Sperm aster formation and pronuclear decondensation during rabbit fertilization and development of a functional assay for human sperm

Microtubule organization and chromatin configurations in rabbit eggs after in vivo rabbit fertilization and after intracytoplasmic injection with huma n sperm were characterized. In unfertilized eggs, an anastral barrel-shaped meiotic spindle, oriented radially to the cortex, was observed. After rabb it sperm incorporation, microtubules were organized into a radial aster fro m the sperm head, and cytoplasmic microtubules were organized around the ma k! and female pronuclei. The microtubules extending from the decondensed sp erm head participated in pronuclear migration, and organization around the female pronucleus may also be important for pronuclear centration. Support for these observations was found in parthenogenetically activated eggs, in which microtubule arrays were organized around the single female pronucleus that formed after artificial activation. These observations support a bipa rental centrosomal contribution during rabbit fertilization as opposed to a strictly paternal inheritance pattern suggested from previous studies, In rabbit eggs that received injected human donor sperm, an astral array of mi crotubules radiated from the sperm neck and enlarged as the sperm head unde rwent pronuclear decondensation. gamma-Tubulin was observed in the center o f the sperm aster. We conclude that the rabbit egg exhibits a blended centr osomal contribution necessary for completion of fertilization and that the rabbit egg may be a novel animal model for assessing centrosomal function i n human sperm and spermatogenic cells following intracytoplasmic injection.