The Distribution of Actin Filaments in the Egg of the Rose Bitterling during the Sperm Entry Process in Monospermic Fertilization

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The distribution of actin filaments and morphological changes in the portion of egg cortex（PAS）at and around the sperm entry site during sperm entry in eggs of a teleost undergoing monospermic fertilization were investigated by using fluorescence and scanning electron microscopy. The fish studied was the rose bitterling, Rhodeus ocellatus ocellatus. The fertilized spermatozoon moves from the sperm entry site to the inner cortex to fuse with the egg nucleus. Actin filaments have been suggested as possible candidates for cell organelles that take part in the movement of the sperm head based on results obtained in studies using the actin polymerization inhibitor, cytochalasin B（CB, Ohta et al.,1998）. In the present study, the validity of this suggestion was further examined by using rhodamine phalloidin（RhPh）, which specifically stained actin filaments. The PAS, which is devoid of cortical alveoli and adheres to the inside of the egg membrane（chorion）, was stained strongly with RhPh in eggs fixed from one to fifteen min after insemination. On the other hand, the PAS was only faintly stained with RhPh in CB-treated eggs. This report presents evidence that a number of actin filaments are present in the PAS which separates from the rest of the egg after sperm penetration.
2009-03-01