MICROTUBULE ORGANIZATION IN PORCINE OOCYTES DURING FERTILIZATION AND PARTHENOGENESIS

Microtubule configurations in porcine oocytes after sperm penetration or after artificial activation by electrical stimulation were imaged b y immunocytochemistry and laser scanning confocal microscopy. Soon aft er sperm penetration, an aster was seen adjacent to the incorporated s perm head. Polyspermic penetrations led to the presence of multiple sp erm asters in association with each sperm. The sperm aster enlarged an d, at the time of pronuclear apposition, filled the cytoplasm. After m ale and female gamete union, the microtubule matrix was reduced. At th e mitotic metaphase stage, microtubules were detected in the spindle, which was anastral and fusiform. At anaphase, asters assembled at each spindle pole, and at telophase, large asters filled the cytoplasm. Ar tificial activation by electrical stimulation induced in the cytoplasm a dense network of microtubules, which seem to be involved in proper positioning of the female pronucleus. At mitotic metaphase, microtubul es were concentrated around the chromatin. The results of experiments using taxol, a microtubule stabilizing agent, suggest that maternal ce ntrosomal material is present in the mature porcine oocyte as disperse d undetectable material that can form a microtubule network after part henogenetic activation. However, at fertilization, the paternal centro some collects centrosomal material to form a sperm aster. These result s suggest that the functional centrosome that forms during fertilizati on is a result of the blending of paternal and maternal centrosomal co mponents.