Cofilin is a small protein that belongs to the family of actin-depolynterizing factors (ADF). The main cellular function of cofilin is to change cytoskeletal dynamics and thus to modulate cell motility and cytokinesis. We have recently demonstrated that the actin cytoskeleton is involved in the modulation of Ca2+ signalling in starfish oocytes. To extend these observations, we have explored whether cofilin influences Ca2+ signalling in the oocytes. Here we show that microinjection of the functionally active cofilin alters the Ca2+ signalling mediated by the three major second messengers, InSP3, NAADP, and cADPr. Cofilin intensifies the Ca2+ signals induced by InSP3 and NAADP, and delays those induced by cADPr. Furthermore, the injection of cofilin increases the Ca2+ signals during hormone-induced oocyte maturation and fertilization. The results suggest that the dynamic regulation of F-actin by its binding proteins may play an important role in the modulation of intracellular Ca2+ signalling. (c) 2006 Elsevier Inc. All rights reserved.