The dynamics of reconstitution of microtubules around the cell center after cooling.

In interphase PE cells, after cooling (2 h at 0 degree C), some microtubules are retained in the cytoplasm. After the transfer of the cells to a thermostat (37 degrees C), the reconstitution of the microtubule network begins near the cell center. At this time in most of the cells around the center one can see the electron-dense foci of convergence of microtubules which then disappear. The number of microtubules diverging radially from the mother centriole reaches a maximum after 15 to 16 min, that of microtubules growing from the daughter centriole 12 min after the cells are placed at 37 degrees C. 45 min after the heating started the number of radially diverging microtubules somewhat exceeds the control level. These data show that microtubules are associated with the centers only during their growth. The mature microtubule is separated from the center and may be replaced by a new one. Thus, most, of not all, microtubules originate from the cell center, but at any moment only some of the microtubules are associated with it.