CSB429H1 Lecture Notes - Stem-Cell Niche, Germ Cell, Somatic Cell

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19 Apr 2012
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Lecture 1 Jan 12
CSB429
Germ Cell Development in Drosophila
Drosophila embryo
In many animals (not all), there is a separation between germ line cells (which happens very early on)
and the soma (all other cell types)
Drosophila GLC separate from soma early, and form at the posterior pole (before the soma actually
begins deviding)
Note: slide 2 not important
PGCs = undifferentiated state (primordial germ cells)
Vasa = genetic marker of early development? (not sure)
Larvae undergo morphogenesis / gastrulation (cell movements) and the PGCs end up in the midgut
(early germ cells associated with midgut)
These PGCs then need to move through midgut, and migrate to the mesoderm (through the midgut
walls
Three germline layers:
Ecto Endo Meso
Ectoderm (skin and nervous system)
Endoderm (gut)
Mesoderm (makes muscle) (for drosophila) makes the somatic part of the gonad
Development of these layers does not depend on the PGCs. Even without PGCs, you still have a somatic
gonad (although no function because no germline cells)
Gonad Formation
PGCs and SGPs recognize each other and they will eventually aggregate and SGPs will wrap around PGCs
and together they will form a nice round gonad (so they aggregate and coalesce)
Now the gonad has begun formation, however the cells are undifferentiated and now a compolex
process of differentiation must occur before you reach functional gonad
Mouse Embryo
Germ cells labelled with GFP (don’t see much of surrounding tissue)
E9 = very active GCs, moving at random
E9.5 = all start at center and eventually separates
E10.5 = germ cells form 2 populations to form 2 gonads
How to identify genes involved in gonad formation?
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Observe embryo with deletions, allows you to identify gene involved
Vaasa marker = localizes to cytoplasm and the dark center is the nucleus
TJ marker = specific for somatic cells of gonads (SGPs) and is a TF that localizes to nucleus
So with these markers you see green with a red dot in the middle
With these 2 markers we can see if there are any gonad defects
Gonad Phenotypes of deletion Mutants
Normal = tj marker in SGPs, allows you to see where PGCs are (center, surrounded by the marker)
Size regulation phenotype = SGPs region much larger than WT (defect in cell divisions perhaps?).
Another are tiny SGPs with huge nuclei (mutant with no cell divisions)
Aggregation / compaction mutants = can see a band of SGPs because cells did not aggregate properly, or
a streak instead of a round organ (surrounding PGCs)
Association of germ cells and somatic gonad cells pdd dostronitopm?
Prescence of PGCs = in this you can see that the SGPs (with tj marker) are not surrounding anything,
PGCs did not form! (so gonad with only SGPs and no GCs)
Germ Cell Migration
Move from midgut until they eventually reach area where they will form gonad
Gonad Differentiation during larval and pupal development
Drosophila lifecycle
Embryo > larvae > larger larvae > larger larvae > pupae > adult > embryo
Embryo = gonads simple at this stage, 2 cell types (PGCs and SGCs)
- This ball of cells will undergo growth (but still remain undifferentiated)
At third instar larvae
- Massive rearrangement of cells and we see a number of different cell populations
- Germ cells themselves s don’t really change, they multiple/divide and form large pool of
primordial cells but are far away from being a mature gonad
- However, we form a number of somatic cell populations that play a role in development of germ
cells
- Different SCs guide the GCs i ndifferentiation
First cells that form (differentiate) the terminal filaments
- Little stalks (orange) that protrude like fingers
- Are important because they are a signalling center (important signals for gametogenesis)
Next: the gonad divides into a bunch of egg tubes or ovarioles through cells that migrate down and
compartmentalize the gonad into units and each egg tube unit is a productionline for gametogenesis
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