ARRANGEMENT OF ACTIN-FILAMENTS AND CYTOPLASMIC GRANULES IN THE SEA-URCHIN EGG AFTER TPA TREATMENT

Elongation of microvilli and formation of actin filaments after treatm ent with a phorbol ester, TPA, were investigated in unfertilized eggs of Hemicentrotus pulcherrimus. Microvilli on the egg surface were exam ined by scanning electron microscopy. Actin filaments in the cortical layer of the eggs were observed by fluorescence microscopy using rhoda mine-labeled phalloidin. The actin molecules were polymerized and bund led to form long filaments inside the cortical layer of eggs after TPA treatment. Arrangement of the actin filaments was followed by spiral elongation of microvilli. Transmission electron microscopic studies sh owed that the cortical granules under the cell membrane of sea urchin eggs were transferred after TPA treatment from the surface to the inte rior of the cell [Ciapa et al., 1988: Dev. Biol. 128:142-149]. This mo vement of the cortical granules was inhibited by cytochalasin B, but n ot by nocodazole. Furthermore, the distribution of clear granules was changed following TPA treatment. From these results we conclude that i ntracellular actin filaments may cause the transport of cortical granu les and clear granules into the central area of the egg by the activat ion of protein kinase C. The possible involvement of actin in the inwa rd displacement of granules might be the result of the :rearrangement of actin filaments in the cortical layer. (C) 1998 Wiley-Liss, Inc.