Impaired gene activity for 18S and 28S rRNA in early embryonic development of mouse parthenogenones

In vitro development of spontaneously activated bovine oocytes

PURPOSE

The aim of this study was to compare the development of bovine parthenogenetic and in vitro fertilization-derived (IVF) embryos. Oocytes were matured, fertilized, or allowed to activate spontaneously by aging and then cultured for up to 14 days in vitro. Cleavage and development rates, morphology, ultrastructure, and transcriptional activity were compared.

RESULTS

Very few parthenogenotes (7.5% of aged oocytes) were obtained and none developed to the hatched blastocyst stage. The pattern of 3H-uridine incorporation at the two-, four-, and eight-cell stages was similar in both types of embryos. Morphological study, however, revealed that none of the parthenogenotes showed features associated with long-term development: they were developmentally delayed and usually arrested before reaching the blastocyst stage (only 0.5% of aged oocytes developed to the blastocyst stage). Structural differences between parthenogenotes and the IVF-derived embryos were observed at all stages of development.

CONCLUSIONS

Structural observation suggested that failure of long-term development of bovine parthenogenotes may have a metabolic basis. Some functional changes appeared to coincide with chronological age rather than developmental age. Even though development of parthenogenotes was limited; some features of nuclear maturation and activation of the embryonic genome occur without contribution of the paternal genome.

Preimplantation mammalian aggregation and injection chimeras

The preimplantation embryo is highly resilient to experimental manipulations. A specific manipulation that has revealed many clues to the developmental process is chimera production. Chimeras have been used to describe the importance of developmental characteristics of embryonic cells and how these characteristics are involved with developmental fate. These characteristics have been monopolized in the production of interspecific chimeras and the production of transgenic animals. This review attempts to discuss the major factors affecting preimplantation mammalian embryo chimera production.

A study of hetero-specific sperm-egg interactions in the rat, mouse, and deer mouse using in vitro fertilization and sperm injection

Hetero-specific fertilization of zone-free eggs is used in these experiments as a tool to analyze the barriers to hybridization and to gain insight into the mechanisms of normal fertilization. When the zonae of rat eggs, which are a barrier to hetero-specific fertilization, are removed with pronase, the eggs can be fertilized by mouse sperm and the zygotes start to develop normally. A rat egg fertilized with mouse sperm completes meiosis and forms both male and female pronuclei. Chromosomes from both parents are found on he spindle at the metaphase stage of the first cleavage division. Under present culture conditions, embryos develop only to the two-cell stage, but this initial development of the hybrid is apparently normal. The question of whether sperm and egg membrane fusion is requisite for normal development is addressed by injecting sperm directly into the cytoplasm of unfertilized eggs. The injection of mouse sperm into rat eggs frequently leads to activation and formation of male and female pronuclei. The first cleavage division is indistinguishable from that following hetero-specific fertilization. Capacitated and uncapacitated sperm react alike when injected into eggs. Egg activation, however, is necessary for male pronucleus formation. Sperm from the deer mouse Peromyscus maniculatus bairdii, which are incapable of fertilizing even zonea-free eggs, respond like mouse sperm when injected into rat eggs. These data indicate that sperm interactions with the egg cytoplasm are less species-specific than interactions at the egg surface. Furthermore, the normal surface interactions of sperm and eggs are not essential for the start of development.