Microtubule Organization in Hamster Oocytes after Fertilization with Mature Spermatozoa and Round Spermatids

Abstract

The golden hamster is a laboratory species that has provided a good experimental model for mammalian fertilization. The present study was undertaken to investigate the microtubule organization pattern during fertilization in the golden hamster. Mature unfertilized oocytes and zygotes obtained in vivo or in vitro were stained immunocytochemically with anti-α-tubulin monoclonal antibody. In mature unfertilized oocytes, microtubules were distributed as cytoplasmic foci of small aster-like arrays and in the meiotic spindle. After penetration by spermatozoa, microtubules in the meiotic spindle proceeded through the telophase configurations, while no obvious changes could be observed in the cytoplasmic astral microtubules. Throughout these early fertilization processes, incorporated spermatozoa were not associated with any detectable microtubules. At the pronuclear stage, astral microtubules in the cytoplasm moved to the peripheries of the male and female pronuclei. At prometaphase of the first mitotic division, the aster split and formed the poles for the mitotic spindle. After the first mitotic division, these asters developed into the interphase array of microtubules in the daughter blastomeres. In the second series of experiments, some oocytes were fertilized with hamster round spermatids by intracytoplasmic injection. The behavior of chromosomes and microtubules during fertilization in these oocytes were quite similar to those in oocytes fertilized with mature spermatozoa. These findings indicate that the centrosome in the hamster zygotes is completely of maternal origin.