Polymorphism Of Lactation Related Genes In Three Horse Breeds And Its Correlation With Milk Yield In Yili Horse

Mare milk has the highest nutritional value in all kinds of dairy products,which is rich in vitamins and minerals,and the fat content is half as in milk with a degree of 1.5%,but mare milk yield is far less than milk.With the development of the tourism industry and people's living standard,the demand for mare milk is getting greater and greater.Therefore,it is necessary to strengthen the study on the genetic basis of horse lactation to lay the foundation for diary horse breeding.The lactation performance of horse is controlled by multiple genes.The PRL gene,PRL gene,POU1F1 gene,GH1 gene,GHR gene,LTF gene,ESR gene and the ABCG2 gene were all reported as candidate genes of the lactation performance in other livestock.At present,few reports of Chinese horse breeds about lactation related genes have been seen.In this experiment,337 horses in 3 Chinese domestic horse breeds(Yili horse,Mongolia horse,Guanzhong horse)were taken as research object,and jugular venous blood samples were collected to extract DNA.DNA mixed pool was used to amplify the exon sequences of the 9 lactation related genes.After detecting polymorphic sites in candidate genes by sequencing,PCR-RFLP technique was used to genotype the polymorphic sites,and correlation analysis of SNPs and Yili horse daily milk production was conducted.This experiment aimed at screening polymorphic sites associated with Chinese horse lactation performance,while at the same time providing identifiable ground of efficient Chinese dairy horse breeding and preservation,utilization of germplasm resources.The conclusions were as follows:1..10 SNPs(PRL c.210 C > T,PRL g.9115 T > G,PRL g.9119 C > A,PRL g.11090 A > G,PRLR g.145227 T > G,POU1F1 g.2758 T > C,GH1 c.22 A > C,GH1 g.1584 C > G,GHR g.-562 C > T,LTF c.172,G > A)were found in 9 lactation related genes of 3 Chinese horse breeds for the first time.Among these,3 sites(PRLR g.145227 T > G.GHR,g.-562 C > T,LTF c.172 G > A)were found only in Yili horse,while 4 sites(PRL g.9115 T > G,PRL g.11090 A > G,GH1 c.22 A > C,GH1 g.1584 C > G)were found only in Guanzhong horse.PRL g.9119 C > A site was found in both Mongolian horse and Guanzhong horse.2 SNP sites(PRL c.210 C > T,POU1F1 g.2758 T > C)were found in all three breeds.Of all 10 SNP sites,3 were in CDS region that cause missense mutations;1 was in promoter region,and the remaining 6 sites were found in introns.2.We used PCR-RFLP method to genotype SNPs found in Yili horse,then analyzed it with daily milk yield of 120 days.5 different SNPs were found and genotyped(PRL C > T c.210,PRLR g.145227 T > G,POU1F1 g.2758 T > C,GHR g.-562 C > T,LTF c.172 G > A),PRL c.210 C > T can induce PRL protein's seventieth amino acid changed from phenylalanine to leucine,LTF c.172 G > A can induce LTF protein's fifty-seventh amino acid changed from arginine to lysine.GHR g.-562 C > T site was in the promoter region of GHR gene,the other sites were located in introns.The correlation analysis showed that among the 5 SNP sites in different genes,only PRL c.210 C > T site showed a significant result with the daily milk yield while the other 4 SNP sites showed no difference.In the PRL c.210 C > T site,the daily milk yield of CC genotype was significantly higher than that of CT genotype,while CT genotype and TT genotypes were not significantly different in daily milk yield,suggesting that C allele may have positive genetic effect on Yili horse milk production traits.3.We explored the promoter activity region of equine PRL,PRLR gene using the dual luciferase reporter assay system.The results showed that the upstream-418 ~-1050 bp interval is the main active region of horse PRL gene,while within the upstream-418 ~-738 bp interval there exists the strong cis-acting element;equine PRLR gene promoter active region located in the upstream-702~-2399 bp interval,and between the-1546 ~-1798 bp there exists the strong cis-acting element.At present,few reports of Chinese horse breeds about lactation related genes have been seen.This study was a preliminary investigation on the SNPs in the CDS region of 9 lactation related genes in 3 Chinese horse breeds,with a correlation analysis between SNPs and daily milk yield in Yili horse.The active region of horse PRL and PRLR gene promoter was preliminarily explored.Our aim was to screen polymorphic sites associated with Chinese domestic horse lactation performance,while at the same time providing an identifiable ground of efficient Chinese dairy horse breeding and preservation,utilization of germplasm resources.