L3 - Neurulation Flashcards
definition of neurulation
when the neural plate grows, elongates along A-P axis and rolls into the neural tube
How do we detect neurulation morphologically?
it is obvious morphologically by looking for the expression of Sox2.
(sox2 = a marker for neural stem cells).
How do we detect neurulation molecularly?
In situ hybridisation –> chick embyros incubated in an anti-sense probe, to detect sox2 mRNA where probe binds- shows and can see the neural plate+tube developing.
what is gastrulation? links to neurulation?
Gastrulation = embryo transforms from one dimensional layer of cells to a multi-layered embryo where adult body plan is recognisable.
Neurulation is linked to gastrulation as is germ layers assume their final positions and axes become obvious.
In gastrulation the embyro reorganises from blastula (ball of cells) to a multi-layered organism. So neurulation is driven by changes in cell shape.
What is the organizers transcriptional signature?
e.g. BMP antagonists
The transcriptional signature is under the control of the transcription factors: Siamois and gsc (goocoid).
Siamois and gsc - activate many genes.
- Some of these genes encode factors that activate intrinsically in the organiser to direct emergent behaviour.
This causes cells to undergo convergent extension.
What is the process of convergent extension?
Convergent extension is extensin driven by movement and involves transformation of neural plate to neural tube.
The embryo is restructured to converge (become narrow) along one axis and extend (elongation) along a perpendicular axis by cellular movement.
SO when the doral mesoderm is induced -> it involutes and undergoes convergent extension where it lies under the ectoderm layer. At the same time it differentiates into prechordal mesoderm (right at the front) and notochord.
This process of convergent extension (gastrulation) changes the shape of the developing embyro.
What is neurulation driven by? and how is it linked to F-actin?
Neurulation is driven by changes in cell shape.
The neuroepithelial cells are polarised and there is a band of Factin on the apical membrane. If this pulls tight, the cells are constricted at that edge and change shape.
Many molecules interact with F-actin to make it constrict - and this causes a change in cell shape.
An example of a neural tube defect.
Spina bifida - where neural tube fails to develop.
Folate signals changes in cell shape and so changes in tissue shape.
Deficiencies in folate can cause the neural tube to fail to close = spina bifida.
Folate receptor-a plays a key role at the apical surface of the neural plate as a signal. It causes changes in cell tissue.
Where does the pre-chordal mesoderm lie?
It lies beneath the future forebrain.
What did grafting studies from Spemann-Mangold’ experiment shows?
That the organiser/Node/dorsal mesoderm froms from axial mesoderm which undergoes convergent extension.
What happens in the process of gastrulation?
the organiser undergoes convergent extension and differentiates into axial mesoderm (which is made of pre chordal mesoderm and notochord)
