A dual targeted β-defensin and exome sequencing approach to identify, validate and functionally characterise genes associated with bull fertility

Abstract

Bovine fertility remains a critical issue underpinning the sustainability of the agricultural sector. Phenotypic records collected on >7,000 bulls used in artificial insemination (AI) were used to identify 160 reliable and divergently fertile bulls for a dual strategy of targeted sequencing (TS) of fertility-related β-defensin genes and whole exome sequencing (WES). A haplotype spanning multiple β-defensin genes and containing 94 SNPs was significantly associated with fertility and functional analysis confirmed that sperm from bulls possessing the haplotype showed significantly enhanced binding to oviductal epithelium. WES of all exons in the genome in 24 bulls of high and low fertility identified 484 additional SNPs significantly associated with fertility. After validation, the most significantly associated SNP was located in the FOXJ3 gene, a transcription factor which regulates sperm function in mice. This study represents the first comprehensive characterisation of genetic variation in bovine β-defensin genes and functional analysis supports a role for β-defensins in regulating bull sperm function. This first application of WES in AI bulls with divergent fertility phenotypes has identified a novel role for the transcription factor FOXJ3 in the regulation of bull fertility. Validated genetic variants associated with bull fertility could prove useful for improving reproductive outcomes in cattle.

Selection for bull fertility: a review

“…Beyond standard genomic prediction, there is an additional desire to better understand the underlying biology of male fertility. While utilizing this technology to identify genes in the cattle industry is rare, a few examples include utilizing dual targeted β-defensin and exome sequencing to identify bull fertility genes in the dairy industry ( Whiston et al, 2017 ; Lyons et al, 2018 ). Genes identified have been found to be involved with spermatogenesis ( Whiston et al, 2017 ) and sperm binding ( Lyons et al, 2018 ).…”

Whole-genome scan reveals significant non-additive effects for sire conception rate in Holstein cattle

“…Selective breeding is one strategy for improving bull fertility. Indeed, recent studies have identified and evaluated potential fertility-related biomarkers that could be used to select high fertility bulls [ 16 , 17 , 27 ]. It should be recognized that gene mapping studies have primarily focused on genetic variants with additive effects, whereas the role of non-additive effects has been largely overlooked.…”

“…For instance, using a comparative genomic approach, two conserved spermatogenesis genes, MAP1B and PPP1R11 , were implicated in male fertility in Holsteins [ 12 ]. A recent study has identified novel genetic variants in both β-defensin and FOXJ3 genes related to bull sperm function [ 16 ]. Our group have identified regions in BTA21 and BTA25 strongly associated with service sire fertility in US Holstein bulls [ 17 ].…”

Review: Understanding the causes of variation in reproductive wastage among bulls

“…Beta-defensin 126 increases the net negative charge on sperm (Tollner et al, 2012), increases sperm motility, mucus penetration in vitro (Fernandez-Fuertes et al, 2016) as well as sperm binding to oviductal epithelium in vitro (Lyons et al, 2018). We have also recently characterised the genetic variation in bovine β-defensin genes as well as completing the first whole-exome sequencing of AI bulls of divergent fertility (Whiston et al, 2017). This dual approach successfully identified novel variants in both beta-defensin and FOXJ3 genes as potentially regulating SCR through differential oviductal binding ability, as assessed in vitro (Whiston et al, 2017).…”

“…We have also recently characterised the genetic variation in bovine β-defensin genes as well as completing the first whole-exome sequencing of AI bulls of divergent fertility (Whiston et al, 2017). This dual approach successfully identified novel variants in both beta-defensin and FOXJ3 genes as potentially regulating SCR through differential oviductal binding ability, as assessed in vitro (Whiston et al, 2017). Using a microarray-based approach, Legare et al (2017) characterised the expression of genes along the caput, corpus and cauda epididymis in bulls which differed in SCR.…”