PHENOTYPIC VARIATIONS AMONG PATERNAL CENTROSOMES EXPRESSED WITHIN THEZYGOTE 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 microtu bule organization during bovine fertilization. Immunocytochemistry usi ng tubulin antibodies quantitated with confocal microscopy was used to measure the diameter of the sperm aster and assign a score (0-3) base d on the degree of radial organization (0, least organized; 3, most or ganized). Three bulls (A-C) were chosen based on varying fertility (A, lowest fertility; C, highest fertility) as assessed by nonreturn to e strus after artificial insemination and in vitro embryonic development to the blastocyst stage. The results indicate a statistically signifi cant bull-dependent difference in diameter of the sperm aster and in t he organization of the sperm astral microtubules. Insemination from bu ll 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 insem inations 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 r adial organization of the sperm aster was also bull-dependent. Sperm a sters organized by bull A-derived sperm had an average quality score o f 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 w ith bulls B and C were also significantly different (P less than or eq ual to 0.025). These results indicate that the paternally derived port ion of the centrosome varies among males and that this variation affec ts male fertility, the outcome of early development, and, therefore, r eproductive success.