Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductive disorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulin resistance, independent of obesity. This article summarizes the state of the science since we last reviewed the field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS are insulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is a post-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1 serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulin target tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway may contribute to resistance to insulin's metabolic actions in skeletal muscle. Insulin functions as a co-gonadotropin through its cognate receptor to modulate ovarian steroidogenesis. Ge...

Insulin Resistance and the Polycystic Ovary Syndrome Revisited: An Update on Mechanisms and Implications

Multiple ovulations are uncommon in humans, cattle and many breeds of sheep. Pituitary gonadotrophins and as yet unidentified ovarian factors precisely regulate follicular development so that, normally, only one follicle is selected to ovulate. The Inverdale (FecXI) sheep, however, carries a naturally occurring X-linked mutation that causes increased ovulation rate and twin and triplet births in heterozygotes (FecXI/FecX+; ref. 1), but primary ovarian failure in homozygotes (FecXI/FecXI; ref. 2). Germ-cell development, formation of the follicle and the earliest stages of follicular growth are normal in FecXI/FecXI sheep, but follicular development beyond the primary stage is impaired3,4. A second family unrelated to the Inverdale sheep also has the same X-linked phenotype5 (Hanna, FecXH). Crossing FecXI with FecXH animals produces FecXI/FecXH infertile females phenotypically indistinguishable from FecXI/FecXI females6. We report here that the FecXI locus maps to an orthologous chromosomal region syntenic to human Xp11.2–11.4, which contains BMP15, encoding bone morphogenetic protein 15 (also known as growth differentiation factor 9B (GDF9B)). Whereas BMP15 is a member of the transforming growth factor β (TGFβ) superfamily and is specifically expressed in oocytes, its function is unknown7,8,9. We show that independent germline point mutations exist in FecXI and FecXH carriers. These findings establish that BMP15 is essential for female fertility and that natural mutations in an ovary-derived factor can cause both increased ovulation rate and infertility phenotypes in a dosage-sensitive manner.

Mutations in an oocyte-derived growth factor gene (BMP15) cause increased ovulation rate and infertility in a dosage-sensitive manner.

In recent years, exciting progress has been made towards unravelling the complex intraovarian control mechanisms that, in concert with systemic signals, coordinate the recruitment, selection and growth of follicles from the primordial stage through to ovulation and corpus luteum formation. A plethora of growth factors, many belonging to the transforming growth factor-beta (TGF-beta ) superfamily, are expressed by ovarian somatic cells and oocytes in a developmental, stage-related manner and function as intraovarian regulators of folliculogenesis. Two such factors, bone morphogenetic proteins, BMP-4 and BMP-7, are expressed by ovarian stromal cells and/or theca cells and have recently been implicated as positive regulators of the primordial-to-primary follicle transition. In contrast, evidence indicates a negative role for anti-Mullerian hormone (AMH, also known as Mullerian-inhibiting substance) of pre-granulosa/granulosa cell origin in this key event and subsequent progression to the antral stage. Two other TGF-beta superfamily members, growth and differentiation factor-9 (GDF-9) and BMP-15 (also known as GDF-9B) are expressed in an oocyte-specific manner from a very early stage and play key roles in promoting follicle growth beyond the primary stage; mice with null mutations in the gdf-9 gene or ewes with inactivating mutations in gdf-9 or bmp-15 genes are infertile with follicle development arrested at the primary stage. Studies on later stages of follicle development indicate positive roles for granulosa cell-derived activin, BMP-2, -5 and -6, theca cell-derived BMP-2, -4 and -7 and oocyte-derived BMP-6 in promoting granulosa cell proliferation, follicle survival and prevention of premature luteinization and/or atresia. Concomitantly, activin, TGF-beta and several BMPs may exert paracrine actions on theca cells to attenuate LH-dependent androgen production in small to medium-size antral follicles. Dominant follicle selection in monovular species may depend on differential FSH sensitivity amongst a growing cohort of small antral follicles. Changes in intrafollicular activins, GDF-9, AMH and several BMPs may contribute to this selection process by modulating both FSH- and IGF-dependent signalling pathways in granulosa cells. Activin may also play a positive role in oocyte maturation and acquisition of developmental competence. In addition to its endocrine role to suppress FSH secretion, increased output of inhibin by the selected dominant follicle(s) may upregulate LH-induced androgen secretion that is required to sustain a high level of oestradiol secretion during the pre-ovulatory phase. Advances in our understanding of intraovarian regulatory mechanisms should facilitate the development of new approaches for monitoring and manipulating ovarian function and improving fertility in domesticated livestock, endangered species and man.

/pdf/tgf-beta-superfamily-members-and-ovarian-follicle-2f533am5ir.pdf

TGF-beta superfamily members and ovarian follicle development.

I. Introduction II. Biochemical Properties of the FSH Receptor: A Historical Prelude III. Molecular Structure of the FSH Receptor A. Cloning of the FSH receptor B. Predicted primary structure of the FSH receptor C. Molecular mass of the FSH receptor IV. The FSH Receptor Gene A. Chromosomal localization B. Structure and organization of the FSH receptor gene C. The promoter of the FSH receptor gene V. Expression of the FSH Receptor and Its Regulation A. FSH receptor gene expression B. Expression of the FSH receptor in the testis C. Expression of the FSH receptor in the ovary VI. Expression of the FSH Receptor in Cell Lines A. Cell lines expressing the recombinant FSH receptor B. Measurement of FSH by means of “recombinant” in vitro bioassays C. FSH receptor function in cell lines VII. Structure-Function Relationships and Models of FSH-FSH Receptor Interaction A. General features B. Structure-function relationships C. Models of FSH-FSH receptor interaction VIII. Signal Transduction and Postreceptor Events A....

The follicle-stimulating hormone receptor: biochemistry, molecular biology, physiology, and pathophysiology.

/pdf/selection-of-the-dominant-follicle-in-cattle-3isssbg719.pdf

Selection of the dominant follicle in cattle

Growth and paracrine factors regulating follicular formation and cellular function

Early follicular growth refers to the development of an ovarian follicle from the primordial to early antral phase. In sheep and cows these phases of growth can be classified by the configuration of granulosal cells in the largest cross-section of the follicle as types 1 (primordial), 1a (transitory) 2 (primary), 3 and 4 (preantral) and 5 (early antral). Follicles classified as type 1 may be highly variable within each species with respect to number of granulosal cells and diameter of oocyte. Much of the variation in granulosal cell composition of type 1 follicles may occur at formation and this may account for the variability in granulosal cell composition throughout subsequent stages of growth. There appear to be important differences among species (for example sheep and cattle) in the number and function of granulosal cells relative to the diameter of the oocyte during the initiation of follicular growth. There is evidence that most, if not all, of the growth phases from types 1 to 5 are gonadotrophin-independent and that follicles develop in a hierarchical manner. In sheep, cows and pigs, numerous growth factor, growth factor receptor and gonadotrophin receptor mRNAs and peptides (for example c-kit, stem cell factor, GDF-9, beta B and beta A activin/inhibin subunit, alpha inhibin subunit, follistatin, FGF-2, EGF, EGF-R, TGF beta 1,2 and 3 FSH-R and LH-R) are expressed in a phase of growth (for example types 1-5)-specific and cell-specific manner. However, the roles of many of these factors remain to be determined.

/pdf/control-of-early-ovarian-follicular-development-5532siq7w0.pdf

Control of early ovarian follicular development

Apoptosis is a process of selective cell deletion implicated as a mechanism underlying the process of ovarian follicular atresia. The aims of this study were 1) to test the hypothesis that granulosa cell death during follicular (> or = 4 mm diameter) atresia in cows occurs by apoptosis and 2) to define relationships between the occurrence and degree of granulosa cell apoptosis, cAMP response to FSH or LH, extant aromatase activity, and other previously established biochemical and morphometric indices of granulosa cell function and follicular atresia in this species. Granulosa cells and follicular fluid from individual follicles 4-18 mm in diameter were collected from luteal-phase cow ovaries. Follicles were classified by morphometric criteria as "healthy" (n = 45) or atretic (n = 34). Apoptosis in granulosa cells from each follicle was inferred from detection of internucleosomal DNA cleavage by 3'-end radiolabeling; it was quantitated both subjectively from intensity of oligonucleosome labeling (apoptosis [AP] score = 0, 1, 2, or 3) and objectively by beta-counting of low-molecular weight gel fragments (labeling index; LI). Extant aromatase activity (ng estradiol produced/10(6) cells/3 h) and cAMP response (pmol/10(6) cells) to different doses of FSH or LH (1-10,000 ng/ml) was determined for granulosa cells from most healthy follicles (n = 39). Apoptosis was detected in granulosa cells from all atretic follicles as well as from 76% of healthy follicles, from 80% (16 of 20) of follicles with follicular fluid estradiol to progesterone ratios > 1, and from 71% (10 of 14) of follicles with extant aromatase activity (> 2 ng/10(6) cells/3 h). For healthy and atretic follicles, degree of DNA fragmentation was inversely related to the number of granulosa cells recovered (as percentage maximum by follicle size). In healthy follicles, FSH stimulated cAMP synthesis is a dose-dependent manner in granulosa cells from all follicles examined (> or = 4 mm), but only 36% of these had appreciable aromatase activity. The cAMP response to FSH (per cell) increased with follicle size from 4-7 mm in diameter and remained high in granulosa cells from follicles > or = 8 mm with aromatase activity; in cells without aromatase activity, cAMP response to FSH decreased with increasing follicle size > or 8 mm. The cAMP response to LH was generally low or undetectable in granulosa cells from 4-8-mm follicles; it then increased linearly with increasing follicle diameter > or = 8 mm, but to a greater degree in cells with aromatase activity than in cells without.(ABSTRACT TRUNCATED AT 400 WORDS)

/pdf/apoptosis-in-bovine-granulosa-cells-in-relation-to-steroid-5fip6xn8co.pdf

Apoptosis in bovine granulosa cells in relation to steroid synthesis, cyclic adenosine 3',5'-monophosphate response to follicle-stimulating hormone and luteinizing hormone, and follicular atresia.

Control of early ovarian follicular development.

In female sheep fetuses, the mesonephros and genital ridge can be identified at days 20 and 23 of gestation (term = 145 days), respectively. Moreover oogonia can be observed at the genital ridge from as early as day 23. Around day 55 of gestation, some germ cells enter meiosis coincident with the arrival of mesonephric-derived somatic cells (i.e. the rete ovarii). From day 75, 100, 120 and 135 of gestation, primordial (one layer of flattened granulosa cells), primary (one complete layer of cuboidal granulosa cells; early preantral), secondary (preantral) and tertiary (antral) follicles, respectively, develop within the innermost regions of the ovarian cortex. During the early neonatal period highly variable numbers of antral follicles may be present. After examination of Booroola fetuses from day 28 of gestation, it seems that the FecBB gene is associated with retarded development of the heart (day 28) mesonephros (days 30-40) and from day 30 to early neonatal life, the ovary. With respect to the ovary, fewer oogonia (days 30-40), primordial follicles (day 75-90) and growing follicles (day 120 to 6 weeks after birth) have been observed in females carrying the FecBB gene. By contrast, the FecBB gene is not associated with differences in plasma gonadotrophin or immunoreactive inhibin until early neonatal life. In Inverdale (I) fetuses heterozygous for the FecXI gene (I+), retarded germ cell development was observed at days 40 and 90 of gestation. In putative homozygous carriers (II) of the Inverdale gene, germ cell development appeared normal until day 100, but thereafter from day 120 normal secondary follicles were not observed, although many abnormal follicular-like structures were present. In both I+ and II fetuses no obvious differences in gonadotrophin concentrations have been noted. Collectively, the evidence suggests that the fecundity genes FecBB and FecXI, which affect ovulation rate in sexually mature females, are regulating organ differentiation or germ cell maturation or both processes during fetal life.

D J Tisdall

Papers

Growth and paracrine factors regulating follicular formation and cellular function

Control of early ovarian follicular development

Apoptosis in bovine granulosa cells in relation to steroid synthesis, cyclic adenosine 3',5'-monophosphate response to follicle-stimulating hormone and luteinizing hormone, and follicular atresia.

Control of early ovarian follicular development.

Development of the sheep ovary during fetal and early neonatal life and the effect of fecundity genes.