MICROTUBULE ORGANIZATION AND CHROMATIN CONFIGURATIONS IN HAMSTER OOCYTES DURING FERTILIZATION AND PARTHENOGENETIC ACTIVATION, AND AFTER INSEMINATION WITH HUMAN SPERM

The cytoskeletal components of hamster oocytes, zygotes, and spontaneo usly activated parthogenotes were examined after immunocytochemical la beling. Microtubules were found only in the anastral, tangentially arr anged second meiotic spindle of unfertilized oocytes. Taxol treatment of unfertilized oocytes greatly augmented astral microtubules in both the metaphase II spindle and the cortex. Disruption of the meiotic spi ndle microtubules with nocodazole resulted in cortical chromosomal sca ttering. During hamster sperm incorporation and pronuclear formation, no sperm aster was detected in association with the male DNA. Instead, a large overlapping array of microtubules assembled in the cortex. By mitosis, this interphase array disassembled and an anastral: metaphas e spindle formed. Microtubule and chromatin configurations were also i maged in hamster oocytes injected with human sperm. Astral microtubule s were absent from the sperm centrosome. The implications of these res ults are discussed in relation to the hamster oocyte penetration assay , a test commonly used by in vitro fertilization clinics to demonstrat e the fertilizing ability of human sperm. We conclude that since hamst ers and humans follow different methods of centrosome inheritance, mat ernal and paternal, respectively, the hamster may be an inappropriate model for exploring microtubule and centrosomal defects in humans or f or assaying postinsemination forms of human male fertility defects.