oogenesis

overview: oogenesis

• cluster surrounded by pre Granulosa cells

factors involved with oogenesis

germ cell nests

characteristics of tissue structure changes in primordial follicle activation

• flat granulosa = not active

model depicting the mechanisms of primordial follicle activation

• 4 main players:

  • mTOR

  • KIT-KL

  • WNT

  • PI3K

• primordial follicle = no signals available, cannot activate KITL = dormant

  • PI3K cannot become activated, PIP2 cannot be converted into PIP3, AKT can’t be phosphorylated, FOXO3a cannot be activated

• primary follicle = mTORC activated, KITL binds receptor on oocyte

  • complex between PIP2 and PIP3 = PI3K, converts PIP2 → PIP3, AKT phosphorylated, activates FOXO3a

  • FOXO3a combines with genes and wakes follicle up

• mTORC1 activated → kit ligand binds to receptor → activates PI3K → PIP2 converted to PIP3 → AKT activated (PIP3 phosphorylates) → activates FOXO3a, allows for it to bind to DNA/factors on DNA → follicle is activated

mammalian target of rapamycine (mTOR)

KIT and KIT-ligand

• kit ligand = stem cell factor (SCF)

• important for cell to cell communication

• soluble receptor floats around (not membrane bound)

• paracrine signaling

wingless-related integration site (“int” + “Wg”)(Wnt)

• CNTTBi: B-catenin

• CYP19A1: aromatase

• not phosphorylation based

phosphoinositide 3-kinase (PI3K)

• PTEN = huge inhibitor of PI3K signalling

• kit-ligand binds to receptor, activates PI3K, makes PIP2 into PIP3, which phosphorylates AKT

importance

• premature ovarian failure — supplement some factors to rescue failure

• develop solutions to help with livestock fertility

• cancer patients — create solution to rescue follicles

• ovarian tissue “harvest”

meiosis overview

• meiosis: process involving 2 specialized cell divisions in germ cells that generate haploid gametes

• meiotic arrest:

  • females: diplotene stage of prophase 1

  • males: prior to meiosis

timing of meiosis

• 2²³ = >8 million combinations — 2x → 16 million combinations

crossover and genetic recombination

timing of recombination: propose 1

chiasmata

• points of contact between non-sister chromatids; leads to recombination

• chiasmata: plural, chiasma: singular

kinetochore

• protein structure assembled on centromeres that attach to spindle fibers

  • function: facilitate sister chromatin detachment from one another