Fine mapping of the FecL locus influencing prolificacy in Lacaune sheep

In the Lacaune sheep population, two major loci influencing ovulation rate are segregating: FecX and FecL. The FecX(L) mutation is a non-conservative substitution (p.Cys53Tyr) in BMP15 that prevents the processing of the protein. Using a statistical approach, FecL has been shown to be an autosomal major gene. A full genome scan localized the FecL locus on sheep chromosome 11. Fine mapping reduced the interval containing FecL to markers BM17132 and FAM117A, corresponding to a synteny block of 1.1 megabases on human chromosome 17, which encompasses 20 genes. The expression of 16 genes from this interval was observed in tissues of the reproductive axis, but expression was not affected in homozygous FecL(L) females. In this interval, a unique haplotype was associated with the FecL(L) mutation. This particular haplotype could be predicted by the DLX3:c.*803A>G SNP in the 3' UTR sequence of the DLX3 gene. This SNP provided accurate classification of animals (99.5%) as carriers or non-carriers of the mutation and therefore maybe useful in marker assisted selection. A synergistic action of FecL(L) and FecX(L) mutations on both ovulation rate and litter size was demonstrated. Until now, all the Fec genes identified in sheep belong to the bone morphogenetic protein (BMP) system. Based on the human orthologous region, none of the 20 genes in the FecL region corresponds to known molecules in the BMP system. The identification of the FecL(L) mutation could lead to the discovery of a new pathway involved in the regulation of ovulation rate.