Biogenesis of the centrosome during mammalian gametogenesis and fertilization

Summary Mammalian gametogenesis results in the production of highly specialized cells, sperm and oocytes, that are complementary in their arsenal of organelles and molecules necessary for normal embryonic development. Consequently, some of the zygotic structures, as illustrated in this review on the centrosome, are a combination of complementary paternal and maternal contributions. Mammalian oocytes are deprived of their centrioles during oogenesis, yet at the same time they generate a huge cytoplasmic reserve of centrosomal proteins. The active centrosome of spermatogenic stem cells is reduced to a single centriole that does not possess microtubule-nucle-ating activity. This centrosomal activity is restored at fertilization, when the sperm centriole is released into the oocyte cytoplasm, from which it attracts the oocyte-derived proteins of pericentriolar material and ultimately converts itself into an active zygotic centrosome. Subsequently, the microtubules around the zygotic centrosome are organized into a radial array called the sperm aster, that guides the apposition of male and female pronuclei, and the union of paternal and maternal genomes in the cytoplasm of a fertilized oocyte. The original sperm centriole duplicates and gives rise to the first mitotic spindle. This biparental mode of centrosome inheritance is seen in most mammals, except for rodents, where both centrioles are degraded during spermiogenesis and the zygotic centrosome is organized without any paternal contributions. The studies of centrosomal inheritance at fertilization provide the platform for designing new safe methods of assisted-reproduction and infertility treatments in humans.