Phenotypic variations among paternal centrosomes expressed within the zygote as disparate microtubule lengths and sperm aster organization: Correlations between centrosome activity and developmental success

This study describes a paternal effect on sperm aster size and microtubule organization during bovine fertilization. Immunocytochemistry using tubulin antibodies quantitated with confocal microscopy was used to measure the diameter of the sperm aster and assign a score (0-3) based on the degree of radial organization (0, least organized; 3, most organized). Three bulls (A-C) were chosen based on varying fertility (A, lowest fertility; C, highest fertility) as assessed by nonreturn to estrus after artificial insemination and in vitro embryonic development to the blastocyst stage. The results indicate a statistically significant bull-dependent difference in diameter of the sperm aster and in the organization of the sperm astral microtubules. Insemination from bull A resulted in an average sperm aster diameter of 101.4 mu m (76.3% of oocyte diameter). This significantly differs (P less than or equal to 0.0001) from the average sperm aster diameters produced after inseminations from bull B (78.2 mu m; 60.8%) or bull C (77.9 mu m; 57.8%), which themselves displayed no significant differences. The degree of radial organization of the sperm aster was also bull-dependent. Sperm asters organized by bull A-derived sperm had an average quality score of 1.8, which was higher than that of bull B (1.4; P less than or equal to 0.0005) or bull C (1.2; P less than or equal to 0.0001). Results with bulls B and C were also significantly different (P less than or equal to 0.025). These results indicate that the paternally derived portion of the centrosome varies among males and that this variation affects male fertility, the outcome of early development, and, therefore, reproductive success.