Ref ID : 7724
Jean-Pierre Mignot; [Etude Ultrastructurale de la Mitose Vegetative chez L'heliozoaire Actinophrys sol]. Protistologica XX(2):247-263, 1984
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All the stages of the vegetative mitosis of Actinophrys sol were studied using electron microscopy and described with special reference to the nuclear envelope and cytoskeleton. One found again several characteristics already reported as regards the progamic mitosis, namely the persistence up to the end of telophasis of the nuclear envelope and of the nucleolar material segregated at the same time as the chromosomes. The nuclear envelope appears as a particularly dynamic organelle, folding itself, lenghtening, bearing the fibrillar system probably concerned in the biogenesis and setting of the spindle microtubules, and moreover budding the new membranes which will delimit the new nuclei. The spindle is entirely extranuclear up to the metaphasis. It grows and organizes itself in the perinuclear cytoplasm. No MTOC was observed. During the prophasis, some of the spindle microtubules were found mixed with the axonemal microtubules which persist during the whole trophic mitosis. However these two microtubular systems remain independent which raises some problems relating to the nature of the tubulins and the MAPS constituting them and the mechanisms which control their biogenesis. The fibrillar perinuclear system, the nature of which is to determine, may play a role as well as the membranes of the nuclear envelope or of the perinuclear vesicles - presumed sites for the calcium ions - in the determinism of the cell polarity during the interphasis and the division.