1.3 Neurulation Flashcards
What is neurulation?
Formation of neural plate and it transformation into a neural tube
Neural plate develops in ectoderm, starts flat has to become a tube
What is “patterning”?
Development process by which cells acquire different identities, dependant on relative spatial positions in embryo
- ensure tissues + organs develop in correct place + orientation within the body
What is “fate” and a “fate map”?
Fate = what a cell in a certain location at a certain stage in development is most likely to become
Fate map = plan of an early embryo indicating the possibilities for development and differentiation of the various embryonic areas
Why is the node important for neurulation?
Node induces new axis and neurulation in prospective epidermis
What are the stages in neural tube development?
Ectoderm Neuroectoderm Neural plate Neural tube Regionalisation
How does the neuroectoderm form?
After recruitment from the ectoderm, the neuroectoderm undergoes three stages of development: transformation into the neural plate, transformation into the neural groove (with associated neural folds), and transformation into the neural tube.
- plate
- groove
- tube
How is the choice between epidermis and neuroectoderm made?
Ectoderm cell dissociated and washed and grown. All cells become: ectoderm - neuroectoderm
Default pathway for ectoderm is neural
How do you make epidermis?
Lateral plate mesoderm produces a diffusible factor that inhibits neural programme + induces epidermis formation in co-culture experiments
LPM too potent since: ectoderm + LPM factor = only epidermis
No neural tissue produced
How are epidermis and neuroectoderm formed?
LPM secretes BMP4to induce epidermis
Notochord secretes noggin - antagonist of BMP4 allows default neural pathway to be executed
Neuroectoderm induced directly over notochord, as it is laid down (node regression), neural plate extends posteriorly.
In lateral regions, BMP4 not antagonised, lateral ectoderm = epidermis
How is LPM anti-neural factor distributed?
Response to BMP4 (bone morphogenic protein - 4), not found in neural plate, only in presumptive epidermis
- noggin expressed from notochord and antagonises BMP4
How is the neural tube developed from the neural plate?
Neurulation
Neural plate undergoes morphogenic changes (thickening, folding, closure)
Where do primary neurulation and secondary neurulation occur?
Primary = anterior to hindlimb (lumbar region) Secondary = posterior to hindlimb
What are the stages in primary neurulation?
- Epithelium
- Columnarisation - neural plate thickens long + narrow. Driven by convergence and cell shape change
- Rolling/folding - cells along the midline form a hinge by attaching to the notochord. Hinge allows folding forms central depression - neural groove
- Closure- ectoderm pushes from lateral edges. Neural folds rise above the surface. New hinge on either side of the neural fold brings edges together. Dorso-lateral hinge cells bend neural fold to bring edges together.
- Neural tube complete - ectoderm fuses over midline + disengages from neural tube. Neural crest cells break away eventually migrate. Neural folds fuse.
What is neural closure?
Zipping of ectoderm
Simplest form is simultaneous progression anteriorly and posteriorly
In mammals, failure to close at the spinal cord leads to spina bifida and at anterior leads to anencephaly
What happens in secondary neurulation?
- Dispersed mesenchyme - neural plate descends ventrally and medially
- Mesenchymal condensation - neural cells form a solid rod called the medullary cord
- Medullary cord/neural rod - numerous cavities form which eventually fuse into one lumen - cavitation
- Epithelial transition/cavitation
- Neural tube complete - primary and secondary tubes formed by both mechanisms fuse into one tube
