[Morphometrical analysis of endoplasmic reticulum dynamics in growing amphibian oocytes]

Morphological analysis of endoplasmic reticulum (ER) dynamics was carried out in early amphybian oocytes at different stages of their development. Comparative morphometric analysis of ER membrane relative surface area and relative volume has shown that at the 1st-2nd stages of oogenesis the accumulation of ER membranes occurred mainly in the peripheral region of the cell cytoplasm. At the 3rd-4th stages of oocyte growth characterized by active transcription, the increase in the relative volume of ER and relative surface area of ER membranes occurs in the middle and near-nuclear region of cytoplasm, and reduction of these parameters takes place in the peripheral part of the cell. Simultaneously observed fusion of numerous ER vesicles with the outer nuclear membrane may serve as an evidence of active formation of new fragments of nuclear envelope. The 5th-6th stages of oocyte development are characterized by an increase in the relative volume of ER in the whole oocyte. It has been supposed that the revealed reorganization of endoplasmic reticulum in growing amphibians oocytes might be due to yolk accumulation (vitellogenesis), redistribution of calcium ions, and synthesis and storage of lipids and proteins. These processes are necessary for the future embryo development, and also for assembly of new fragments of growing nuclear envelope.