Single-Nucleotide Polymorphisms in the LEPR Gene Are Associated with Divergent Phenotypes for Age at Onset of Puberty in Davisdale Ewes1

Abstract

Attainment of puberty is a key developmental event influenced by genetic and environmental factors. In examining age at attainment of puberty, we observed closely related rams from the Davisdale line whose daughters differed in age at which they attained puberty. A candidate gene approach was used to identify mutations that may underlie these observed differences. Four rams with divergent phenotypes for their daughter's age at onset of puberty were selected for whole-genome sequencing. The coding regions of genes with known roles in regulating reproductive function were searched for single-nucleotide polymorphisms (SNPs) that altered the amino acid sequence of the protein. Of interest were three SNPs in the leptin receptor gene (LEPR). A Sequenom assay was developed to determine the genotype of these SNPs in daughters of 17 sons of a founding sire. A higher percentage of ewe lambs homozygous for the LEPR mutations failed to undergo puberty before 1 yr of age, and those that did undergo puberty during the first breeding season on average were approximately 17 days older than homozygous wild-type ewes. Heterozygous ewes were intermediate for both measurements. Given the predicted change in protein function produced by the mutation in LEPR and the strong associations between the genotype and onset of puberty phenotypes, we propose that this mutation in LEPR underlies the observed difference in age at onset of puberty in the Davisdale line. Furthermore, these animals will likely provide a useful model to better understand the role of leptin in the regulation of puberty.

Mutations in the leptin receptor gene associated with delayed onset of puberty are also associated with decreased ovulation and lambing rates in prolific Davisdale sheep

“…A second group of unrelated commercial ewes (n ¼ 587) were also studied to provide additional validation of the associations between the SNPs and observed reproductive phenotypes. Genotypes for the LEPR SNPs were determined as previously described (Haldar et al 2014) using a Sequenom MassARRAY platform (Sequenom Inc., San Diego, CA, USA). All ewes were pasture-fed with free access to water.…”

“…Evidence for a major gene affecting ovulation rate (fecundity Davisdale, FECD) has been reported for this flock and preliminary evidence for a major gene that affects embryo-fetal survival has also been reported (Juengel et al 2012). Recently we identified mutations in the leptin receptor (LEPR) gene in the Davisdale line of prolific sheep that were strongly associated with a delay in attainment of puberty and increased weight and body-condition score at 18 months of age (Haldar et al 2014).…”

“…Three different mutations in the coding region of LEPR predicted to result in changes to amino acids in the protein were observed (Haldar et al 2014). The first mutation (single nucleotide polymorphisms (SNP) A, C to T, chromosome 1: 40787726) affects the extracellular region, changing amino acid 62 from Arg to Cys.…”

“…The first mutation (single nucleotide polymorphisms (SNP) A, C to T, chromosome 1: 40787726) affects the extracellular region, changing amino acid 62 from Arg to Cys. The other two mutations are in the intracellular region, changing amino acid 1019 from Pro to Ser (SNP B, C to T, chromosome 1: 40857869) and amino acid 1069 from Lys to Glu (SNP C, A to G, chromosome 1: 40858019; Haldar et al 2014). The two mutations affecting amino acids in the intracellular region of the protein were completely linked, with the haplotype C-A observed in wild-type animals and T-G in animals with the mutation.…”

“…The effects of the changes in the amino acids on LEPR function have not been empirically examined at this time. However, based on the amino acid change, the mutation in the extracellular region of the protein is predicted to have a more severe effect than those in the intracellular region (Haldar et al 2014).…”