Abnormal centriolar biomarker ratios correlate with unexplained bull artificial insemination subfertility: a pilot study.

The mechanisms underlying male infertility are poorly understood. Most mammalian spermatozoa have two centrioles: the typical barrel-shaped proximal centriole (PC) and the atypical fan-like distal centriole (DC) connected to the axoneme (Ax). These structures are essential for fertility. However, the relationship between centriole quality and subfertility (reduced fertility) is not well established. Here, we tested the hypothesis that assessing sperm centriole quality can identify cattle subfertility. By comparing sperm from 25 fertile and 6 subfertile bulls, all with normal semen analyses, we found that unexplained subfertility and lower sire conception rates (pregnancy rate from artificial insemination in cattle) correlate with abnormal centriolar biomarker distribution. Fluorescence-based Ratiometric Analysis of Sperm Centrioles (FRAC) found only four fertile bulls (4/25, 16%) had positive FRAC tests (having one or more mean FRAC ratios outside of the distribution range in a group's high-quality sperm population), whereas all of the subfertile bulls (6/6, 100%) had positive FRAC tests (P = 0.00008). The most sensitive biomarker was acetylated tubulin, which had a novel labeling pattern between the DC and Ax. These data suggest that FRAC and acetylated tubulin labeling can identify bull subfertility that remains undetected by current methods and may provide insight into a novel mechanism of subfertility.