Germ cell development

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What are germ cells
Cells that pass on information to the next generation - as distinct from somatic cells. They remain totipotent
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When are germ cells set aside
Early in development
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Difference between egg and sperm
egg must provide sufficient material to get through the first series of cell divisions, the sperm just contributes chromosomes and a centrosome
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Examples of organisms that use a germplasm
flies, nematodes, and frogs
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More about drosophila germ plasm
Posterior pole cells appear in the posterior pole 90 minutes after fertilisation. They are formed from poleplasm, which contain large polar granules containing protein and RNA.
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Two experiments that showed the germ plasm was special
UV irradiation of the posterior pole = no germ cells. Transplantation of the posterior germplasm - the anterior forms germ cells.
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When is germ cell lineage set up in nematode worms
at the end of the fourth cleavage division - the P4 cell is formed from three stem cell like divisions of P1
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What product of P-granule compartments is shown to be needed for germ cell development
the product of gene pgl-1 - by regulating some aspect of mRNA metabolism.
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Germplasm in xenopus
Distinct yolk-free patches of cytoplasm aggregate at the vegetal pole, and this cytoplasm is cleaved assymetrically and only retained in vegetal daughter cells, from which the daughter cells are derived.
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Do mammals have a germ plasm
No - Blimp1 is a repressor that represses pathways of somatic cell development
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Why do germ cells need to migrate?
They often form quite a distance from the gonad - maybe to exlude them from the upheval of patterning the body, maybe to select the healthiest ones
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How do we know the path of migration is controlled by the environment?
in Xenopus, transplanted germ cells dont end up in the gonads.
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How does the vertebrate gonad develop
from the mesoderm lining the abdominal cavity, forming a genital ridge
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The ligand and receptor used for migration in mice
White spotting gene encodes for Kit, the cell surface receptor. Steel is the ligand expressed in the cells the germ cells migrate along
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The germ cell guidance molecules in zebrafish
genital ridge expresses Ligand SDF1, and migrating pgcs express G-protien coupled receptor CXCR4
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The two classes of sex determination
enviromental - eg, fish, crocodiles and reptiles, and genetic - chromosomal differences
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C.elegans - chromosome for male and female
XX hermaphrodite, XO male.
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Drosophila - male and female determination
XX female, XY male
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In birds how does it work
ZW female, ZZ male, but probably dosage.
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In mammals how does it work
XY male, XX female. Y chromosome acts as a dominant male determinantm- a single gene called thE SRY
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How can XY females and XX males be born
pairing and exchange involving the Y unique region below the SRY. 1 IN 10,000, theyre always infertile
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What is the SRY
A gene that codes for a protein that has a DNA binding domain. A member of the Sox gene family, probably evolved from Sox3
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What does SRY do?
binds specific DNA sequences, bending the DNA. Might just distort the chromatin to allow other factors to work. Thought to be a repressor of a repressor - promote male development by preventing an antitestes gene from working
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the effect of SRY on the testes
prospermatogonia, sertoli cells, leydig cells, tunica, stromal cells,
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Effect of NO sry in the ovaries
oogonia, follicle cells, theca cells, tunica, stromal cells, blood vessels
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What is SF1 and what's it used for
A transcription factor required for gonad development in both sexes, in males it is required for SRY, SOX9 AND FGF9
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What causes sox9 expression
SRY, SF1 and autoregulation to maintain it's own expression after a critical threshold
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What does sox9 do at critical threshold
acts on other genes - sf1, fgf9, pgds, sox8, to reinforce it's expression and effects. Also acts on genes for sertoli differentiation - Amh. And it represses ovarian genes
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What happens if Sry is absent?
Wnt signalling and B-catenin activity repress Sox9, leading to differentiation of granluosa cells
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What does ovarian development depend on
Wnt4 signalling and other factors acting in redundancy - to repress Sox9 by beta catenin
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How are ovaries maintained
continous activity of FOXL2 to repress sox9 transcription.
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How do we know the ovary is not default?
XXWnt4-/- is male. XXBcat^ = male
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What is a female determining factor and what does it do
Foxl2, which activates a cascade to signal Wnt2 and B-catenin
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When are germ cells set aside

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Early in development

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Difference between egg and sperm

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Card 4

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Examples of organisms that use a germplasm

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More about drosophila germ plasm

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