Association Between Novel Polymorphisms In BMP15 Gene And Litter Size In Mongolia And Ujimqin Sheep Breeds

Litter size is one of the important economic traits of sheep,which affects the production efficiency of mutton sheep industry.Many sheep breeds are single birth and low fertility in Inner Mongolia,which limit the rapid development of grassland animal husbandry.Therefore,the identification of fecundity-related candidate gene and mutation in Mongolia and Ujimqin sheep breeds,and utilization of marker-assisted selection(MAS)technology for increasing the fecundity of Mongolia and Ujimqin sheep breeds,are very important aims of the development of Mongolia sheep industry in Inner Mongolia.BMP15 gene is one of the key candidate gene affecting the litter size of sheep,which plays an important role in regulating the growth and development of follicles and oocytes,and the process of ovulation.Multiple polymorphic mutations of BMP15 gene could significantly affect the ovulation rate and litter size in different sheep breeds,showing high breed specificity.In order to analyze the association of mutations in BMP15 gene with litter size in Mongolia and Ujimqin Sheep breeds,in this study,we selected six samples of each of Mongolia and Ujimqin Sheep breeds for direct sequencing to identify breed-specific mutations.A total of 684 sheep were genotyped by Mass ARRAY technology,including250 Mongolia sheep,168 Sonid sheep,116 Ujimqin sheep,30 Tan sheep,30 Hu sheep,30 Small-tailed Han sheep,30 Suffolk sheep and 30 Dorper sheep,and then the associations between mutations and litter size of Mongolia sheep and Ujimqin sheep were analyzed.Genetic diversity of mutations was also analyzed.In addition,the DNA promoter methylation of BMP15 gene,the physicochemical properties,glycosylation sites,phosphorylation sites and three-dimensional structure of BMP15 protein were predicted by bioinformatics.The results showed that:(1)16 mutations were found in the BMP15 gene of Mongolia sheep and Ujimqin sheep,including 3 known mutations and 13 novel mutations.Among them,c.-2016G>A,c.-1760C>A,c.-1145G>A and c.-1491C>T mutations are located in 5’ untranslated region,c.755T>C and c.1047G>A mutations are in exon 1,c.33-31 del CTT polymorphic site in exon 2,g.50985975G>A,g.50984457T>C,g.50986052C>A,g.50983595A>C,g.50984265G>T,g.50984771G>A,g.50985473C>A,g.50986336G>A and g.50981349T>C mutations are in intron of BMP15 gene.(2)Genetic diversity analysis showed that: in this experimental sheep populations,there were no significant departures at the 5% level detected by any test for eight mutations in Mongolia and Ujimqin sheep breeds,including c.-2016G>A,c.-1760C>A,c.-1145G>A,c.33-31 del CTT,c.755T>C,g.50985975G>A,g.50984457T>C and g.50986052C>A mutations.(3)The linkage disequilibrium analysis showed that: the c.755T>C and g.50985975G>A single nucleotide polymorphism(SNP)have strong linkage disequilibrium;Association analysis showed that: the c.-1145G>A SNP was significantly associated with litter size in Mongolia Sheep(P < 0.01),the c.755T>C SNP was significantly associated with litter size in Mongolia Sheep(P < 0.05).(4)Bioinformatics prediction results show that: the c.755T>C mutation had no effect on the physicochemical properties,glycosylation sites and phosphorylation sites of BMP15 protein,and could have an effect on the three-dimensional structure of BMP15 protein.In addition,different alleles at the c.1145G>A SNP in promoter region of BMP15 gene might form different transcription factor binding motifs.In conclusion,the c.-1145G>A and c.755T>C mutations were significantly associated with litter size of Mongolia Sheep.These results could provide scientific and effective molecular markers for improving the litter size in Mongolia sheep breed,and could provide scientific clues for function analysis of BMP15 gene.