Lecture 7- Neurogenesis and determination of cell fate II Flashcards
What is the ventricular zone also called?
-cortex and telencephalon
What is shown in this picture?
-8.5 days old mouse embryo with the telencephalon already forming, which is where neural stem cell division occurs
What does the ventricular zone look like from the dorsal and ventral view?
-in mouse embryo, 10.5 days old
What cells are involved in the divisions ultimately leading to birth of new neurons? (mammalian model)
- neuroepithelial cells (stem cell-like qualities, also called neural stem cells) become the radial glia and those give rise to neurons
- all of these are in the embryonic mouse telencephalon/ventricular zone/cortex
What do neural stem cells generate in their divisions?
- generate neurons (differentiate) and maintain a progenitor/ stem cell population (self-renewal)
- to self-renew a neural stem cell cannot divide and give rise to two neurons, it differentiates into mother glial cell that then produces two neurons and one progenitor (neural stem cell) that can divide again
- this happens via asymmetric division
How is apico-basal cell polarity achieved? (mammals)
- each region has different protein complexes that give the cell its polarity
- LG1/2, Scribble and DLG1 complex are in the basal end of the cell and these force the aPKC complex (includes PAR3 and PAR6) and the Crumbs-3 complex (involves PATJ and PALS1) into the apical end of the cell
- this protein confirguration in the cell generates adherens junction, and anything below the adherens junction is defined as the basal end of the cell
What are the phases of a cell’s life?
- G1/S phase= rest
- G2/M phase= actively undergoing mitosis
- Cytokinesis= the separation of daughter cells
What is the role of cell division in the ventricular zone? (mammals)
- the phase of the cell’s life determines the movement of its nucleus to or away from the ventricular zone
- called interkinetic movement/ interkinetic nuclear migration
What interkinetic movement will a cell be undergoing if it is in G2/M phase?
-when undergoing division the nucleus of this cell migrates to the apical surface, closer to the ventricular zone
What interkinetic movement will a cell be undergoing if it is in G1/S phase?
-when resting a cell’s nucleus will be moving from the apical towards the basal region
What is the first thing that happens to the cell after it is fated to be Neuroblast due to Delta/Notch signalling? (Drosophila)
- delamination
- the neuroblast is in the upper layer of the neuroepithelium and moves downwards then it can divide and give rise to a glial mother cell (GMC) and a progenitor cell (neural stem cell= neuroepithelial cell)
- it moves in a basal direction
How does a neuroepithelial cell divide?
- normally along the apical basal axis
- then each daughter cell gets equal proportion of the apical and basal portion of the cell
- gives rise to more neuroepithelial cells
How does a neuroblast divide?
- on the “horizontal” axis
- neuroblast is a cell fated to become neural and it has completed delamination
- it divides assymetrically
- one daughter cell receives all of the apical region content and the other cell all the basal region content
- the apical region will become the progenitor
- the basal region will become ganglion mother cell and give rise to two new neurons
What is the molecular mechanism of asymmetrical division in Drosophila neuroblast?
- there is an unequal distribution of proteins in the basal and apical region of the neuroblast
- in the apical region: Apical protein complex DaPKC par complex (with Baz as well) bind to Insc (Inscuteable= protein more concentrated in the apical part and it is linked to cytoskeleton to spindle-orientation and protein subcellular distribution)
- in the basal region: basal proteins LGL1/2 and Scribble take with them the Basal protein complex Miranda-Pros (also Brat) complex and the Pon-Numb complex are involved
basal fate determinants: Miranda and Prospero (drive the cell fate)
What are the basal fate determinants?
-basal fate determinants: Miranda and Prosper- drive the non-stem cell fate
What is Prospero?
- one of the basal fate determinants
- Homeodomain DNA binding protein required for GMC (glial mother cell) fate
What happens in Prospero mutants?
- favours the formation of ganglion mother cell
- can’t generate the progenitors
- here the cells will be really small
- too many ganglion mother cells and not many neuroblasts
How do a neuroblast and a ganglion mother cell compare in size?
-ganglion mother cell= much smaller than the neural stem cell
How does a cell become a neuroblast?
-when cells within the epithelium delaminate
What does asymmetric division generate?
- a larger self-renewing neuroblast
- a smaller differentiated neural cell (GMC)
What confers cell fate to GMCs?
- unequal segregation of cellular proteins (prospero) confers cell fate to the GMC
- promotes differentiation, inhibits self-renewal
How are neural stem cells/progenitors/neuroblasts generated?
-via extrinsic signals such as the Notch and Delta signalling (act via a feedback mechanism (proneural genes)
How does the Drosophila compare to the mammalian embryonic cortex?
- in mammals the stem cells are the neuroepithelial cells as well
- the neuroblasts are the radial glial cells in mammals, they differ from neuroblasts morphologically (long, stringy)
- the radial glial cells are the self-renewing cells
- basal progenitors are the equivalents of the GMC (the glial mother cell), will give rise to two new neurons
What is the mammalian equivalent of the Drosophila Polarity complex aPKC, Baz, Par6? (the apical protein complex)
-Polarity complex PKCι, Par3, Par6
What is the mammalian equivalent of the Drosophila protein Insc (Inscuteable)?
-mlnsc
What is the mammalian equivalent of the Drosophila protein Partner of Inscuteable (Pins)?
LGN
What is the mammalian equivalent of the Drosophila protein Mushromm body defect (Mud)?
-Nuclear Mitotic Apparatus (NUMA)
What is the mammalian equivalent of the Drosophila protein Prospero?
Prox1
What is the mammalian equivalent of the Drosophila protein Miranda?
-not yet found/identified
Are the cell proteins involved in assymetric division in Drosophilas conserved in mammals?
-yes, they have their mammalian equivalents except for Miranda, the equivalent of which has not been found yet
How does neuron differentiation work in mammals? (picture)
very early neuroepithelial cells= will become early glial cells= they will differentiate to become neurons (2)
How do we examine asymmetric cell division in the mammalian cortex?
- Generate mutant mice: made LGN knockout, to see if the effect is identical to Pins knockouts in Drosophila
- Quantify asymmetric cell division: in both mutant and wild type individuals
- Compare wildtype (control) with mutant: the mutants have symmetrical division, thus loss of LGN function affects spindle orientation
What else happens in the LGN knockout mice?
- affects the fate of apical neurons
- increase in Pax6 and Tbr2 neurons in LGN knockout mice= loss of apical progenitors
- have more basal progenitors
- orientation of spindle thus contributes to the number of progenitors in the developing embryo
What are the cell fate determinants in mammalian asymmetric cell division?
- unknown (not prospero/Prox1)
- Numb-a component of Notch signalling?
Where does this type of cell division occur?
-“normal” cell division in many parts of the body
Where does this type of cell division occur?
-the nervous system of a Drosophila
Where does this type of cell division occur?
- nervous system of a mammal
- one cell receives the adherence junction and the other doesn’t (also true in Drosophila)
What is assymetric division key to?
- to maintaining a pool of neural progenitors and generating differentiated neurons in both Drosophila and mammalian neurogenesis
What animals are the models for exploring the way cells are specified, differentiated and become neurons?
-flies, worms, chicks, frogs and mice
