the answers

What is the role of BMP4 in dorsal axis formation?

Natural inhibitor of dorsal axis formation Signup and view all the answers

What is the outcome of the interaction between the dorsal lip of the blastopore and the overlying prospective neuroectoderm/dorsal ectoderm?

Induction of dorsal development Signup and view all the answers

What is the significance of the cranio-caudal axis in embryonic development?

Gradual formation of the body axis Signup and view all the answers

What is the role of the dorsal mesoderm in axis formation?

Establishment of dorsal mesoderm Signup and view all the answers

What is the outcome of the inhibition of BMP4 activity?

Favoring of dorsal development Signup and view all the answers

What is the significance of the dorsal-ventral patterning of the neural tube?

Axis induction involves the signaling factor BMP4 Signup and view all the answers

What is the role of the Hensen's node in gastrulation?

Establishment of the primitive streak Signup and view all the answers

What is the outcome of the establishment of the dorsal mesoderm?

Establishment of the axial mesoderm Signup and view all the answers

What is the significance of the spatial temporal expression of genes in axis formation?

Timing and location of BMP4 activity Signup and view all the answers

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

They migrate to the roof of the rhombencephalon and underneath the epidermal cells. Signup and view all the answers

At what stage of embryonic development does the amnion cut to expose the dorsal view of the neural plate?

19D embryo Signup and view all the answers

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

Formation of the neural tube Signup and view all the answers

What is the significance of the gray crescent region formed in the fertilized egg?

It determines the dorsal side of the embryo Signup and view all the answers

What is the role of the cortical movement in the fertilized egg?

It moves the granules to the sperm entry point, dragging the pigment granules Signup and view all the answers

What is the molecular marker expressed in ventral cells during the gastrula stage?

Epi 1 Signup and view all the answers

What is the process by which the neural induction occurs?

Synthesis of competence factors Signup and view all the answers

What is the characteristic of the rhombomeres formed during the development of the rhombencephalon?

They are periodic swellings on the rhombencephalon Signup and view all the answers

What is the significance of the neural crest cells in determining the location of the cranial nerves?

They migrate to the roof of the rhombencephalon and underneath the epidermal cells Signup and view all the answers

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

Formation of the neural tube Signup and view all the answers

Study Notes

CNS (Brain & Spinal Cord) Formation

Neuralation involves the generation of neural crest cells (NCCs) and the formation of the brain and spinal cord
Neural crest cells are mesenchymal cells that can migrate to different parts of the body and give rise to various structures
During neurulation, the various brain divisions become distinctly defined
Neurulation marks the start of organogenesis (the formation of organs)

Embryonic Axis Establishment

The embryonic axis, including the dorsal-ventral axis, anterior-posterior axis, and left-to-right axis, starts to establish during the gastrula stage
This establishment is continued in the neurulation stage

Gastrulation Recap

The formation of the chordamesoderm in amphibians and the axial mesoderm in chick embryos is the same as the notochordal process in mammalian embryos
The axial mesoderm/notochordal process has an overlying ectoderm derived from the epiblast
The generation of the chordamesoderm/axial mesoderm/notochordal process has a powerful inductive effect, facilitating neural induction

Neural Induction

Neural induction is the process where the mesodermal, axial mesodermal, and notochordal cells act on the overlying ectoderm, transforming the dorsal ectoderm into the neural plate
The neural plate is formed through the bending and folding of the ectoderm, resulting in a V-shaped form

Neural Plate Formation

The neural plate formation involves the bending and folding of the ectoderm, resulting in a V-shaped form
There are three different populations of cells in the dorsal ectoderm: presumptive neural plate cells, presumptive neural crest cells, and presumptive epidermal cells
The neural plate cells undergo columnarization, transforming from low columnar cells to tall columnar cells

Neurulation

The first phase of neurulation involves the compression and thickening of the epithelial cells
The neural plate cells express genes coding for N-cadherin, a neural cell adhesion protein
The presumptive epidermis expresses genes coding for E-cadherin, an epithelial cell adhesion protein

Formation of Neural Tube

The neural folds then merge, cutting off the neural groove, and forming the neural tube
The closure of the neural tube disconnects the neural crest cells from the epidermis
The neural crest cells migrate away from the neural tube

Dorsal-Ventral Specification of the Neural Tube

Two primary signaling centers are established: the ectodermal cells of the epidermis producing BMP4 and BMP7, and the notochordal cells producing Sonic hedgehog protein
Two concentration gradients are established: gradients of TGF-β and Shh
Different concentrations of the signaling factors activate the expression of different sets of genes
Different exposure levels of cells result in different identities

Primary and Secondary Neurulation

Primary neurulation: the development of the neural tube as induced by the notochord and the mesoderm
Secondary neurulation: the caudal end of the neural tube develops into the neural notochord, then canalized
The extent of use of primary and secondary neurulation depends on the class of vertebrates

Neural Tube Defects

Anencephaly: failure of the anterior neuropore to close, resulting in parts of the forebrain missing
Spina Bifida: failure of the posterior neuropore to close, resulting in different degrees of severity

Extent of Use of Neurulation

Fishes: exclusively secondary neurulation
Birds: primary neurulation in the anterior region and secondary neurulation in the caudal region
Amphibians: mostly primary neurulation, with secondary neurulation in the tail end
Humans: secondary neurulation around the level of the 35th somite

Developmental Events of the Human Embryo

16D embryo: visible primitive streak with the primitive node
18D embryo: pear-shaped, with the cephalic end broader than the caudal end
19D embryo: neural plate visible, with epithelium columnarization
20D embryo: neural groove and fold formed, with somites forming lateral to the neural structures
22D embryo: 7 distinct somites, with the fusion of the neural folds beginning in the cervical region
23D embryo: pericardial bulge in each side of the midline in the cephalic part
25D embryo: 18-20 somites, with the closure of the cranial (anterior) neuropore
28D embryo: 25 somites, with the closure of the posterior neuropore

Neurulation as a Multistep Process

Cytoplasmic movement in the fertilized egg
Cortical movement after fertilization
Gray crescent region determines the dorsal side of the embryo
Dorsal mesoderm sends planar induction signals at the gastrula stage
Neuroectoderm is primed to respond to signal stimuli

Axis Induction

Vertebrate embryonic cells develop dorsal organ rudiments unless told differently
Bone morphogenetic protein 4 (BMP4) as the natural inhibitor of dorsal axis formation
Goosecoid gene codes for the transcription factor that regulates the activity of chordin and noggin
Dorsal development allowed, leading to the establishment of the dorsal mesoderm### Embryonic Development
From Hensen's node upward, the embryonic disc will form upward and eventually establish the precursors of the central nervous system (head and spinal cord).
The cranio-caudal axis of the embryo is gradually laid down during this process.
Gastrulation gives rise to neurulation, which involves the gradual formation of the body axis.
The dorsal-ventral patterning of the neural tube illustrates the process of neurulation or axis induction.
The signaling factor BMP4 plays a crucial role in axis induction, with inhibited activity favoring dorsal development and activated activity favoring ventral development.
The timing and location of BMP4 activation and inactivation govern the establishment of axis formation, which is characterized by spatial temporal expression of genes.
The spatial temporal expression of genes occurs at specific times and locations in the embryonic body, allowing for dorsal and ventral development to take place.

CNS (Brain & Spinal Cord) Formation

Neuralation involves the generation of neural crest cells (NCCs) and the formation of the brain and spinal cord
Neural crest cells are mesenchymal cells that can migrate to different parts of the body and give rise to various structures
During neurulation, the various brain divisions become distinctly defined
Neurulation marks the start of organogenesis (the formation of organs)

Embryonic Axis Establishment

The embryonic axis, including the dorsal-ventral axis, anterior-posterior axis, and left-to-right axis, starts to establish during the gastrula stage
This establishment is continued in the neurulation stage

Gastrulation Recap

The formation of the chordamesoderm in amphibians and the axial mesoderm in chick embryos is the same as the notochordal process in mammalian embryos
The axial mesoderm/notochordal process has an overlying ectoderm derived from the epiblast
The generation of the chordamesoderm/axial mesoderm/notochordal process has a powerful inductive effect, facilitating neural induction

Neural Induction

Neural induction is the process where the mesodermal, axial mesodermal, and notochordal cells act on the overlying ectoderm, transforming the dorsal ectoderm into the neural plate
The neural plate is formed through the bending and folding of the ectoderm, resulting in a V-shaped form

Neural Plate Formation

The neural plate formation involves the bending and folding of the ectoderm, resulting in a V-shaped form
There are three different populations of cells in the dorsal ectoderm: presumptive neural plate cells, presumptive neural crest cells, and presumptive epidermal cells
The neural plate cells undergo columnarization, transforming from low columnar cells to tall columnar cells

Neurulation

The first phase of neurulation involves the compression and thickening of the epithelial cells
The neural plate cells express genes coding for N-cadherin, a neural cell adhesion protein
The presumptive epidermis expresses genes coding for E-cadherin, an epithelial cell adhesion protein

Formation of Neural Tube

The neural folds then merge, cutting off the neural groove, and forming the neural tube
The closure of the neural tube disconnects the neural crest cells from the epidermis
The neural crest cells migrate away from the neural tube

Dorsal-Ventral Specification of the Neural Tube

Two primary signaling centers are established: the ectodermal cells of the epidermis producing BMP4 and BMP7, and the notochordal cells producing Sonic hedgehog protein
Two concentration gradients are established: gradients of TGF-β and Shh
Different concentrations of the signaling factors activate the expression of different sets of genes
Different exposure levels of cells result in different identities

Primary and Secondary Neurulation

Primary neurulation: the development of the neural tube as induced by the notochord and the mesoderm
Secondary neurulation: the caudal end of the neural tube develops into the neural notochord, then canalized
The extent of use of primary and secondary neurulation depends on the class of vertebrates

Neural Tube Defects

Anencephaly: failure of the anterior neuropore to close, resulting in parts of the forebrain missing
Spina Bifida: failure of the posterior neuropore to close, resulting in different degrees of severity

Extent of Use of Neurulation

Fishes: exclusively secondary neurulation
Birds: primary neurulation in the anterior region and secondary neurulation in the caudal region
Amphibians: mostly primary neurulation, with secondary neurulation in the tail end
Humans: secondary neurulation around the level of the 35th somite

Developmental Events of the Human Embryo

16D embryo: visible primitive streak with the primitive node
18D embryo: pear-shaped, with the cephalic end broader than the caudal end
19D embryo: neural plate visible, with epithelium columnarization
20D embryo: neural groove and fold formed, with somites forming lateral to the neural structures
22D embryo: 7 distinct somites, with the fusion of the neural folds beginning in the cervical region
23D embryo: pericardial bulge in each side of the midline in the cephalic part
25D embryo: 18-20 somites, with the closure of the cranial (anterior) neuropore
28D embryo: 25 somites, with the closure of the posterior neuropore

Neurulation as a Multistep Process

Cytoplasmic movement in the fertilized egg
Cortical movement after fertilization
Gray crescent region determines the dorsal side of the embryo
Dorsal mesoderm sends planar induction signals at the gastrula stage
Neuroectoderm is primed to respond to signal stimuli

Axis Induction

Vertebrate embryonic cells develop dorsal organ rudiments unless told differently
Bone morphogenetic protein 4 (BMP4) as the natural inhibitor of dorsal axis formation
Goosecoid gene codes for the transcription factor that regulates the activity of chordin and noggin
Dorsal development allowed, leading to the establishment of the dorsal mesoderm### Embryonic Development
From Hensen's node upward, the embryonic disc will form upward and eventually establish the precursors of the central nervous system (head and spinal cord).
The cranio-caudal axis of the embryo is gradually laid down during this process.
Gastrulation gives rise to neurulation, which involves the gradual formation of the body axis.
The dorsal-ventral patterning of the neural tube illustrates the process of neurulation or axis induction.
The signaling factor BMP4 plays a crucial role in axis induction, with inhibited activity favoring dorsal development and activated activity favoring ventral development.
The timing and location of BMP4 activation and inactivation govern the establishment of axis formation, which is characterized by spatial temporal expression of genes.
The spatial temporal expression of genes occurs at specific times and locations in the embryonic body, allowing for dorsal and ventral development to take place.

CNS (Brain & Spinal Cord) Formation

Neuralation involves the generation of neural crest cells (NCCs) and the formation of the brain and spinal cord
Neural crest cells are mesenchymal cells that can migrate to different parts of the body and give rise to various structures
During neurulation, the various brain divisions become distinctly defined
Neurulation marks the start of organogenesis (the formation of organs)

Embryonic Axis Establishment

The embryonic axis, including the dorsal-ventral axis, anterior-posterior axis, and left-to-right axis, starts to establish during the gastrula stage
This establishment is continued in the neurulation stage

Gastrulation Recap

The formation of the chordamesoderm in amphibians and the axial mesoderm in chick embryos is the same as the notochordal process in mammalian embryos
The axial mesoderm/notochordal process has an overlying ectoderm derived from the epiblast
The generation of the chordamesoderm/axial mesoderm/notochordal process has a powerful inductive effect, facilitating neural induction

Neural Induction

Neural induction is the process where the mesodermal, axial mesodermal, and notochordal cells act on the overlying ectoderm, transforming the dorsal ectoderm into the neural plate
The neural plate is formed through the bending and folding of the ectoderm, resulting in a V-shaped form

Neural Plate Formation

The neural plate formation involves the bending and folding of the ectoderm, resulting in a V-shaped form
There are three different populations of cells in the dorsal ectoderm: presumptive neural plate cells, presumptive neural crest cells, and presumptive epidermal cells
The neural plate cells undergo columnarization, transforming from low columnar cells to tall columnar cells

Neurulation

The first phase of neurulation involves the compression and thickening of the epithelial cells
The neural plate cells express genes coding for N-cadherin, a neural cell adhesion protein
The presumptive epidermis expresses genes coding for E-cadherin, an epithelial cell adhesion protein

Formation of Neural Tube

The neural folds then merge, cutting off the neural groove, and forming the neural tube
The closure of the neural tube disconnects the neural crest cells from the epidermis
The neural crest cells migrate away from the neural tube

Dorsal-Ventral Specification of the Neural Tube

Two primary signaling centers are established: the ectodermal cells of the epidermis producing BMP4 and BMP7, and the notochordal cells producing Sonic hedgehog protein
Two concentration gradients are established: gradients of TGF-β and Shh
Different concentrations of the signaling factors activate the expression of different sets of genes
Different exposure levels of cells result in different identities

Primary and Secondary Neurulation

Primary neurulation: the development of the neural tube as induced by the notochord and the mesoderm
Secondary neurulation: the caudal end of the neural tube develops into the neural notochord, then canalized
The extent of use of primary and secondary neurulation depends on the class of vertebrates

Neural Tube Defects

Anencephaly: failure of the anterior neuropore to close, resulting in parts of the forebrain missing
Spina Bifida: failure of the posterior neuropore to close, resulting in different degrees of severity

Extent of Use of Neurulation

Fishes: exclusively secondary neurulation
Birds: primary neurulation in the anterior region and secondary neurulation in the caudal region
Amphibians: mostly primary neurulation, with secondary neurulation in the tail end
Humans: secondary neurulation around the level of the 35th somite

Developmental Events of the Human Embryo

16D embryo: visible primitive streak with the primitive node
18D embryo: pear-shaped, with the cephalic end broader than the caudal end
19D embryo: neural plate visible, with epithelium columnarization
20D embryo: neural groove and fold formed, with somites forming lateral to the neural structures
22D embryo: 7 distinct somites, with the fusion of the neural folds beginning in the cervical region
23D embryo: pericardial bulge in each side of the midline in the cephalic part
25D embryo: 18-20 somites, with the closure of the cranial (anterior) neuropore
28D embryo: 25 somites, with the closure of the posterior neuropore

Neurulation as a Multistep Process

Cytoplasmic movement in the fertilized egg
Cortical movement after fertilization
Gray crescent region determines the dorsal side of the embryo
Dorsal mesoderm sends planar induction signals at the gastrula stage
Neuroectoderm is primed to respond to signal stimuli

Axis Induction

Vertebrate embryonic cells develop dorsal organ rudiments unless told differently
Bone morphogenetic protein 4 (BMP4) as the natural inhibitor of dorsal axis formation
Goosecoid gene codes for the transcription factor that regulates the activity of chordin and noggin
Dorsal development allowed, leading to the establishment of the dorsal mesoderm### Embryonic Development
From Hensen's node upward, the embryonic disc will form upward and eventually establish the precursors of the central nervous system (head and spinal cord).
The cranio-caudal axis of the embryo is gradually laid down during this process.
Gastrulation gives rise to neurulation, which involves the gradual formation of the body axis.
The dorsal-ventral patterning of the neural tube illustrates the process of neurulation or axis induction.
The signaling factor BMP4 plays a crucial role in axis induction, with inhibited activity favoring dorsal development and activated activity favoring ventral development.
The timing and location of BMP4 activation and inactivation govern the establishment of axis formation, which is characterized by spatial temporal expression of genes.
The spatial temporal expression of genes occurs at specific times and locations in the embryonic body, allowing for dorsal and ventral development to take place.

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Description

This quiz covers the process of neural plate development, including the role of cadherins and morphogenetic events during gastrulation. Topics include the separation of neural cells from epidermal cells and the formation of the neural groove and neural folds.