Lecture 6-7 Flashcards
What did fate mapping experiments of FGF10+ hypothalamic progenitors show
Show that the FGF10+ pre hypothalamic progenitors above the PM give rise to the entire hypothalamus
Are extrinsic signals required for the pre-hypothalamic progenitor or are cells able to intrinsically self-renewal and differentiate. How was this shown?
Chicken fillet experiment: isolate embryonic hypothalamic progenitors - culture ex vivo in 3D collagen matrix - does it differentiate to anterior and mammillary cells, and is it retained as an FGF10+ cell? Yes
What are the markers of an anterior hypothalamic cell
Islet 1
What is the marker for a posterior cell
Emx 2
What are chicken fillet cells treated with in order to create slices of isolated neural tissue
Dispase
What markers are used in order to determine the isolated cells are in fact embryonic hypothalamic progenitors
Positive for FGF10, negative for Foxg 1
Is a single FGF10+ cell capable of producing all the cell types of the mature hypothalamus
Yes, in the right conditions
What is a label retaining cell and what is an example of it in the hypothalamus
Long term fate mapping showed that FGF10+ hypothalamic progenitors are label retaining cells. After 126 hours, Dye was retained - suggesting a very slow-dividing cell, typical of a stem cell.
What is the current model for hypothalamic development
- New cells are provided by an FGF10+ stem cell region
- New cells acquire a new identity (anterior progenitor)
- They move anteriorly and differentiate
- This is thought to underlie development of many neurons in the tuberal and anterior hypothalamus that are crucial for homeostasis
Outline the stages of differentiation
1) Shh, FGF10, pSmad1/5/8, BMP7, Tbx2 positive cell divides to give 2 daughters, one is displaced from the PM. The cell not displaced sees Shh downregulation by high levels of BMP7 and Tbx2. Through LDA, Shh now diffuses to displaced daughter cells, retaining Shh in these cells.
Where else in the developing nervous system is an Shh pattern of differentiating progenitor cells seen
Developing spinal cord - Progenitors differentiate into neurons. The differentiating progeny move laterally, so that the mature neurons are in the mantle zone whereas the progenitors are retained at the ventricular zone
What is another clue of Shh signalling being responsible for inducing a transit amplifying population of cells
Shh (GliA) signalling activates transcription of genes such as Myc, Cyclin D1, Bcl-2. All these genes are implicated in cell cycle, cell proliferation, survival and renewal. All of which are properties of a transit amplifying population
What are the three actions of Shh signalling in the developing telencephalon
1) Early in development Shh forms a reciprocal gradient witht the repressor form of Gli3. The relative expression of these two signals works to establish dorso-ventral patterning
2. Through prenatal development, Shh supports the expansion of radial glial stem cells, promoting overall growth of the developing brain.
3) During neurogenesis Shh maintains Nkx2.1 expression in progenitor cells that asymmetrically divide. In the presence of Shh signalling, these progenitors migrate into the sub-ventricular zone where they continue to divide to produce striatal and cortical interneurons. In the absence of Shh, the progenitors continue to divide, but Nkx1.2 expression is lost, as is their fate to become interneurons
What are the four potential roles of Shh in the developing hypothalamus
1) Induce the pre-hypothalamic cell
2) Select the anterior progenitor
3) Amplify the anterior progenitor
4) Play a role in the differentiation of the anterior progenitor
