De novo formation of centrioles in parthenogenetically activated, diploidized rabbit embryos.

In rabbit oocytes activated parthenogenetically by repetitive electric pulses, centrioles develop de novo in blastocysts. Centrioles were not observed in earlier stages of development, not until the blastocoele is formed. Up to the morula stage (between 8-32 cells), a filamentous, electron-dense material develops and aggregates with a small vesicle fraction within the well developed Golgi apparatus. A spherical to ovoid electron dense mass forms, which is comparable to the deuterosome or to the blepharoplast. The quantity of the electron dense material enlarges and it seems to give rise to the centriole "generating complex". Centrioles arise in all three differentiated cell types of the blastocysts, the mural and polar trophoblasts and the embryonal cell mass at the same time. Some of the forming centrioles in parthenotes have a co-linear arrangement, as in control blastocysts. It is not yet known whether the co-linearly arranged centrioles represent a maturation phase, prior to the formation of the usual diplosome, with centrioles oriented perpendicularly to each other. Nor is it known whether the forming centrioles are functioning as the polar organizer of the mitotic spindle or if they can perform any other centriolar function.