Association between expression of reproductive seasonality and alleles of melatonin receptor 1A in goats

To determine whether a link exists between reproductive seasonality and the structure of the melatonin receptor 1A (MTNR1A) gene, the latter was studied in year-round estrous breeds (Jining Grey and Boer goats) and seasonal estrous breeds (Liaoning Cashmere, Inner Mongolia Cashmere, Wendeng milk and Beijing native goats). A large fragment of exon 2 of MTNR1A gene was amplified by PCR using sheep sense and antisense primers in 260 does of six breeds. The uniform 824 bp PCR product was digested with restriction endonucleases MnII and RsaI, and checked for the presence of restriction sites. No polymorphism at the MnII cleavage sites was detected in all six goat breeds and no relationship could be established between the MnII cleavage sites of MTNR1A gene and reproductive seasonality in goats. For polymorphic RsaI cleavage site at base position 53, only genotype RR (267 bp/267 bp) was detected in Jining Grey goats, both genotype RR and genotype Rr (267 bp/320 bp) were found in all other goat breeds, no genotype rr (320 bp/320 bp) was detected in all six goat breeds. Frequency of genotype RR was obviously higher, and frequency of genotype Rr was obviously lower in year-round estrous goat breeds than in seasonal estrous goat breeds. Sequencing revealed one mutation (G52A) in genotype Rr compared with genotype RR. For polymorphic RsaI cleavage site, the differences of genotype distributions were significant (P < 0.05) between year-round estrous goat breeds and seasonal estrous goat breeds. These results preliminarily showed an association between genotype RR and year-round estrus in goats, and an association between genotype Rr and seasonal estrus in goats.