Ref ID : 7560
Jean-Pierre Mignot; [Etude Ultrastructurale de la Pedogamie chez Actinophrys sol (Heliozoaire) II. Les Divisions de Maturation]. Protistologica XVI(2):205-225, 1980
Reprint
In File
Notes
We have reinvestigated with electron microscopy the sexual of Actinophrys sol described by Belar (1923). The present study concerns only the two divisions of meiosis that end with the degeneration of one of the two daughter nuclei considered as a polar body. Our electron micrographs confirm the essential features established by Belar and show that the ultrastructural characteristics of prophase I are fundamentally the same as those known in Metazoa. We precise the persistence of the nuclear envelope during division I and II as in the progamic division, and the formation during telophase around each progeny nucleus of a new nuclear envelope inside the old one. The spindle including peri- and intranuclear microtubules growths between area of cytoplasm which lack distinct centriolar structures, but include many membranous vesicles. As during progamic mitosis microtubules seem to be nucleated on the surface of these membranous structures and on kinetochores. However, in contrast to the progamic mitosis, breakdown of the nuclear envelope is more important in the polar regions and the spindle is longer. Moreover the synthesis of nuclear membrane in the polar regions is asynchronous during late prophase, so that the components of the nucleus seem to be heteropolar arranged. It could be argued that this heteropolar activity explains the future differentiation of a pronucleus and a pynotic nucleus. The relations between membrane biosynthesis in the nuclear environment and the spatial distribution or chromatin organization are discussed.