Evidence for Positive Selection of Taurine Genes within a QTL Region on Chromosome X Associated with Testicular Size in Australian Brahman Cattle

This study builds upon previous GWAS findings that identified two QTL on the X chromosome strongly associated with scrotal circumference (SC) in two Bos indicus-influenced breeds: Brahman and Tropical Composites. This trait is favourably correlated with a number of other reproductive traits in both males and females. Both of these QTL spanned large areas under which a significant number of potential candidate genes were mapped.

Using genomics data from 16 Brahman bulls previously sequenced as part of the Beef CRC project, a bioinformatic approach was undertaken to identify novel non-synonymous SNP within the QTL regions of interest in Brahman cattle. We then performed further association studies with these novel SNP and investigated a subset of candidate genes in both breeds. A standout candidate gene was identified, namely Testis-expressed gene 11 (Tex11) which was associated with SC (P < 0.001) and percentage of normal sperm cells (P < 0.05) in both breeds.

Further evidence for a biological role of Tex11 in reproductive performance was obtained in genomic examioination of taurine versus indicine content. Relative to the remainder of the genome, SNP within the Tex11 gene form a haplotype segment of Bos taurus origin that is retained within cattle with greatest reproductive potential in both Brahman and Tropical Composites.