Appearance of the Incorporation Cone and Extrusion of the Second Polar Body in Hamster Eggs.

Abstract

Fertilized hamster eggs were recovered from the ampulla of the oviduct at various times after in vivo insemination. To examine the distribution of the egg cortical actin and the position of nuclei from freshly ovulated unfertilized eggs to the 2-cell stage, they were double stained with Rhodamine-phalloidin and Hoechst 33342. In the freshly ovulated hamster eggs arrested at metaphase-II of meiosis, the egg surface above the meiotic spindle was devoid of microvilli and had instead conical projections. This area showed strong fluorescence, indicating that the actin was aggregated. As the sperm head was incorporated and began to decondense in the ooplasm, an incorporation cone was formed at the site of sperm entry. The cone consisted of relatively long, conical projections which closely resembled those of freshly ovulated eggs, and also showed strong fluorescence. This cone lasted while the sperm nucleus was decondensing and diminished at the time when the male pronucleus was formed. The results obtained with regard to the formation of the incorporation cone were comparable with those of mouse and rat eggs. Moreover, as to the elimination of second polar body, it was found that the body underwent two constrictions, resulting in a gourd-like body.