lecture 4 Flashcards
A-P regions
anterior is brain and posterior is spinal cord
what do ectoderm cells become?
SOX2 positive stem cells which inhibit BMP signalling or epidermal cells
what do SOX2 stem cells become?
brain progenitor cells or spinal cord progenitor cells
when the neural plate is induced
the cells are in the same plane and just beginning to change their relative position (inverlute)
what happens after gastrulation?
some of ectoderm is induced to become neural plate and organiser cells undergo convergent extension and gastrulation and lying underneath neural plate
organiser cells differences
not entirely uniform and have slightly different transcriptional factors
the cells closer to the endoderm and at the leading edge of the developing rod
what organiser cells transcribe and secrete
all transcribe and secrete BMP antagonists but only a subset will also transcribe and secrete Wnt antagonists e.g. Dikkopf
organiser cells that express Wnt antagonists
first cells to involute and will differentiate into prechordal mesoderm
organiser cells that do not express Dkk
these will differentiate into notochord
how the embryo is exposed to Wnt signalling
exposed with a gradient of Wnt signalling, posterior region is exposed to high levels of Wnt from posterior tissue during gastrulation and neurulation
anterior portion with Wnt signalling
there is antagonists of Wnt signalling and have no Wnt signalling. for the brain, Wnt signalling has to be antagonised
where is Wnt signalling secreted?
prechordal mesoderm
how the sheet of neural tissue becomes regionalised
there is a signal of Wnt at one end and an antagonist of the signal at the other end
evidence of Wnt signalling
there is discrete transcriptional signals using in-situ hybridisation for mRNA and immunohistochemistry for proteins
where is SOX2?
in all neural plate/tube cells where Otx2 only in brain progenitors in the anterior region.
evidence for pre-chordal mesoderm with organiser cells
- organiser cells from early gastrulation transplanted onto host embryo, there is a twined embryo because different cells will give prechordal and other will be norchrodal cells
- organiser cells from late gastrulation and transplant it, there is not a twined axis as the Wnt antagonists are lost
pre-chordal mesoderm graft
graft into early gastrulate and the pre-chordal mesoderm and results in extra brain
notachord transplant
will have posterior neural tissue induced with an extra spinal with Wnt signalling
forebrain experiments
overexpression of Dkk as it is a Wnt antagonist
knock out of Dkk results in more Wnt signalling and no forebrain is developed
Wnt signalling in mesoderm
there is graded signalling in mesoderm
