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

Trio a novel bovine high-fecundity allele: II. Hormonal profile and follicular dynamics underlying the high ovulation rate

The newly discovered Trio high-fecundity allele produces multiple ovulations in cattle. This study evaluated (1) size and growth rates of follicles in Trio carriers during a synchronized follicular wave, induced by follicle aspiration; (2) follicle-stimulating hormone (FSH) patterns associated with the follicular wave; (3) size of corpora lutea (CL) and circulating progesterone; and (4) intrafollicular estradiol concentrations prior to normal deviation. Trio carriers had mean dominant follicles that were significantly smaller in diameter and volume than noncarriers. Onset of diameter deviation occurred at ∼3 days after the last follicle aspiration in both genotypes despite Trio carriers having much smaller individual follicles. Follicles of Trio carriers grew at a slower rate than noncarrier follicles (∼65% in mm/day or ∼30% in mm3/day) resulting in much smaller individual dominant follicles (∼25% volume). However, total dominant follicle volume, calculated as the sum of all dominant follicles in each animal, was similar in carriers and noncarriers of Trio throughout the entire follicular wave. Circulating FSH was greater in Trio carriers during the 24 h encompassing deviation. Trio carriers had significantly more ovulations than noncarriers, and individual CL volume was smaller, although total luteal tissue volume and circulating P4 were not different. Thus, increased ovulation rate in Trio carriers relates to smaller individual follicles (one-third the volume) near the time of deviation due to slower follicle growth rate, although time of deviation is similar, with increased circulating FSH near deviation leading to selection of multiple dominant follicles in Trio carriers with similar total follicle volume.

The ovarian expression of mRNAs for aromatase, IGF-I receptor, IGF-binding protein-2, -4 and -5, leptin and leptin receptor in cycling ewes after three days of leptin infusion

An experiment was carried out to determine the pattern of follicular expression of mRNAs for aromatase, IGF-I receptor (IGF-IR), IGF-binding protein (IGFBP)-2, -4 and -5, leptin and the long form of the leptin receptor (Ob-Rb) in ten ewes infused with human recombinant leptin (n = 5; 1 microg/h) or saline (n = 5) for 72 h in the luteal phase of the oestrous cycle. At the end of infusion a follicular phase was induced with a luteolytic dose of a prostaglandin F2alpha analogue and the ovaries were collected 32 h later. One ovary from each ewe was serially sectioned at 10 microm using a cryostat at -20 degrees C. All follicles >1 mm in diameter were counted and probed with specific oligoprobes for aromatase, IGF-IR and IGFBP-2, -4 and -5 and specific riboprobes for leptin and Ob-Rb. Leptin mRNA was detected in theca and granulosa cells and Ob-Rb mRNA was detected only in granulosa cells, of some, but not all antral follicles. Leptin doubled the number of follicles with a diameter >/=3.5 mm (1.0 +/- 0.36 (s.e.m.) vs 2.4 +/- 0.24; control vs leptin; P < 0.02) but had no effect on the number of >/=1 < 3.5 mm follicles. Leptin had no effect on the number of follicles expressing aromatase mRNA but it decreased significantly the number of follicles expressing mRNA for IGF-IR (10.7 +/- 0.79 vs 7.4 +/- 0.81; control vs leptin; P < 0.05), IGFBP-2 (10.0 +/- 0.82 vs 5.2 +/- 0.87; control vs leptin; P < 0.05) and IGFBP-5 (5.2 +/- 1.60 vs 1.2 +/- 0.30; control vs leptin; P < 0.05). Leptin increased the diameter of IGFBP-2 mRNA-positive follicles (1.5 +/- 0.15 vs 2.2 +/- 0.31 mm; control vs leptin; P < 0.05) and increased follicular mRNA expression for IGFBP-2 (0.30 +/- 0.021 vs 0.39 +/- 0.027 arbitrary units; control vs leptin; P < 0.05) and IGFBP-5 (0.46 +/- 0.019 vs 0.25 +/- 0.053 arbitary units; control vs leptin; P < 0.05). The mRNA for IGFBP-4 was detected in the theca of only two follicles from the control group. Leptin increased the number of follicles expressing Ob-Rb mRNA (0.25 +/- 0.25 vs 1.40 +/- 1.17; control vs leptin; P < 0.05) but had no effect on the number expressing leptin mRNA. Leptin decreased plasma concentrations of oestradiol (P < 0.05) and increased concentrations of FSH (P < 0.001) and insulin (P < 0.001), with no effect on glucose concentrations. These data show that: (i) ovine granulosa cells express mRNA for Ob-Rb and leptin and (ii) leptin increased the number of follicles >/=3.5 mm. Furthermore, the data suggest that suppression of oestradiol production by leptin is not mediated by inhibition of aromatase gene expression. Finally, the data indicate that the action of leptin in ovarian follicles is mediated by the IGF system, because leptin increased mRNA expression of IGFBP-2 and -5. Leptin also decreased the number of follicles expressing IGF-IR and IGFBP-2 and -5. We suggest that these actions of leptin on the IGF system decrease the bioavailability of IGF-I, resulting in decreased oestradiol production.

Co-expression of messenger ribonucleic acids encoding IGF-I, IGF-II, type I and II IGF receptors and IGF-binding proteins (IGFBP-1 to -6) during follicular development in the ovary of seasonally anoestrous ewes

In recent years, it has become apparent that components of the insulin-like growth factor (IGF) system are involved in the regulation of ovarian follicular development in sheep. The majority of previous studies have concentrated on investigating only a select few components and not the whole system. The aim of the present study was to use five seasonally anoestrous ewes to investigate the expression of mRNA encoding all 10 components of the sheep IGF system among various-sized follicles within the ovary, using sheep-specific ribonucleotide probes and in situ hybridisation. IGF-I mRNA expression was low and did not vary with follicle size. IGF-II mRNA expression was significantly higher (P < 0.05) in small follicles compared to large follicles. Both IGF receptors had significantly higher (P < 0.05) levels of mRNA expression in small follicles, with the type I receptor being expressed to a slightly greater extent than the type II receptor. IGFBP-2, -3, -4 and -5 gene expression followed a similar pattern to IGF-II and the IGF receptors, whereby expression decreased with increasing follicle size. Similar to IGF-I, IGFBP-6 mRNA expression showed little variation with follicle size. IGFBP-1 mRNA expression was observed at low and constant levels, albeit in small and medium-sized follicles only. These data demonstrate that all of the components of the IGF system are produced in the ovine follicle, and for some of the components, their gene expression varied with stage of follicle development. This study further emphasises the importance of IGF-II as the major IGF in the autocrine and paracrine regulation of follicle development in sheep.

Effect of ageing on hormone secretion and follicular dynamics in sheep with and without the Booroola gene

It has been suggested that ewes carrying the Booroola gene (Fec(B)) consistently ovulate more follicles because they recruit more primordial follicles and/or have a lower rate of atresia. If the former is correct, the pool of follicles would be depleted sooner in Fec(B) animals. We have studied follicular dynamics and endocrine function during follicular and early luteal phases of the estrous cycle of older ewes with or without the fecundity gene and compared this data with data obtained 6 yr previously in the same animals. Older sheep carrying the Booroola gene maintained a significantly higher ovulation rate than noncarrier ewes [4.2 +/- 0.8 vs. 2.2 +/- 0.6 corpora lutea (CL), respectively; P < 0.05], and in keeping with data from young animals, both ovulatory follicles and CL (4.7 +/- 0.3 vs. 6.9 +/- 0.7 mm and 12.8 +/- 0.5 vs. 16.7 +/- 0.8 mm, respectively) were smaller than those of noncarrier ewes (P < 0.05). The interval from luteolysis to the onset of the LH surge increased with age in all the animals (from 52.0 +/- 8.0 to 67.0 +/- 7.5 h in gene carrier sheep and from 56.0 +/- 2.0 to 79.5 +/- 9.6 h in noncarrier sheep, P < 0.05). The concentration of estradiol and inhibin A in the early luteal phase was lower in older noncarrier ewes (P = 0.08 and P < 0.05, respectively), and the level of inhibin A was inversely related to the level of FSH in aged sheep of both genotypes (P < 0.0001). In contrast, the number of developing follicles in older ewes of both genotypes was similar to the number found in younger ewes, suggesting that increased ovulation rate in sheep carrying the Fec(B) mutation is related to a reduced rate of atresia.

Expression and functional role of peroxisome proliferator-activated receptor-gamma in ovarian folliculogenesis in the sheep

Peroxisome proliferator-activated receptor (PPARgamma) is a nuclear receptor that is activated by fatty acids and derivatives and the antidiabetic glitazones, which plays a role in the control of lipid and glucose homeostasis. In the present work, we tested the hypothesis that PPARgamma plays a role in reproductive tissues by studying its expression and function in the hypothalamo-pituitary-ovary axis in the sheep. PPARgamma 1 and PPARgamma 2 proteins and mRNAs were detected in whole ovine pituitary and ovary but not in hypothalamic extracts. In situ hybridization on ovarian section localized PPARgamma mRNA in the granulosa layer of follicles. Interestingly, PPARgamma expression was higher in small antral (1-3 mm diameter) than in preovulatory follicles (>5 mm diameter) (P < 0.001) and was not correlated with healthy status. To assess the biological activity of ovarian PPARgamma, ovine granulosa cells were transfected with a reporter construct driven by PPARgamma-responsive elements. Addition of rosiglitazone, a PPARgamma ligand, stimulated reporter gene expression, showing that endogenous PPARgamma is functional in ovine granulosa cells in vitro. Moreover, rosiglitazone inhibited granulosa cell proliferation (P < 0.05) and increased the secretion of progesterone in vitro (P < 0.05). This stimulation effect was stronger in granulosa cells from small than from large follicles. In contrast, rosiglitazone had no effect on LH, FSH, prolactin and growth hormone secretion by ovine pituitary cells in vitro. Overall, these data suggest that PPARgamma ligands might stimulate follicular differentiation in vivo likely through a direct action on granulosa cells rather than by modulating pituitary hormone secretion.

Expression and localization of IGF family members in bovine antral follicles during final growth and in luteal tissue during different stages of estrous cycle and pregnancy

The objectives of the study were to monitor the detailed pattern for mRNA expression (RT-PCR and RPA) of IGFs, IGFR-1, IGFBPs, GHR and localization of protein (immunohistochemistry) for IGF-1 and IGFR-1 in bovine follicle classes during final maturation and different corpus luteum (CL) stages during estrous cycle and during pregnancy. A relative high expression of IGF-1 in theca interna (TI) was observed before selection (E<0.5ng/mL). In GC, mRNA expression increased after selection. In contrast, IGF-2 was mainly expressed in the TI. The IGFR-1 mRNA was present in the TI and GC with increasing levels during final development. The expression results were confirmed by localization of IGF-1 and IGFR-1 proteins in GC and TI. There is clear evidence for the local expression of IGFBPs in TI and GC compartment with clear regulatory differences. In CL, the highest mRNA expression of IGF-1, IGF-2 and IGFR-1 was observed during early luteal phase, followed by a decrease, and then by a tendency of an increase during the mid and late luteal phases of the cyclic CL. This level remained low during pregnancy. Intense immunostaining for IGFR-1 in CL was observed mainly in large luteal cells. Evidence for a mRNA for all six IGFBPs were obtained with distinct differences for BP-3, -4 and -5. In conclusion, this comprehensive study gives clear evidence for an important role of the IGFs and IGFBPs in bovine follicular development and CL function. The relative amounts of IGFBPs may ultimately determine ovarian IGF action.

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.