Activation of oocytes by latrunculin A

Actin depolymerization by latrunculin A (LAT-A) in mature starfish oocytes induces a massive calcium mobilization that results in the discharge of the cortical granules and in the elevation of the fertilization envelope. The Ca²⁺ liberation starts as a circumscribed subplasma membrane hotspot, which is followed by a flash of Ca²⁺ increase restricted to the cortical layer. Ca²⁺ propagates rapidly from these peripheral regions to the center of the oocyte, initiating calcium oscillations. Blockade of the inositol 1,4,5-trisphosphate receptors with heparin does not affect the liberation of Ca²⁺ at the initial hotspot or the cortical flash, but abolishes the centripetal spreading of the wave and the Ca²⁺ oscillations. In Ca²⁺-free medium, LAT-A also initiates Ca²⁺ release at a discrete cortical point, but then propagates throughout the cell without first forming the uniform cortical flash. The latter is thus linked to the influx of external Ca²⁺, somehow promoted by the depolymerization of cortical (microvillar) actin. The Ca²⁺ response to spermatozoa (i.e., peripheral hotspot, cortical flash, globalization of the signal) closely mimics that promoted by LAT-A. Thus, the initial cortical release of Ca²⁺ promoted by the sperm may be due to the depolymerization of actin.-Lim, D., Lange, K., Santella, L. Activation of oocytes by latrunculin A.