Association of Osteopontin Gene Promoter Single Nucleotide Polymorphisms with Bull Semen Quality

Abstract

Osteopontin (OPN) is a protein found at higher concentrations in the seminal plasma of bulls with above average fertility. Polymorphisms have been reported within the OPN gene promoter that can affect production of this protein and thus, affect fertility. Therefore, Angus (n = 5) and Angus x Gelbvieh (Balancer, n = 14) and Angus x Brahman (n = 15) bulls were evaluated for presence of single nucleotide polymorphisms (SNP) in the Bos taurus OPN gene (GenBank: AY878328.1) promoter region, and their possible effects on bull semen quality as evaluated by computer-assisted semen analysis (CASA). Semen was collected by electroejaculation 6 to 9 times from each bull, and each semen collection was evaluated by CASA for motile, progressive and rapid sperm within 5 mins of ejaculation. The bulls were genotyped for reported single nucleotide polymorphisms (SNP) in the promoter region of the OPN gene through amplification of two 700 base pair (bp) DNA fragments and sequencing of the resulting PCR products. Seven SNP sites were identified, at bp 3379, 3490, 3492, 5075, 5205, 5209, and 5263 of the OPN gene. The SNP identified at bp 5205, 5209 and 5263 had not been previously reported. Individual SNP sites were evaluated as the main effect on CASA sperm motility variables in a SAS MIXED model for repeated measures. A thymine to guanine substitution at bp 3379 was associated with increased (P ≤ 0.02) percentage of motile, progressive and rapid sperm in Angus x Brahman bulls, and tended (P ≤ 0.10) to increase the same sperm motility parameters in Angus, and Angus x Gelbvieh bulls. The percentages of motile, progressive and rapid sperm were similar (P ≥ 0.05) among genotypes for the other 6 SNP identified. These results suggest that identification and genotyping of polymorphisms within the promoter region of the bovine OPN gene may be useful for selecting bulls with improved sperm motility parameters.