The rabbit zygote: Formation of annulate lamellae

Abstract

Annulate lamellae are not formed in rabbit follicular oocytes, unfertilized eggs, or fertilized eggs prior to and during formation of pronuclei. By 16 hours post coitum, blebbing activity of the pronuclear envelopes becomes apparent and continues for several hours. Annulate lamellae are formed at two different sites in the cytoplasm. First, the vesicles thought to be derived from the pronuclear envelopes accumulate in the cytoplasm and, together with already existing flocculent vesicles, give rise to annulate lamellae which are located at random sites, but near the pronuclei. These annulate lamellae continue to grow by further addition of vesicles. Large aggregates of vesicles and cisternae develop in the zygotes by 20 hours, and these are the second site of formation of annulate lamellae. The peripheral and some of the central vesicles of the aggregates organize into elongated laminae and become annulated. By 24 hours post coitum the stacks of annulate lamellae associated with the aggregates of vesicles and cisternae are large, and may have 25 to 30 lamellae. It is concluded that in the rabbit zygote annulate lamellae form from fusion of vesicles.