Biomedical subjects

K P McNatty

Publications and source records attributed to K P McNatty.

At least 19 recordsLinked to original sources

PubMed2005

Oocyte-expressed genes affecting ovulation rate.

From examination of inherited patterns of ovulation rate in sheep, several breeds have been identified with point mutations in two growth factor genes (BMP15 and GDF9) and a related receptor (ALK6) that are expressed in oocytes. Five different point mutations have been identified in the BMP15 gene, one in GDF9 and one in ALK6. Animals heterozygous for these mutations or heterozygous for two of these mutations or homozygous for the ALK6 mutation have higher ovulation rates (i.e. +0.6-10) than their wild-type contemporaries. Animals homozygous for the BMP15 or GDF9 mutations are sterile due to arrested follicular development from the primary stage of growth. The BMP15 and GDF9 mutations are thought to result in reduced levels of mature protein or altered binding to cell-surface receptors. In sheep, GDF9 mRNA is present in germ cells before and after ovarian follicular formation as well as throughout follicular growth, whereas BMP15 mRNA is found in oocytes only from the primary stage of growth. Also ALK6 together with related cell-surface receptors such as ALK5 and BMPRII mRNA are present in oocytes at most, if not all, stages of follicular growth. Both GDF9 and BMP15 proteins are present in follicular fluid indicating that they are secreted products. Immunisation of sheep with GDF9 or BMP15 peptides shows that both growth factors are essential for follicular development, ovulation and/or corpus luteum formation. In animals with the ALK6 mutation, ovarian follicles undergo precocious maturation leading to three to seven follicles ovulating at smaller diameters without any increase above wild-types in the ovarian secretions of steroid or inhibin. One important consequence of the ALK6 mutation appears to be a decreased ability of some BMPs to inhibit differentiation of follicular cells. Current findings in sheep suggest that BMP15, GDF9 and ALK6 are targets for new methods of fertility regulation in some mammals.

Animals↗

PubMed2005

The role of proteins of the transforming growth factor-beta superfamily in the intraovarian regulation of follicular development.

Ovarian follicular development occurs in a hierarchical manner with each follicle having a unique biochemical composition at any moment in time. It has long been understood that a precise coordination between the growth and maturation of the oocyte and adjacent follicular cells (i.e. somatic cells) is essential in order to produce an oocyte that is fully competent to undergo fertilization and embryo development. In addition to the critical endocrine signalling pathways between the hypothalamus, pituitary and ovary, it is now evident that the oocyte itself is important in influencing the microenvironment of the developing follicle by regulating, via paracrine and autocrine mechanisms, its own maturation as well as somatic cell proliferation, differentiation and ovulation rate. Several of the key oocyte-derived regulating factors are members of the transforming growth factor-beta (TGF-beta) superfamily and to date the best understood are growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15) and BMP6. Significant species differences appear to exist in the relative importance of these growth factors and much remains to be elucidated about their roles in the human ovary. More information on the roles of these factors during ovarian follicular development is likely to advance new therapeutic applications for management of fertility as well as our understanding of how better to assess oocyte quality.

Animals↗

PubMed2004

Physiology of GDF9 and BMP15 signalling molecules.

Two related oocyte-derived members of the transforming growth factor-beta (TGF-beta) superfamily, namely growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15, also known as GDF9B), have recently been shown to be essential for ovarian follicular growth. In addition, both proteins have been shown to regulate ovulation rate in sheep, and although it is evident that these growth factors interact both with one another and with other intra- and extra-ovarian factors, the precise mechanisms by which they influence follicular growth and ovulation rate have not been thoroughly elucidated.

Animals↗

PubMed2004

The oocyte and its role in regulating ovulation rate: a new paradigm in reproductive biology.

Ovulation rate in mammals is determined by a complex exchange of hormonal signals between the pituitary gland and the ovary and by a localised exchange of hormones within ovarian follicles between the oocyte and its adjacent somatic cells. From examination of inherited patterns of ovulation rate in sheep, point mutations have been identified in two oocyte-expressed genes, BMP15 (GDF9B) and GDF9. Animals heterozygous for any of these mutations have higher ovulation rates (that is, + 0.8-3) than wild-type contemporaries, whereas those homozygous for each of these mutations are sterile with ovarian follicular development disrupted during the preantral growth stages. Both GDF9 and BMP15 proteins are present in follicular fluid, indicating that they are secreted products. In vitro studies show that granulosa and/or cumulus cells are an important target for both growth factors. Multiple immunisations of sheep with BMP15 or GDF9 peptide protein conjugates show that both growth factors are essential for normal follicular growth and the maturation of preovulatory follicles. Short-term (that is, primary and booster) immunisation with a GDF9 or BMP15 peptide-protein conjugate has been shown to enhance ovulation rate and lamb production. In summary, recent studies of genetic mutations in sheep highlight the importance of oocyte-secreted factors in regulating ovulation rate, and these discoveries may help to explain why some mammals have a predisposition to produce two or more offspring rather than one.

Animals↗

PubMed2003

Expression of the FcRn receptor (alpha and beta) gene homologues in the intestine of suckling brushtail possum (Trichosurus vulpecula) pouch young.

The neonatal IgG transporter FcRn consists of two chains, FcRn alpha and beta (also known as beta(2) microglobulin), and is involved in transferring IgG molecules across both mammary and intestinal epithelial cells. Developmental changes in FcRn IgG alpha and beta chain mRNA levels were investigated in the gut of brushtail possum (Trichosurus vulpecula) pouch young (PY) using Northern hybridisation. FcRn alpha transcripts were detected in the PY proximal intestine at all times examined, between days 1 and 195 of post-natal life, with increased levels detected from around day 110. The beta(2) microglobulin transcript levels in the PY proximal intestine were low to undetectable until day 110 of post-natal life and then increased dramatically after day 159. Both the FcRn alpha and beta gene transcripts were detected in a wide range of tissues in the adult possum (>365 days). Genomic sequences located 5' to the start of transcription of the FcRn alpha and beta(2) microglobulin genes were cloned and analysed for predicted cis-acting transcription control elements. Both the FcRn alpha and beta(2) microglobulin genomic sequences contained STAT5 binding motifs consistent with the transcription of both genes being modulated by prolactin. Using in situ hybridisation, the FcRn alpha and beta(2) microglobulin transcripts were localised to the epithelial cells of the PY intestine. However, no prolactin receptor transcripts were detected in the same epithelial cells suggesting that the observed changes in FcRn alpha and beta(2) microglobulin gene expression in the proximal intestine are not modulated directly by prolactin. The results are consistent with the hypothesis that changes in FcRn alpha and beta(2) microglobulin gene expression take place in the possum PY intestine to accommodate changes in maternal milk composition to meet the changing immunological demands of the PY.

Animals↗

PubMed2003

Production of biologically active tethered ovine FSHbetaalpha by the methylotrophic yeast Pichia pastoris.

The pituitary-derived glycoprotein hormone FSH plays a central role in controlling vertebrate gonadal function. In female mammals the maturation of ovarian follicles is critically dependent upon stimulation by FSH. Moreover, injection of exogenous FSH is used extensively to stimulate increased numbers of follicles to ovulate. Structurally FSH is a heterodimeric glycoprotein composed of two non-covalently associated polypeptide subunits. The tertiary structures of both the alpha- and beta-subunits are constrained by intramolecular disulphide bonds and are post-translationally modified with two N-linked carbohydrate moieties, the structure of which appears to modulate in vivo biological activity. Here we report the expression of ovine FSH (oFSH) as a biologically active single-chain polypeptide using the methylotrophic yeast Pichia pastoris. Sequences encoding the mature oFSH alpha- and beta-proteins were fused to form a gene encoding a fusion protein with the C-terminus of the beta-chain joined to the N-terminus of the alpha-chain, with the chains separated by a two amino acid linker sequence. This fusion gene was itself fused to two alternative Pichia leader sequences (mating factor alpha and acid phosphatase) and transformed into the Pichia strains GS115 and SMD1168. The recombinant fusion protein (oFSHbetaalpha) was expressed at approximately 0.1 microg/ml in 'shake-flask' cultures. The Pichia-expressed tethered protein was biologically active in an in vitro bioassay, had a molecular mass of 28 kDa, as determined by SDS-PAGE, and bound the bovine FSH receptor with a binding profile similar to that of native oFSH.

Animals↗

PubMed2003

Oocyte-derived growth factors and ovulation rate in sheep.

The physiological mechanisms controlling ovulation rate in mammals involve a complex exchange of endocrine signals between the pituitary gland and the ovary, and a localized exchange of intraovarian hormones between the oocyte and its adjacent somatic cells. The discoveries in sheep of mutations in bone morphogenetic protein 15 (BMP15) and bone morphogenetic protein receptor type IB (BMPR-IB) together with recent findings on the physiological effects of growth differentiation factor 9 (GDF9) and BMP15 on follicular development and ovulation rate highlight some important differences in the way in which the oocyte may function in mammals with different ovulation rate phenotypes. In sheep, BMP15 and GDF9 have each been shown to be essential for the early and later stages of follicular development. In addition, ovulation rate is sensitive to changes in the dose of either of these two oocyte-derived growth factors. These findings are in contrast to those reported for mice in which GDF9, but not BMP15, is essential for follicular development. The evidence to date is consistent with the hypothesis that the oocyte plays a central role in regulating key events in the process of follicular development and hence, is important in determining ovulation rate. Moreover, it appears that the mechanisms that the oocyte uses to control these processes differ between species with low and high ovulation rate phenotypes.

Animals↗

PubMed2002

Bmp15 mutations and ovarian function.

BMP15, also known as growth and differentiation factor 9B (GDF9B), is a member of the transforming growth factor beta superfamily (TGFbeta) which in humans, rodents and sheep is expressed exclusively in the oocyte. BMP15 is closely related to GDF9, another oocyte-specific member of this superfamily which has been shown to be essential for early ovarian folliculogenesis. Inactivation of the BMP15 gene in mice has shown only minor effects on fertility. However, Inverdale and Hanna lines of sheep carry naturally occurring mutations in BMP15 which highlight differences in the action of this gene between mice and other mammals. Sheep which are heterozygous show an increase in ovulation rate whereas homozygotes are infertile. The granulosa cell receptor which mediates the BMP15 response has not yet been identified, but the discovery that a point mutation in the BMP1B receptor in Booroola sheep is responsible for increased ovulation rate highlights the importance of the TGFbeta signalling molecules in early folliculogenesis.

Animals↗

PubMed2001

Genetic mutations influencing ovulation rate in sheep.

Ovulation rate in mammals is determined by a complex exchange of endocrine signals between the pituitary gland and the ovary, and by paracrine signals within ovarian follicles between the oocyte and its adjacent somatic cells. One approach to identifying factors regulating ovulation rate is to find mutations that influence the target phenotype and, in this context, sheep are proving to be remarkable experimental models. Recently, in three sheep families, namely Inverdale, Hanna and Booroola, the inherited mutation was mapped to a specific region of the sheep X chromosome (Inverdale, Hanna) or sheep chromosome 6 (Booroola) and in each, a point mutation was identified in genes from the bone morphogenetic protein (BMP) relatives of the transforming growth factor beta superfamily or their receptors. In Inverdale (I) and Hanna (H) sheep, separate point mutations were identified in the BMP15 gene corresponding to sites in the mature peptide coding region of the BMP15 growth factor (also known as growth differentiation factor 9B; GDF9B). Expression of the BMP15 gene was located exclusively in oocytes from the primary stage of follicular growth. There is a complete block of normal follicular development in females carrying two copies of the Inverdale mutation (II), two copies of the Hanna mutation (HH), or one copy of each mutation (HI). Increased ovulation rates are found in females with only one copy of either mutation (I+ or H+). In Booroola sheep, a point mutation was identified in the highly conserved intracellular serine threonine kinase signalling domain of the BMP-1B receptor. Within the ovary, this gene is expressed in oocytes in primordial and pre-antral follicles and in granulosa cells from the primary stage of growth as well as in corpora lutea. The effect of the Booroola mutation is additive for ovulation rate: animals with one copy of the mutation have an ovulation rate of 3 or 4, whereas those with two copies have an ovulation rate of between 5 and 14. Physiological studies of the above mutations demonstrate that the oocyte plays an active role with respect to its adjacent somatic cells during follicular development and support the hypothesis that the oocyte has a significant influence on the number of follicles that proceed to ovulation.

Animals↗

PubMed2001

Highly prolific Booroola sheep have a mutation in the intracellular kinase domain of bone morphogenetic protein IB receptor (ALK-6) that is expressed in both oocytes and granulosa cells.

The Booroola fecundity gene (FecB) increases ovulation rate and litter size in sheep and is inherited as a single autosomal locus. The effect of FecB is additive for ovulation rate (increasing by about 1.6 corpora lutea per cycle for each copy) and has been mapped to sheep chromosome 6q23-31, which is syntenic to human chromosome 4q21-25. Bone morphogenetic protein IB (BMP-IB) receptor (also known as ALK-6), which binds members of the transforming growth factor-beta (TGF-beta) superfamily, is located in the region containing the FecB locus. Booroola sheep have a mutation (Q249R) in the highly conserved intracellular kinase signaling domain of the BMP-IB receptor. The mutation segregated with the FecB phenotype in the Booroola backcross and half-sib flocks of sheep with no recombinants. The mutation was not found in individuals from a number of sheep breeds not derived from the Booroola strain. BMPR-IB was expressed in the ovary and in situ hybridization revealed its specific location to the oocyte and the granulosa cell. Expression of mRNA encoding the BMP type II receptor was widespread throughout the ovary. The mutation in BMPR-IB found in Booroola sheep is the second reported defect in a gene from the TGF-beta pathway affecting fertility in sheep following the recent discovery of mutations in the growth factor, GDF9b/BMP15.

Activin Receptors↗

PubMed2001

Ontogeny of steroidogenesis in the fetal sheep gonad.

The aim of this study was to determine 1) the time of onset and cellular localization of gene expression for steroidogenic factor-1 (SF-1), steroidogenic acute regulatory protein, 3beta-hydroxysteroid dehydrogenase/Delta(5),Delta(4) isomerase (3beta-HSD), and the cytochrome P450 enzymes for cholesterol side-chain cleavage (P450(scc)), 17alpha-hydroxylase (P450(17alphaOH)), and aromatase (P450(arom)) during gonadal development; and 2) the amount of progesterone, androstenedione, testosterone, and 17beta-estradiol present in the fetal sheep gonad. Fetuses were collected on Days 24, 26, 28, 30, 32, 35, 40, 55, and 75 of gestation, and gene expression was determined by in situ hybridization. The steroid content of gonads collected on Days 30, 35, 55, and 75 of gestation was determined by RIA. Developing gonads collected from both male and female fetuses were steroidogenically active around the time of morphological sexual differentiation. In the female, the steroidogenic cells were initially located at the boundary of the cortex and medulla but become increasingly restricted to the mesonephric-derived cell streams. In the male, once tubules were identifiable, steroidogenesis was restricted to the interstitial regions. Interestingly, expression of both SF-1 and 3beta-HSD was observed prior to morphological sexual differentiation. In addition, expression of both of these genes was more widespread than the other genes in both males and females.

3-Hydroxysteroid Dehydrogenases↗

PubMed2001

Genes controlling ovulation rate in sheep.

Sheep provide a valuable model for studying the genetic control of ovulation rate. Recent progress includes the identification of mutations in BMP15 (bone morphogenetic protein 15) that increase ovulation rate in heterozygous carriers and block follicular development in homozygous carriers. The genes characterized to date appear to act principally within the ovary and result in earlier maturity of granulosa cells and reduced follicular size. There may also be other sites of action, and increased FSH concentrations appear to be important in the expression of the FecB phenotype. A new locus on the X chromosome in New Zealand Coopworth sheep increases ovulation rate by about 0.4 and is maternally imprinted. Results from studies in the Cambridge and Belclare breeds indicate that further genes remain to be characterized. Finding the first mutations leading directly to variation in ovulation rate is likely to speed up the identification and molecular analysis of these other genes. There is still much to learn about follicular development and the control of litter size from genetic models in sheep.

Animals↗

PubMed2001

Variation in antral follicle development during the follicular phase of the oestrous cycle in red deer (Cervus elaphus) hinds.

The aim of this study was to quantify antral follicle populations in cyclic red deer hinds and to monitor follicle development leading to ovulation. Oestrus was synchronized with exogenous progesterone and ovaries were recovered approximately 0, 12, 24 or 36 h (follicular phase) or 10 days (luteal phase) after progesterone withdrawal (n = 5 per group). All follicles > or = 2 mm in diameter were dissected out, health status was assessed, follicular fluid oestradiol content was measured, granulosa cells were harvested and their capacity for oestradiol and cAMP production was determined. The time of oestrus and the preovulatory LH surge were monitored in five control hinds. Deer ovaries contained 26.6 +/- 3.45 (mean +/- SEM) follicles > or = 2 mm in diameter (range 4-81), with at least one large antral follicle (diameter: 8.3 +/- 0.38 mm) per hind. There was a strong correlation between follicle size and granulosa cell population (r(2) = 0.676). Approximately half (50.7%) of the follicles were classified as healthy, with the percentage classified as atretic decreasing with increasing follicle size. Neither the total number of antral follicles nor their size distribution differed significantly among groups. There were significantly more (P < 0.05) healthy follicles at 24 h after progesterone withdrawal than at 0 h, when large oestrogenic follicles had fewer granulosa cells, lower follicular fluid oestradiol concentrations and lower aromatase activity (P < 0.05) than did those from other groups. In summary, antral follicle development in red deer is similar to that in other monovulatory ruminants, and at least one large follicle is present at all stages of the oestrous cycle.

Animals↗

PubMed2000

Growth and paracrine factors regulating follicular formation and cellular function.

The purpose of this paper is to review, using fetal sheep as the animal model, aspects of ovarian development related to follicular formation and to report on the identity of growth and paracrine factors which might be involved in this process. Before follicular formation there is a massive and sustained colonisation of the fetal ovary by mesonephric cells, which become a precursor source of follicular cells. From within the ovarian medulla, somatic 'cell-streams' branch into the cortex around nests of oogonia and oocytes. These 'cell-streams', which contain elongated cells with either flattened or cuboidal shaped nuclei, express steroidogenic factor-1 (SF-1), steroid acute regulatory protein (StAR), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), cytochrome P450(scc), and P450(aromatase) mRNA and/or protein. Follicles form from the association of an oocyte with the 'cell-stream' with either a single layer of flattened cells (i.e. type 1 follicle) or with a mixture of flattened and cuboidal cells (i.e. type 1a follicle). These newly-formed follicles have between 3 and 57 somatic cells (i.e. granulosa cells) and contain oocytes which vary in diameter between 23 and 52 microm. Newly formed and early growing follicles have been identified with growth factors or growth factor receptors in either the oocytes or granulosa cells. Many of the growth factors are from the TGFbeta superfamily and are expressed in a cell- and stage-specific manner.

Animals↗

PubMed2000

A model of follicular development and ovulation in sheep and cattle.

A dynamic model to describe ovarian follicular development following commitment has been developed. It identifies follicular growth with oestradiol production and assumes that this growth is the result of intra-ovarian stimulation, gonadotrophin stimulation, and inhibitory interactions among the follicles, where larger follicles suppress the growth of the smaller follicles. The variables of the model are the levels of oestradiol in each follicle at commitment, the rate of change of oestradiol production by individual follicles during follicular development, and the level of oestradiol that will induce luteinizing hormone (LH) surge. Changes in the variables of the model could be associated with both genetic and environmental effects. The behaviour of the model is consistent with experimental observations. The model can be expanded to include exogenous follicle-stimulating hormone (FSH) administration assuming that FSH is associated with advancing the maturation of gonadotrophin-dependent follicles without affecting the number of committed follicles. The use of the model to explore FSH administration strategies is demonstrated. The model confirms that the response to FSH administration depends on both the amount of FSH and the time of administration. The largest number of double ovulations occurred when FSH was given at the time of the deviation of the dominant and subordinate follicles.

Animals↗

PubMed2000

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

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 impaired. A second family unrelated to the Inverdale sheep also has the same X-linked phenotype (Hanna, FecXH). Crossing FecXI with FecXH animals produces FecXI/FecXH infertile females phenotypically indistinguishable from FecXI/FecXI females. 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 beta (TGFbeta) superfamily and is specifically expressed in oocytes, its function is unknown. 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.

Amino Acid Sequence↗

PubMed2000

Gene expression in abnormal ovarian structures of ewes homozygous for the inverdale prolificacy gene.

Animals heterozygous (I+) for the Inverdale prolificacy gene (FecX(I)) have an increased ovulation rate whereas those homozygous (II) for FecX(I) are infertile with "streak" ovaries and follicular development arrested at the primary (type 2 follicle) stage. The streak ovaries also contain small oocyte-free nodules with granulosa-like cells and often tumor-like structures. It has been hypothesized that these abnormal structures are of granulosa cell origin, and the aim of this study was to determine whether genes normally expressed in granulosa cells are also expressed in the nodules and tumor-like structures. The mRNAs encoding c-kit and its ligand stem cell factor (SCF), FSH receptor (FSH-R), follistatin, alpha-inhibin subunit, and the beta(A)- and beta(B)-activin/inhibin subunits were localized in ovaries of ewes with 0 (++), 1 (I+), or 2 (II) copies of the FecX(I) gene (n = 4-9 animals per genotype per gene) using in situ hybridization. Ontogeny of expression of all mRNAs examined was similar between ++ and I+ ewes. Expression of c-kit mRNA was observed in the oocyte of all follicular types present in ++, I+, and II ewes. Moreover, granulosa cells of type 2 (II) and type 2 and larger follicles (++, I+) expressed SCF mRNA. The mRNAs encoding FSH-R, follistatin, alpha-inhibin subunit, and beta(B)-activin/inhibin subunit were identified in type 3 and larger follicles of ++ and I+ ewes but not in follicles of II ewes that were only at the type 1, 1a, or 2 stages of development. However, the cells within the oocyte-free nodules of II ewes expressed all of these genes. The mRNAs encoding c-kit and beta(A)-activin/inhibin subunit were not observed in granulosa cells until antrum formation (type 5 follicles) or in the nodules of II ewes. Tumors from 4 ewes were obtained and classified as cystic, semisolid, or solid structures containing granulosa-like cells or as solid structures containing predominately fibroblast- and luteal-like cells. Often, two tumors were present on the same ovary. Tumors containing granulosa-like cells (n = 3-4 per gene) expressed the mRNAs encoding alpha-inhibin subunit, beta(A)-, and beta(B)-activin/inhibin subunits, follistatin, and the FSH-R but did not contain detectable amounts of mRNA for c-kit or SCF. Tumors composed predominately of fibroblast- and luteal-like cells expressed very low levels of SCF mRNA; of the other mRNAs examined, none were detected. Also, none of the genes examined were found to be expressed by the surface epithelium, theca externa, fibroblast, or vascular cells within the ovary of animals of any genotype. These findings are consistent with the hypothesis that the somatic cells in oocyte-free nodules and tumor-like tissue in II ewes originate from the granulosa cells of the small follicles.

Activins↗

PubMed2000

Expression of growth and differentiation factor-9 in the ovaries of fetal sheep homozygous or heterozygous for the inverdale prolificacy gene (FecX(I)).

Abnormal follicular and oocyte growth in ovaries of sheep homozygous (II) for the Inverdale gene, FecX(I), suggest that this gene may influence a fundamental event in initiation of folliculogenesis, with two copies of the gene inhibiting growth at the primordial/primary stage. In addition, striking similarities in ovarian morphology between mice deficient in growth and differentiation factor-9 (GDF-9) and II sheep suggest a relationship between the FecX(I) gene and GDF-9 function in the ovary. Therefore, it was hypothesized that GDF-9 mRNA expression would be inhibited in ovaries of II fetal sheep. To test this hypothesis, in situ hybridization was used to characterize GDF-9 mRNA expression in ovaries of homozygous (II), heterozygous (I+), and control (++) fetal sheep at Day 135 of gestation. GDF-9 mRNA expression was localized exclusively to oocytes from the type 1 follicle stage onward in all genotypes and is the first demonstration of GDF-9 mRNA expression in ovaries of fetal sheep. In addition, GDF-9 mRNA expression was detected in oocytes of abnormal type 2 follicles in the ovaries of II sheep. Thus, it does not appear that inhibition of GDF-9 gene expression is the mechanism of action whereby the FecX(I) gene exerts its influence. However, the possibility of translation at specific stages of follicular development cannot presently be ruled out. In addition, the FecX(I) gene may be involved, either directly or indirectly, in regulating expression of receptors for GDF-9. At present, however, neither the FecX(I) gene product nor the GDF-9 receptor has been isolated or characterized.

Animals↗