Abstract
A study was made of the structure of the centrosome in the cell cycle in a nonsynchronous culture of pig kidney embryo (PE) cells. In the spindle pole of the metaphase cell there are two mutually perpendicular centrioles (mother and daughter) which differ in their ultrastructure. An electron-dense halo, which surrounds only the mother centriole and is the site where spindle microtubules converge, disappears at the end of telophase. In metaphase and anaphase, the mother centriole is situated perpendicular to the spindle axis. At the beginning of the G1 period, pericentriolar satellites are formed on the mother centriole with microtubules attached to them; the two centrioles diverge. The structures of the two centrioles differ throughout interphase; the mother centriole has appendages, the daughter does not. Replication of the centrioles occurs approximately in the middle of the S period. The structure of the procentrioles differs sharply from that of the mature centriole. Elongation of procentrioles is completed in prometaphase, and their structure undergoes a number of successive changes. In the G2 period, pericentriolar satellites disappear and some time later a fibrillar halo is formed on both mother centrioles, i.e., spindle poles begin to form. In the cells that have left the mitotic cycle (G0 period), replication of centrioles does not take place; in many cells, a cilium is formed on the mother centriole. In a small number of cells a cilium is formed in the S and G2 periods, but unlike the cilium in the G0 period it does not reach the surface of the cell. In all cases, it locates on the centriole with appendages. At the beginning of the G1 period, during the G2 period, and in nonciliated cells in the G0 period, one of the centrioles is situated perpendicular to the substrate. On the whole, it takes a mature centriole a cycle and a half to form in PE cells.
Highlights
A study was made of the structure of the centrosome in the cell cycle in a nonsynchronous culture of pig kidney embryo (PE) cells
This allows us to state that in interphase both the satellites and the mitotic halo form on the mother centriole. It appears that the daughter centríole first becomes engaged in mícrotubule assembly only a whole cycle after its origination; in the subsequent S period, a new daughter centriole forms near it. It plays the role of mother centriole in mitosis, and only after mitosis does it become capable of carrying pericentriolar satellites and forming a cilium
Throughout the cell cycle, centrioles in PE cells are connected with microtubules by means of two structures, namely pericentriolar satellites in interphase and the halo in mitosis
Summary
A study was made of the structure of the centrosome in the cell cycle in a nonsynchronous culture of pig kidney embryo (PE) cells. The behavior of centrioles in the cell cycle has been described in a number of works (13, 21, 22, 24, 29, 30), but the majority of authors have confined themselves to a description of some individual cycle phases rather than making a comprehensive analysis of all the periods of interphase and mitosis. The emphasis in these works is on the location of centrioles in the cell and on the time of their duplication, whereas the interaction between interphase centrioles and cytoplasmic microtubules and the dynamics of all centrosome structures are hardly mentioned. The method was essentially as follows: we marked the individual cell under the light microscope and examined the serial sections of this cell under the electron microscope
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