Biomedical subjects

T B Aĭzenshtadt

Publications and source records attributed to T B Aĭzenshtadt.

13 recordsLinked to original sources

PubMed1978

[Oogenesis in Hydra. III. The growth and fusion of the oocytes].

The ultrastructure of oocytes in Hydra has been studied prior to the beginning of their phagocytic activity. The formation of Golgi complexes and vacuolar system by means of the rough endoplasmic reticulum budding and the formation of numerous enzymatic granules within the Golgi complex are considered with respect to the preparation of cells for the processes of phagocytosis and intracellular digestion of structures. The oocyte situated in the center of each accumulation of syncytially connected cells, descendants of one interstitial cell, becomes the egg, whereas all others are consumed by it and transform into endocytes. The partial and complete confluence of oocytes is described. In the first case, a part of cytoplasm of the cells surrounding the growing oocyte is torn away and included in this oocyte. In the second case, the confluence of large oocytes containing endocytes in their cytoplasm takes place. The growing oocyte forms pseudopodia and cytoplasmic processes which move apart the epithelial-muscle cells, reach the mesogloea and come in contact with the gastroderm cells. The role of these contacts in the oocyte growth is discussed.

Animals↗

PubMed1975

[Current concepts about the determinants of germ cells].

The cytoplasm of the egg vegetal hemisphere plays the determining role in the isolation and differentiation of germ cells. Cytoplasmic factors of unknown nature prevent certanin blastomeres from somatic differentiation. In the developing germ cells, a large amount of material (in which acid proteins are a constant component) passes from the nucleus to the cytoplasm. This fine fibrous material may take the form of nucleolus-like bodies or dense granules (polar granules in the insect eggs, dense bodies in the amphibian germ plasm, intermitochondrial cement in oocytes of various animals, chromatoid body in spermatocytes). The application of the term "determinants of germ cells" for designation of these structure, as it takes in the electron microscopy literature, appears to be incorrect. Their appearance is a consequence of the determining influence of cytoplasmic factors, rather than their cause. In lower invertebrates, the germ cells may arise in adult specimens due to the embryonic reserve of totipotent elements (neoblasts or interstitial cells). The transformation of these cells in the germ ones is accompanied by the release of a great amount of fine fibrous material from the nucleus to the cytoplasm as well. The problem of determinants of germ cells is considered with respect to the problem of ooplasmic segregation.

Animals↗

PubMed1974

[Oogenesis in hydra. II. Cytophotometric determination of DNA concentration in the nuclei of somatic and sex cells].

During sexual reproduction in Hydra, interstitial cells in the female sex zone of the body (i-cells) undergo mitotic division and form a thickening in the epiderm. The proliferation of i-cells is accompanied by the increase of cytoplasm volume and by the appearance in the cytoplasm of a great number of membranous structures (rough endoplasmic reticulum, Golgi apparatus and mitochondria), enzymatic granules, lipid inclusions and glycogen. All cells of the epidermal thickening soon (in approximately twenty four hours) acquire the characteristics of typical phagocytes. However it is the cell situated inside the group of syncytially connected ones and adjacent to mesogloea that begins to grow rapidly and phagocytize surrounding cells. The cells of the epidermal thickening, though they are often given the name of oogonia, were found to have a tetraploid DNA content in their nuclei. The presence of four unseparated centrioles of equal size suggests that all preparatory processes for division were completed. A conclusion was drawn that cells of the epidermal thickening undergo premeiotic DNA synthesis prior to their phagocytizing by the growing oocyte and, thus, are oocytes themselves. The oogonial stage in Hydra coincides with the early period of mitotic reproduction of i-cells. The data obtained are discussed from the viewpoint of the formation of the accessory gonad apparatus.

Animals↗

PubMed1971