[Nuclear organization of the oocytes from atretic follicles of the lake frog].

Oocytes of Rana ridibunda were examined by light and electron microscopy. A peculiarity of these oocytes is the availability of the vast local growings of the inner nuclear membrane, their expansion into the nucleus and the formation of cluster accumulations of membrane structures - intranuclear vesicles filled with fibrillar protein material. In the regions of nuclear membrane expansion some disturbances in the nuclear envelope are noted: disappearance of nuclear pores, replacement of membranes by filamentous material, and formation of nuclear membrane gaps. It is suggested that growings of the inner nuclear membrane are related to the isolation of cytoplasmic proteins penetrating into the nucleus. A general pattern of the karyospheric structure, characteristic of the normal developing oocytes, remains unchanged during degeneration as well. The karyosphere is a complex consisting of the central protein body (CPB), chromosomes associated with this body and numerous nucleoli surrounding the chromosomes. Some differences in details of the structure of karyosphere in the examined oocytes are revealed. Thus, the CPB in these oocytes consists of pseudomembranes, but autonomous pore complexes here occur seldom. The chromosomes have a tendency to fuse forming in some cases a unique network of the chromatin material associated with the material of CPB. In the contact zone the transfer of chromatin fibrils into pseudomembranes is observed. The nucleoli bear no granules and demonstrate a segregation of the fibrillar material. As the result, DNA-containing material of the fibrillar centre appears at the periphery of nucleoli. Analysis of our own and literature evidence on the morphology of the oocyte nuclei from the atretic follicles of different vertebrates, and on the structure of ciliate micronuclei degenerating during conjugation allows a conclusion on the identical response of sexual cells to different stimuli evoking degeneration.