Functional States of Sperm-Derived Centrioles in Androgenetic Sheep Embryos

Centrioles are essential regulators of spindle organization and chromosome segregation during early embryonic development. In most mammals, the spermatozoon provides the functional centriole to the zygote, while the oocyte centriole is inactivated. Dispermic fertilization introduces two sperm-derived centrioles, frequently resulting in abnormal spindle assembly and defective cleavage. Interestingly, androgenetic embryos generated by fertilizing enucleated oocytes with two spermatozoa can still develop to the blastocyst stage, suggesting the existence of regulatory mechanisms controlling centriole activity. This study investigated sperm-derived centriole behaviour in ovine androgenetic embryos. Embryos were produced by injecting two spermatozoa into enucleated metaphase II oocytes followed by in vitro activation. IVF- and ICSI-derived embryos were used as controls. Centriole activity was assessed through α-tubulin immunofluorescence and confocal microscopy analysis of microtubule aster formation. Analysis performed 6–7 hours after activation revealed heterogeneous patterns of aster nucleation: two asters were detected in 24% of embryos, one aster in 43%, and no asters in 33%. Notably, the proportion of embryos displaying a single aster closely matched the cleavage rate (46%) observed in androgenetic embryos. These preliminary findings suggest that selective repression of one sperm-derived centriole may represent a prerequisite for developmental progression.