Abstract

BackgroundImpaired fertility in cattle limits the efficiency of livestock production systems. Unraveling the genetic architecture of fertility traits would facilitate their improvement by selection. In this study, we characterized SNP chip haplotypes at QTL blocks then used whole-genome sequencing to fine map genomic regions associated with reproduction in a population of Nellore (Bos indicus) heifers.MethodsThe dataset comprised of 1337 heifers genotyped using a GeneSeek® Genomic Profiler panel (74677 SNPs), representing the daughters from 78 sires. After performing marker quality control, 64800 SNPs were retained. Haplotypes carried by each sire at six previously identified QTL on BTAs 5, 14 and 18 for heifer pregnancy and BTAs 8, 11 and 22 for antral follicle count were constructed using findhap software. The significance of the contrasts between the effects of every two paternally-inherited haplotype alleles were used to identify sires that were heterozygous at each QTL. Whole-genome sequencing data localized to the haplotypes from six sires and 20 other ancestors were used to identify sequence variants that were concordant with the haplotype contrasts. Enrichment analyses were applied to these variants using KEGG and MeSH libraries.ResultsA total of six (BTA 5), six (BTA 14) and five (BTA 18) sires were heterozygous for heifer pregnancy QTL whereas six (BTA 8), fourteen (BTA 11), and five (BTA 22) sires were heterozygous for number of antral follicles’ QTL. Due to inadequate representation of many haplotype alleles in the sequenced animals, fine mapping analysis could only be reliably performed for the QTL on BTA 5 and 14, which had 641 and 3733 concordant candidate sequence variants, respectively. The KEGG “Circadian rhythm” and “Neurotrophin signaling pathway” were significantly associated with the genes in the QTL on BTA 5 whereas 32 MeSH terms were associated with the QTL on BTA 14. Among the concordant sequence variants, 0.2% and 0.3% were classified as missense variants for BTAs 5 and 14, respectively, highlighting the genes MTERF2, RTMB, ENSBTAG00000037306 (miRNA), ENSBTAG00000040351, PRKDC, and RGS20. The potential causal mutations found in the present study were associated with biological processes such as oocyte maturation, embryo development, placenta development and response to reproductive hormones.ConclusionsThe identification of heterozygous sires by positionally phasing SNP chip data and contrasting haplotype effects for previously detected QTL can be used for fine mapping to identify potential causal mutations and candidate genes. Genomic variants on genes MTERF2, RTBC, miRNA ENSBTAG00000037306, ENSBTAG00000040351, PRKDC, and RGS20, which are known to have influence on reproductive biological processes, were detected.

Highlights

  • Impaired fertility in cattle limits the efficiency of livestock production systems

  • The identification of heterozygous sires by positionally phasing Single nucleotide polymorphism (SNP) chip data and contrasting haplotype effects for previously detected Quantitative trait loci (QTL) can be used for fine mapping to identify potential causal mutations and candidate genes

  • The 1337 heifers were genotyped on a GeneSeek® genomic profiler (GGP) Bos indicus High density (HD) array (74677 SNPs), which is a subset of the 777962 SNPs from the Illumina® BovineHD BeadChip, chosen for being informative in Bos indicus cattle

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Summary

Introduction

Impaired fertility in cattle limits the efficiency of livestock production systems. Unraveling the genetic architecture of fertility traits would facilitate their improvement by selection. Fertility is a major determinant of female reproductive efficiency, in Zebu (Bos indicus) cattle, where heifers take longer to reach puberty compared to Taurine (Bos taurus) animals [1, 2]. Advances in genomic technologies have led to the identification of thousands of DNA markers (single nucleotide polymorphisms – SNPs) spread across the genome, which can be rapidly and inexpensively genotyped [6]. Such SNP information is commonly reported as unphased genotypes, which means that it is not immediately apparent which heterozygous allele was paternally or maternally inherited. Fine mapping of haplotypes that span QTL regions can be performed to detect possible causative mutations on traits of interest [7]

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