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Danielle Monniaux, J. C. Mariana and W. R. Gibson

Summary. The short-term action of PMSG on the population of growing follicles in cattle was studied using histological methods. On Day 7 of a synchronized oestrous cycle 10 Friesian heifers were unilaterally ovariectomized. The remaining ovary was immediately stimulated by an injection of PMSG (2000 i.u.) and was removed 48 h after the preovulatory discharge of LH. Control animals did not receive any injection of PMSG. In all ovaries, follicles > 70 μm diameter were counted, measured and checked for atresia. The mitotic index in granulosa cells of follicles of different sizes was estimated in both ovaries of all the PMSG-injected animals.

Unilateral ovariectomy alone had no significant effect on follicular populations. In the interval between PMSG injection and removal of the second ovary (148 ± 22·7 h), PMSG significantly increased the number of normal preantral follicles but did not change the number of normal antral follicles. The mitotic index doubled in preantral and early antral follicles but remained unchanged in large antral follicles. PMSG stimulated slightly the growth of the antrum in large antral follicles but did not stimulate its formation in preantral follicles. The incidence of atresia among antral follicles, particularly the largest ones (diam. > 1·7 mm), was significantly reduced after PMSG, suggesting some 'rescue' of follicles from atresia.

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Danielle Monniaux, Gérard Baril, Anne-Lyse Laine, Peggy Jarrier, Natividad Poulin, Juliette Cognié and Stéphane Fabre

Recently, we demonstrated the relationship between anti-Müllerian hormone (AMH) circulating concentrations, ovarian follicles, and embryo production in cattle. However, they have not yet been established in a species with a seasonal breeding activity. Thus, goats were subjected to repeated in vivo embryo production during the breeding season, at the end of the breeding season, and at the end of the anestrus season. Embryo production after FSH treatment was highly repeatable for each goat. Plasma AMH concentrations, measured before the first FSH treatment, were highly correlated with the number of collected, transferable, and freezable embryos, resulting from the three sessions of embryo production. Plasma AMH concentrations transiently decreased after each exogenous FSH treatment, but they showed little change with season, and no relationship was observed between AMH and endogenous FSH concentrations during seasonal transitions. Follicles of 1–5 mm in diameter were the main target of the FSH treatment and were major contributors to circulating AMH concentrations. Granulosa cell AMH expression decreased as the follicle approached terminal development, while the expression of maturation markers (CYP19A1 and FSHR) increased. In conclusion, circulating AMH concentrations can be predictive of the capacity of a donor goat to produce high or low numbers of high-quality embryos. This prediction could be accurately made from a single blood measurement of AMH during either breeding or anestrus seasons. Variability in the number of gonadotropin-responsive follicles of 1–5 mm in diameter between individuals resulted in the differences in circulating AMH concentrations measured between individuals.

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Anthony Estienne, Belén Lahoz, Peggy Jarrier, Loys Bodin, José Folch, José-Luis Alabart, Stéphane Fabre and Danielle Monniaux

Polymorphisms in the gene encoding bone morphogenetic protein 15 (BMP15) have been associated with multiple ovulations in sheep. As BMP15 regulates inhibin expression in rodents, we assumed that the ovarian inhibin/activin system could mediate part of the effect of BMP15 mutations in the regulation of ovulation rate in sheep. To answer this question, we have studied the effects of two natural loss-of-function mutations of BMP15 on the expression of components of this system. The FecX R and the FecX Gr mutations, when present respectively in Rasa Aragonesa ewes at the heterozygous state and in Grivette ewes at the homozygous state, were associated with a twofold increase in ovulation rate. There were only small differences between mutant and wild-type ewes for mRNA expression of INHA, INHBA, ACVR1B, ACVR2A, FST or TGFBR3 in granulosa cells and inhibin A or activin A concentrations in follicular fluid. Moreover, the effects of mutations differed between breeds. In cultures of granulosa cells from wild-type ewes, BMP15, acting alone or in synergy with GDF9, stimulated INHA, INHBA and FST expression, but inhibited the expression of TGFBR3. Activin A did not affect INHBA expression, but inhibited the expression of ACVR2A also. The complexity of the inhibin/activin system, including positive and antagonistic elements, and the differential regulation of these elements by BMP15 and activin can explain that the effects of BMP15 mutations differ when present in different genetic backgrounds. In conclusion, the ovarian inhibin/activin system is unlikely to participate in the increase of ovulation rate associated with BMP15 mutations in sheep.

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Véronique Cadoret, Cynthia Frapsauce, Peggy Jarrier, Virginie Maillard, Agnès Bonnet, Yann Locatelli, Dominique Royère, Danielle Monniaux, Fabrice Guérif and Philippe Monget

In this study, we systematically compared the morphological, functional and molecular characteristics of granulosa cells and oocytes obtained by a three-dimensional in vitro model of ovine ovarian follicular growth with those of follicles recovered in vivo. Preantral follicles of 200 µm diameter were recovered and cultured up to 950 µm over a 20-day period. Compared with in vivo follicles, the in vitro culture conditions maintained follicle survival, with no difference in the rate of atresia. However, the in vitro conditions induced a slight decrease in oocyte growth rate, delayed antrum formation and increased granulosa cell proliferation rate, accompanied by an increase and decrease in CCND2 and CDKN1A mRNA expression respectively. These changes were associated with advanced granulosa cell differentiation in early antral follicles larger than 400 µm diameter, regardless of the presence or absence of FSH, as indicated by an increase in estradiol secretion, together with decreased AMH secretion and expression, as well as increased expression of GJA1, CYP19A1, ESR1, ESR2, FSHR, INHA, INHBA, INHBB and FST. There was a decrease in the expression of oocyte-specific molecular markers GJA4, KIT, ZP3, WEE2 and BMP15 in vitro compared to that in vivo. Moreover, a higher percentage of the oocytes recovered from cultured follicles 550 to 950 µm in diameter was able to reach the metaphase II meiosis stage. Overall, this in vitro model of ovarian follicle development is characterized by accelerated follicular maturation, associated with improved developmental competence of the oocyte, compared to follicles recovered in vivo.

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Achraf Adib, Sandrine Freret, Jean-Luc Touze, Didier Lomet, Lionel Lardic, Didier Chesneau, Anthony Estienne, Pascal Papillier, Danielle Monniaux and Maria-Teresa Pellicer-Rubio

The first ovulation induced by male effect in sheep during seasonal anoestrus usually results in the development of a short cycle that can be avoided by progesterone priming before ram introduction. In elucidating the involvement of the hypothalamic–pituitary–gonadal axis in the occurrence of short cycles, the effects of progesterone and the time of anoestrus on the development of male-induced preovulatory follicles were investigated in anoestrous ewes using morphological, endocrine and molecular approaches. Ewes were primed with progesterone for 2 (CIDR2) or 12 days (CIDR12) and untreated ewes used as controls during early (April) and late (June) anoestrus. The duration of follicular growth and the lifespan of the male-induced preovulatory follicles were prolonged by ∼1.6 days in CIDR12 ewes compared with the controls. These changes were accompanied by a delay in the preovulatory LH and FSH surges and ovulation. Intra-follicular oestradiol concentration and mRNA levels of LHCGR and STAR in the granulosa and theca cells of the preovulatory follicles were higher in CIDR12 ewes than the control ewes. The expression of mRNA levels of CYP11A1 and CYP17A1 also increased in theca cells of CIDR12 ewes. CIDR2 ewes gave intermediate results. Moreover, ewes ovulated earlier in June than in April, without changes in the duration of follicular growth, but these effects were unrelated to the lifespan of corpus luteum. Our results give the first evidence supporting the positive effect of progesterone priming on the completion of growth and maturation of preovulatory follicles induced by male effect in seasonal anoestrous ewes, thereby preventing short cycles.

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Laura Torres-Rovira, Sara Succu, Valeria Pasciu, Maria Elena Manca, Antonio Gonzalez-Bulnes, Giovanni Giuseppe Leoni, Maria Grazia Pennino, Antonio Spezzigu, Marilia Gallus, Maria Dattena, Danielle Monniaux, Salvatore Naitana and Fiammetta Berlinguer

The importance of postnatal pituitary activation as regards female reproductive development is not yet understood. By taking advantage of the experimental model developed in a previous study, i.e. ewe lambs expressing markedly different ovarian phenotypes at 50 days of age, we designed this study to determine whether differences found in ovarian status during the early prepubertal period are due to different patterns of postnatal pituitary activation, and to assess whether these differences have long lasting effects on subsequent reproductive performance. Results showed that ewe lambs with high antral follicle count (AFC) at 50 days of age had significantly lower plasma FSH concentrations and higher anti-Mullerian hormone (AMH) concentrations during the first 9 weeks of age compared with low AFC ewe lambs (P<0.0001). With a longitudinal experiment we showed that a high AFC in the early prepubertal period is associated with consistently higher AMH concentrations and numbers of antral follicles up to the postpubertal period, and with higher pregnancy rates in the first breeding season. In addition, the effect of age in decreasing AMH concentrations was more marked in the low AFC group. Results of the present study demonstrate that ewe lambs undergo different patterns of postnatal pituitary activation. A high AFC at 50 days of age indicates an advanced phase of ovarian maturation, which was accompanied by constantly higher AMH concentrations up to the postpubertal period, a greater ovarian response to FSH stimulation and by higher pregnancy rates at first mating, as compared with the low AFC group.