Electron Microscopy of Growing Oocytes of Rana Pipiens

Abstract

1. In the cytoplasm of oocytes of stage Y0, prior to the appearance of yolk, one observes a few scattered profiles of endoplasmic reticulum and numerous filamentous mitochondria, usually distributed at random but sometimes clustered. As the nuclear membrane begins to bulge outward, small granules and short rods appear in the perinuclear cytoplasm and endoplasmic reticulum becomes more prominent throughout the cytoplasm. 2. Coincident with the appearance of the first yolk platelets, which are deposited in a narrow peripheral ring within the endoplasm at stage Y1, protoplasmic processes, the microvilli, push out all over the surface of the oocyte. At the same time follicle cells pull away but remain attached to the oocyte at some points through finger-like processes which interdigitate with neighboring microvilli. It is estimated that the microvilli increase the absorptive area of the surface to about thirty-five times that of a simple sphere. Just beneath the microvillous layer is the basal protoplasm of the cortex, now containing tiny granules probably synthesized from newly absorbed raw materials. Cortical granules appear and become aligned below the basal layer on the external border of the endoplasm. Both the cortical granules and the yolk platelets measure up to 1 µ in diameter at this stage. 3. By stage Y3 (yolk filling peripheral three-fourths of cytoplasm), the basal layer of the cortex is folded so that it appears in section as alternating ridges and valleys. The microvilli now extend from the summits of the cortical ridges. Small, ring-shaped granules are abundant in the cortex. Cortical granules have increased to 2 µ in diameter. 4. Yolk platelets continue to be synthesized around the cortical granules and in the subjacent endoplasm. The largest platelets measured in the interior cytoplasm at stage Y4 (cytoplasm filled with yolk) were 3.7 µ wide by 5.8 µ long. Pigment granules increase in size from 0.15 µ in diameter at stage Y3 to 0.30 µ in diameter at stage Y4.

The partition of sodium fluxes in isolated toad oocytes

“…In fact the surface area is greatly increased by microvilli; Bradbury, Dick & Dick (1967) have estimated from electron micrographs that the area is increased approximately 10-12 times in a 750It cell. (The previously quoted figure of 35 times given by Kemp (1956) was based on the assumption 'that half of this (surface) area is occupied by the bases of the microvilli'. Kemp gives no grounds for this assumption and careful re-examination of his electron micrographs suggests it is probably an over-estimation).…”

Nuclear pore flow rate of ribosomal RNA and chain growth rate of its precursor during oogenesis of Xenopus laevis

“…tions can be found in the literature that the nuclear envelope of germinal vesicles in growing amphibian oocytes increases in area through the development of irregular contours or saclike protrusions (e.g., Duryee, 1950;Kemp, 1956;Wischnitzer, 1967). As a consequence, the total nuclear surface should then be greater than the corresponding sphere surface.…”

On the Interrelations between the Macronucleus and the Cytoplasm in the Gymnostome Ciliate <i>Chlamydodon pedarius</i>

“…The size and morphology of these aggregates are very similar to those of the nurse cells of Rhodnius mentioned above. , The ex tensions of the extruding materials from nucleus in echinoderm oocytes (Afzelius, 1955), in Spisula and Otala (Rebhun 1956) and in the growing oocytes of Rana pipiens (Kemp 1956) seem to be much smaller than those of the aggregates described just above, but they may correspond to the simple masses of granules on the outer surface of the macronucleus taken up in this study. The outpocketing of nuclear membrane in salivary gland cells of third instar larvae of Drosophila (Gay 1956), and in spermatid of crayfish (Moses 1956) may correspond to the blisters of the nuclear mem brane of the macronucleus.…”