An ultrastructural analysis of spontaneous activation of hamster eggs aged in vivo

摘要

AbstractIn an effort to elucidate various aspects involving the initiation of development, the morphogenesis of the spontaneously activated egg of the golden hamster was examined at the light and electron microscopic levels of observation. Spontaneous activation of the unfertilized hamster egg occurs upon prolonged incubation within the oviduct, i.e., aging in vivo, and may include the formation of the second polar body and the development of one or several pronuclei. In many instances the activated egg resembles the inseminated ovum at the pronuclear stage of fertilization. Occasionally the activated egg will divide and yields a structure which is morphologically similar to the two‐cell stage. Development beyond the two‐cell stage was not observed. Even though a number of events exhibited by the aging hamster egg mimic those of the fertilized, many are indicative of cellular degeneration. Such processes include, for example, the aggregation of organelles into fairly homogeneous clusters, the budding of portions of the cortex of the egg containing cortical granules into the perivitelline space, the accumulation of vesicles within the ooplasm and the structural modification of microvilli. All activated eggs, at every period investigated (6 to 66 hours post‐ovulation), contained cortical gra