Morphology and physiology of Mammalian (hamster) eggs before and after fertilization

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1989.Includes bibliographical references.Microfiche.xviii, 137 leaves, bound ill. 29 cmPreovulatory mature ovarian hamster eggs were compared with recently ovulated eggs. Although these two groups of eggs were at metaphase of the second meiotic division, there were quantitative differences between the two. The most striking difference was found in the zona pellucida. The zona of the oviductal egg was "heterogeneous" in its optical density and had a stronger acrosome reaction-inducing ability than that of the ovarian egg. When cultured in artificial media, the ooplasm of ovarian eggs became like that of oviductal eggs. However, their zonae remained unchanged. Zonae of ovarian eggs became like those of oviductal eggs only when they were exposed to oviductal fluid. To investigate egg morphology after centrifugation, and how egg fragments respond to spermatozoa, zona-free hamster eggs were centrifuged in a Percoll gradient. Each egg was separated into a light and a heavy half. Chromosomes remained in their original cortical position in the egg during centrifugation or after separation into either light or heavy half. When the eggs were treated with cytochalasin D (CD) and then centrifuged, the chromosomes were extruded quickly before each egg was separated into halves or fragment. Fertilizability was different between light and heavy halves. Most of the heavy halves supported development of sperm nuclei into pronuclei, whereas only a few light halves could do so. When the light and heavy halves were centrifuged further, each separated into two quarters. The lightest quarter was fragile and few of them could fuse with spermatozoa. In this quarter, the sperm nucleus could decondense but could not develop into a pronucleus, whereas in the other quarters the sperm nuclei could develop into well-formed pronuclei. The rigidity of eggs at various stages were examined by determining the minimum time needed for complete separation of all eggs in a group into halves. The rigidity of the egg diminished sharply with the progression of meiotic maturation, reaching a minimum at metaphase' of second meiosis, then increasing progressively after fertilization. Cytochalasin D reduced the rigidity of any stages of eggs, indicating that the actin-based cytoskeleton in the cortical region is largely responsible for the rigidity of the egg