REPRODUCTIVE CYCLE OF FEMALE MAMMAL

REPRODUCTIVE CYCLE OF FEMALE MAMMAL

Fig. 8-12

Secondary follicles growing follicles increase in number of layers of granulosa cells Tertiary follicles maturing follicles antrum formation fluid filled space oocyte on mound of granulosa Cumulus oophorus granulosa layer immediately around oocyte Corona radiata Granulosa surrounded by Theca interna Theca externa Ovarian Histology

Ovarian Pool of Follicles Non-growing Follicles (90%) Oocyte Inactive Single layer of flattened granulosa cells (GC) Growing Follicles Oocyte increases in size GC become cuboidal and active mitosis Formation of zona pellucida Vascularization of thecal cells (TC) begins

Ovarian Pool of Follicles Recruitable Pool (>2 mm in sheep) 4 layers of GC gonadotropin independent Multiple follicles to tertiary follicle stage Atresia affects many follicles, but pool necessary to support development of dominant follicle Atresia: condensation of chromosomes DNA fragmentation wrinkling of nuclear envelope fragmentation of oocyte degeneration (pyknosis) of nulcei of GC GC detach from basement membrane and float GC and TC FSH and LH receptors low or no estrogen production

Dominant Follicle Exists around mid-cycle and takes 12-14 days to go through recruitment, selection and maturation Follicle Recruitment increase in FSH TC increase LH receptors (LHCGR) and androgen production GC increase expression of FSH receptors (FSHR), production of ACTIVIN, aromatase activity and conversion of androgens to estrogens Activin acts on Gonadotrops to increases FSH secretion GC do not express LHCGR

Theca Cells Mature Graffian Follicle LHCGR, PGE receptors increase camp and androgen production Granulosa Cells FSH and Activin stimulate aromatase and estradiol production FSH and estradiol stimulate LHCGR Increase in Inhibin and Follistatin to block FSH release Inhibin blocks FSH release and stimulates androgens Decrease growth of subordinate follicles Increase estrogen production by Graffian Follicle Follistatin binds Activin to inactivate its effects

Granulosa Cells Insulin-Like Growth Factor 1 (IGF1) Mitogenic Stimulates progesterone production Enhances expression of LHCGR with FSH and E2 Increases camp production in response to PGE2 Stimulates inhibin production Epidermal Growth Factor (EGF) Stimulates FSHR May prevent premature ovulation by modulating time of LHCGR expression by GC

Granulosa Cells (Continued) Fibroblast Growth Factor Beta Stimulates angiogenesis in TC LATER angiogenic factor for Corpus Luteum Vascular Endothelial Growth Factor and Angiopoietins Angiogenic factors for TC for capillary growth Transforming Growth Factor Beta from TC Receptors on GC Modulates GC differentiation Enhances FSH effects Inrease aromatase activity Increase EGF receptors Increase LHCGR expression

Granulosa Cells (Continued) Tranforming Growth Factor Alpha (TGFA) increases EGF Receptors Activin (B A B B ;B A B A ) increases FSH secretion by gonadotrophs increases FSHR on GC decreases LH-induced secretion of androgens enhances FSH stimulation on LHCGR on GC increases aromatase activity for estrogen production

Granulosa Cell (continued) Inhibin (αβ A Inhibin A; αβ B Inhibin B) Inhibits FSH secretion by gonadotrophs Increases aromatase activity Increases androgens from TC Follistatin (32, 25 and 39 kda forms) Binds to activin and inhibits activity Stimulated by FSH Inhibits expression of LHCGR on GC Inhibits production of estradiol, progesterone and inhibin by GC Tumor Necrosis Factor Alpha (TGFA) Increases PGE2 mostly from GC

Granulosa Cells (continued) Interleukin -1 Beta (IL1B) Increases PGEs from GC and macrophages Platelet Activating Factor Increases vascular permeability Allows movement of selected serum proteins and water into antrum to form follicular fluid

Granulosa Cells (continued) Mural GC Abundant LHCGR Cumulus GC Few LHCGR Oocyte No LHCGR

Steroidogenesis Before LH Surge A FSH GL Ch P A 2 E Arom 2 P450scc 3b-HSD BM TI TE Ch P A 2 P450scc 3b-HSD 17a-HSD E 2 A: Antrum; GL: Granulosas; BM; Basement Memb TI: Theca Int. TE: T Ext.; C: Capillaries LH Ch: Cholesterol; P: Progesterone; A 2 : Endrogen; E 2 : Estradiol

Luteal Steroidogenesis Large Luteal Cells Ch P A 2 E 2 P450scc 3b-HSD 17a-HSD (Some Species) Arom Ch P A 2 E 2 P450scc 3b-HSD 17a-HSD Arom Small Luteal Cells Ch: Cholesterol; P: Progesterone; A 2 : Endrogen; E 2 : Estradiol

The expression of neurotropin 4 (NT4) in oogonia and the presence of its receptor proteins TrkB and p75 may indicate involvement of neurotropins in early oogenesis. Neurotransmitters like norepinephrine and vasoactive intestinal peptide (VIP) can stimulate major enzymes in regulation of steroidogenesis. SF-1 Differentiation of gonads. Fig α trancription factor for Zona Pellucida proteins (ZP1, ZP2 and ZP3)

Growth Hormone (GH), FSH, LH, Insulin, and Estrogens from Maternal System delivered to follicle to initiate development and differentiation of follicle and oocyte.

Kit ligand (stem cell factor), EGF, and Activin act jointly to stimulate formation of antrum and transport of water, electrolytes and proteins into the follicular fluid of the antrum

FSH stimulates E2, inhibin, and IGF1 and inhibits IGFBP2. Bone Morphogenic proteins (BMPs) and EGF enhance E2 production. LH and Inhibin stimulate androgens from TC to increase estrogens from GC. NO LHCGR on GC at this stage.

High IGF1 and estradiol stimulate LHCGR for GC. Follistatin (FS) begins to bind and inactivate Activin. Inhibin becomes dominant to Stimulate more androgens for E2 and suppress FSH to dominant and then Mature Graffian Ovulatory Follicle(s) are established.

Bone Morphogenic Protein (BMP), Nerve Growth Factor (NGF), Leukemia Inhibitory Factor (LIF), Kit Ligand/Stem Cell Factor (KL), Growth Differentiation Factor 9 (GDF9), Antimullerian hormone (AMH), Wilm s Tumor Suppressor Gene (WT1). GDF9, LIF, FGF2 and NGF my stimulate transition from primordial follicle to primary follicle. GDF deficient mice have large oocytes, but little develoment of GC. GDF9 considered primary regulator of GC proliferation and differentiation. LIF and KL co-regulators of transition from primordial to primary follicles.

Connective Tissue Growth Factor (CTGF), Fibroblast Growth Factor 7 (FGF7). FSH stimulates Gap Junctions between oocyte and GC. NGF deficientmice have few primary follicles; VIP - maturing follicles and steroidogenesis; CTGF for mitosis, angiogenesis and extra-cellular matrix; BMP15 stimulates GC proliferation; GDF9 inhibits KL to regulate ultimate size of follicle.

GDF9 and BMP15 are mitogenic. No GC proliferation in GDF-/- mice, so sterile GDF9 also stimulates SCF and inhibin. Role in luteinization after ovulation BMP15 regulation of GC mitosis regulated by SCF in negative feed- Back whereby BMP15 stimulates SCF and SCF suppresses BMP15. GDF9 and BMP15 inhibit steroidogenesis in GC of early follicles, perhaps to prevent premature maturation BMP15 deficient sheep sterile, no follicles beyond primary stage- same as for GDF-/- mice BMP-/- mice: fertility reduced, follicles appear normal GDF9 and BMP15 may be redundant with GDF9 more important in mice and BMP15 more important in sheep

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