Centrosome formation in the bovine early embryo

Summary Centrosome formation during early development in mice and rats occurs due to the appearance of centrioles de novo . In contrast, in humans and other non-rodent mammals, centrioles are thought to be derived from spermatozoa. Ultrastructural study of zygotes and early embryos of cattle at full series of ultrathin sections showed that the proximal centriole of the spermatozoon disappears by the end of the first cleavage division. Centrioles appear in 2–4 cell embryos in fertilized oocytes and in parthenogenetic embryos. Centriole formation includes the appearance of atypical centrioles with randomly arranged triplets and centrioles with microtubule triplets of various lengths. After the third cleavage, four centriolar cylinders for the first time appear in the blastomeres while each embryo still has two atypical centrioles. Our results showed that the mechanisms of centriole formation in different groups of mammals are universal, differing only in the stage of development in which they occur.