GLOBAL ARREST OF TRANSLATION DURING INVERTEBRATE QUIESCENCE

Comparing the translational capacities of cell-free systems from aerob ically developing embryos of the brine shrimp Artemia franciscana vs. quiescent embryos has revealed a global arrest of protein synthesis. I ncorporation rates of [H-3]leucine by lysates from 4-h anoxic embryos were 8% of those from aerobic (control) embryos, when assayed at the r espective pH values measured for each treatment in vivo. Exposure of e mbryos to 4 h of aerobic acidosis (elevated CO2 in the presence of oxy gen) suppressed protein synthesis to 3% of control values. These latte r two experimental treatments promote developmental arrest of Artemia embryos and, concomitantly, cause acute declines in intracellular pH. When lysates from each treatment were assayed over a range of physiolo gically relevant pH values (pH 6.4-8.0), amino acid incorporation rate s in lysates from quiescent embryos were consistently lower than value s for the aerobic controls. Acute reversal of pH to alkaline values du ring the 6-min assays was not sufficient to return the incorporation r ates of quiescent lysates to control values, Thus, a stable alteration in translational capacity of quiescent lysates is indicated. Addition of exogenous mRNA did hot rescue the suppressed protein synthesis in quiescent lysates, which suggests that the acute blockage of amino aci d incorporation is apparently not due to limitation in message. Thus, the results support a role for intracellular pH as an initial signalin g event in translational control during quiescence yet, at the same ti me, indicate that a direct proton effect on the translational machiner y is not the sole proximal agent for biosynthetic arrest in this primi tive crustacean.