Lecture 1 - Jan 12.docx

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Department
Cell and Systems Biology
Course
CSB429H1
Professor
Dorothea Godt
Semester
Winter

Description
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?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 gametogenesisBlue = terminal filaments and we see germ cells and other somatic cells Gonad continues to mature and when the fly hatches the gonad becomes functional and consists of different portions Adult image: one of the egg tubes Tip = egg filament Near top / tip = early stages of gametonesis that are surrounded by follicle cells As you move farther down = the green egg chamber is surrounded by follicle (developed from follicle cells) The Egg chamber eventually develops an egg Ovaries vs. testes - Very different morphology - Ovaries much larger with many egg tubes producing eggs Germ Line Stem Cells Diagram of ovaries and different cell types (good to lookat) Mammalian females born with a set number of PGCs and all eggs derive from these PGCs - In humans, males have the stem cells In flies, its different – both sexs have stem cells Ovariole (egg tube) Anterior end = terminal filament Cap (next to term fila) = in direct contact with germline stem cells - These cells produce signals that are important in establishing and maintaining the germline stem cells - Niche is composed of somatic cells that establish and maintain stem cell niche Stem cell niche = very small, 2 germmline stemcells maintained by the cap - As soon as these GSCs lose contact with the cap, they are no longer being maintined by the cap cells and will differentiate into eggs - Flies continue to produce eggs over a period of 14 days (which requires stem cells that are continually producing daughter cells that can differentiate into eggs) Aside: comparison with males - Very similar situation - At anterior end of testes, you have a “hub” (similar to a cap cells) that maintain the germline stem cell niche - Are organized differently but function is the same, establish and maintain GSCs - Also responsible for maintaining cyst stem cells (somatic cells that will wrap around the daughter cells of the stem cells and support differentiation of the GSC) GSCS = form a rosette like structure around the hub So both in females and males we have GSCs and they are supported by somatic niche cells (cap and hub cells)Begining from embryo to adult stage, these SCs are in contact with mesoderm cells (somatic cells) and communicating to maintain their synchronous development (somatic cells signal germ line cells to guide it through development) Picture of
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