Effect of calyculin A on the surface structure of unfertilized sea urchin eggs

Calyculin A, a potent inhibitor of type 1 and type 2A protein phosphatases, induces contractile ring formation when applied to unfertilized sea urchin eggs [Tosuji et al., 1992: Proc. Natl. Acad. Sci. USA 89:10613-10617]. We report here the elongation of microvilli in the unfertilized eggs exposed t o calyculin A. The elongated microvilli and associated sperm-egg binding si tes (egg receptor for sperm) then became concentrated into a constriction s ite corresponding to the cleavage furrow. The egg receptor for sperm was al so in close connection to the microfilaments. Okadaic acid is another known inhibitor of protein phosphatase type-1 and type-2A. Its effect, however, is about a hundredfold feebler for type-1 phosphatase than type-2A. Even af ter treatment with okadaic acid, no change was observed, suggesting that th ese morphological changes were induced by calyculin A solely though its inh ibitory effect on the type-1 protein phosphatase. (C) 2000 Wiley-Liss, Inc.