A new polymorphism in the Growth and Differentiation Factor 9 (GDF9) gene is associated with increased ovulation rate and prolificacy in homozygous sheep

Ovulation rate, antral follicle count, and circulating anti-Müllerian hormone in Trio allele carriers, a novel high fecundity bovine genotype

High fecundity genotypes in sheep are a valuable model to study the physiological mechanisms underlying follicle selection and the control of ovulation rate. Similar genotypes in cattle had not been described until the recent identification of a major bovine allele, termed Trio, which had a large effect on ovulation rate. The present study was designed to evaluate ovulation rate, antral follicle count (AFC), circulating ant-müllerian hormone (AMH), and the association among these measures in unstimulated and superstimulated Trio carrier cattle. We hypothesized that AFC and AMH would be variable among individual cows but would be similar between Trio carriers and non-carrier control cows and that there would be no association between these measures of follicle numbers and ovulation rate. In experiment 1, ovulation rate was determined during 4 consecutive estrous cycles in Trio carriers (n = 34) and non-carrier controls (n = 27). Ovulation rate, on average, was greater (P < 0.01) in Trio carriers (3.5 ± 0.2) compared to non-carrier controls (1.1 ± 0.1) with ∼70% of carrier cycles (n = 136) having 3-4 ovulations while only ∼5% had single ovulations. In contrast, non-carrier cycles (n = 108) were mostly single ovulation (89%) with none having more than two ovulations. In experiment 2, AFC, determined at wave emergence, was not different (P = 0.54) between Trio carriers (24.5 ± 1.3; n = 45) and non-carrier controls (23.1 ± 0.9; n = 37), and no correlation was found between AFC and mean ovulation rate in either genotype (r = -0.009 and r = -0.07; P > 0.70, respectively). In Experiment 3, circulating AMH was also not different between genotypes (P = 0.65) while correlations were found between AFC and AMH in Trio carriers (r = 0.43; P = 0.05; n = 27) and non-carrier controls (r = 0.78; P < 0.01; n = 19). In experiment 4, AFC and AMH were determined in Trio-carriers (n = 9) in relation to a synchronized follicular wave which was unstimulated or stimulated with exogenous FSH. Stimulation with FSH increased ovulation rate, compared to unstimulated Trio carriers, however no association was found between AFC or AMH and ovulation rate regardless of whether superstimulation with exogenous FSH was used. In conclusion, the novel high fecundity bovine genotype Trio, results in consistent multiple ovulations despite having similar AFC and AMH. Therefore, our results suggest that differences in antral follicle numbers during the final stages of follicle development are not a key component of the mechanism underlying multiple ovulations in Trio carriers.

Variant <i>GDF9</i> mRNA is likely not the main cause of larger litter size in Iranian Lori-Bakhtyari, Shal, Ghezel, and Afshari sheep breeds

Abstract. This study was carried out to screen the GDF9 gene and evaluate the polymorphism effect on litter size of four Iranian sheep breeds using the PCR-RFLP and PCR-SSCP methods. First, sequencing of the GDF9 gene in 16 twin-birth, 4 triplet-birth, and 2 infertile ewes showed that, in addition to G2, G3, G4, G5, and G6 mutations that have been previously reported in other breeds, a new G0 mutation, called C25T, exists in the GDF9 sequence of 1 out of 22 ewes and causes L9F substitution in the signal peptide region. None of the triplet-birth or infertile ewes carried G1, G4, G7, FecGE, G8, or FecGT mutations. In the second experiment, a large dataset was used: 605 individuals including 496 ewes (145 Afshari, 54 Shal, 126 Ghezel, and 171 Lori-Bakhtyari sheep), and 109 rams (26 Afshari, 23 Shal, 10 Ghezel, and 50 Lori-Bakhtyari sheep. There were no sheep carrying the G7, G8, or Thoka mutations. Among all 109 rams that were used in this study, none of them were homozygous for the G1 mutation. Moreover, abundance of heterozygote rams (G1/G+) varied from 0.0 (Afshari) to 28.6 % (Lori-Bakhtyari and Ghezel). The highest and the lowest frequencies of the G4 mutation were 30.6 and 3.0 % in Shal and Afshari breeds, respectively. Moreover, G4 abundance varied from 0.0 to 42.3 %, from 3.0 to 26.9, and from 3.0 to 30.6 % in rams, ewes, and overall, respectively. There was a significant difference in the abundance of G1 and G4 mutations between breeds. However, neither the G1 nor the G4 mutation was associated with litter size in Afshari, Ghezel, Lori-Bakhtyari, or Shal sheep breeds. In conclusion, the results of this study showed that GDF9 G1 and G4 mutations are not the reason for higher litter size in Iranian sheep. Moreover, the GDF9 G0 and G6 mutations do not cause triplet births or infertility in Iranian ewes. Therefore, it is unlikely that variant GDF9 mRNA induces larger litter size or infertility in Iranian ewes.

FecX Bar a Novel BMP15 mutation responsible for prolificacy and female sterility in Tunisian Barbarine Sheep

Background

Naturally occurring mutations in growth and differentiation factor 9 (GDF9) or bone morphogenetic protein 15 (BMP15) genes are associated with increased ovulation rate (OR) and litter size (LS) but also sterility. Observing the Tunisian Barbarine ewes of the “W” flock selected for improved prolificacy, we found prolific and infertile ewes with streaky ovaries. Blood genomic DNA was extracted from a subset of low-ovulating, prolific and infertile ewes of the “W” flock, and the entire coding sequences of GDF9 and BMP15 were sequenced.

Results

We evidenced a novel polymorphism in the exon 1 of the BMP15 gene associated with increased prolificacy and sterility. This novel mutation called FecX^Bar is a composite polymorphism associating a single nucleotide substitution (c.301G > T), a 3 bp deletion (c.302_304delCTA) and a C insertion (c.310insC) in the ovine BMP15 cDNA leading to a frame shift at protein position 101. Calculated in the “W” flock, the FecX^Bar allele increased OR by 0.7 ova and LS by 0.3 lambs (p = 0.08). As for already identified mutations, homozygous females carrying FecX^Bar exhibited streaky ovaries with a blockade at the primary stage of folliculogenesis as shown by histochemistry.

Conclusions

Our investigation demonstrates a new mutation in the BMP15 gene providing a valuable genetic tool to control fecundity in Tunisian Barbarine, usable for diffusion program into conventional flocks looking for prolificacy improvement.

Allelic and genotypic frequencies in polymorphic Booroola fecundity gene and their association with multiple birth and postnatal growth in Chhotanagpuri sheep

AIM

Chhotanagpuri breed of sheep reared for mutton in Jharkhand, India, having problem of low litter size and body weight. The response of genetic improvement for traits with low heritability through traditional selection method is time-consuming. Therefore, marker-assisted selection based on a polymorphism study of suitable candidate gene can response quickly. Thus, this study was aimed at identification of different allelic and genotypic frequencies of Booroola fecundity (FecB) gene and its association with multiple birth and postnatal growth in Chhotanagpuri sheep.

MATERIALS AND METHODS

DNA isolation and gene-specific amplification of FecB gene was performed from blood samples of from 92 Chhotanagpuri lambs maintained under similar feeding and management conditions. Custom nucleotide sequencing and single-strand conformational polymorphism analysis were performed to identify different genotypes with respect to the target gene. Statistical analysis was performed for determination of allelic and genotypic frequencies of FecB gene polymorphisms and its association with multiple birth and postnatal growth of lambs from birth to 52 weeks age.

RESULTS

"AA," "AB," and "BB" genotypes were found at locus-1 as it is polymorphic for FecB gene while locus-2 was found to be monomorphic for FecB gene. Higher frequency of "A" allele at locus-1 was found in single born lambs, whereas "B" allele was predominant among multiple born lambs. The lambs having "BB" genotype weighed significantly (p≤0.01) heavier than those of "AB" and "AA" genotype at 52 weeks of age.

CONCLUSION

"BB" genotype has emerged as favored genotype for multiple births and better growth indicator. Therefore, homozygous lambs for "B" allele should be selected and utilized in breeding program for better growth rate.

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.

A Major Gene for Bovine Ovulation Rate

Half-sib daughters sired by a bull believed to be a carrier of a major gene for high ovulation rate were evaluated for ovulation rate and genotyped in an effort to both test the hypothesis of segregation of a major gene and to map the gene’s location. A total of 131 daughters were produced over four consecutive years at a University of Wisconsin-Madison research farm. All were evaluated for ovulation rate over an average of four estrous cycles using transrectal ultrasonography. The sire and all daughters were genotyped using a 3K SNP chip and the genotype and phenotype data were used in a linkage analysis. Subsequently, daughters recombinant within the QTL region and the sire were genotyped successively with 50K and 777K SNP chips to refine the location of the causative polymorphism. Positional candidate genes within the fine-mapped region were examined for polymorphism by Sanger sequencing of PCR amplicons encompassing coding and 5’ and 3’ flanking regions of the genes. Sire DNA was used as template in the PCR reactions. Strong evidence of a major gene for ovulation rate was observed (p<1x10^-28) with the gene localized to bovine chromosome 10. Fine-mapping subsequently reduced the location to a 1.2 Mb region between 13.6 and 14.8 Mb on chromosome 10. The location identified does not correspond to that for any previously identified major gene for ovulation rate. This region contains three candidate genes, SMAD3, SMAD6 and IQCH. While candidate gene screening failed to identify the causative polymorphism, three polymorphisms were identified that can be used as a haplotype to track inheritance of the high ovulation rate allele in descendants of the carrier sire.

Designing, optimization and validation of tetra-primer ARMS PCR protocol for genotyping mutations in caprine Fec genes

New, quick, and inexpensive methods for genotyping novel caprine Fec gene polymorphisms through tetra-primer ARMS PCR were developed in the present investigation. Single nucleotide polymorphism (SNP) genotyping needs to be attempted to establish association between the identified mutations and traits of economic importance. In the current study, we have successfully genotyped three new SNPs identified in caprine fecundity genes viz. T(-242)C (BMPR1B), G1189A (GDF9) and G735A (BMP15). Tetra-primer ARMS PCR protocol was optimized and validated for these SNPs with short turn-around time and costs. The optimized techniques were tested on 158 random samples of Black Bengal goat breed. Samples with known genotypes for the described genes, previously tested in duplicate using the sequencing methods, were employed for validation of the assay. Upon validation, complete concordance was observed between the tetra-primer ARMS PCR assays and the sequencing results. These results highlight the ability of tetra-primer ARMS PCR in genotyping of mutations in Fec genes. Any associated SNP could be used to accelerate the improvement of goat reproductive traits by identifying high prolific animals at an early stage of life. Our results provide direct evidence that tetra-primer ARMS-PCR is a rapid, reliable, and cost-effective method for SNP genotyping of mutations in caprine Fec genes.

Effects of the FecL major gene in the Lacaune meat sheep population

Background

The major prolificacy gene FecL was first described in the Lacaune sheep meat breed Ovi-Test in 1998. A few studies estimated the effect of this gene on prolificacy but little data is available. In 2010, the Ovi-Test cooperative started genotyping FecL in all of their replacement ewe lambs. Thanks to the large amount of genotyping data that is available now, gene effects on litter size and other relevant traits can be estimated more accurately.

Methods

Our study included 5775 ewes genotyped since 2010 and 1025 sires genotyped since 2002. Performances and pedigrees were extracted from the French national database for genetic evaluation and research. Analysis of the effect of the gene on different traits was based on linear or threshold genetic animal models using the ASReml software.

Results

The female population was composed of 71% homozygous wild type ewes (++), 27% heterozygous ewes for the FecL mutation (L+) and 2% homozygous mutant (LL) ewes. On average, L + ewes produced 0.5 more lambs per lambing than ++ ewes. The FecL gene not only affected the mean litter size but also its variability, which was lower for ++ than for L + ewes. Fertility after insemination was higher for L + ewes than for ++ ewes. Lambs from ++ dams were heavier (+300 g) than the lambs of L + dams and the mortality of twin lambs born from ++ dams was lower than those from L + dams. In addition, bias in estimated breeding values for prolificacy when ignoring the existence of this major gene was quantified.

Conclusions

The effect of the FecL gene on prolificacy was estimated more accurately and we show that this gene affects both the mean and the variability of litter size and other traits. This paper also shows that ignoring the existence of this major gene in genetic evaluation of prolificacy can lead to a large overestimation of polygenic breeding values.

Evolutionary origin of bone morphogenetic protein 15 and growth and differentiation factor 9 and differential selective pressure between mono- and polyovulating species

Bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) are TGFbeta-like oocyte-derived growth factors involved in ovarian folliculogenesis as critical regulators of many granulosa cell processes and ovulation rate. Ovarian phenotypic effect caused by alterations in BMP15 and GDF9 genes appears to differ between species and may be relevant to their mono- or polyovulating status. Through phylogenetic analysis we recently showed that these two paralogous genes are strongly divergent and in rapid evolution as compared to other members of the TGFbeta superfamily. Here, we evaluate the amino acid substitution rates of a set of proteins implicated in the ovarian function, including BMP15 and GDF9, with special attention to the mono- or polyovulating status of the species. Among a panel of mono- and polyovulating mammals, we demonstrate a better conservation of some areas in BMP15 and GDF9 within mono-ovulating species. Homology modeling of BMP15 and GDF9 homodimer and heterodimer 3-D structures was suggestive that these areas may be involved in dimer formation and stability. A phylogenetic study of BMP15/GDF9-related proteins reveals that these two genes diverged from the same ancestral gene along with BMP3 and GDF10, two other paralogous genes. A substitution rate analysis based on this phylogenetic tree leads to the hypothesis of an acquisition of BMP15/GDF9-specific functions in ovarian folliculogenesis in mammals. We propose that high variations observed in specific areas of BMP15 and GDF9 in polyovulating species change the equilibrium between homodimers and heterodimers, modifying the biological activity and thus allowing polyovulation to occur.

The fundamental role of bone morphogenetic protein 15 in ovarian function and its involvement in female fertility disorders

BACKGROUND

A large number of studies have contributed to understanding the general mechanisms driving ovarian folliculogenesis in humans and show a complex endocrine dialog between the central nervous system, the pituitary and the ovary, integrated by various intraovarian paracrine messages. The role of intraovarian paracrine regulation has acquired more relevance in the recent years owing to the discovery of previously unknown factors, such as the oocyte-derived bone morphogenetic protein (BMP)15.

METHODS

A thorough literature search was carried out in order to summarize what has been reported so far on the role of BMP15, and the BMP15 paralog, growth and differentiation factor 9 (GDF9), in ovarian function and female fertility. Research articles published in English until March 2014 were included.

RESULTS

The biological actions of BMP15 include: (i) the promotion of follicle growth and maturation starting from the primary gonadotrophin-independent phases of folliculogenesis; (ii) the regulation of follicular granulosa cell (GC) sensitivity to FSH action and the determination of ovulation quota; (iii) the prevention of GC apoptosis and (iv) the promotion of oocyte developmental competence. The existence of biologically active heterodimers with GDF9, and/or the synergistic co-operation of BMP15 and GDF9 homodimers are indeed relevant in this context. Experimental disruption of the bmp15 gene in mice resulted in a mild fertility defect limited to females, whereas natural missense mutations in ewes cause variable phenotypes (ranging from hyperprolificacy to complete sterility) depending on a fine gene dosage mechanism also involving GDF9. Strong evidence supports the concept that such a mechanism plays an important role in the regulation of ovulation rate across mammalian and non-mammalian species. Following the discovery of sheep fecundity genes, several research groups have focused on alterations in human BMP15 associated with primary ovarian insufficiency (POI) or polycystic ovary syndrome. Several variants of BMP15 are significantly associated with POI supporting their pathogenic role, but the underlying biological mechanism is still under investigation and of great interest in medicine. BMP15 maps to the Xp locus involved in the determination of the ovarian defect in Turner syndrome and significantly contributes to the determination of ovarian reserve. Pioneering studies in women undergoing controlled ovarian stimulation indicate that BMP15 may represent a marker of ovarian response or oocyte quality.

CONCLUSIONS

BMP15, an oocyte-derived growth and differentiation factor, is a critical regulator of folliculogenesis and GC activities. Variations in BMP15 gene dosage have a relevant influence on ovarian function and can account for several defects of female fertility. The modulation of BMP15 action may have interesting pharmacological perspectives and the analysis of BMP15 may become a useful marker in IVF procedures. Recent outcomes indicate that the close interactions of BMP15/GDF9 have a critical biological impact that should be taken into account in future studies.

Direct evidence on the contribution of a missense mutation in GDF9 to variation in ovulation rate of Finnsheep

The Finnish Landrace (Finnsheep) is a well known high-prolificacy sheep breed and has been used in many countries as a source of genetic material to increase fecundity of local breeds. Analyses to date have indicated that mutations with a large effect on ovulation rate are not responsible for the exceptional prolificacy of Finnsheep. The objectives of this study were to ascertain if: 1) any of 12 known mutations with large effects on ovulation rate in sheep, or 2) any other DNA sequence variants within the candidate genes GDF9 and BMP15 are implicated in the high prolificacy of the Finnish Landrace breed; using material from lines developed by divergent selection on ovulation rate. Genotyping results showed that none of 12 known mutations (FecB^B, FecX^B, FecX^G, FecX^GR, FecX^H, FecX^I, FecX^L, FecX^O, FecX^R, FecG^E, FecG^H, or FecG^T) were present in a sample of 108 Finnsheep and, thus, do not contribute to the exceptional prolificacy of the breed. However, DNA sequence analysis of GDF9 identified a previously known mutation, V371M, whose frequency differed significantly (P<0.001) between High and Low ovulation rate lines. While analysis of ovulation rate data for Finnsheep failed to establish a significant association between this trait and V371M, analysis of data on Belclare sheep revealed a significant association between V371M and ovulation rate (P<0.01). Ewes that were heterozygous for V371M exhibited increased ovulation rate (+0.17, s.e. 0.080; P<0.05) compared to wild type and the effect was non-additive (ovulation rate of heterozygotes was significantly lower (P<0.01) than the mean of the homozygotes). This finding brings to 13 the number of mutations that have large effects on ovulation rate in sheep and to 5, including FecB^B, FecG^E, FecX^O and FecX^GR, the number of mutations within the TGFβ superfamily with a positive effect on prolificacy in the homozygous state.

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.

Genome-wide association studies identify two novel BMP15 mutations responsible for an atypical hyperprolificacy phenotype in sheep

Some sheep breeds are naturally prolific, and they are very informative for the studies of reproductive genetics and physiology. Major genes increasing litter size (LS) and ovulation rate (OR) were suspected in the French Grivette and the Polish Olkuska sheep populations, respectively. To identify genetic variants responsible for the highly prolific phenotype in these two breeds, genome-wide association studies (GWAS) followed by complementary genetic and functional analyses were performed. Highly prolific ewes (cases) and normal prolific ewes (controls) from each breed were genotyped using the Illumina OvineSNP50 Genotyping Beadchip. In both populations, an X chromosome region, close to the BMP15 gene, harbored clusters of markers with suggestive evidence of association at significance levels between 1E(-05) and 1E(-07). The BMP15 candidate gene was then sequenced, and two novel non-conservative mutations called FecX(Gr) and FecX(O) were identified in the Grivette and Olkuska breeds, respectively. The two mutations were associated with the highly prolific phenotype (p FecX (Gr) = 5.98E(-06) and p FecX(O) = 2.55E(-08)). Homozygous ewes for the mutated allele showed a significantly increased prolificacy (FecX(Gr)/FecX(Gr), LS = 2.50 ± 0.65 versus FecX(+)/FecX(Gr), LS = 1.93 ± 0.42, p<1E(-03) and FecX(O)/FecX(O), OR = 3.28 ± 0.85 versus FecX(+)/FecX(O), OR = 2.02 ± 0.47, p<1E(-03)). Both mutations are located in very well conserved motifs of the protein and altered the BMP15 signaling activity in vitro using a BMP-responsive luciferase test in COV434 granulosa cells. Thus, we have identified two novel mutations in the BMP15 gene associated with increased LS and OR. Notably, homozygous FecX(Gr)/FecX(Gr) Grivette and homozygous FecX(O)/FecX(O) Olkuska ewes are hyperprolific in striking contrast with the sterility exhibited by all other known homozygous BMP15 mutations. Our results bring new insights into the key role played by the BMP15 protein in ovarian function and could contribute to a better understanding of the pathogenesis of women's fertility disorders.

Screening of indigenous goats for prolificacy associated DNA markers of sheep

The present study was undertaken to explore the genetic basis of caprine prolificacy and to screen indigenous goats for prolificacy associated markers of sheep in BMPR1B, GDF9 and BMP15 genes. To detect the associated mutations and identify novel allelic variants in the candidate genes, representative samples were collected from the breeding tract of indigenous goat breeds varying in prolificacy and geographic distribution. DNA was extracted and PCR amplification was done using primers designed or available in literature for the coding DNA sequence of candidate genes. Direct sequencing was done to identify the genetic variations. Mutations in the candidate genes associated with fecundity in sheep were not detected in Indian goats. Three non-synonymous SNPs (C818T, A959C and G1189A) were identified in exon 2 of GDF9 gene out of which mutation A959C has been associated with prolificacy in exotic goats. Two novel SNPs (G735A and C808G) were observed in exon 2 of BMP15 gene.

Investigation of prolific sheep from UK and Ireland for evidence on origin of the mutations in BMP15 (FecX(G), FecX(B)) and GDF9 (FecG(H)) in Belclare and Cambridge sheep

This paper concerns the likely origin of three mutations with large effects on ovulation rate identified in the Belclare and Cambridge sheep breeds; two in the BMP15 gene (FecX^G and FecX^B) and the third (FecG^H) in GDF9. All three mutations segregate in Belclare sheep while one, FecX^B, has not been found in the Cambridge. Both Belclare and Cambridge breeds are relatively recently developed composites that have common ancestry through the use of genetic material from the Finnish Landrace and Lleyn breeds. The development of both composites also involved major contributions from exceptionally prolific ewes screened from flocks in Ireland (Belclare) and Britain (Cambridge) during the 1960s. The objective of the current study was to establish the likely origin of the mutations (FecX^G, FecX^B and FecG^H) through analysis of DNA from Finnish Landrace and Lleyn sheep, and Galway and Texel breeds which contributed to the development of the Belclare breed. Ewes with exceptionally high prolificacy (hyper-prolific ewes) in current flocks on Irish farms were identified to simulate the screening of ewes from Irish flocks in the 1960s. DNA was obtained from: prolific ewes in extant flocks of Lleyn sheep (n = 44) on the Lleyn peninsula in Wales; hyper-prolific ewes (n = 41); prolific Galway (n = 41) ewes; Finnish Landrace (n = 124) and Texel (n = 19) ewes. The FecX^G mutation was identified in Lleyn but not in Finnish Landrace, Galway or Texel sheep; FecX^B was only found among the hyper-prolific ewes. The FecG^H mutation was identified in the sample of Lleyn sheep. It was concluded from these findings that the Lleyn breed was the most likely source of the FecX^G and FecG^H mutations in Belclare and Cambridge sheep and that the FecX^B mutation came from the High Fertility line that was developed using prolific ewes selected from commercial flocks in Ireland in the 1960′s and subsequently used in the genesis of the Belclare.

A missense mutation in growth differentiation factor 9 (GDF9) is strongly associated with litter size in sheep

Background

A genome wide association study for litter size in Norwegian White Sheep (NWS) was conducted using the recently developed ovine 50K SNP chip from Illumina. After genotyping 378 progeny tested artificial insemination (AI) rams, a GWAS analysis was performed on estimated breeding values (EBVs) for litter size.

Results

A QTL-region was identified on sheep chromosome 5, close to the growth differentiation factor 9 (GDF9), which is known to be a strong candidate gene for increased ovulation rate/litter size. Sequencing of the GDF9 coding region in the most extreme sires (high and low BLUP values) revealed a single nucleotide polymorphism (c.1111G>A), responsible for a Val→Met substitution at position 371 (V371M). This polymorphism has previously been identified in Belclare and Cambridge sheep, but was not found to be associated with fertility. In our NWS-population the c.1111G>A SNP showed stronger association with litter size than any other single SNP on the Illumina 50K ovine SNP chip. Based on the estimated breeding values, daughters of AI rams homozygous for c.1111A will produce minimum 0.46 - 0.57 additional lambs compared to daughters of wild-type rams.

Conclusion

We have identified a missense mutation in the bioactive part of the GDF9 protein that shows strong association with litter size in NWS. Based on the NWS breeding history and the marked increase in the c.1111A allele frequency in the AI ram population since 1983, we hypothesize that c.1111A allele originate from Finnish landrace imported to Norway around 1970. Because of the widespread use of Finnish landrace and the fact that the ewes homozygous for the c.1111A allele are reported to be fertile, we expect the commercial impact of this mutation to be high.

Identification of novel candidate genes for follicle selection in the broiler breeder ovary

BACKGROUND

Broiler breeders fed ad libitum are characterised by multiple ovulation, which leads to poor shell quality and egg production. Multiple ovulation is controlled by food restriction in commercial flocks. However, the level of food restriction raises welfare concerns, including that of severe hunger. Reducing the rate of multiple ovulation by genetic selection would facilitate progress towards developing a growth profile for optimum animal welfare.

RESULTS

The study utilised 3 models of ovarian follicle development; laying hens fed ad libitum (experiment 2) and broiler breeders fed ad libitum or a restricted diet (experiments 1 & 3). This allowed us to investigate gene candidates for follicular development by comparing normal, abnormal and "controlled" follicle hierarchies at different stages of development. Several candidate genes for multiple ovulation were identified by combining microarray analysis of restricted vs. ad libitum feeding, literature searches and QPCR expression profiling throughout follicle development. Three candidate genes were confirmed by QPCR as showing significant differential expression between restricted and ad libitum feeding: FSHR, GDF9 and PDGFRL. PDGFRL, a candidate for steroidogenesis, showed significantly up-regulated expression in 6-8 mm follicles of ad libitum fed broiler breeders (P = 0.016), the period at which follicle recruitment occurs.

CONCLUSIONS

Gene candidates have been identified and evidence provided to support a possible role in regulation of ovarian function and follicle number. Further characterisation of these genes will be required to assess their potential for inclusion into breeding programmes to improve the regulation of follicle selection and reduce the need for feed restriction.

Genetic control of multiple births in low ovulating mammalian species

In mammals, litter size is a highly variable trait. Some species such as humans or cattle are monotocous, with one or sometimes two newborns per birth, whereas others, the polytocous species such as mice or pigs, are highly prolific and often produce a dozen newborns at each farrowing. In monotocous species, however, two or three newborns per birth may sometime be unwanted. In more polytocous species such as sheep or pigs, litter size is studied in order to increase livestock prolificacy. By contrast, twinning rates in humans or cattle may increase birth difficulties and health problems in the newborns. In this context, the aim of our review was to provide a clearer understanding of the genetic and physiological factors that control multiple births in low-ovulating mammalian species, with particular focus on three species: sheep, cattle, and humans, where knowledge of the ovulation rate in one may enlighten findings in the others. This article therefore reviews the phenotypic and genetic variability observed with respect to ovulation and twinning rates. It then presents the QTL and major genes that have been identified in each species. Finally, we draw a picture of the diversity of the physiological mechanisms underlying multiple ovulation. Although several major genes have been discovered in sheep, QTL detection methods in humans or cattle have suggested that the determinism of litter size is complex and probably involves several genes in order to explain variations in the number of ovulations.

Genetic testing for phenotype-causing variants in sheep and goats

This review gives an overview on ovine and caprine defects/disorders, disease predispositions, production traits and coat colours for which causal gene variants are known. Most phenotypes are inherited autosomal-recessive or dominant and in the majority are caused by single nucleotide substitutions or deletions. Causative sequence variants mainly were identified by sequencing candidate genes in the past, and recently also by whole genome analysis using the ovine 50k SNP chip. While PCR-fragment length polymorphism analyses were developed for the majority of causative sequence variants, other low- to medium-throughput PCR-based methods as PCR-single strand conformation analysis and allele-specific PCR were also established frequently. For processing large sample numbers, high-throughput methods as MALDI-ToF MS or real-time PCR are available for some gene variants. Further progress in development of ovine and caprine genome sequences and SNP chips will be beneficial for the discovery of additional causative variants in these two species.

[Progress in exploring genes for high fertility in ewes]

Fecundity trait in sheep is regulated by some major genes. Among them, BMPR-IB, BMP-15, and GDF-9 are most distinguishing. The mutant FecB of BMPR-IB has multiplicative effects on ovulation. GDF-9's mutants FecGH, FecI, and BMP-15's mutants FecXI, FecXH, FecXG, FecXB, FecXL, and FecXR increase ovulation rate in the heterozygote but result in sterile phenotypes in the homozygote, while GDF-9's mutant, FecGE, only increases ovulation rate in the homozygote. In addition, Woodlands and Lacaune are known as inheritable major genes. Woodlands gene is an X-linked maternally imprinted gene, and Lacaune is similar to FecB with a multiplicative effect on ovulation rate. The size of the effect of one copy of a mutation on ovulation rate ranges from an extra 0.4 ovulations for the woodlands mutation to an extra 1.5 ovulations for the BMPR-IB and Lacaune mutation. Investigation into these genes will not only help to select breeds with high fertility, but also give a chance to further elucidate the mechanism involved in the phenomenon. This review summaries the source, location, phenotype, and mechanism of the major genes in all breeds of sheep.

Polymorphism of GDF9 gene and its association with litter size in goats

Growth differentiation factor 9 (GDF9) was studied as a candidate gene for high prolificacy in goats. The polymorphism of exon 1 and flanking of GDF9 gene was detected by PCR-SSCP in five goat breeds with different prolificacy. Three genotypes (AA, AB and BB) were detected in goat breeds joined and two silent mutations (c.183A>C and c.336C>T) were identified in comparison genotype AA with genotype BB. Heterozygous genotype AB and wild type BB were detected in all five goat breeds and homozygous genotype AA was only detected in Jining Grey goats. The frequencies of genotypes AA, AB and BB were 0.18, 0.42 and 0.40 in Jining Grey goats, respectively. The genotype distribution was different (P < 0.01) between high prolificacy breed (Jining Grey goat) and low prolificacy breeds (Boer, Wendeng Dairy, Liaoning Cashmere and Beijing native goats). The Jining Grey goat does with genotype AA and AB had 0.72 (P < 0.01) and 0.56 (P < 0.01) kids more than those with genotype BB, respectively. The does with genotype AA had 0.16 (P > 0.05) kids more than those with genotype AB. These indicated that the allele A may have certain correlation with prolificacy in Jining Grey goats.

Identification of a line of sheep carrying a putative autosomal gene increasing ovulation rate in sheep that does not appear to interact with mutations in the transforming growth factor beta superfamily

Sheep lines with mutations in single genes that have major effects on ovulation rate have been very useful in gaining a better understanding of pathways important in controlling follicular development and ovulation rate. To date however, all known mutations are in the transforming growth factor beta (TGFB) superfamily. Ovulation rates were measured in 720 progeny of 20 rams that were descendants of a single prolific ewe. Evaluation of ovulation rates of daughters of closely related sires suggests the presence of a segregating major gene Fecundity Davisdale (FECD) that increases ovulation rate between 0.4 and 0.8 in heterozygous daughters. Key features of mutations in genes of the TGFB superfamily pathway, such as synergistic interactions with other family members, infertility in homozygous carriers, and increased responsiveness to exogenous gonadotropins, were not observed in this line; thus, the mutation does not appear to be acting in the TGFB pathway. Hence, there is likely a novel mutation being carried in this line of sheep that alters ovulation rate. Future identification of the causative mutation may provide new insights into regulation of follicular development and ovulation rate.

Genetic defects of ovarian TGF-β-like factors and premature ovarian failure

Premature ovarian failure (POF) is an ovarian defect characterized by the premature depletion of ovarian follicles; POF affects approximately 1-2% of women under the age of 40 yr, thus representing one major cause of female infertility. POF relevance is continuously growing because women tend to conceive always more frequently beyond 30 yr. Frequently, POF is the end-stage of an occult process [primary ovarian insufficiency (POI)]. POI is a heterogeneous disease caused by a variety of mechanisms. Though the underlying cause remains unexplained in the majority of cases, several data indicate that POI has a strong genetic component. These data include the existence of several causal genetic defects in human, experimental, and natural models, as well as the frequent familiarity. The candidate genes are numerous, but POF remains unexplained in most of the cases. Several recent evidences have driven the attention of researchers on the possible involvement of various elements belonging to the transforming growth factor β family, which includes bone morphogenetic proteins, growth/differentiation factors, and inhibins. These peptides are produced by either the oocyte or granulosa cells to constitute a complex paracrine network within the ovarian follicle. Here, we review the studies reporting the genetic alterations of these factors in human and animal defects of ovarian folliculogenesis which support the fundamental roles played by these signals in ovarian morphogenesis and function.

GDF9 as a candidate gene for prolificacy of Small Tail Han sheep

Growth differentiation factor 9 (GDF9) which controls the fecundity of Belclare, Cambridge, Santa Ines, Moghani, Ghezel and Thoka ewes was studied as a candidate gene for the prolificacy of Small Tail Han sheep. According to the sequence of ovine GDF9 gene, six pairs of primers were designed to detect single nucleotide polymorphisms of two exons of GDF9 gene in both high fecundity breed (Small Tail Han sheep) and low fecundity breed (Dorset sheep) by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). Only the products amplified by primers 2-1 and 2-2 displayed polymorphisms. For primer 2-1, three genotypes (AA, AB and BB) were detected in both sheep breeds. Sequencing revealed one silent mutation (G477A) in exon 2 of GDF9 gene in the BB genotype in comparison with the AA, which was known as G3 mutation of GDF9 gene in Belclare and Cambridge ewes. The relationship of least squares means for litter size was AA > AB > BB in Small Tail Han sheep (P > 0.05). For primer 2-2, two genotypes (CC and CD) were detected in both sheep breeds. Sequencing revealed one novel single nucleotide mutation (G729T) in exon 2 of GDF9 gene in the CD genotype in comparison with the CC, which resulted in an amino acid change (Gln243His). The ewes with mutation heterozygous genotype CD had 0.77 (P < 0.01) lambs more than those with wild type CC in Small Tail Han sheep. These results preliminarily indicated that allele D of GDF9 gene was a potential genetic marker for improving litter size in Small Tail Han sheep.

Polymorphisms of caprine GDF9 gene and their association with litter size in Jining Grey goats

The exons 1, 2 and flanking region of growth differentiation factor 9 (GDF9) gene in five randomly selected does of Jining Grey, Boer and Liaoning Cashmere goats were amplified and analyzed. Thirteen nucleotide differences were identified in GDF9 gene between sheep (AF078545) and goats. Four SNPs (G3288A in intron 1, G423A, A959C [Gln320Pro] and G1189A [Val397Ile] in exon 2) were detected in four goat breeds with different prolificacy, in which G3288A was a new SNP in goats. The results showed that loci 3288, 423 and 1189 in Boer goats, loci 3288 and 423 in Guizhou White goats, loci 423 and 1189 in Liaoning Cashmere goats were all in complete linkage disequilibrium (D' = 1, r (2) = 1), respectively. In moderate (Boer goat) and low prolificacy (Liaoning Cashmere goat) breeds, linkage analysis indicated that there were more fervent linkage disequilibrium among loci 3288, 423 and 1189 than high prolificacy (Jining Grey and Guizhou White goats) breeds. For the 959 locus, the genotype distribution showed obvious difference between high prolificacy breeds and moderate or low prolificacy breeds (P < 0.05 or P < 0.01). The Jining Grey goat does with genotype CC or AC had 0.81 (P < 0.01) or 0.63 (P < 0.01) kids more than those with genotype AA, respectively. The present study preliminarily showed an association between allele C at 959 locus of GDF9 gene and high litter size in Jining Grey goats. These results provide further evidence that the GDF9 gene may be significantly correlated with high prolificacy in goats.