EFFECT OF ANAEROBIOSIS ON CYSTEINE PROTEASE REGULATION DURING THE EMBRYONIC-LARVAL TRANSITION IN ARTEMIA-FRANCISCANA

Hydrated encysted embryos of the brine shrimp Artemia franciscana have the ability to withstand years in anaerobic sea water using metabolic strategies that enable them to inactivate all cell metabolic activiti es and then to resume development when placed in aerobic sea water. Ho wever, this unique characteristic of Artemia franciscana embryos is lo st during a very short period, at the embryonic-larval transition peri od of development, coincident with the appearance of prenauplius larva e. Thus, while encysted embryos show complete inhibition of proteolysi s over at least 4 years under anoxia, control of this activity, togeth er with resistance to anoxia, is lost in newly hatched nauplius larvae after only a few days in anaerobic sea water. In contrast to encysted embryos, young larvae in anaerobic sea water produce large amounts of lactic acid, which reaches a concentration of nearly 50 mmol l(-1) wi thin 12 h of incubation. The accumulated lactic acid is believed to re duce the intracellular pH (pHi) to considerably less than 6.3, the val ue found in encysted embryos after 5 months in anaerobic sea water. We find that larvae, in contrast to embryos, lose cytoplasmic proteins a t the rate of 4-5 ngh(-1) larva(-1) upon transfer to anaerobic sea wat er, while yolk proteins are not degraded in either embryos or larvae u nder anoxic conditions. The decline in cytoplasmic protein levels in a naerobic larvae may be due to activation of an endogenous cysteine pro tease (CP) as the pHi becomes acidic. Contributing to the apparent unc ontrolled CP activity is a decrease in the level of cysteine protease inhibitor (CPI) activity during the embryonic-larval transition period , resulting in an increase in the CP/CPI ratio, from approximately 0.5 in embryos to greater than 1.0 in newly hatched larvae. Finally, data are presented to suggest that loss of the 26 kDa stress protein from embryos during the embryonic-larval transition may also contribute to the loss in resistance of young nauplius larvae of A. franciscana to a naerobic conditions.