Maturation and fertilization in starfish oocytes

Concanavalin A induces germinal vesicle breakdown in Barnea candida (Mollusca, Pelecypoda) oocytes

Treatment of Barnea candida oocytes with 5 micrograms/ml Con A or above elicits germinal vesicle breakdown (GVBD), the timing for this event being dose dependent. At 100 micrograms/ml, GVBD occurs within 20 to 30 min, a lag time corresponding to that observed after fertilization. Con A-induced GVBD requires the presence of 2 mM external calcium during all the treatment period while at 10 mM external Ca2+, the calcium-dependent period is slightly reduced. It is sensitive to low pH Na-acetate sea water, 50 microM trifluoperazine, 20 microM D-600 or 2,4-dinitrophenol, as well as to 10 micrograms/ml cytochalasin B. A straightforward interpretation of these data would be that Con A-induced maturation is sustained by an energy-requiring effector mechanism involving intracellular contractile proteins.

Calmodulin in starfish oocytes. II. Trypsin treatment suppresses the trifluoperazine-sensitive step

The 1-methyladenine-induced oocyte maturation in starfish is reversibly inhibited by the anticalmodulin drug, trifluoperazine (TFP). However, when oocytes are exposed for 10 min to trypsin, they lose their sensitivity to TFP. Trypsin does not alter the length of the hormone-dependent period (1-methyladenine minimal contact time) or the 1-methyladenine concentration requirements. Trypsin-treated oocytes remain sensitive to other maturation inhibitors such as procaine, theophylline, caffeine, and D-600. Trypsin exposure modifies the protein pattern composition of the oocyte cortex (breakdown of a 140-kDa protein). TFP binding site localization was studied using fluorescence microscopy: in addition to a general diffuse fluorescence, staining is localized to probably acidic granules located in the cortex. Results are discussed in relation to calmodulin and plasma membrane calmodulin-dependent enzyme involvement in the stimulation of starfish oocyte maturation.