Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Animal Science

First Advisor

Robert A. Godke

Abstract

The objective of the present study was to evaluate the effect of post-block mouse and bovine embryos on the development of pre-block embryos around the in vitro developmental block stage. The effect of the post-block embryos on the development of the pre-block embryos was evaluated in culture, in chimeras and in cytoplasmic hybrid embryos. The results indicate that post-block embryos were able to stimulate the development of the pre-block embryos in culture. The stimulatory effect of the post-block mouse and bovine embryos was found not to be species-specific and was synergistic with that of bovine granulosa cells. Chimeric parthenogenetic bovine embryos were used as a model to study the role of the blastomeric interaction in the development of pre-block bovine embryos. The development of the pre-block parthenogenetic bovine embryos was significantly improved when fertilized bovine blastomeres were injected into the parthenogenetic bovine embryos. The degree of the stimulatory effect of the fertilized blastomeres was found to be positively related to the number of the fertilized blastomeres in the chimeric embryos. Cytoplasm of mouse or bovine embryos was introduced into mouse pronuclear embryos to evaluate the role of embryonic cytoplasm during preimplantation development. It was found that pre-block cytoplasm was inhibitory while cytoplasm at the in vitro developmental block stage was stimulatory to the in vitro development of mouse pronuclear embryos. The pre-block bovine cytoplasm was also inhibitory to the in vivo development of mouse pronuclear embryos. On the basis of the results in the present study it was proposed that the embryonic cytoplasm contains inhibitory factor(s) before the in vitro developmental block stage, preventing the pre-block embryos to develop through the in vitro developmental block stage. The inhibitory factor degrades before the in vitro developmental block stage, allowing the development of the mammalian embryos through the in vitro developmental block. The autocrine/paracrine activity and the blastomeric interaction within the embryos are capable of stimulating the development of the pre-block embryos through the in vitro developmental block stage.

Pages

161

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