Apoptosis of Sertoli cells after conditional ablation of murine double minute 2 (Mdm2) gene is p53-dependent and results in male sterility

Beside its well-documented role in carcinogenesis, the function of p53 family has been more recently revealed in development and female reproduction, but it is still poorly documented in male reproduction. We specifically tested this possibility by ablating Mdm2, an E3 ligase that regulates p53 protein stability and transactivation function, specifically in Sertoli cells (SCs) using the AMH-Cre line and created the new SC-Mdm2^−/− line. Heterozygous SC-Mdm2^−/+ adult males were fertile, but SC-Mdm2^−/− males were infertile and exhibited: a shorter ano-genital distance, an extra duct along the vas deferens that presents a uterus-like morphology, degenerated testes with no organized seminiferous tubules and a complete loss of differentiated germ cells. In adults, testosterone levels as well as StAR, P450c17 (Cyp17a1) and P450scc (Cyp11a1) mRNA levels decreased significantly, and both plasma LH and FSH levels increased. A detailed investigation of testicular development indicated that the phenotype arose during fetal life, with SC-Mdm2^−/− testes being much smaller at birth. Interestingly, Leydig cells remained present until adulthood and fetal germ cells abnormally initiated meiosis. Inactivation of Mdm2 in SCs triggered p53 activation and apoptosis as early as 15.5 days post conception with significant increase in apoptotic SCs. Importantly, testis development occurred normally in SC-Mdm2^−/− lacking p53 mice (SC-Mdm2^−/−p53^−/−) and accordingly, these mice were fertile indicating that the aforementioned phenotypes are entirely p53-dependent. These data not only highlight the importance of keeping p53 in check for proper testicular development and male fertility but also certify the critical role of SCs in the maintenance of meiotic repression.

Regulation of folliculogenesis and the determination of ovulation rate in ruminants

The paper presents an update of our 1993 model of ovarian follicular development in ruminants, based on knowledge gained from the past 15 years of research. The model addresses the sequence of events from follicular formation in fetal life, through the successive waves of follicular growth and atresia, culminating with the emergence of ovulatory follicles during reproductive cycles. The original concept of five developmental classes of follicles, defined primarily by their responses to gonadotrophins, is retained: primordial, committed, gonadotrophin-responsive, gonadotrophin-dependent and ovulatory follicles. The updated model has more extensive integration of the morphological, molecular and cellular events during folliculogenesis with systemic events in the whole animal. It also incorporates knowledge on factors that influence oocyte quality and the critical roles of the oocyte in regulating follicular development and ovulation rate. The original hypothetical mechanisms determining ovulation rate are retained but with some refinements; the enhanced viability of gonadotrophin-dependent follicles and increases in the number of gonadotrophin-responsive follicles by increases in the throughput of follicles to this stage of growth. Finally, we reexamine how these two mechanisms, which are thought not to be mutually exclusive, appear to account for most of the known genetic and environmental effects on ovulation rate.

Insights into the mechanism by which kisspeptin stimulates a preovulatory LH surge and ovulation in seasonally acyclic ewes: potential role of estradiol

We have previously demonstrated that a constant intravenous infusion of kisspeptin (Kp) for 48 h in anestrous ewes induces a preovulatory luteinizing hormone (LH) surge followed by ovulation in approximately 75% of animals. The mechanisms underlying this effect are unknown. In this study, we investigated whether Kp-induced preovulatory LH surges in anestrous ewes were the result of the general activation of the whole gonadotropic axis or of the direct activation of central GnRH neurons required for the GnRH/LH surge. In the first experiment, a constant iv infusion of ovine kisspeptin 10 (Kp; 15.2 nmol/h) was given to 11 seasonally acyclic ewes over 43 h. Blood samples were taken every 10 min for 15 h, starting 5h before the infusion, and then hourly until the end of the infusion. We found that the infusion of Kp induced a well-synchronized LH surge (around 22 h after the start of the Kp infusion) in 82% of the animals. In all ewes with an LH surge, there was an immediate but transient increase in the plasma concentrations of LH, follicle-stimulating hormone (FSH), and growth hormone (GH) at the start of the Kp infusion. Mean (+/- SEM) concentrations for the 5-h periods preceding and following the start of the Kp infusion were, respectively, 0.33 +/- 0.09 vs 2.83 +/- 0.49 ng/mL (P = 0.004) for LH, 0.43 +/- 0.05 vs 0.55 +/- 0.03 ng/mL (P = 0.015) for FSH, and 9.34 +/- 1.01 vs 11.51 +/- 0.92 ng/mL (P = 0.004) for GH. In the first experiment, surges of LH were observed only in ewes that also had a sustained rise in plasma concentrations of estradiol (E(2)) in response to Kp. Therefore, a second experiment was undertaken to determine the minimum duration of Kp infusion necessary to induce such a pronounced and prolonged increase in plasma E(2) concentration. Kisspeptin (15.2 nmol/h) was infused for 6, 12, or 24h in seasonally acyclic ewes (N = 8), and blood samples were collected hourly for 28 h (beginning 5h before the start of infusion), then every 2h for the following 22 h. Kisspeptin infused for 24h induced LH surges in 75% of animals, and this percentage decreased with the duration of the infusion (12h = 50%; 6h = 12.5%). The plasma concentration of E(2) was greater in ewes with an LH surge compared to those without LH surges; mean (+/- SEM) concentrations for the 5-h period following the Kp infusion were, respectively, 2.23 +/- 0.16 vs 1.27 +/- 0.13 pg/mL (P < 0.001). Collectively, our results strongly suggest that the systemic delivery of Kp induced LH surges by activating E(2)-positive feedback on gonadotropin secretion in acyclic ewes.

Factors affecting oocyte quality: who is driving the follicle?

Mammalian ovaries contain a large stock of oocytes enclosed in primordial follicles. Ovarian cyclic activity induces some of these follicles to initiate growth towards a possible ovulation. However, most of these follicles terminate their growth at any moment and degenerate through atresia. In growing follicles, only a subset of oocytes are capable to support meiosis, fertilization and early embryo development to the blastocyst stage, as shown through embryo in vitro production experiments. This proportion of competent oocytes is increasing along with follicular size. Growing lines of evidence suggest that oocyte competence relies on the storage of gene products (messenger RNA or protein) that will be determinant to support early stages of embryo development, before full activation of embryonic genome. Given these facts, the question is: are these gene products stored in oocytes during late folliculogenesis, allowing an increasing proportion of them to become competent? Alternatively, these transcripts may be stored during early folliculogenesis as the oocyte grows and displays high transcription activity. Several arguments support this latter hypothesis and are discussed in this review: (i) many attempts at prolonged culture of oocytes from antral follicles have failed to increase developmental competence, suggesting that developmental competence may be acquired before antral formation; (ii) the recent discovery of oocyte secreted factors and of their ability to regulate many parameters of surrounding somatic cells, possibly influencing the fate of follicles between ovulation or atresia, suggests a central role of oocyte quality in the success of folliculogenesis. Finally, in addition to their role in interfollicular regulation of ovulation rate, late folliculogenesis regulation and atresia could also be seen as a selective process aimed at the elimination through follicular atresia of oocytes that did not succeed to store proper gene products set during their growth.

The effect of AMP-activated kinase activation on gonadotrophin-releasing hormone secretion in GT1-7 cells and its potential role in hypothalamic regulation of the oestrous cyclicity in rats

Hypothalamic AMP-activated kinase (AMPK) is a key regulator of food intake in mammals. Its role in reproduction at the central level and, more precisely, in gonadotrophin-releasing hormone (GnRH) release has never been investigated. We showed that each subunit of AMPK is present in immortalised GnRH neurones (GT1-7 cells). Treatment with 5-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR) and metformin, two activators of AMPK, increased dose-dependent and time-dependent phosphorylation of AMPKalpha atThr172 in GT1-7 cells. Phosphorylation of acetyl-coenzyme A carboxylase at ser79 also increased. Treatment with AICAR (5 mM) or metformin (5 mM) for 4 h inhibited GnRH release in the presence or absence of GnRH (10(-8) M). Specific AMPK inhibitor compound C completely eliminated the effects of AICAR or metformin on GnRH release. Finally, we determined the central effects of AICAR in vivo on food intake and oestrous cyclicity. Ten-week-old female rats received a 50 microg AICAR or a saline i.c.v. injection. We detected increased AMPK and acetyl-CoA carboxylase phosphorylation, specifically in the hypothalamus, 30 min after AICAR injection. Food intake was significantly higher (P < 0.05) in animals treated with AICAR than in animals injected with saline, 24 h after injection. This effect was abolished after 1 week. Moreover, during the 4 weeks following injection, the interval between two oestrous stages was significantly lower in the AICAR group than in the saline group. Our findings suggest that AMPK activation may act directly at the hypothalamic level to affect fertility by modulating GnRH release and oestrous cyclicity.

Expression and biological effects of bone morphogenetic protein-15 in the hen ovary

The bone morphogenetic protein 15 (Bmp15) and growth differentiation factor 9 (Gdf9) genes are two members of the transforming growth factor-beta superfamily. In mammals, these genes are known to be specifically expressed in oocytes and to be essential for female fertility. However, potential ovarian roles of BMPs remain unexplored in birds. The aim of the present work was to study for the first time the expression of Bmp15 in the hen ovary, to compare its expression pattern with that of Gdf9, and then to investigate the effects of BMP15 on granulosa cell (GC) proliferation and steroidogenesis. We found that chicken Bmp15 and Gdf9 genes were preferentially expressed in the ovary. We showed using in situ hybridization that Bmp15 and Gdf9 mRNAs were specifically localized in oocytes of all ovarian follicles examined. We also demonstrated using real-time quantitative RT-PCR that Bmp15 and Gdf9 expression was maintained during hierarchical follicular maturation in the gerrminal disc region and then progressively declined after ovulation. BMP15 was able to activate Smad1 (mothers against decapentaplegichomolog1) signaling pathway in hen GCs. Moreover, we showed a strong inhibitory effect of BMP15 on gonadotropin-induced progesterone production in hen GCs. This inhibitory effect was associated with a decrease in steroidogenic acute regulatory protein (STAR) level. Taken together, our results suggest that BMP15 may have a key role in the female fertility of birds.

Peroxisome proliferator-activated receptors in reproductive tissues: from gametogenesis to parturition

Peroxisome proliferator-activated receptors (PPARalpha, PPARbeta/delta and PPARgamma) are a family of nuclear receptors that are activated by binding of natural ligands, such as polyunsaturated fatty acids or by synthetic ligands. Synthetic molecules of the glitazone family, which bind to PPARgamma, are currently used to treat type II diabetes and also to attenuate the secondary clinical symptoms frequently associated with insulin resistance, including polycystic ovary syndrome (PCOS). PPARs are expressed in different compartments of the reproductive system (hypothalamus, pituitary, ovary, uterus and testis). Conservative functions of PPARs in mammalian species could be suggested through several in vivo and in vitro studies, especially in the ovary and during placental development. Several groups have described a strong expression of PPARgamma in ovarian granulosa cells, and glitazones modulate granulosa cell proliferation and steroidogenesis in vitro. All these recent data raise new questions about the biologic actions of PPARs in reproduction and their use in therapeutic treatments of fertility troubles such as PCOS or endometriosis. In this review, we first describe the roles of PPARs in different compartments of the reproductive axis (from male and female gametogenesis to parturition), with a focus on PPARgamma. Secondly, we discuss the possible molecular mechanisms underlying the effect of glitazones on PCOS. Like other 'insulin sensitizer' molecules, such as metformin, glitazones may in fact act directly on ovarian cells. Finally, we discuss the eventual actions of PPARs as mediators of environmental toxic substances for reproductive function.

Molecular basis of bone morphogenetic protein-4 inhibitory action on progesterone secretion by ovine granulosa cells

We have recently reported that bone morphogenetic protein-4 (BMP-4) can inhibit progesterone production by ovine granulosa cells (GCs). Here, we have investigated the underlying mechanisms of this effect in basal as well as in FSH-induced conditions. We have confirmed that treatment with BMP-4 decreased basal GC progesterone secretion and totally abolished FSH-stimulating action. This inhibitory action was associated with a decrease in the expression of cAMP-regulated genes, steroidogenic acute regulatory protein (StAR) and P450 side-chain cleavage (P450 scc) at mRNA and protein levels. However, BMP-4 did not alter basal cAMP production by GCs. In contrast, BMP-4 decreased by half the FSH-induced cAMP production and strongly inhibited cAMP-induced progesterone production. Thus, the inhibitory effect of BMP-4 was exerted both upstream and downstream of cAMP signalling. We next examined the downstream effect, focusing on cAMP-dependent transcription factors, steroidogenic factor-1 (SF-1) and CREB, through the BMP factor signalling intermediary, Smad1. As expected, BMP-4 induced phosphorylation and transcriptional activity of Smad1 in ovine GCs. BMP-4-activated Smad1 did not affect CREB activity but inhibited the transcriptional activity of SF-1 on the canonical SF-1 responsive element. Interestingly, this transcriptional inhibitory mechanism occurred on transfected StAR and P450 scc promoter. Based on these results, we propose that SF-1 is a key target in the inhibitory mechanism exerted by BMP-4 on progesterone synthesis by ovine GCs in culture. Because SF-1 plays an essential role in the differentiation of GCs, our findings could have new implications in understanding the role of BMP family members in the control of ovarian folliculogenesis.

Alterations of somatotropic function in prion disease in sheep

This study aimed at investigating the possible linkage between natural scrapie and alterations of the somatotropic axis. Scrapie-affected ewes exhibited 2-fold higher mean GH concentrations during both autumn and spring. GH pulse frequencies were higher in scrapie-affected ewes than in control animals (mean+/-S.E.M. number of pulses/24 h: 10.4+/-0.9 and 7.6+/-0.9 for scrapie-affected and control ewes respectively) suggesting the involvement of central mechanisms. GH secretion induced by administration of an alpha(2)-adrenergic agonist, which acts centrally to stimulate GH secretion, was similar between healthy and scrapie-affected ewes (ratios of the area under the curve (AUC) of GH concentration after to the GH AUC before the agonist administration were 3.6+/-1.6 and 4.9+/-1.0 for scrapie-affected and control ewes respectively). Finally, humoral markers and parameters of the metabolic status were determined to test the hypothesis that scrapie-associated alterations of GH secretion could be related to disruption of metabolic homeostasis. Glucose, insulin and urea plasma concentrations were higher in scrapie-affected than in healthy ewes. Neither leptin nor IGF-I levels were affected by scrapie. Total thyroxine (T4) was decreased in scrapie-affected ewes but free T4 and total and free triiodothyronine were not modified. In conclusion, our results showed the existence in scrapie-affected ewes of endocrine and metabolic alterations typical of acute illness proceeding, at least in part, from central mechanisms.

Proteolytic degradation of IGF-binding protein (IGFBP)-2 in equine ovarian follicles: involvement of pregnancy-associated plasma protein-A (PAPP-A) and association with dominant but not subordinated follicles

In the ovary of mammalian species, terminal follicular growth is accompanied by a decrease in intrafollicular levels of IGF-binding protein-2 (IGFBP-2) and IGFBP-4. The decrease in IGFBP-4 levels is essentially due to an increase in proteolytic cleavage by intrafollicular pregnancy-associated plasma protein-A (PAPP-A) in growing healthy follicles. The decrease in IGFBP-2 levels is partly due to a decrease in mRNA expression by follicular cells. In addition, we have recently shown that IGFBP-2 is also proteolytically cleaved by PAPP-A in bovine and porcine growing follicles. In the present work, we showed that follicular fluid from late dominant equine follicles (35 mm diameter) contains a proteolytic activity against IGFBP-2. First follicular fluid from dominant follicles contained lower levels of native IGFBP-2 than the corresponding serum, as assessed by Western ligand blotting. In contrast, immunoblotting experiments showed much higher levels of a 12 kDa proteolytic fragment in dominant follicular fluid than in the serum. Moreover, equine dominant follicular fluid was able to induce proteolysis of exogenous recombinant bovine (rb)IGFBP-2, this degradation being dose-dependently enhanced by IGFs. The proteolytic activity against IGFBP-2 in equine follicles was partially immunoneutralized by a polyclonal antibody raised against human PAPP-A. Moreover, cleavage of rbIGFBP-2 by equine follicular fluid was dose-dependently inhibited by a peptide derived from the heparin-binding domain of IGFBP-5, as well as by peptides derived from other heparin-binding domain-containing proteins such as connective tissue growth factor, vitronectin and heparin-interacting protein, previously shown to inhibit PAPP-A. Finally, the proteolytic activity was very low in subordinate follicles, was high in both early (25 mm diameter) and late (35 mm diameter) dominant follicles, and was slightly lower in preovulatory follicles recovered 35 h after human chorionic gonadotropin (hCG) treatment.Overall, these data show that in the equine ovary, the selection of dominant follicles is associated with an increase of the proteolytic degradation of IGFBP-2 by PAPP-A, as for IGFBP-4, and potentially other protease(s), probably contributing to the increase in IGF bioavailability. In atretic subordinate follicles, the decrease in the proteolytic degradation of IGFBP-2, probably due in part to a direct inhibition by peptides containing heparin-binding domains, contributes to the increase in IGFBP-2 levels and the decrease in IGF bioavailability. The expression of PAPP-A and IGFBP-2 mRNA during folliculogenesis remain to be investigated in the mare.

Growth kinetics of the granulosa cell population in ovarian follicles: an approach by mathematical modelling

This paper describes, from a mathematical viewpoint, the cellular changes in the granulosa of ovarian follicles during their terminal development. A dynamic model takes into account the processes of (1) cell division, (2) exit from the cell cycle towards differentiation, and (3) apoptotic cell death. Proliferative cells leave the cycle in an irreversible way. The risk of entering apoptosis applies to non-cycling cells. Changes in the cell numbers and in the growth fraction are derived from differential equations. The transitions between the different cell states are ruled by time-dependent rates. Numerical applications of the model concern ovulating and degenerating ovarian follicles in the ewe. The main feature of the ovulating case is the progressive exhaustion of the proliferating compartment for the benefit of the non-cycling cells. From an initial mainly proliferative state the granulosa progressively switches to a highly differentiated state, so that the growth fraction continuously decreases. In the atretic cases, the pattern of changes in the total viable cell number is influenced by the follicular age at the onset of the apoptotic process and by the intensity of the cell death rate. As apoptosis affects the non-cycling cells, the growth fraction is no longer strictly decreasing. The sensitivity of the model to the parameters is studied in a more general framework than the granulosa cell population.

The insulin-like growth factor system: a key determinant role in the growth and selection of ovarian follicles? a comparative species study

The aim of the present paper is to make a comparative study of the expression of the elements of the insulin-like growth factor (IGF) system in different mammalian species and thus illuminate their potential role in the process of ovarian folliculogenesis in mammals. In most mammalian species, IGFs and IGFBPs (in particular IGFBP-2 and IGFBP-4) are considered, respectively, as stimulators and inhibitors of follicular growth and maturation. In mammalian species, IGFs might play a key role in sensitizing ovarian granulosa cells to FSH action during terminal follicular growth. Concentrations of IGFBP-2 and IGFBP-4 in follicular fluid strongly decrease and increase during follicular growth and atresia, respectively, leading to an increase and a decrease in IGF bioavailability, respectively. The decrease in these IGFBPs is because of a decrease in mRNA expression (IGFBP-2) and an increase in proteolytic degradation by PAPP-A in follicular fluid (IGFBP-2, IGFBP-4 and IGFBP-5), and likely participates in the selection of dominant follicles. In contrast, levels and/or sites of expression of IGF-I, IGF-II, IGFBP-4, IGFBP-5 and type II receptor in follicular cells strongly differ between mammalian species, suggesting that these phenomena might play species-specific or secondary roles in ovarian folliculogenesis.

The Booroola mutation in sheep is associated with an alteration of the bone morphogenetic protein receptor-IB functionality

The hyperprolificacy phenotype of Booroola ewes is due to the presence of the FecB(B) allele at the FecB locus, recently identified as a single amino acid substitution (Q249R) in the bone morphogenetic protein (BMP) type-IB receptor (BMPR1B), and is associated with a more precocious differentiation of ovarian granulosa cells (GCs). To evaluate the consequences of the Booroola mutation on BMPR1B functions, the action of ligands of the transforming growth factor-beta (TGFbeta)/BMP family that act through (growth and differentiation factor-5, BMP-4) or independently of (activin A, TGFbeta-1) BMPR1B were studied on primary cultures of GCs from homozygous FecB(+) and FecB(B) ewes. All the tested TGFbeta/BMP family ligands inhibited progesterone secretion by FecB(+) GCs. Those inhibitory effects were lower for GCs from preovulatory (5-7 mm diameter) than from small antral follicles (1-3 mm diameter). The presence of the Booroola mutation was associated with a 3- to 4-fold (P<0.001) decreased responsiveness of GCs from FecB(B) compared with FecB(+) small follicles to the action of BMPR1B ligands. In contrast, TGFbeta-1 and activin A had similar inhibitory effects on progesterone secretion by GCs from FecB(+) and FecB(B) small follicles. No difference between genotypes was observed with GCs from preovulatory follicles. In transfection experiments with HEK-293 cells, co-expression of FecB(+) BMPR1B and BMPR2 resulted in a 2.6-fold (P<0.01) induction of the activity of a BMP-specific luciferase reporter construct by BMP-4. Interestingly, no response to BMP-4 was observed when cells were transfected with the FecB(B) form of the BMPR1B receptor. Overall, these data strongly suggest that the Q249R mutation is associated with a specific alteration of BMPR1B signaling in hyperprolific Booroola ewes.

Prolificacy genes in sheep: the French genetic programmes

It has been demonstrated that variations in litter size or ovulation rate in different breeds of sheep can be associated with the segregation of several major genes. This set of natural mutants constitutes a valuable resource to determine key points in the biochemical pathways controlling the development of ovarian follicles. The French genetic programmes were devised to identify two of these genes: the Booroola (FecB) and Lacaune genes. The FecB prolific mutation corresponds to a non-conservative mutation (Q249R) in the intracellular kinase-signalling domain of the bone morphogenetic protein receptor type IB (BMPR-IB) gene. The Lacaune gene is situated on ovine chromosome 11. Positional cloning is currently in progress to identify the relevant gene and mutation. A similar approach, limited to linkage testing of candidate genes, is proposed to classify the different prolificacy genes in sheep.

Clinical, hormonal, and hematologic characteristics of bovine calves derived from nuclei from somatic cells

Although healthy animals are born after nuclear transfer with somatic cells nuclei, the success of this procedure is generally poor (2%-10%) with high perinatal losses. Apparently normal surviving animals may have undiagnosed pathologies that could develop later in life. The gross pathology of 16 abnormal bovine fetuses produced by nuclear transfer (NT) and the clinical, endocrinologic (insulin-like growth factors I and II [IGF-I and IGF-II], IGF binding proteins, post-ACTH stimulation cortisol, leptin, glucose, and insulin levels), and biochemical characteristics of a group of 21 apparently normal cloned calves were compared with those of in vitro-produced (IVP) controls and controls resulting from artificial insemination. Oocytes used for NT or IVP were matured in vitro. NT to enucleated oocytes was performed using cultured adult or fetal skin cells. After culture, Day 7, grade 1-2 embryos were transferred (one per recipient). All placentas and fetuses from clones undergoing an abnormal pregnancy showed some degree of edema due to hydrops. Mean placentome number was lower and mean placentome weight was higher in clones than in controls (69.9 +/- 9.2 placentomes with a mean weight of 144.3 +/- 21.4 g in clones vs. 99 and 137 placentomes with a mean individual weight of 34.8 and 32.4 g in two IVP controls). Erythrocyte mean cell volume was higher at birth (P < 0.01), and body temperature and plasma leptin concentrations were higher and T4 levels were lower during the first 50 days and the first week (P < 0.05), respectively, in clones. Plasma IGF-II concentrations were higher at birth and lower at Day 15 in clones (P < 0.05). Therefore, apparently healthy cloned calves cannot be considered as physiologically normal animals until at least 50 days of age.

Laminin-alpha6beta1 integrin interaction enhances survival and proliferation and modulates steroidogenesis of ovine granulosa cells

This study aimed to determine the physiological role of laminin (LN) and its receptor, alpha(6)beta(1) integrin, in controlling the functions of granulosa cells (GC) during follicular development in sheep ovary. Immunohistochemistry experiments showed the presence of increasing levels of LN (P<0.0001), and high levels of mature alpha(6)beta(1) integrin in GC layers of healthy antral follicles during the follicular and the preovulatory phases of the estrous cycle. In vitro, the addition of a function-blocking antibody raised against alpha(6) subunit (anti-alpha(6) IgG) to the medium of ovine GC cultured on LN impaired cell spreading (P<0.0001), decreased the proliferation rate (P<0.05) and increased the apoptosis rate (P<0.05). Furthermore, addition of anti-alpha(6) IgG enhanced estradiol (E2) secretion by GC in the presence or absence of follicle-stimulating hormone (FSH), luteinizing hormone or insulin-like growth factor-I in culture medium (P<0.0001), and inhibited progesterone (P4) secretion in basal conditions or in the presence of low (0.5 ng/ml) FSH concentrations only (P<0.0001). The anti-alpha(6) IgG effect was specific to an interaction of LN with alpha(6)beta(1) integrin since it was ineffective on GC cultured on heat-denatured LN, RGD (arginine-glycine-aspartic acid) peptides and non-coated substratum. Hence, this study established that alpha(6)beta(1) integrin 1) was expressed in GC of antral follicles, 2) mediated the actions of LN on survival, proliferation and steroidogenesis of GC, and 3) was able to dramatically modulate P4 and E2 secretion by GC in vitro. It is suggested that during the follicular and the preovulatory phases of the estrous cycle, the increasing levels of LN in GC of large antral follicles might support their final development to ovulation.

Pregnancy-associated plasma protein-A (PAPP-A) in ovine, bovine, porcine, and equine ovarian follicles: involvement in IGF binding protein-4 proteolytic degradation and mRNA expression during follicular development

IGF binding protein-4 (IGFBP-4) proteolytic degradation is a common feature of preovulatory follicles from human, ovine, bovine, porcine, and equine ovary. In all these species, the protease is a zinc-dependent metalloprotease and its ability to degrade IGFBP-4 is IGF dependent. The human intrafollicular IGFBP-4-degrading protease has recently been identified as pregnancy-associated plasma protein-A (PAPP-A). The aim of this study was to investigate whether PAPP-A is also involved in IGFBP-4 degradation in ovine, bovine, porcine, and equine preovulatory follicles and to study the expression of PAPP-A mRNA in bovine and porcine granulosa cells from different classes of follicles. Immunoneutralization and immunoprecipitation with polyclonal antibodies raised against human PAPP-A inhibited IGFBP-4 proteolytic degradation in preovulatory follicular fluid from the four species studied. As previously reported for the intrafollicular proteolytic activity degrading IGFBP-4, recombinant human PAPP-A generated in vitro 17- and 10-kDa IGFBP-4-proteolytic fragments. Recombinant PAPP-A activity was also shown to be IGF dependent and was inhibited by heparin-binding domain-containing peptides. In all mammalian species studied, the PAPP-A sequences showed high degree of identity. Moreover, the PAPP-A gene was localized on porcine chromosome 1 (1q29-1q213), in agreement with the localization of human PAPP-A gene on human chromosome 9q33.1. In bovine and porcine ovaries, real-time quantitative RT-PCR showed that PAPP-A mRNA expression in granulosa cells was maximal in fully differentiated follicles and was positively correlated with expression of P450 aromatase and LH receptor mRNAs. Overall, these data show that PAPP-A is responsible for IGFBP-4 degradation in ovine, bovine, porcine, and equine preovulatory follicles. The high expression of PAPP-A mRNA in granulosa cells from large, differentiated follicles suggest that it is a new functional marker of follicular development.

Genotyping of Cre-lox mice and detection of tissue-specific recombination by multiplex PCR

Conditional gene targeting, based on Cre-lox or other systems, requires frequent genotyping of transgenic mouse populations and monitoring of tissue-specific Cre recombinatory efficiency. This is currently achieved by Southern analysis from tail- and tissue-derived DNA. Multiplex PCR amplification of the floxed (flanked by loxP sites) genomic region, combined with the PCR detection of the Cre transgene, simplifies this task. Here, we show that complete genotyping of a floxed locus is possible with three appropriately placed primers and that this triplex PCR can be performed simultaneously with a universal PCR assay for the detection of Cre transgenes. Using this approach, we also determined the ratios of recombined versus non-recombined floxed genomic segments in genomic DNA samples. This allowed us to estimate the efficiency of in vivo conditional inactivation from biopsy material and tissue samples that were too small for Southern analysis. As many new conditional knockouts are spatiotemporally restricted, such assays will become increasingly useful. The proposed PCR strategy is flexible and may be adapted to the structural specificities of any target gene.

Insulin-like growth factor binding proteins (IGFBPs) as potential physiological substrates for human kallikreins hK2 and hK3

Insulin-like growth factors (IGFs) are important growth regulators of both normal and malignant prostate cells. Their action is regulated by six insulin-like growth factor binding proteins (IGFBPs). The proteolytic cleavage of IGFBPs by various proteases decreases dramatically their affinity for their ligands and therefore enhances the bioavailability of IGFs. To elucidate the putative biological role of prostatic kallikreins hK2 and hK3 (prostate-specific antigen) in tumour progression, we analyzed the degradation of IGFBP-2, -3, -4 and -5 by these two tissue kallikreins. We found that hK3, already characterized as an IGFBP-3 degrading protease, cleaved IGFBP-4 but not IGFBP-2 and -5, whereas hK2 cleaved all of the IGFBPs much more effectively, and at concentrations far lower than those reported for other IGFBP-degrading proteases. The proteolytic patterns after cleavage of IGFBPs by hK2 and hK3 were similar and were not modified in the presence of IGF-I. Heparin, but not other glycosaminoglycans, enhanced dramatically the ability of hK3 but not hK2 to degrade IGFBP-3 and IGFBP-4. More importantly, the IGFBP fragments generated by hK2 and hK3 had no IGF-binding capacity, as assessed by Western ligand blotting. Our results suggest that the prostatic kallikreins hK2 and hK3 may influence specifically the tumoral growth of prostate cells through the degradation of IGFBPs, to increase IGF bioavailability.

Extracellular matrix regulates ovine granulosa cell survival, proliferation and steroidogenesis: relationships between cell shape and function

The extracellular matrix (ECM), constituting the follicular basal lamina and present also between follicular cells and in the follicular fluid, is believed to regulate granulosa cell (GC) function during follicular development. Ovine GCs isolated from small (1-3 mm in diameter) or large (4-7 mm in diameter) antral follicles were cultured on various pure ECM components (type I collagen, fibronectin, laminin), synthetic substrata enhancing (RGD peptides) or impairing (poly 2-hydroxyethylmethacrylate (poly-hema)) cell adhesion, or in the presence of heparin. The effects of these factors, used alone or in combination with IGF-I and/or FSH, were evaluated in terms of GC spread, survival, proliferation and steroidogenesis. When grown on type I collagen (CI) gel, poly-hema or heparin, GCs from both large and small follicles exhibited a round shape and a low proliferation rate. Compared with non-coated plastic substratum as a control, these ECM or synthetic compounds enhanced estradiol secretion and reduced progesterone secretion by large-follicle GCs. In contrast, GCs from both large and small follicles spread extensively on CI coating, fibronectin, laminin and RGD peptides. Fibronectin and laminin dramatically increased the proliferation rate and enhanced survival of GCs from both origins. Moreover, fibronectin, laminin and RGD peptides reduced estradiol secretion by large-follicle GCs. Unexpectedly, CI coating increased estradiol secretion and reduced progesterone secretion by large-follicle GCs, suggesting that type I collagen was able to maintain estradiol secretion independently of GC shape. Finally, GC responsiveness to IGF-I and FSH, in terms of proliferation and steroidogenesis, was generally maintained when cells were grown on ECM components, RGD peptides and in the presence of heparin. However, when large-follicle GCs were grown as non-adherent clusters (as observed on poly-hema) basal and IGF-I- and/or FSH-stimulated progesterone secretions were totally abolished. Overall, this study shows that GC shape, survival, proliferation and steroidogenesis can be modulated in vitro by pure ECM components in a specific and coordinated manner. It is suggested that, in vivo, fibronectin and laminin would sustain follicular development by enhancing the survival and proliferation of GCs, whereas type I collagen might participate in the maintenance of estradiol secretion in large antral follicles.

Mutation in bone morphogenetic protein receptor-IB is associated with increased ovulation rate in Booroola Mérino ewes

Ewes from the Booroola strain of Australian Mérino sheep are characterized by high ovulation rate and litter size. This phenotype is due to the action of the FecB(B) allele of a major gene named FecB, as determined by statistical analysis of phenotypic data. By genetic analysis of 31 informative half-sib families from heterozygous sires, we showed that the FecB locus is situated in the region of ovine chromosome 6 corresponding to the human chromosome 4q22-23 that contains the bone morphogenetic protein receptor IB (BMPR-IB) gene encoding a member of the transforming growth factor-beta (TGF-beta) receptor family. A nonconservative substitution (Q249R) in the BMPR-IB coding sequence was found to be associated fully with the hyperprolificacy phenotype of Booroola ewes. In vitro, ovarian granulosa cells from FecB(B)/FecB(B) ewes were less responsive than granulosa cells from FecB(+)/FecB(+) ewes to the inhibitory effect on steroidogenesis of GDF-5 and BMP-4, natural ligands of BMPR-IB. It is suggested that in FecB(B)/FecB(B) ewes, BMPR-IB would be inactivated partially, leading to an advanced differentiation of granulosa cells and an advanced maturation of ovulatory follicles.

Consequences of the presence of the Booroola F gene on the intraovarian insulin-like growth factor system and terminal follicular maturation in Mérinos d'Arles ewes

In sheep, the presence of the Booroola F gene has several important consequences for ovarian function. This study investigated the consequences of the presence of the F gene for the insulin-like growth factor (IGF) system in the ewe ovary. Studies were undertaken in ovaries from F+ and ++ Mérinos d'Arles ewes to determine 1) the levels of type I IGF receptors and IGF binding proteins (IGFBPs) in follicular cells by quantitative autoradiography of [(125)]-IGF-I binding sites on ovarian sections; 2) the pattern of intrafollicular IGFBPs, by Western-ligand blotting on follicular fluids; and 3) the effects of IGF-I and FSH on proliferation and differentiation of granulosa cells in vitro, assessed by progesterone secretion and cytochrome P450 side-chain cleavage (P450(scc)) expression. The amounts of type I IGF receptors were similar in F+ and ++ follicular cells; however, at the same follicular size, F+ healthy follicles contained lower concentrations of IGFBPs smaller than 40 kDa (particularly IGFBP-2) than ++ healthy follicles. In vitro, in basal conditions as well as in IGF-I- or FSH-stimulated conditions (or both), granulosa cells from F+ follicles had a lower proliferative activity, secreted higher amounts of progesterone, and expressed higher levels of P450(scc) than granulosa cells from ++ follicles of the same size. When F+ and ++ preovulatory follicles were compared at the end of the follicular phase, IGFBPs <40 kDa concentrations were slightly higher, and responsiveness of granulosa cells to FSH in vitro was lower in F+ than in ++ follicles, suggesting that terminal maturation of F+ follicles, although precocious, was less complete than it was in ++ follicles. The early decrease in intrafollicular IGFBPs <40 kDa concentrations observed in F+ antral follicles, which likely leads to an early increase in IGF bioavailability, may at least partly account for the increased ovulation rate that characterizes F-carrier ewes.

Insulin-like growth factor (IGF)-binding protein-4 proteolytic degradation in bovine, equine, and porcine preovulatory follicles: regulation by IGFs and heparin-binding domain-containing peptides

We recently showed that insulin-like growth factor-binding protein-4 (IGFBP-4) proteolytic degradation in ovine preovulatory ovarian follicles is IGF-dependent and regulated by the heparin-binding domain (HBD) from IGFBP-3 and from connective tissue growth factor (CTGF), heparan/heparin-interacting protein (HIP), and vitronectin. The present study investigated regulation of IGFBP-4 proteolytic degradation in porcine, bovine, and equine ovarian preovulatory follicles. Follicular fluid from such preovulatory follicles contains proteolytic activity, degrading exogenous IGFBP-4. An excess of IGF-I enhanced IGFBP-4 degradation. In contrast, IGFBP-2 or -3 or monoclonal antibodies against IGF-I or -II dose-dependently inhibited IGFBP-4 degradation, and IGF-I or -II reversed this inhibition in a dose-dependent manner. Heparin-binding peptides derived from the C-terminal domain of IGFBP-3 or -5 inhibited IGFBP-4 degradation. Other heparin-binding peptides derived from CTGF, HIP, and vitronectin also inhibited IGFBP-4 degradation, except in porcine follicles. Finally, IGFBP-3 that was mutated in its HBD was less effective at inhibiting IGFBP-4 degradation. Thus, in bovine, porcine, and equine preovulatory follicles, IGFBP-4 proteolytic degradation both depends on IGFs and is inhibited by peptides containing HBD. Overall, these results suggest that during terminal development of follicles to the preovulatory stage in domestic animal species, the increase in IGF bioavailability might enhance IGFBP-4 degradation. In contrast, in atretic follicles, the decrease in IGF bioavailability, resulting partly from the increase in IGFBP-2 (sow, heifer, mare) and IGFBP-5 (heifer) expression would participate in the decrease of IGFBP-4 degradation. In bovine atretic follicles, IGFBP-5 would also strengthen the inhibition of IGFBP-4 degradation by direct interaction of its HBD with the protease. The involvement of other HBD-containing proteins in the modulation of intrafollicular proteases degrading IGFBP-4 remains to be investigated.

Importance of the IGF system in early folliculogenesis

In the primate ovary, androgens promote oocyte insulin-like growth factor (IGF) I expression as well as initiation of follicle development. In most other mammals, IGFs do not appear to be required for the entry of follicles into the pool of growing follicles and for their gonadotropin-independent development. In contrast, IGFs are involved in the increase in FSH-responsiveness of granulosa cells when follicles enter into the gonadotropin-dependent stages of follicular development (200 microm in mouse, 2 mm in sheep, 5 mm diameter in cattle). In the late stages of folliculogenesis, the decrease in IGFBPs participates in the increase in IGF bioavailability, leading to a further amplification of FSH action.

Insulin-like growth factor binding protein-4 proteolytic degradation in ovine preovulatory follicles: studies of underlying mechanisms

The regulation of insulin-like growth factor binding protein (IGFBP)-4 proteolytic degradation by insulin-like growth factors (IGFs) has been largely studied in vitro, but not in vivo. The aim of this study was to investigate the involvement of IGFs, IGFBP-2, IGFBP-3, and IGFBP-3 proteolytic fragments in the regulation of IGFBP-4 proteolytic activity in ovine ovarian follicles. Follicular fluid from preovulatory follicles contains proteolytic activity degrading exogenous IGFBP-4. The addition of an excess of IGF-I enhanced IGFBP-4 proteolytic degradation, whereas addition of IGFBP-2 or -3 or monoclonal antibodies against IGF-I and -II dose dependently inhibited IGFBP-4 proteolytic degradation. IGF-I and IGF-II, but not LongR3-IGF-I, reversed this inhibition in a dose-dependent manner. C-terminal, but not N-terminal, proteolytic fragments derived from IGFBP-3 (aa 161-264), as well as heparin-binding domain-containing peptides derived from the C-terminal domain of IGFBP-3 and -5 also induced the inhibition of IGFBP-4 proteolytic degradation. Other heparin-binding domain-containing peptides derived from the connective tissue growth factor (CTGF) and from proteins not related to IGFBP, heparan/heparin interacting protein (HIP) and vitronectin, but not from p36 subunit of annexin II tetramer, inhibited IGFBP-4 degradation. Furthermore, IGFBP-3, mutated on its heparin-binding domain, was not able to inhibit IGFBP-4 proteolytic degradation. So, in ovine preovulatory follicles, IGFBP-4 proteolytic degradation both 1) depends on IGFs, and 2) is inhibited by IGFBP-3 via its C-terminal heparin-binding domain as well as by heparin-binding domain containing peptides. These data suggest that in early atretic follicles, the increase in IGFBP-2 participates in the decrease in IGFBP-4 degradation. In late atretic follicles, the increase in the levels of C-terminal IGFBP-3 proteolytic fragments, generated by IGFBP-3 degradation, as well as the increase in IGFBP-5 expression would strengthen the inhibition of IGFBP-4 degradation. This inhibition might be partly mediated by direct interaction of IGFBP-4 proteinase(s) and heparin-binding domain within the C-terminal region from IGFBP-3 and -5.

Comparative expression of luteinizing hormone and follicle-stimulating hormone receptors in ovarian follicles from high and low prolific sheep breeds

Expression of gonadotropin receptors and granulosa cell sensitivity to gonadotropin hormones by small (1-3 mm) and large (3.5-7 mm) follicles were compared in Romanov (ROM, ovulation rate = 3) and Ile-de-France (IF, ovulation rate = 1) ewes in the early and late follicular phase. In healthy follicles, LH receptor levels in granulosa cells increased with increasing follicular size (p < 0. 001) while FSH receptor levels decreased (p < 0.05). In granulosa cells of large follicles, LH receptor (LHR) mRNA levels were greater in the late than in the early follicular phase (p < 0.001, p < 0.05, for ROM and IF, respectively). In the early follicular phase, LHR levels in granulosa (p < 0.001) and theca cells (p < 0.05) of small follicles were greater in ROM than in IF ewes. FSH receptor mRNA levels in granulosa cells of small and large ROM follicles were greater than in the corresponding IF follicles (p < 0.05). Finally, a greater responsiveness (increase in cAMP secretion) to both FSH and hCG was observed by granulosa cells collected during the early follicular phase from ROM vs. IF ewes. Data provide evidence that the greater ovulation rate in the ROM as compared to the IF breed is associated with a greater gonadotropin responsiveness during the early follicular phase.

Expression of insulin-like growth factor binding protein-5 by ovine granulosa cells is regulated by cell density and programmed cell death in vitro

In vivo, in the sheep ovary, the expression of insulin-like growth factor binding protein (IGFBP)-2 and particularly IGFBP-5 has been shown to increase dramatically in apoptotic granulosa cells from atretic follicles. The aim of this work was to study the relationship between apoptosis induced by serum starvation in vitro and expression of IGFBP-2 and -5 by ovine granulosa cells. For this purpose, granulosa cells from follicles 1-3 mm in diameter were cultured in the presence of serum for 2 days, then cultured in the presence or absence of serum for 24, 48, or 72 hr. At the end of the culture, cells were counted, cell viability was assessed by studying DNA fragmentation, and IGFBPs expression was studied by quantitative autoradiography, Western-ligand blotting, immunoblotting, and quantitative in situ hybridization. In vitro, IGFBP-2 and particularly IGFBP-5 were the main IGFBPs secreted by ovine granulosa cells. Serum starvation provoked (i) apoptosis of granulosa cells within 48 hr, (ii) a marked decrease in cell density, and (iii) a marked increase in the amount of IGFBP-5 associated with cell membranes and with the walls of culture wells, but no change in culture medium. The increase in the amount of cell- and wall-associated IGFBP-5 after serum starvation was essentially due to the consecutive decrease in cell density rather than to an increase in cell apoptosis. Indeed, irrespective of the presence or absence of serum, the amount of IGFBP-5 associated to cell membranes was inversely correlated to cell density. In contrast, the amount of IGFBP-5 present in culture medium was positively correlated to cell density. Furthermore, expression of IGFBP-5 mRNA was shown to increase with both cell density and cell death. Indeed, the expression of IGFBP-5 mRNA dramatically increased with cell density, irrespective of the presence or absence of serum, but at a similar cell density, expression was higher in serum-free than in serum conditions. Overall, these results indicate that, in vitro, the localization of IGFBP-5 on ovine granulosa cell membranes and in culture medium, respectively, was mainly dependent on cell density, whereas expression of IGFBP-5 mRNA was related to both cell density and cell death. These data suggest that IGFBP-5 is involved in both growth arrest and apoptosis of granulosa cells in the sheep.

[Mechanism, regulation, and manipulations of follicular atresia]

In ovaries of mammals, an intense loss of germinal cells occurs by follicular atresia throughout the life. In atretic antral follicles, granulosa cells stop proliferating and become apoptotic. Main effectors of apoptosis are caspases which are activated by two ways in granulosa cells, the one involving Fas/TNF-alpha receptor, the other involving factors of the bel-2 family. Atresia is triggered when some essential factors supporting follicular development are lacking. Particularly, terminal follicular development is strictly dependent upon gonadotropin (FSH, then LH in the final preovulatory stage) supply, but factors acting in a paracrine way (growth factors, cytokines, steroids, constituents of extracellular matrix) play also important roles in amplifying gonadotropin action in follicular cells. Some pathological situations such as premature ovarian failure would result from accelerated follicular atresia, triggered by interactions between follicular cells and cells of the immune system. Current methods to control atresia consist in administrating exogenous gonadotropins, or indirectly increasing endogenous gonadotropins, or increasing follicular cell responsiveness to gonadotropins.

[Metabolism-reproduction interactions in domestic animals]

In farm animals as in human, reproduction is affected by changes in the level of energetic balance. The main factors that link metabolism and reproduction, like insulin, IGFs, glucose, FFA, leptin and NPY, act on hypothalamo-pituitary axis as well as on gonads by directly altering gametogenesis.

Intrafollicular insulin-like growth factor-binding protein levels in equine ovarian follicles during preovulatory maturation and regression

The profiles of insulin-like growth factor-binding proteins (IGFBPs) in follicular fluid have been characterized in a number of mammals (rats, pigs, sheep, cattle, humans) and are good indicators of follicular status. We studied the IGFBP profiles of equine serum and ovarian follicular fluid recovered at various stages of the follicular phase. The levels of IGFBPs were related to the morphology and the steroidogenic activity of the follicles. Follicular fluids were recovered by ultrasound-guided follicular aspiration. In the first experiment, the dominant follicles of 10 mares were partly punctured (aspiration of 0.5-2.2 ml of fluid) once at the early dominant stage (22-25 mm in diameter) and a second time at the preovulatory stage (PO), 34 h after induction of ovulation. Among these 10 PO follicles, 5 were classified as healthy whereas the other 5 were classified as hemorrhagic, as assessed by ultrasonic morphology and subsequent ovulation or not. In another group of mares (n = 5), the largest follicle was punctured once at the late dominant stage (33-35 mm in diameter) and then at the PO stage, 34 h after induction of ovulation. Serum was prepared at each puncture session. In the second experiment, follicular fluid was recovered from the dominant and contemporary cohort subordinate follicles (n = 5 mares). Samples were individually assayed for estradiol-17beta and progesterone content by RIA, and IGFBPs were studied by using Western ligand blotting and densitometry. Equine serum and follicular fluid displayed IGFBP at 42-44 kDa (likely corresponding to IGFBP-3), 28-32 kDa (likely corresponding to IGFBP-5), 24 kDa (likely corresponding to IGFBP-4), and 35 kDa, identified as IGFBP-2 by immunoblotting, plus one band at 120 kDa. IGFBP were clearly more abundant in serum than in fluid from healthy follicles. In the follicular fluid, 42-44-kDa IGFBP was the major binding protein, and its level was almost constant at the various physiological statuses studied. Follicular development of the dominant follicle in each mare was characterized by a decrease in intrafollicular IGFBP-2 and 28-32-kDa IGFBP levels before LH stimulation and by an increase in IGFBP-2 after LH stimulation. Follicular regression of large follicles, as well as subordinate ones, was characterized by a low level of intrafollicular estradiol-17beta and was associated with an increase in IGFBP-2, 24-kDa IGFBP, and 28-32-kDa IGFBP intrafollicular levels. Taking these results together, we have demonstrated clear correlations between the intrafollicular levels of estradiol-17beta and IGFBP-2 and 28-32-kDa IGFBP. Therefore, follicular growth and regression in the mare are associated with specific changes in IGFBP levels. These changes could be of crucial importance for follicular development in ovulation or atresia.

Chronology of events accompanying follicular atresia in hypophysectomized ewes. Changes in levels of steroidogenic enzymes, connexin 43, insulin-like growth factor II/mannose 6 phosphate receptor, extracellular matrix components, and matrix metalloproteinases

The chronology of changes in levels of some proteins known to be altered during atresia of ovarian follicles was studied in ewes hypophysectomized at the end of the follicular phase of the estrous cycle. This study was performed by quantitative immunohistochemistry and zymography on large antral follicles (diameter > 3.5 mm) normally destined to ovulate, recovered 24, 36, or 72 h after pituitary ablation. The process of atresia was followed by comparing healthy follicles from intact ewes, with early atretic follicles recovered 24 h after hypophysectomy, clearly atretic follicles recovered 36 h after hypophysectomy, and late atretic follicles recovered 72 h after hypophysectomy. The earliest events of atresia induced by hypophysectomy were detected in theca and consisted of a strong decrease in levels of fibronectin (p < 0.001) and insulin-like growth factor II/mannose 6 phosphate (IGF-II/M6P) receptors (p < 0.05), occurring within the first 24 h following pituitary ablation. In intact animals, similar changes were observed in theca of early atretic follicles, suggesting that these changes may be important events involved in the onset of follicular atresia. In parallel, intrafollicular levels of matrix metalloproteinase-2 and -9 were shown to increase as early as 24 h after hypophysectomy, and a further increase was observed until 72 h after hypophysectomy. These early events were followed by the disappearance of P450 aromatase in granulosa cells 36 h after hypophysectomy (p < 0.05), and a progressive decrease in levels of P450 17alpha-hydroxylase in the theca interna and of gap junction protein connexin-43 in granulosa cells; these markers were still detectable in late atretic follicles 72 h after hypophysectomy. The increase in levels of fibronectin, type IV collagen, laminin, and IGF-II/M6P receptors within granulosa cell layers (p < 0.05) was significant only in late atretic stages, suggesting that these changes may be consequences rather than causes of atresia.

Involvement of insulin-like growth factors in the interactions between nutrition and reproduction in female mammals

The effects of nutrition on the reproductive system of female mammals are discussed in an attempt to determine the importance of the role of the insulin-like growth factor (IGF) system of proteins in the physiological mechanisms. The IGF system comprises IGF-I, IGF-II, their receptors and binding proteins. For this review, insulin and its receptors have been included in this system. The reproductive responses have been separated into two classes, based on fundamental differences in the reproductive biology and physiological mechanisms underlying them. The first involves the effects of nutrition on the induction of ovulation, at puberty or postpartum. In this case, the question is whether or not the animal will reproduce. The second class of response, changes in ovulation rate, involves consideration of reproductive efficiency in animals in which ovulation is inevitable.

Estrogen receptor protein and mRNA expression in the ovary of sheep

Using immunohistochemistry and in situ hybridization, we attempted to identify the estrogen receptor (ER) protein and messenger RNA (mRNA) in sheep ovaries during the follicular phase of the estrous cycle. Monoclonal anti-ER antibodies H222 and 1D5 were used for localizing estrogen receptor on ovarian cryo-sections. Labeling for ER was found over the nuclei of surface epithelium, interstitial tissue, and granulosa cells of small as well as large ovarian follicles. In the preantral and small antral follicles, intense nuclear ER labeling was observed in mural granulosa cells and particularly in cumulus/granulosa cells surrounding the oocyte. In the large healthy looking follicles, greater diversity in labeling for ER was observed, which is characterized by mixed populations of granulosa cells expressing positive and more or less negative nuclear labeling. Such a pattern of labeling was particularly evident in follicles showing the signs of atresia. Generally, more intense nuclear staining was localized in granulosa cells proximal to basal membrane. In situ hybridization studies revealed the presence of ER mRNA in ovarian tissue. Autoradiographic visualization localized ER mRNA expression over the granulosa cells of healthy follicles of all sizes. Level of hybridization signal was comparable in mural and cumulus granulosa cells. In atretic follicles, the level of hybridization signal in granulosa cells was comparable to that of healthy follicles. A relatively weaker level of labeling was observed in granulosa cells dispersed in follicular antrum in follicles with advanced atretic lesions. Theca cells expressed a lower level of labeling than granulosa cells. Specificity of labeling for both ER protein and mRNA in ovary was proved by parallel probing the ovine uterus. Ovine ER recognition by both H222 and 1D5 antibodies was also proved by immunoblotting. These studies demonstrate the presence of the estrogen receptor and its messenger RNA in the sheep ovary and suggest an autocrine/paracrine role of estradiol and its receptor in the regulation of ovarian follicle development in sheep.

Changes in extracellular matrix components and steroidogenic enzymes during growth and atresia of antral ovarian follicles in the sheep

To investigate the involvement of extracellular matrix (ECM) in folliculogenesis in the sheep, parallel changes in ECM components and key steroidogenic enzymes were studied by quantitative immunohistochemistry and immunoblotting during follicular growth and atresia. Growth of ovarian follicles from 1 to 5 mm in diameter was characterized by a progressive increase in P450 cholesterol sidechain cleavage levels in both thecal (p < 0.001) and granulosa cells (p < 0.001), an increase in P450 aromatase levels in granulosa cells of follicles larger than 3.5 mm (p < 0.001), and an increase in levels of P450 17 alpha-hydroxylase C17,20 lyase (P450(17 alpha)) in the theca interna. In addition, during follicular growth, a change in localization of cells expressing P450(17 alpha) within the theca interna was observed, positive cells being sparse within the theca interna of small follicles and specifically located close to the basal laminae in large follicles. In parallel, follicular growth was associated with an increase in levels of type I collagen in granulosa cell layers (p < 0.01) and an increase in levels of fibronectin (p < 0.05), particularly the specific ED-A alternatively spliced variant of fibronectin, in the theca externa. Follicular atresia was characterized by a loss of P450 aromatase in granulosa cells (p < 0.001) and a decrease in levels of P450(17 alpha) in the theca interna (p < 0.05). Simultaneously, levels of fibronectin (p < 0.05), particularly the ED-A variant of fibronectin, decreased in the theca externa of atretic follicles. Within the wall of granulosa cells, levels of fibronectin (p < 0.05), laminin, type IV collagen, and heparan sulfate proteoglycans strongly increased during follicular atresia. Overall, these results show that follicular growth and atresia were associated with distinct changes in levels of ECM components, suggesting that ECM components may play a role in the regulation of proliferation, differentiation, and apoptosis of follicular cells.

Proteolytic activity degrading insulin-like growth factor-binding protein-2, -3, -4, and -5 in healthy growing and atretic follicles in the pig ovary

In the pig, ovarian follicular growth is characterized by an increase in intrafollicular levels of insulin-like growth factor-binding protein (IGFBP)-3 and a decrease in the levels of IGFBPs < 40 kDa (IGFBP-2, -4 and, to a lesser extent, a 30-kDa IGFBP likely corresponding to IGFBP-5). In contrast, atresia is primarily associated with a strong increase in intrafollicular levels of IGFBP-2 and -4, with intrafollicular levels of IGFBP-3 and -5 varying slightly or not at all. The purpose of the present study was to determine whether intrafollicular proteases are involved in such changes. Porcine follicular development was synchronized with a progestin, and individual follicles were isolated 12 h and 96 h after progestin withdrawal. Follicular fluid from follicles of various sizes and qualities was collected and incubated alone or with a source of exogenous bovine IGFBP-2 or human IGFBP-3, -4, or -5 for 20 h at 37 degrees C. Samples were then analyzed by Western ligand blotting and by immunoblotting using specific antisera. Porcine follicular fluid from various classes of follicles contained proteolytic activity degrading IGFBP-2, -4, and -5. In contrast, intrafollicular IGFBP-3 proteolytic activity was very low or nondetectable. In preovulatory follicles, degradation of IGFBPs < 40 kDa was 1) accompanied by the generation of small proteolytic fragments visualized by immunoblotting, 2) strongly inhibited by EDTA and 1,10-phenanthroline, and 3) dependent on the presence of zinc and calcium chloride. PMSF (1 mM, serine protease inhibitor) inhibited degradation of IGFBP-2 and to a lesser extent IGFBP-4, but not IGFBP-5. Other serine and cysteine protease inhibitors as well as TIMP-2 and BB-2116 (natural tissue inhibitor-2 and synthetic inhibitor of matrix metalloproteinases [MMPs], respectively) were ineffective. Gelatin-substrate zymography revealed the presence of two major intrafollicular gelatinase MMPs at 60 kDa and 76-85 kDa (likely MMPs 2 and 9, respectively), the levels of which decreased (76-85 kDa) or strongly increased (60 kDa) during follicular atresia. Follicular growth at diameters between 2 and 6-7 mm was characterized by a dramatic increase in proteolytic activity degrading IGFBP-2, -5 and, to a lesser extent, IGFBP-4. Atresia, in contrast, was associated with a marked decrease in proteolytic activity degrading IGFBP-2, -4, and -5. These results suggest that 1) changes in proteolytic activity of intrafollicular IGFBPs < 40 kDa are at least partly responsible for the changes in intrafollicular IGFBP levels during follicular growth and atresia in the pig and 2) calcium- and zinc-dependent metalloprotease(s) as well as serine protease(s) are involved in degradation of intrafollicular IGFBPs < 40 kDa.

Follicular growth and ovarian dynamics in mammals

General characteristics of female reproductive activity, such as seasonality, cyclicity and triggering of ovulation differ widely among mammals, but common mechanisms underlie ovarian function. In all mammals, follicles begin to grow from a pool of primordial follicles constituted early in life, continuously throughout the life of the female. Follicular development involves two phases. In a first phase (basal follicular growth), follicles grow slowly and follicular growth rate is tightly related to proliferation of granulosa cells. Basal follicular growth is mainly under the control of growth factors of paracrine origin. In these follicles, FSH may exert an indirect mitogenic effect on granulosa cells by enhancing expression of growth factors or growth factor receptors. In a second phase (terminal follicular growth), follicular growth is rapid and occurs by enlargement of the antrum. In addition, it is accompanied by important changes in differentiation of follicular cells. Terminal follicular development is strictly dependent on gonadotrophins. FSH plays determinant roles in enhancing granulosa cell differentiation and survival. These actions are mediated or modulated in an important way by paracrine factors, particularly steroids and growth factors. LH stimulates steroidogenesis in theca cells and sustains terminal maturation of granulosa cells in preovulatory follicles. Follicular growth, atresia and ovulation are accompanied by important tissue remodelling processes, which are under the fine control of proteinases and inhibitors of proteinases. In particular matrix metalloproteinases and their inhibitors are probably involved in the control of rapid terminal follicular growth and regression of atretic follicles as well as in follicular rupture at ovulation.

Expression of messenger ribonucleic acids of insulin-like growth factor binding protein-2, -4, and -5 in the ovine ovary: localization and changes during growth and atresia of antral follicles

In the sheep as in many mammalian species, growth and atresia of antral follicles are characterized, respectively, by a decrease and a high increase in the intrafollicular levels of insulin-like growth factor binding proteins of less than 40 kDa (IGFBPs < 40 kDa), mainly IGFBP-2, -4, and -5. The objective of this study was to investigate whether such changes are associated with changes in follicular expression of the corresponding mRNA. For this purpose, ovaries were recovered from ewes slaughtered at the end of follicular phase (i.e., 30 h after progestagen sponge removal; control ewes) or at 24 h, 36 h or 72 h after hypophysectomy (hypox) performed 30 h after sponge removal. The expression of mRNA of IGFBPs of less than 40 kDa (IGFBPs < 40 kDa mRNA) was studied in ovine antral follicles from control and hypox ewes by in situ hybridization using [35S]-labeled human IGFBP-2, -4, and -5 cRNA as probes. In control ewes, IGFBP-2 mRNA was mainly expressed in granulosa as a gradient in healthy follicles, the expression being higher in granulosa cells close to the basal membrane than in granulosa cells bordering the antrum and within the cumulus. The level of IGFBP-2 mRNA was lower both in granulosa cells close to the basal membrane and in those bordering the antrum from small follicles than in the corresponding compartments of granulosa cells from large healthy follicles (p < 0.05). In healthy follicles, IGFBP-4 and -5 mRNA were mainly expressed in thecal cells. No change in level of IGFBP-4 mRNA was observed between small and large follicles, whereas the level of IGFBP-5 mRNA tended to be lower in thecal cells from large compared to small follicles (p = 0.055). In atretic follicles, expression of IGFBPs < 40 kDa mRNA strongly increased in granulosa (IGFBP-2 and -5, p < 0.01) and in thecal cells (IGFBP-2 and -4, p < 0.01). In hypox ewes, the chronology of changes in expression of follicular IGFBPs < 40 kDa mRNA and in intrafollicular levels of the corresponding proteins was studied during atresia of large antral follicles. Early atresia of large follicles was associated with a strong decrease in intrafollicular estradiol levels (p < 0.001); an increase in intrafollicular levels of IGFBP-2, -4, and -5 (p < 0.001) an increase in both IGFBP-2 (p < 0.001) and -5 (p < 0.01) mRNA expression in granulosa and thecal cells; but no changed in IGFBP-4 mRNA expression. Late atresia of large follicles was associated with a further decrease in intrafollicular estradiol levels (p < 0.01); a further increase in intrafollicular levels of IGFBP-2, -4, and -5 (p < 0.001); an increase in IGFBP-4 (p < 0.01) and -5 (p < 0.05) mRNA expression in theca and granulosa, respectively; a decrease in IGFBP-5 mRNA expression in theca (p < 0.05); but no further increase in IGFBP-2 mRNA expression. Overall, these data suggest that the decrease and the increase in expression of mRNA of follicular IGFBPs < 40 kDa during follicular growth and atresia, respectively, are involved in the decrease and the increase in intrafollicular levels of the corresponding proteins. Moreover, the increases in expression of follicular IGFBPs < 40 kDa during atresia of large follicles in hypophysectomized ewes followed a specific time course, the increase in IGFBP-2 and -5 mRNA expression being early than the increase in IGFBP-4 mRNA expression.

Proteolytic activity is involved in changes in intrafollicular insulin-like growth factor-binding protein levels during growth and atresia of ovine ovarian follicles

In the sheep, follicular growth is characterized by both an increase and a decrease in the level of intrafollicular insulin-like growth factor-binding protein-3 (IGFBP-3) and IGFBPs less than 40 kDa (IGFBP-2, -4, and -5), respectively. In contrast, follicular atresia is associated with a decrease and a large increase in levels of IGFBP-3 and IGFBPs less than 40 kDa, respectively. To assess whether intrafollicular proteases are involved in such changes, follicular fluid from follicles of different sizes and degrees of atresia was incubated alone or with pure human IGFBP-3, -4, or -5 or serum (as a source of exogenous IGFBP-2) for 20 h at 37 C. Samples were then analyzed by Western ligand blotting and by immunoblotting using specific antisera. Ovine follicular fluid from different classes of follicles contained proteolytic activity degrading IGFBP-2, -3, -4, and -5. Degradation of IGFBPs was accompanied by the generation of small proteolytic fragments visualized by immunoblotting or after autoradiography using radiolabeled IGFBP-4. Moreover, follicular growth and atresia were characterized by changes in IGFBP proteolytic activity. Indeed, follicular growth (between 2 and 6 mm in diameter) was characterized by 1) a decrease in IGFBP-3 proteolytic activity and 2) a dramatic increase in proteolytic activity degrading IGFBP-4 and, to a lesser extent, IGFBP-2 and -5. Atresia, in contrast, was associated with a strong increase in IGFBP-3 proteolytic activity in small ( < 3-mm diameter) follicles and a decrease in IGFBP-4 and -5 proteolytic activity in large ( > 5-mm diameter) follicles. Regardless of the follicle class, IGFBP proteolytic activity was strongly inhibited by EDTA and 1,10-phenanthroline, but very slightly or not at all inhibited by tissue inhibitor of matrix metalloprotease-1 and-2 and BB-2116 (natural and synthetic inhibitors of matrix metalloproteases, respectively) as well as cysteine and serine proteases inhibitors, with the exception of phenylmethylsulfonylfluoride (1 mM) in atretic follicles. In addition, IGFBP proteolytic activity was dependent on the presence of zinc and calcium chloride. Zymography experiments showed the presence of 72- and 92- to 96-kDa gelatinases in follicular fluid; their levels were dramatically increased during follicular atresia. These results suggest that 1) changes in intrafollicular IGFBP proteolytic activity could be at least partly responsible for the changes in intrafollicular IGFBP levels that occur during follicular growth and atresia in the sheep; and 2) metalloprotease(s) in healthy and atretic follicles as well as serine protease(s) in atretic follicles are involved in IGFBP degradation.

Effect of follicle size and quality on the ability of follicular fluid to support cytoplasmic maturation of bovine oocytes

Recent studies have shown that the developmental capacity of in vitro-matured oocytes is affected by the origin of follicular fluid (FF) supplemented to the maturation medium. The aims of this study were (1) to determine if follicle size and quality would influence the capacity of FF to support bovine oocyte maturation and (2) to determine if fetal calf serum (FCS) and FF had an additive effect when added together to the maturation medium. Follicular fluid collected from 108 follicles was classified according to size ( < 6, 6-8, > 8 mm in diameter) and quality (healthy, early atretic, and atretic). Quality, first determined by mitosis/pycnosis ratios in granulosa cell smears, was subsequently confirmed by insulin-like growth factor binding protein (IGFBP) patterns and estradiol concentrations. While most small- or medium-sized follicles showed some atresia (88% and 67%, respectively), fewer of the large follicles were atretic (30%). In experiment 1 bovine oocytes (n = 2,152) were matured either in TCM199 alone, with 10% FCS, or with 10% FF from the following follicle types: small healthy (SH); small early atretic (SEA); small atretic (SA); medium healthy (MH); medium early atretic (MEA); medium atretic (MA); large healthy (LH); large early atretic (LEA); and large atretic (LA). Following IVM, oocytes were fertilized and subsequently cultured in synthetic oviduct fluid (SOF). Day 8 blastocyst yields were 23% in TCM199 alone; 37% in TCM199 plus FCS; and, in medium supplemented with FF, SH, 36%; MH, 32%; LH, 30%; SEA, 21%; MEA, 26%; LEA, 28%; SA, 32%; MA, 33%; and LA, 38%. All FF from healthy or atretic follicles resulted in significantly improved blastocyst yields compared to M199 alone (P < 0.05). However, FF from early atretic follicles irrespective of size did not yield a significant improvement. In experiment 2 we examined the effect of addition of FF-LH and serum together to the maturation medium. In terms of blastocyst yield, no additional benefit was observed when TCM199 was supplemented with 10% FCS + 10% FF (33%) compared to 10% FCS or FF alone (35% and 30%, respectively). The efficacy of FF as a supplement to the maturation medium to improve cytoplasmic maturation appears to vary with follicle quality but not size. However, in general, the addition of 10% FF or FCS to the maturation media resulted in a similar blastocyst yield with no additional improvement when media was supplemented with both FCS and FF.

Insulin-like growth factor-binding proteins and ovarian folliculogenesis

In the ovary, insulin-like growth factors (IGFs) enhance both proliferation and differentiation of follicular cells by potentiating gonadotropin's actions. The biological effects of IGFs are strikingly modulated by IGF-binding proteins (IGFBPs), whose levels in follicular fluid dramatically change during folliculogenesis. Indeed, in most mammalian species, follicular growth and atresia are characterized by an increase and a great decrease in the IGFBP-3/IGFBPs < 40 kD (IGFBP-2, -4 and -5) ratio in follicular fluid, respectively. These variations result from both changes in expression of these IGFBPs by follicular cells, and in local degradation by specific intrafollicular proteases. Such changes in IGFBP levels lead to great decrease and increase in IGF bioavailability in atretic and growing healthy follicles, respectively. Hence intrafollicular IGFBPs play a key role in the regulation of follicular development by modulating IGFs and therefore gonadotropin's actions.

Localization and quantification of insulin-like growth factor-I (IGF-I) and IGF-II/mannose-6-phosphate (IGF-II/M6P) receptors in pig embryos during early pregnancy

To assess a potential role of insulin-like growth factor-I (IGF-I) and -II (IGF-II) in early embryonic development, the presence of their receptors was investigated by both immunohistochemistry and autoradiography experiments on whole embryos at Days 4 and 6 of pregnancy, on embryo sections at Days 8 and 10, and on placenta at Day 20 of pregnancy. Immunohistochemistry experiments were performed by using specific polyclonal antibodies raised against human IGF-I and IGF-II/mannose-6-phosphate (IGF-II/M6P) receptors. By autoradiography, specificity of [125I]-IGF-I and [125I]-IGF-II binding on embryonic cells was assessed by competition with unlabeled IGF-I and IGF-II, and quantification of the autoradiographic signal was performed by image analysis. The presence of IGF-I receptors on porcine trophectoderm cells was detected neither by immunohistochemistry nor by autoradioradiography on whole embryos or embryo sections. IGF-I receptors were present in the placenta at Day 20 of pregnancy, but only on endometrial cells. In contrast, IGF-II/M6P receptors were detected on porcine trophectoderm cells by both immunohistochemistry and autoradiography on whole embryos, on embryo sections at Day 8 and Day 10 of pregnancy, and on fetal and maternal compartments of the placenta at Day 20. The number of IGF-II/M6P receptors on trophectoderm cells was greatly heterogeneous between embryos within the same litters. There was no relationship between the number of IGF-II/M6P receptors on trophectoderm cells and the age or size of embryos between Day 8 and Day 10 of pregnancy. The involvement of the IGF-II/M6P receptor in early embryonic development in the pig remains to be determined.