l1 Flashcards
what is the neural plate?
single cell thick neuroepithelium which is induced by ectoderm on dorsal side of embryo (BMP antagonists)
where does the neural plate sit?
sits above mesoderm and endoderm
- grows and elongates along AP axis then roles into neural tube (neuralation)
(above prechordal mesoderm/notochord)
how do neural plate cells form?
via DIFFERENTIATION
- cells become different to one another and aquire specialised properties which are caused by changes in gene expression
what is gene expression governed by?
both extrinsic factors (morphogens) and instrinsic factors (TFs)
give the two fates of an ectoderm determined by BMP
- BMP antagonism - neural plate cell
- BMP agonism - epidermal cell
What TFs does the spemann organiser release?
- BMP ANTAGONISTS
- noggin
- chordin
- gsc
- follastatin
where is the neural plate induced?
-induced in dorsal ectoderm where BMP is inibited
by BMP antagonists released by organiser
what TFs are released ventrally?
BMP4
tolloid
what happens to spemann organiser once it begins to induce the neural plate?
It differentiates into axial mesoderm
notochord, prechordal mesoderm, anterior endoderm
what happens to AM when spemann organiser is differentiated?
axial mesoderm involutes, intercalates and undergoes convergent extension - extends anteriorly.
-released BMP antagonists
(led by leading edge cells)
what happens in convergent extension?
sheet of cells changes shape by extending in one direction and narrowing and converging in another. (cells intercalate)
where are BMP antagonists maintained in axial mesoderm?
- BMP antagonists are only maintained in the prechordal mesoderm.
- node changes and node and notochord stop producing BMP antagonists (promote proliferation and posteriorisation)
what are the characteristics of the late node and notochord?
- change BMP antagonistic properties
- - have new characteristics which promote proliferation and growth of neural cells and POSTERIORISATION
what are posteriorising signals?
- Fgf, Wnt and RA
- promote growth and posteriorisation
where are BMP and Wnt antagonists maintained?
maintained anteriorly in prechordal mesoderm
what do the specialised border of cells at the edge of the neural plate and ectoderm express?
msx
what leads to dorsalisation?
Bmps work with Wnts and FGF signalling toinitiate cascade of events which lead to dorsalisation
-gives rise to NCCs
what are edge cells crucial for?
- neural crest cell formation
- patterning of the dorsal NT
- roof plate formation
how does neural tube ventralisation occur?
- there is secreted Shh in notochord and then floorplate
- Shh acts as a morphogen to induce different progenitor cells along D-V axis of future spinal cord
- Shh diffused from NT and FP to induce a conc gradient - cells have different thresholds - different responses to Shh gradient
- different TFs are induced in bands of of different progenitors along DV axis - read out of Shh gradient
where do differentiating cells move?
move laterally
Give the pathway from the ectoderm when BMP antagonists are present
- ectoderm exposed to BMP antagonists
- low Smad1, high smad 7
- neuralating TFs activated
- neurogenin
- neuroD
- neural differentiation
Give the pathway from the ectoderm when BMP is present
ectoderm - exposed to BMPs
- hgh smad1, low smad 7
- epidermalizing TFs
- LEF1
- epidermal differentiation
