Oocytes in sheep homozygous for a mutation in bone morphogenetic protein receptor 1B express lower mRNA levels of bone morphogenetic protein 15 but not growth differentiation factor 9

The Roles of GDF-9, BMP-15, BMP-4 and EMMPRIN in Folliculogenesis and In Vitro Fertilization

Growth differentiation factor 9 (GDF-9) contributes to early ovarian development and oocyte survival. Higher concentrations of GDF-9 in follicular fluid (FF) are associated with oocyte nuclear maturation and optimal embryo development. In in vitro fertilization (IVF), GDF-9 affects the ability of the oocyte to fertilize and subsequent embryonic development. Bone morphogenetic protein 15 (BMP-15) is involved in the regulation of ovarian function and affects oocyte development. During IVF, BMP-15 contributes to the formation of competent blastocysts. BMP-15 may play a role in embryo implantation by affecting endometrial receptivity. Bone morphogenetic protein 4 (BMP-4) is involved in the regulation of follicle growth and development and affects granulosa cell (GC) differentiation. In relation to IVF, BMP-4 is important for embryonic development, influences cell fate and differentiation, and plays a role in facilitating embryo-endometrial interactions during the implantation process. Extracellular matrix metalloproteinase inducer (EMMPRIN) is associated with ovulation and follicle rupture, promotes the release of mature eggs, and affects the modification of the extracellular matrix of the follicular environment. In IVF, EMMPRIN is involved in embryo implantation by modulating the adhesive properties of endometrial cells and promotes trophoblastic invasion, which is essential for pregnancy to occur. The purpose of the current article is to review the studies and recent findings of GDF-9, BMP-15, BMP-4 and EMMPRIN as fundamental factors in normal follicular development and in vitro fertilization.

Single-cell RNA-seq reveals the effects of the FecB mutation on the transcriptome profile in ovine cumulus cells

Genetic variations in the ovine ovulation rate, which are associated with the FecB mutation, provide useful models by which to explore the mechanisms regulating the development of mammalian antral follicles. In order to study the effects of the FecB mutation on cumulus cell differentiation, preovulatory follicles were aspirated and cumulus cells were isolated from three FecB genotypes (homozygous, heterozygous and wild type) of Small Tail Han (STH) sheep superstimulated with FSH. Transcriptome information from tens of thousands of cumulus cells was determined with the 10 × Genomics single-cell RNA-seq technology. Under the superovulation treatment, the observed number of preovulatory follicles in the ovaries of FecB carriers was still significantly higher than that in the wild-type (P < 0.05). The expression patterns of cumulus cells differed between FecB carriers and wild-type ewes. The screened cumulus cells could also be further divided into different cell clusters, and the differentiation states and fates of each group of cumulus cells also remained different, which supports the notion that heterogeneity in gene expression is prevalent in single cells. The oxidative phosphorylation pathway was significantly enriched in differentially expressed genes among the cell differentiation branch nodes of cumulus cells and among the differentially expressed genes of cumulus cells from the three genotypes. Combined with the important role of oxidative phosphorylation in the maturation of COCs, we suggest that the oxidative phosphorylation pathway of cumulus cells plays a crucial role in the differentiation process of cumulus cells and the mutation effect of the FecB gene.

An Identification of Functional Genetic Variants in B4GALNT2 Gene and Their Association with Growth Traits in Goats

β-1,4-N-acetylgalactosamine transferase 2 (B4GALNT2) is a vital candidate gene that affects the growth traits in sheep. However, whether it has the same function in goats remains to be investigated further. This study selected 348 Nanjiang Yellow goats, screened all exons, and conserved non-coding regions of the B4GALNT2 gene for single-nucleotide polymorphisms (SNPs). Our results revealed the presence of a synonymous mutation, rs672215506, within the exon of the B4GALNT2 gene in the Nanjiang Yellow goat population. The mutation resulted in a decrease in the mRNA stability of the B4GALNT2 gene. The results of SNP detection of the conserved non-coding region of the B4GALNT2 gene showed five potential regulatory SNPs in the Nanjiang Yellow goat population. Except for rs66095343, the ~500 bp fragments of the other four SNPs (rs649127714, rs649573228, rs652899012, and rs639183528) significantly increased the luciferase activity both in goat skeletal muscle satellite cells (MuSCs) and 293T cells. The genetic diversity indexes indicated low or intermediate levels for all six SNPs analyzed, and the genotype frequencies were in Hardy-Weinberg equilibrium. Association analysis showed that rs660965343, rs649127714, and rs649573228 significantly correlate with growth traits in the later stage of growth and development of Nanjiang Yellow goats. The haplotype combinations of H2H3 and H2H2 had higher body weight and greater body size. Moreover, H2H2 haplotype combinations significantly correlated with the litter size of the Nanjiang Yellow goats. The results of our study demonstrate the potential role of the B4GALNT2 gene as a functional genetic marker in the breeding programs of Nanjiang Yellow goats.

Identification of polymorphism of FecX gene in indigenous sheep of Meghalaya

Fecundity gene such as FecX, govern fertility and litter size in sheep. Selection of animals with the help of molecular markers through identification of polymorphism of fecundity genes is an impactful method of genetic improvement. The present study was carried out to identify the polymorphism of FecX gene in indigenous sheep of Meghalaya. Blood samples were collected from 50 randomly selected ewes from 2 districts of Meghalaya namely, East Khasi Hills and West Khasi Hills. Genomic DNA was extracted from the samples and PCR amplification of FecX gene with specific primer set was done. PCR product size of 141 bp was obtained. Further, digestion of the PCR product with restriction enzyme HinfI through PCR-RFLP technique was conducted to identify the variants in FecX gene. Upon digestion, 2 types of fragment pattern identified, arbitrarily designated as AA and AB genotype, where AA genotype yielded one fragment (141 bp) and AB genotype yielded 2 fragments (100 and 41 bp). Presence of polymorphism can be an important indicator for selection with the help of molecular markers.

Two novel mutations in exon 2 of bone morphogenetic protein (BMP) 15 gene in Pakistani infertile females

Objective

To determine the proportion of fertility in Pakistani infertile females and discover if there are considerable connection among BMP15 gene polymorphism, follicle maturation and hormonal regulation in Pakistani infertile females.

Methods

All selected participants were initially examined through follicle-stimulating hormones (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), Prolactin, and Trans-vaginal scan (TVS). BMP15 gene polymorphism among infertile and fertile females was done by extracted Genomic DNA from whole blood. Sanger sequencing was performed for the identification of mutation in exons-intron boundaries of the BMP15 gene. Bioinformatics tools were used to assess the protein structure.

Results

The total five mutations including two novel missense variants of BMP15 in exon 2, whereas three previously reported i.e. two cosmic mutations (c.615delC), (c.584InsG) and one frame shift mutations (c.635delA) were also observed. The first novel mutation was found at (c.1038InsGG) (p.346Gln < Gly) in which the insertion of GG at DNA position 1038 of exon 2 resulting in a substitution of glutamine into glycine at 346th amino acid of BMP15 protein. The second novel variant (c.1049delT) (p. Ser334Pro) was also observed in exon 2 of the BMP15 gene, which substituted serine into proline at 334th amino acid of the BMP15 protein.

Conclusion

It is concluded that there are various missense mutations present in exon 2 of the BMP15 gene of Pakistani infertile females, consequently expected function of protein changes due to change in codons of amino acids. Provean and SIFT suggest the two novel variants as potentially deleterious. Although three other variants were also found in Pakistani infertile females which were previously reported. These mutations may result in early blockage of folliculogenesis and ovaries become streaky. Further research is required to resolve the actual allusion of these variations in the BMP15 gene.

Effect of the Booroola fecundity (FecB) gene on the reproductive performance of ewes under assisted reproduction

Reproductive traits are important factors in sheep production. The Booroola fecundity (FecB) gene-the first major gene for prolificacy identified in sheep-has a positive effect on ovulation rates and litter size under natural reproductive conditions. However, the effect of the FecB gene on reproductive performance under assisted reproduction, which uses many artificial hormones, remains unclear. In the present study, we evaluated the effect of FecB (BMPR-1B mutation) on reproductive performance under assisted reproduction, and examined offspring body weight at birth and weaning and survival rate at weaning. There were no differences among three genotype groups (homozygous carrier, BB; heterozygous carrier, B+; non-carrier, ++) in terms of estrus detection rate, time to estrus onset, or estrus duration following estrus synchronization (P > 0.05). The pregnancy rates at 60 d were similar among three genotype groups after artificial insemination (P > 0.05). However, the B allele had an additive effect on litter size (one copy resulted in an increase of 0.88 lambs and two copies produced an additional 0.41 lambs; P < 0.01), and increased lambing and fecundity rates (P < 0.01). After multiple ovulation, the average numbers of recovered embryos per ewe were 9.16 ± 0.79, 8.20 ± 0.77, and 8.44 ± 0.61 in the BB, B+, and ++ ewes, respectively (P > 0.05). There were no differences in the fertilization rate or numbers of grade 1-2 embryos among different groups (P > 0.05). The birth and weaning weights of lambs from BB and B+ ewes were lower than those of lambs born from ++ ewes (P < 0.01) owing to the high fecundity. The survival rate of lambs at weaning did not differ among groups (P > 0.05). Our results indicated that the presence of the B allele had an additive effect on litter size after artificial insemination, but it did not influence the parameters of estrus synchronization and multiple ovulation. Furthermore, the higher prolificacy in ewes carrying the B allele was associated with a reduction in offspring body weight at birth and weaning.

Expression Analysis of the Prolific Candidate Genes, BMPR1B, BMP15, and GDF9 in Small Tail Han Ewes with Three Fecundity (FecB Gene) Genotypes

Simple Summary

As important prolific candidate genes, BMPR1B, BMP15, and GDF9 may affect the lambing performance of sheep. Therefore, regarding the three FecB genotypes of Small Tail Han (STH) sheep (FecB BB, FecB B+, and FecB ++), this study explored the gene expression characteristics of different tissues using reverse transcription PCR (RT-PCR) and real-time quantitative PCR (qPCR). The results showed that BMPR1B, BMP15, and GDF9 expression differed between the selected tissues, with all being highly expressed in the ovaries. Further analysis indicated that there was no significant difference in BMPR1B expression among the three FecB genotypes, but both GDF9 and BMP15 had the highest expression in FecB B+. As for other non-ovarian tissues, expression also varied. This study is relevant to understanding the high prolificacy of the STH breed.

Abstract

The expression characteristics of the prolific candidate genes, BMPR1B, BMP15, and GDF9, in the major visceral organs and hypothalamic–pituitary–gonadal (HPG) axis tissues of three FecB genotypes (FecB BB, FecB B+, and FecB ++) were explored in STH ewes using RT-PCR and qPCR. The results were as follows, BMPR1B was expressed in all FecB BB genotype (Han BB) tissues, and GDF9 was expressed in all selected tissues, but BMP15 was specifically expressed in the ovaries. Further study of ovarian expression indicated that there was no difference in BMPR1B expression between genotypes, but the FecB B+ genotype (Han B+) had greater expression of GDF9 and BMP15 than Han BB and FecB ++ genotype (Han ++) (p < 0.05, p < 0.01). BMP15 expression was lower in the ovaries of Han BB than in Han ++ sheep, but the reverse was shown for GDF9. The gene expression in non-ovarian tissues was also different between genotypes. Therefore, we consider that the three genes have an important function in ovine follicular development and maturation. This is the first systematic analysis of the tissue expression pattern of BMPR1B, BMP15, and GDF9 genes in STH sheep of the three FecB genotypes. These results contribute to the understanding of the molecular regulatory mechanism for ovine reproduction.

Molecular Cloning of the B4GALNT2 Gene and Its Single Nucleotide Polymorphisms Association with Litter Size in Small Tail Han Sheep

Simple Summary

In French Lacaune sheep, the B4GALNT2 (beta-1, 4-N-acetyl-galactosaminyl transferase 2) gene was considered as the potential gene for a FecL (mutation), which regulates the ovine ovulation rate. Three specific mutation sites linked with the FecL mutation have not been previously found in 11 sheep breeds. However, two mutations of g.36946470C > T and g.36933082C > T in the exon of B4GALNT2 were found to have had a significant effect on the litter size in the first parity for Small Tail Han (STH) Sheep (p < 0.05). B4GALNT2, which is mainly expressed in ovine ovary, also plays an important role in sheep reproduction. Furthermore, we discovered two transcription start sites (TSS) of B4GALNT2 in its 5′-flanking region in ovine granule cells in vitro.

Abstract

A new fecundity gene named the FecL (mutation), which regulates the ovulation rate, was discovered in French Lacaune sheep. The B4GALNT2 (beta-1, 4-N-acetyl-galactosaminyl transferase 2) gene was considered as the potential FecL mutation gene. This study explores whether the effect of the FecL mutation exists in other sheep breeds, and the features of the B4GALNT2 gene in terms of the molecular structure and its expression profile. Using Sanger sequencing, we found that high and low fecundity breeds from among 11 measured sheep breeds all had no variation in the three specific mutation sites, which were linked with the FecL mutation. However, two mutations of g.36946470C > T and g.36933082C > T in the exon of B4GALNT2 had a significant effect on litter size in the first parity for Small Tail Han (STH) Sheep (p < 0.05). Two transcription start sites (TSS) of B4GALNT2 in its 5′-flanking region were discovered in ovine granule cells in vitro, through the RACE (Rapid amplification of cDNA ends) method. Except for in the kidney and oviduct, no significant difference in expression levels had been found between STH sheep and Tan sheep breeds. The B4GALNT2 gene, as a candidate for FecL, may have a relationship with the differences in litter size in STH sheep. B4GALNT2 is mainly expressed in the ovine ovary, which also suggests that B4GALNT2 plays an important role in sheep reproduction.

The local regulation of folliculogenesis by members of the transforming growth factor superfamily and its relevance for advanced breeding programmes

Regulation of the growth and maturation of the ovarian follicle is critical for normal reproductive function. Alterations in this growth can lead to pathological conditions, such as cystic follicles, reduced oocyte quality, or an abnormal endocrine environment leading to poor fertility. Alterations in follicular growth also influence the number of follicles ovulating and thus can change litter size. Both endocrine factors, such as follicle stimulating hormone and luteinizing hormone, as well as local factors, are known to regulate follicular growth and development. This review will focus on the role of local factors in regulation of ovarian follicular growth in ruminants, with a focus on members of the transforming growth factor superfamily. The potential role of these factors in regulating proliferation, apoptosis, steroidogenesis and responsiveness to gonadotrophins will be considered.

Metabolic Effects of FecB Gene on Follicular Fluid and Ovarian Vein Serum in Sheep (Ovis aries)

The FecB gene has been discovered as an important gene in sheep for its high relationship with the ovulation rate, but its regulatory mechanism remains unknown. In the present study, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) techniques were adopted to detect the metabolic effects of FecB gene in follicular fluid (FF) and ovarian vein serum (OVS) in Small Tail Han (STH) sheep. ANOVA and random forest statistical methods were employed for the identification of important metabolic pathways and biomarkers. Changes in amino acid metabolism, redox environment, and energy metabolism were observed in FF from the three FecB genotype STH ewes. Principal component analysis (PCA) and hierarchical clustering analysis (HCA) showed that metabolic effects of FecB gene are more pronounced in FF than in OVS. Therefore, the difference of the metabolic profile in FF is also affected by the FecB genotypes. In Spearman correlation analysis, key metabolites (e.g., glucose 6-phosphate, glucose 1-phosphate, aspartate, asparagine, glutathione oxidized (GSSG), cysteine-glutathione disulfide, γ-glutamylglutamine, and 2-hydrosybutyrate) in ovine FF samples showed a significant correlation with the ovulation rate. Our findings will help to explain the metabolic mechanism of high prolificacy ewes and benefit fertility identification.

PCR-RFLP of bone morphogenetic protein 15 (BMP15/FecX) gene as a candidate for prolificacy in sheep

Bone morphogenetic protein 15 (BMP15/FecX) gene is considered one of the major genes and a candidate marker for the reproduction in farm animals, especially sheep. The present study aimed to detect the genetic polymorphisms of BMP15 gene in sheep using PCR-RFLP technique. In the present study, 115 ewes were assigned into high and low prolificacy categories according to their reproductive history. In high prolific group (n = 20), ewes produced twins more than single births. In the low prolific type (n = 95), the ewes produced single births more than twins. DNA was extracted from blood samples of all ewes, subjected to PCR-RFLP analysis and confirmed by sequence analysis. The PCR products of 356 bp size were cut with HinƒI restriction enzyme. Three digested fragments of 70, 117 and 169 bp were obtained in both types of sheep. All animals were homozygous with CC genotype. In conclusion, the accessible findings did not detect any mutation in FecX gene in sheep, regardless their prolificacy. Therefore, further attempts are necessary to detect other SNP for BMP-15 gene in Egyptian sheep breeds.

Differential expression of CART in ewes with differing ovulation rates

We hypothesised that cocaine- and amphetamine-regulated transcript (CARTPT) would be differentially expressed in ewes with differing ovulation rates. Expression of mRNA forCARTPT, as well asLHCGR,FSHR,CYP19A1andCYP17A1was determined in antral follicles ≥1 mm in diameter collected during the follicular phase in ewes heterozygous for the Booroola and Inverdale genes (I+B+; average ovulation rate 4) and ++ contemporaries (++; average ovulation rate 1.8). In ++ ewes (n = 6),CARTPTwas expressed in small follicles (1 to <3 mm diameter), where 18.8 ± 2.5% follicles expressedCARTPT. CART peptide was also detected in follicular fluid of some follicles of ++ ewes. In I+B+ ewes, 5/6 ewes did not have any follicles that expressedCARTPT, and no CART peptide was detected in any follicle examined. Expression pattern ofCYP19A1differed between I+B+ and ++ ewes with an increased percentage of small and medium follicles (3 to <4.5 mm diameter) but decreased percentage of large follicles (≥4.5 mm diameter) expressingCYP19A1in the I+B+ ewes. Many of the large follicles from the I+B+ ewes appeared non-functional and expression ofLHCGR,FSHR,CYP17A1andCYP19A1was less than that observed in ++ ewes. Expression ofFSHRandCYP17A1was not different between groups in small and medium follicles, butLHCGRexpression was approximately double in I+B+ ewes compared to that in ++ ewes. Thus, ewes with high ovulation rates had a distinct pattern of expression ofCARTPTmRNA and protein compared to ewes with normal ovulation rates, providing evidence for CART being important in the regulation of ovulation rate.

Ovarian characteristics in sheep with multiple fecundity genes

Ewes heterozygous for combinations of the Inverdale (FecX^I; I+), Booroola (FecB; B+) and Woodlands (FecX2^W; W+) mutations have ovulation rates higher than each mutation separately. The aims of the experiments described herein were to examine the ovarian phenotypes in I+B+ and I+B+W+ ewes and to compare these with the appropriate ++ (controls), I+ and BB animals available for this study. The mean ± s.e.m. ovulation rates in the ++ (n = 23), I+ (10), I+B+ (7), I+B+W+ (10) and BB (3) animals were 1.8 ± 0.1, 2.5 ± 0.2, 6.6 ± 1.0, 9.6 ± 0.9 and 9.7 ± 0.9 respectively. The maximum number of granulosa cells per follicle in the ++ and I+ genotypes was accumulated after exceeding 5 mm diameter, whereas in I+B+, I+B+W+ and BB animals, this was achieved when follicles reached >2-3 mm. The number of putative preovulatory follicles, as assessed from those with LH-responsive granulosa cells, 24 h after the induction of luteolysis, was higher (P < 0.01) in the I+B+ and I+B+W+ compared to the ++ and I+ genotypes. The median follicular diameters of these follicles in the ++, I+, I+B+, I+B+W+ and BB genotypes were 6, 5, 3, 3 and 3 mm respectively. The total number of granulosa cells in the putative preovulatory follicles when added together, and total mass of luteal tissue, did not differ between the genotypes. Thus, despite large ovulation rate differences between animals with one or more fecundity genes, the total cell compositions over all preovulatory follicles and corpora lutea, when added together, are similar to that from the one or two such follicles in the wild types.

Driving folliculogenesis by the oocyte-somatic cell dialog: Lessons from genetic models

This review focuses on the role of the dialog between the oocyte and its companion somatic cells in driving folliculogenesis from the primordial to the preovulatory follicle stage. Mouse and sheep genetic models have brought complementary evidence of these cell interactions and their consequences for ovarian function. In mouse, the deletion of genes encoding connexins has shown that functional gap junction channels between oocytes and granulosa cells and between granulosa cells themselves maintain the follicle in a functionally integrated state. Targeted deletions in oocytes or granulosa cells have revealed the cell- and stage-specific role of ubiquist factors belonging to the phosphatidylinositol 3 kinase signaling pathway in primordial follicle activation, oocyte growth and follicle survival. Various models of transgenic mice and sheep carrying natural loss-of-function mutations associated with sterility have established that the oocyte-derived factors, bone morphogenetic protein (BMP) 15 and growth differentiation factor 9 orchestrate follicle development, support cumulus metabolism and maturation and participate in oocyte meiosis arrest. Unexpectedly in sheep, mutations resulting in the attenuation of BMP signaling lead to enhanced ovulation rate, likely resulting from a lowered follicular atresia rate and the enhancement of FSH-regulated follicular maturation. Both the activation level of BMP signaling and an adequate equilibrium between BMP15 and growth differentiation factor 9 determine follicle survival, maturation, and development toward ovulation. The physiological approaches which were implemented on genetic animal models during the last 20 years have opened up new perspectives for female fertility by identifying the main signaling pathways of the oocyte-somatic cell dialog.

Relationship between the concentration of bone morphogenetic protein-15 (BMP-15) and growth differentiation factor-9 (GDF-9) in pre-ovulatory follicles, ovarian cysts and serum in sows

The aim of the study was to compare and assess the relationship between peripheral and ovarian bone morphogenetic protein-15 (BMP-15) and growth differentiation factor-9 (GDF-9) concentration in cysts-bearing and non-cysts-bearing sows. The research involved multiparous sows (cysts-bearing sows, n = 20; non-cysts-bearing sows, n = 26). Serum, cystic follicular fluid or fluid from the ovulatory follicles was collected from each of the sows at the time of the slaughter. The collected serum and cystic/follicular fluid samples were tested for BMP-15 and GDF-9 concentrations. BMP-15 and GDF-9 concentrations in fluid from ovarian cysts were significantly higher than in the follicular fluid (P < 0.01). The concentration of BMP-15 and GDF-9 in the serum of sows with cysts was also higher than in ovulating sows (P < 0.05 and P < 0.01, respectively). The concentration of BMP-15 in serum was positively correlated with the concentration of said protein in pre-ovulatory follicles and cysts (r = 0.70; P < 0.01 and r = 0.50; P < 0.05, respectively). A positive correlation was also found between the concentration of serum GDF-9 and cyst GDF-9 (r = 0.55; P < 0.05). Moreover, another positive correlation was detected between the BMP-15 and GDF-9 concentrations, with the highest correlation coefficient recorded in the cyst fluid (r = 0.87; P < 0.01). This study for the first time demonstrates the presence of BMP-15 and GDF-9 in the cyst fluid in sows and determines a positive correlation between the concentration of the above factors in the follicular/cystic fluid and serum. Therefore, it is possible that the determination of BMP-15 and GDF-9 serum concentration may assist diagnosing ovarian cysts in sows. However, it is suggested that further studies involving a more in-depth analysis of the role of BMP-15 and GDF-9 in the pathogenesis of ovarian cysts in pigs are needed.

Flow cytometric analysis of FSHR, BMRR1B, LHR and apoptosis in granulosa cells and ovulation rate in merino sheep

The aim of the present study was to determine the direct cause of the mutation-induced, increased ovulation rate in Booroola Merino (BB) sheep. Granulosa cells were removed from antral follicles before ovulation and post-ovulation from BB (n=5) and WT (n=12) Merino ewes. Direct immunofluorescence measurement of mature cell surface receptors using flow cytometry demonstrated a significant up-regulation of FSH receptor (FSHR), transforming growth factor beta type 1, bone morphogenetic protein receptor (BMPR1B), and LH receptor (LHR) in BB sheep. The increased density of FSHR and LHR provide novel evidence of a mechanism for increasing the number of follicles that are recruited during dominant follicle selection. The compounding increase in receptors with increasing follicle size maintained the multiple follicles and reduced the apoptosis, which contributed to a high ovulation rate in BB sheep. In addition, we report a mutation-independent mechanism of down-regulation to reduce receptor density of the leading dominant follicle in sheep. The suppression of receptor density coincides with the cessation of mitogenic growth and steroidogenic differentiation as part of the luteinization of the follicle. The BB mutation-induced attenuation of BMPR1B signaling led to an increased density of the FSHR and LHR and a concurrent reduction in apoptosis to increase the ovulation rate. The role of BMPs in receptor modulation is implicated in the development of multiple ovulations.

Polymorphisms of the Ovine BMPR-IB, BMP-15 and FSHR and Their Associations with Litter Size in Two Chinese Indigenous Sheep Breeds

The Small Tailed Han sheep and Hu sheep are two prolific local sheep in China. In this study, the polymorphisms of BMPR-IB (Bone morphogenetic protein receptor IB), BMP-15 (Bone morphogenetic protein 15) and FSHR (follicle stimulating hormone receptor) were investigated to check whether they are associated with litter size in Small Tailed Han sheep and Hu sheep. Consequently, three polymorphisms, FecB mutation in BMPR-IB (c.746A>G), FecG mutation in BMP-15 (c.718C>T) and the mutation (g. 47C>T) in FSHR were found in the above two sheep breeds with a total number of 1630 individuals. The single marker association analysis showed that the three mutations were significantly associated with litter size. The ewes with genotype FecBB/FecBB and FecBB/FecB+ had 0.78 and 0.58 more lambs (p < 0.01) than those with genotype FecB+/FecB+, respectively. The heterozygous Han and Hu ewes with FecXG/FecX+ genotype showed 0.30 (p = 0.05) more lambs than those with the FecX+/FecX+ genotype. For FSHR gene, the ewes with genotype CC had 0.52 (p < 0.01) and 0.75 (p < 0.01) more lambs than those with genotypes TC and TT, respectively. Combined effect analyses indicated an extremely significant interaction (p < 0.01) between the random combinations of BMPR-IB, BMP-15 and FSHR genes on litter size. In addition, the Han and Hu ewes with BB/G+/CC genotype harbor the highest litter size among ewes analyzed in current study. In conclusion, BMPR-IB, BMP-15 and FSHR polymorphisms could be used as genetic markers in multi-gene pyramiding for improving litter size in sheep husbandry.

The microenvironment of the ovarian follicle in the postpartum dairy cow: effects on reagent transfer from cumulus cells to oocytes in vitro

This study's hypothesis was that the nutrient composition in follicular fluid (FF) of ovarian follicles in early lactating postpartum cows may influence reagent transfer from cumulus cells (CC) to the oocyte. To test this, concentrations of amino acids (AA), cholesterol, glucose, and nonesterified fatty acids were measured in FF from the largest antral follicles at Days 21 and 46 postpartum during which time, most animals were expected to have resumed ovulatory activity. From the range of concentrations measured, two media compositions (Lac and Half-Lac) were prepared to compare with medium 199 (M199). The AA and cholesterol concentrations in FF were on average, approximately 35% and greater than 1000% higher than in M199, respectively. The nonesterified fatty acids, but not glucose, concentrations also exceeded those in M199. The transfer of fluorescent dye from CC to oocytes in bovine cumulus-oocyte complexes incubated with and without phosphodiesterase inhibitors (dipyridamole and milrinone) and/or forskolin was assessed. Maximum dye accumulation in oocytes incubated in M199 occurred after 4 hours and was further increased (P < 0.001) by dipyridamole. The addition of dipyridamole to Lac, but not Half-Lac, media also increased dye accumulation. There were effects of media (P < 0.001), cholesterol (P < 0.001), and forskolin (P < 0.05) on dye accumulation but no effects of stearic or palmitic acid in either Lac or Half-Lac media. The addition of oleic acid in Half-Lac (P < 0.01), but not Lac, media inhibited dye accumulation. These results support the hypothesis that reagent transfer from CC to oocytes is compromised when the AA composition in FF is low, as sometimes occurs during early lactation.

Using sheep lines with mutations in single genes to better understand ovarian function

Livestock populations have been subjected to strong selection pressure to improve reproductive success, and this has led to the identification of lines of animals with increased fecundity. These animals provide a rich biological resource for discovery of genes and regulatory mechanisms that underpin improved reproductive success. To date, three genes, all related to the transforming growth factor β pathway, have been identified as having mutations that lead to alterations in ovulation in sheep. In addition, several other sheep lines have been identified with putative mutations in single genes with major effects on ovulation rate. This review is focused on the identification of the mutations affecting ovulation rate and how these discoveries have provided new insights into control of ovarian function.

Effects of species differences on oocyte regulation of granulosa cell function

The aims were to investigate whether oocyte-secreted growth factors from a high (i.e. rat) and low (i.e. sheep) ovulation rate species could stimulate 3H-thymidine incorporation in granulosa cells (GC) from antral follicles from the same or across species. Denuded oocytes (DO) were co-incubated with GC with or without specific antibodies to growth differentiating factor 9 (GDF9) or bone morphogenetic protein 15 (BMP15). Co-incubations of DO-GC from the same or across species significantly increased thymidine incorporation in GC with increasing numbers of DO. GDF9 immuno-neutralisation reduced thymidine incorporation in rat GC co-incubated with either rat or ovine DO and in ovine GC co-incubated with ovine or rat DO. BMP15 immuno-neutralisation only reduced thymidine incorporation when ovine DO were co-incubated with either ovine or rat GC. Western blotting of oocytes co-incubated with GC identified GDF9 and BMP15 proteins for sheep and GDF9 protein for rats in oocyte lysates and incubation media. With respect to rat BMP15, a promature protein was identified in the oocyte lysate but not in media. Expression levels of GDF9 relative to BMP15 mRNA in DO co-incubated with GC were highly correlated (R 2=0.99) within both species. However, the expression ratios were markedly different for the rat and sheep (4.3 vs 1.0 respectively). We conclude that during follicular development, rat oocytes secrete little, if any, BMP15 and that GDF9 without BMP15 can stimulate proliferation of rat and ovine GC. In contrast, ovine oocytes secrete both BMP15 and GDF9, and both were found to stimulate proliferation in ovine and rat GC.

Characterization of bmp15 and its regulation by human chorionic gonadotropin in the follicle of gibel carp (Carassius auratus gibelio)

Bone morphogenetic protein (BMP15) is a member of the transforming growth factor β (TGF-β) superfamily with a key role in regulating follicle development in mammals and birds. However, potential ovarian roles of BMPs remain unexplored in teleosts. In this study, the full-length sequences of bmp15 were obtained using rapid-amplification of cDNA ends (RACE). The full-length cDNA sequence of bmp15 is 2217 bp which contained 214 bp 5'-UTR and 845 bp 3'-UTR. The open reading frame (ORF) sequence of bmp15 is 1158 bp, encoding a predicted protein of 385 amino acid residues. BMP15 has a specific RXXR protease cleavage site of TGF-β superfamily (is RIRR) and six conserved cysteine residues. Using real-time quantitative PCR revealed that bmp15 mRNA was largely expressed in the ovary and testis and mostly in oocytes within the follicle, slightly expressed in muscle, liver and pituitary. BMP15 is mainly present at stage I follicles by real-time quantitative PCR and immunohistochemistry. Phylogenetic analysis showed that gibel carp bmp15 was similar to bmp15 of zebrafish and other fish species. Treatment with human chorionic gonadotropin (hCG) in isolated follicles of gibel carp in vitro showed altered bmp15 mRNA expression: when treated with 10 ng/mL hCG for 10h, the expression level of bmp15 was significantly increased. However, with proceeding cultivation, the expression level of BMP15 mRNA decreased. The results of this study indicate that bmp15 may play a key role during development of follicles in gibel carp, especially in early stage follicles.

A covalently dimerized recombinant human bone morphogenetic protein-15 variant identifies bone morphogenetic protein receptor type 1B as a key cell surface receptor on ovarian granulosa cells

Genetic studies have identified bone morphogenetic protein-15 (BMP15) as an essential regulator of female fertility in humans and in sheep. Oocyte-derived BMP15 is a noncovalently linked dimeric growth factor mediating its effects to ovarian somatic cells in a paracrine manner. Although receptor ectodomains capable of binding BMP15 have previously been reported, no cell surface receptor complex involved in BMP15 signaling has previously been characterized. Here we have expressed and purified recombinant human BMP15 noncovalent and covalent dimer variants. The biological effects of these BMP15 variants were assessed in cultured human granulosa-luteal cells or COV434 granulosa cell tumor cells using BMP-responsive transcriptional reporter assays and an inhibin B ELISA. Biochemical characterization of ligand-receptor interactions was performed with affinity-labeling experiments using [(125)I]iodinated BMP15 variants. Both ligand variants were shown to form homodimers and to stimulate Smad1/5/8 signaling and inhibin B production in human granulosa cells in a similar manner. [(125)I]Iodination of both ligands was achieved, but only the covalent dimer variant retained receptor binding capacity. The [(125)I]BMP15(S356C) variant bound preferentially to endogenous BMP receptor 1B (BMPR1B) and BMPR2 receptors on COV434 cells. Binding experiments in COS cells with overexpression of these receptors confirmed that the [(125)I]BMP15(S356C) variant binds to BMPR1B and BMPR2 forming the BMP15 signaling complex. The results provide the first direct evidence in any species on the identification of specific cell surface receptors for a member of the GDF9/BMP15 subfamily of oocyte growth factors. The fact that BMP15 uses preferentially BMPR1B as its type I receptor suggests an important role for the BMPR1B receptor in human female fertility. The result is well in line with the demonstration of ovarian failure in a recently reported human subject with a homozygous BMPR1B loss-of-function mutant.

The ratio of growth differentiation factor 9: bone morphogenetic protein 15 mRNA expression is tightly co-regulated and differs between species over a wide range of ovulation rates

Recent evidence suggests that the species-specific ovulation-rate phenotypes may be influenced by differences in the expression levels of bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) mRNA and protein. The aim of this study was to compare GDF9 and BMP15 mRNA levels in individual denuded oocytes (DO) from a range of single (i.e. cow, red deer), single-to-triple (i.e. sheep) and high (i.e. pig, mouse, rat) ovulation-rate species. Compared to all other species studied, GDF9 mRNA levels were lower in DO of cows and deer, whilst BMP15 levels were highest in DO of pigs. There was no detectable expression of either GDF9 or BMP15 mRNA in CC from any species. The ratio of GDF9:BMP15 mRNA expression was highly correlated (R(2)>0.80) within each species but differed markedly between species (P<0.01). Thus, we conclude that the ratio of GDF9:BMP15 mRNA is species-specific across a wide range of ovulation-rate phenotypes.