HypFP -> Tuberal progenitors + ARCH neurons Flashcards
(21 cards)
What is the first step of the development of the hypothalamus?
specification of distinct progenitor cells from HypFP
How was the specification of distinct progenitor cells from HypFP discovered?
- Dissect hypothalamus at 5 further time points
- Dissociate cells
- scRNA seq
- Distinct gene expression libraries from each distinct stage
- Thousands of cells barcoded and cell profiles were read
- Distinct clusters were made depending on the most common transcriptional profiles
- Generate UMAP’s
What are the key differences between the UMAPs at different stages of hypothalamic development?
- As cells begin to differentiate they become more and more distinct from one another
-Distinct differentiation trajectories - More different colours, showing cells with different transcriptional profiles
How do you annotate the UMAP clusters?
- Based on previous knowledge (e.g. what genes are expressed in tuberal neurons)
- Can use the bioinformatics database to type in the gene name and see if its in the cluster
What is meant by a common lineage?
One cell type rises from another
If you wanted to see if there was a common lineage between HypFP cells and mamillary and tuberal progenitors, what would be the clue that there is?
- conduct lots of expression profiling studies
- you would see markers from HypFP overlapping with Mammillary and tuberal progenitors as cell fate develops gradually
What did expression profiling allow scientists to discover regarding HypFP and mamillary+tuberal progenitors?
- They found that in the early neural tube they could see a specific type of gene expression, which expanded (HypFP)
- From this expansion, expression profiling showed that mamillary and tuberal progenitors were born very close
What is the only REAL way you can accurately identify a lineage?
Fate mapping
- Using RNA velocity to observe pseudotime lineage
What did fate mapping via pseudotime lineage show regarding HypFP and their common lineages?
- PVN trajectories are NOT lineage related to HypFP cells
- Mamillary and tuberal progenitors DO rise from HypFP cells
Where are HypFP cells initially located and where do they move to?
Initially arranged along the midline
Expand across the A-P axis to form ‘secondary HypFP cells’
What is the fate of the different HypFP cells arranged across the A-P axis?
Original Midline HypFP: Give rise to tuberal progenitors and mammillary progenitors.
Secondary HypFP: Contribute to tuberal progenitors located farther from the midline.
Dorsal Cells (to Original HypFP): Give rise to PVN progenitors.
How is Shh involved in the establishment of progenitor cells from HypFP cells?
- Shh derives from HypFP and their secondary recruited ones, establishes an early gradient and then the cells that respond to Shh become PVN progenitors
- T/M progenitors express Shh and were originally a midline/recruited cell whereas PVN have RECEIVED Shh not EXPRESSED it
What is meant by there is no cell mixing during expansion?
- As expansion occurs, the original place where the cells were in the HypFP cell pool dictates their future spatial position, there is no mixing between the diff.cells, everything is where its meant to be
What is Rathke’s pouch?
- Tuberal progenitors lie dorsal to Rathke’s pouch
- Rathke pouch is the embryonic structure that will give rise to the anterior pituitary, coming from ectoderm that has moved posteriorly as progenitors have expanded
What are the three types of progenitors that tuberal progenitors give rise to?
- Tuberal neurogenic progenitors - formed from the most anterior HypFP cells
- Tuberal gliogenic progenitors - formed from the middle HypFP cells
- Mamillary progenitors - formed from the posterior most HypFP cells
What is the molecular signalling involved in the differentiation of tuberal progenitor cells?
- Wave of canonical BMP signalling sweeps from A-P via HypFP cells
- ‘Blip’ of signalling where it is quickly activated in the first few anterior cells
- Brief activation
- In the middle HypFP, pSmad1,5,8 and canonical BMP signalling is activated AND MAINTAINED
- Posterior cells never have BMP signalling, therefore never activating pSmad1
What is the role of BMP signalling in this pathway?
- quick BMP signalling triggers a pathway which sends cells down the route of differentiating in to a tuberal neurogenic progenitor
- Sustained BMP activation in HypFP cells sends the different trajectory down tuberal gliogenic progenitors
What is the role of FGF10?
- Molecule involved in BMP signalling
- Transient BMP signalling = transient FGF10 effects = neurogenic progenitors
- Sustained BMP signalling = sustained FGF10 upregulation = gliogenic progneitors
- No BMP signalling = No FGF10 expression = mamillary progenitors
What is the relationship between Shh and FGF10?
Upregulation of FGF10 means downregulation of Shh
Theres a gap of Shh expression where tuberal gliogenic cells are
What is the evidence for the effects of FGF10?
- When FGF10 is electroporated into posterior floor plate (FP) cells, which normally express Shh and GFP, it downregulates Shh expression. - This effect is concentration-dependent—higher levels of FGF10 cause greater Shh downregulation.
- Partial reduction of Shh is required for neurogenesis, while complete loss of Shh is necessary for gliogenesis.
What other process is FGF10 also responsible for?
- Expansion
- It regulates proliferation and survival
**Therefore: FGF is doing two things at this point in time: regulating Shh and therefore the differentiation of tuberal cells, also responsible for marked expansion of cells along A-P axis **
