[An electron microscopic study of centriole and centrosome morphogenesis in the early development of the mouse]

Using ultrathin section electron microscopy, the precise time of the appearance of centrioles and centrosomes and their morphogenesis in early mouse development was followed. It turns out that in murine morulae and early blastocyst stage centrosomes, centrioles or other microtubule organizing centres are absent; the network of microtubules in interphase cells is diffuse. In 4-day blastocyst four nascent centrioles were found in two cells of trophectoderm in addition to one nascent centriole in the only cell of the inner cell mass. The nascent centrioles were not connected with microtubules. In the late blastocyst (more than 4.5-days of development) among the cells of inner cell mass, cells without centrioles were found, with nascent centrioles but not connected with microtubules; sometimes cells with true centrosomes were seen, having double centrioles and microtubule organizing centres associated with them. Thus, the centrosomes appear asynchronously in different cell types of blastocyst at the preimplantation stage. The centrosome development begins from a self-assembly de novo of the nascent centrioles without any association with microtubules.