Electron Microscopic Studies on Ovarian Oocytes and Unfertilized Tubal Ova in the Rat

Abstract

Developing rat ova have been studied with the electron microscope. Special attention was paid to relations of ova to the granulosa cells, the developmental stages of ovarian follicles, and the cytology of the unfertilized tubal ova. The relationship of the oocyte to the surrounding granulosa cells was found to change from one of a simple apposition of the plasma membranes to a complex interdigitation of microvilli from the ovular surface and processes from the granulosa cells extending into the matrix of the zona pelfucida. This complex interrelation is maintained until the formation of the first polar body is initiated. At this time no microvilli are found and the oolemma presents a gently undulating outline. Also at this time, a perivitelline space forms and the granulosa cell processes retract. In the unfertilized tubal ova no microvilli are present and the processes of the follicular cells are completely withdrawn.The cytoplasmic elements of the oocyte in various stages of development are described in some detail. Of particular interest is the change noted in position and degree of aggregation of the Golgi complex as maturation proceeds. Tile distribution and structural characteristics of the mitochondria, ergastoplasm, dense particles, and multivesicular bodies are described.

Studies on Guinea Pig Oocytes

“…Somewhat similar aggregates have been described in the mouse oocyte by Yamada et al (1957) and Rhodin (1963) and in rat oocytes at much later developmental stages by both Odor (1960), who called them a "vesicular complex," and Sotelo and Porter (1959) who noted their resemblance to similar concentrations of vesicles in the centrosphere region of somatic cells. Sotelo and Porter postulated that these clumps of vesicles in mature or fertilized rat ova are derived from earlier accumulations of vesicles liberated from muhivesicular bodies.…”

“…In addition, the close association of the dense core of the rosettes with primitiveappearing mitochondria whose peripheral membranes or cristae look incomplete suggests the participation of this material in the elaboration of mitochondria. The variation in size and internal structure of mitochondria illustrated has previously been observed in various mammalian oocytes by Anderson and Beams (1960), Odor (1960), and Blanchette (1961).…”

“…follicle cells and the oocyte follows the pattern previously illustrated and described by Anderson and Beams (1960) for guinea pig oocytes, by Odor (1960) and Franchi (1960) for rats, by Merker (1961) for rabbits, and by Chiquoine (1960) for a variety of mammals. As the cytoplasmic organelles in the oocyte develop, the widening zona pellucida may well begin to act as a filter between the oocyte and the substances collecting in the expanding intercellular spaces of the follicle wall.…”

“…Electron microscopic studies of the development and interrelationships of ultrastructure in invertebrate oocytes have been extensively reported by Rebhun (1961), Afzelius (1957), and others. Yamada et al (1957) and Sotelo and Porter (1959) were the first to report on mammalian oocytes (mouse and rat, respectively), followed by Odor (1960), Chiquoine (1960), Anderson and Beams (1960), and others working on a variety of species. Their reports were concerned primarily with oocytes developing in secondary follicles or with tubal ova.…”

Early Follicular Development and Atretic Changes in the Ovary of the Lamb? Fine Structure and Histochemistry

“…These probably are associated with the retraction of the microvilli which occurs subsequently during both maturation and atresia (Odor 1960;Hertig and Barton 1973). Actin and myosin have been reported as being present in rat oocytes near the oolemma (Amsterdam et al 1977).…”