Association between expression of reproductive seasonality and alleles of the gene for Mel(1a) receptor in the ewe

To determine whether a link exists between reproductive seasonality and the structure of the gene for melatonin receptor Mel(1a), the latter was studi ed in two groups of Merinos d'Arles (MA) ewes previously chosen for their g enetic value, which took into account their own out-of-season ovulatory act ivity adjusted by environmental parameters and that of their relatives. The genomic DNA of 36 ewes found regularly cycling in spring (group H) and tha t of 35 ewes never cycling in spring (group L) during the 2-3 yr before the present study was prepared, and the cDNA corresponding to almost all exon II was amplified and checked for the presence of Mnll restriction sites. Th e presence (+) or absence (-) of an Mnll site at position 605 led to genoty pes "++", "+-", and "--", whose frequencies differed significantly (P < 0.0 01) between the H and L groups: 52.8%, 47.2%, and 0% vs. 28.5%, 42.9%, and 28.5%, respectively. Sequencing of exon II cDNA in group L ewes with genoty pe -- showed the presence of only one allele - with 4 mutations, while that in ewes with genotype ++ showed different types of alleles unrelated to th e H or L groups. These + alleles exhibited a combination of 1 to 7 of the 8 mutations recorded in the part of exon Il studied. The genotyping of 29 ew es from the more seasonal Ile-de-France breed indicated that 38% of animals had a -- genotype and exhibited the same mutations as in the MA ewes. Fina lly, a comparison of I-125-melatonin binding to membrane preparations of pa rs tuberalis showed a lower number of binding sites (P < 0.0005) in MA ewes with genotype ++ than in those with genotype -- (43.2 +/- 4.4 vs. 75.4 +/- 8.4 fmol/mg protein in genotype ++ and genotype --, respectively). In conc lusion, the data show an association between genotype -- for site Mnll at p osition 605 and seasonal anovulatory activity in MA ewes.