Association Between Novel Variants In BMPR1B Gene And Litter Size In Mongolia And Ujimqin Sheep Breeds

Promoting litter size of sheep is an important aim in livestock breeding.The identification of fecundity-related functional candidate genes and molecular genetic markers has always been the study focus of researchers in the world.Mongolia and Ujimqin sheep breeds are excellent local sheep breeds and valuable livestock genetic resources in China.They are resistant to low temperature,resistant of crude feed,fast fat and produce quality meat.However,due to their low prolificacy,such as seasonal estrus and almost single ovulation,the development of modern grassland animal husbandry in Inner Mongolia was limited.With the rapid development of molecular biotechnology and the wide application of molecular marker assisted selection(MAS)technology,it is possible to rapidly improve the fecundity of Mongolia and Ujimqin sheep breeds by identifying the functional candidate genes and their molecular markers related to the fecundity in Mongolia and Ujimqin sheep breeds.Bone morphogenetic protein receptor 1B(BMPR1B)is a member of the transforming growth factor β(transforming growth factor beta,TGF-β)receptor family,which can affect the differentiation of ovarian granulosa cells and the maturation of follicles in female animals,and then affect the litter size in sheep.A large number of studies have shown that the Fec B mutation site of BMPR1 B,which cause amino acid changes(Q249R)in the highly conserved intracellular kinase signaling domain of BMPR1 B exon 6,plays an important role in improving ovulation rate and litter size in sheep.However,there were few studies on the relationship between BMPR1 B gene and litter size of Mongolia and Ujimqin sheep breeds.Therefore,the aim of this study is to identify the breed-specific mutation of BMPR1 B gene in Mongolia and Ujimqin sheep breeds,and analyze the association between the mutation and the litter size of Mongolia and Ujimqin sheep breeds,and then finally investigate the useful molecular markers associated with fecundity in Mongolia and Ujimqin sheep breeds.In this study,six Mongolia sheep and six Ujimqin sheep were directly sequenced,and the single nucleotide polymorphisms(SNPs)were identified.Then 250 Mongolia and 166 Ujimqin sheep breeds were genotyped by Mass ARRAY technology.The associations between the novel SNPs of BMPR1 B gene and the litter size of Mongolia and Ujimqin sheep breeds were analyzed,as well as the genetic diversity linkage disequilibrium and haplotype were analyzed.In addition,the m RNA secondary structure,amino acid sequence characteristics,protein secondary structure and tertiary structure of BMPR1 B gene were analyzed by bioinformatics.The results showed that:(1)The sequence analysis revealed ten novel variants in the BMPR1 B gene in Mongolia and Ujimqin sheep breeds.Among them the g.29346567C>T and g.29346564A>G are in the intron 1,the g.29334643T>A and g.29334435G>A are in the intron 2,the g.29324039C>T is in the intron 3,the g.29323530G>A in the intron 4,the c.594C>T(R198R)and c.597C>T(T199T)are in the exon 6,the c.1113T>G(R371R)is in the exon 8,and the c.1470G>T(T490T)SNP is in the region of exon 10 of BMPR1B gene.(2)In Mongolia and Ujimqin sheep breeds,there were no significant departures at the 5% level detected by any test for each mutation in Mongolia and Ujimqin sheep breeds.The association analysis between ten SNP and the litter size of Mongolia and Ujimqin sheep breeds showed that g.29346567C>T and c.1470G>T were significantly associated with the litter size of Mongolia sheep(P < 0.05 and P < 0.01,respectively),while the litter size of Ujimqin sheep was not associated with each of ten SNP.Linkage disequilibrium results showed that there was strong linkage between g.29323530G>A and g.29324039C>T in Mongolia and Ujimqin sheep breeds.Haplotype results showed that there was no significant difference between haplotype combination and litter size in Mongolia and Ujimqin sheep breeds.(3)Bioinformatics analysis of BMPR1 B gene showed that the total number of atoms of sheep BMPR1 B protein was 7971,the relative molecular weight was56907.45 Da.The whole peptide chain was hydrophobic and had no signal peptide sequence,which was not a secreted protein.There is a transmembrane structure and a Pfam: Activin＿recp,GS and S-TKc domain respectively,the c.594C>T and the c.597C>T were located in the conserved GS domain,while the c.1113T>G and the c.1470G>T were located in S-TKc domain.It was predicted 56 phosphorylation sites and 1 N-glycosylation site.Random curl of protein secondary structure accounted for the most.The c.1470G>T mutation was predicted to change the stability of the m RNA secondary structure by reducing the minimum free energy and was predicted to change the m RNA secondary structure of BMPR1 B gene.In conclusion,the g.29346567C>T and c.1470G>T SNPs of BMPR1 B gene may be potential molecular markers for improving the litter size of Mongolia sheep.In addition,the c.1470G>T mutation could also affect the secondary structure and stability of m RNA of BMPR1 B gene by reducing minimum free energy.Thus,these results are effective molecular markers for improving the fecundity of Mongolia sheep and provide scientific basis for genetic improvement of Mongolia sheep.