Association Between Expression of Reproductive Seasonality and Alleles of the Gene for Mel1a Receptor in the Ewe

To determine whether a link exists between reproductive sea- sonality and the structure of the gene for melatonin receptor Mel1a, the latter was studied in two groups of Merinos d'Arles (MA) ewes previously chosen for their genetic value, which took into account their own out-of-season ovulatory activity adjusted by environmental parameters and that of their relatives. The ge- nomic DNA of 36 ewes found regularly cycling in spring (group H) and that 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 MnlI restriction sites. The presence (1 )o r absence (2 )o f anMnlI site at position 605 led to genotypes ''11'', ''12'', and ''22'', whose frequencies differed signifi- cantly (P , 0.001) 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 genotype 22 showed the presence of only one allele 2 with 4 mutations, while that in ewes with genotype 11 showed different types of alleles un- related to the H or L groups. These 1 alleles exhibited a com- bination of 1 to 7 of the 8 mutations recorded in the part of exon II studied. The genotyping of 29 ewes from the more sea- sonal Ile-de-France breed indicated that 38% of animals had a 22 genotype and exhibited the same mutations as in the MA ewes. Finally, a comparison of 125 I-melatonin binding to mem- brane preparations of pars tuberalis showed a lower number of binding sites (P , 0.0005) in MA ewes with genotype 11 than in those with genotype 22 (43.2 6 4.4 vs. 75.4 6 8.4 fmol/mg protein in genotype 11 and genotype 22, respectively). In conclusion, the data show an association between geno- type 22 for site MnlI at position 605 and seasonal anovulatory activity in MA ewes.