| Melatonin regulates the circadian rhythm and reproductive seasonality of mammals with seasonal reproductive activity, and the melatonin receptor 1A (MTNRIA) is one of the necessary receptors exhibiting the biological function of melatonin. In this research, the exon 2 of MTNRIA gene was amplified and a uniform fragment of 824 bp was obtained in 499 ewes and dose including non-seasonal and seasonal estrous breeds of sheep and goats, and the 824 bp PCR products were detected by RFLP using the restriction endonucleases Mnl I and Rsa I. The PCR products from animals with different genotypes were furtherly cloned and sequenced. The sequences were compared between dominant and necessive genotypes and between sheep breeds with non-seasonal and seasonal estrus respectively. The relation between the marker genotypes and reproductive seasonality of different breeds of sheep and goats, and the association between the marker genotypes and litter size of Small Tail Han Sheep were analysed. The results indicated that:(1) For the Mnl I cleavage sites, three genotypes (MM, Mm, mm) were detected. Frequency of MM genotype in non-seasonal estrous sheep breeds was obviously higher, while those of mm genotype obviously lower than the that in seasonal estrous breeds. Only MM genotype was detected in six goat breeds.(2) For the Rsa I cleavage sites, four genotypes (RR, Rr, Rr, rr) were detected in sheep and goat breeds. Frequency of RR genotype in non-seasonal estrous sheep breeds was significantly higher than that in seasonal estrous breeds. Similar results were also obtained in goats.(3) For the Mnl I and Rsa I cleavage sites, the genotype distribution of Small Tail Han sheep was significantly different from that of the seasonal estrous sheep breeds, and those of Jining Grey goats was also different from that of the seasonal estrous goat breeds.(4) Through cloning and sequencing, 5 nucleotide mutations were found in Small Tail Han sheep, and only one of them resulted in the change of amino acid. One mutation was found in Jining Grey goats, and it was a silence mutation. In addition, the sequence difference of MTNRIA gene exon 2 between Small Tail Han sheep with non-seasonal estros and Dorset sheep with seasonal estros was found in five nucleotides and three amino acids.(5) The differences of litter size of ewes with different marker genotypes in Small Tail Han sheep were analysed by analysis of variance using least squares method. The results showed that MM and Mm genotypes were 0.58 (P<0.01) and 0.52 (P<0.01) higher than mm genotype respectively, RR and Rr genotypes 0.56 (P<0.01) and 0.51 (P<0.01) higher than rr genotype respectively. There was no difference among the combinational genotypes of Mnl I and Rsa I cleavage sites, but at least, the litter size of ewes taken one copy of M was slightly higher than those of ewes taken no M copy.All analyses can be concluded that MM and RR genotypes in sheep and RR genotype in goats were associaled with non-seasonal estrous, and mm and rr genotypes in sheep and Rr in goats associaled with seasonal estrous. |
