ANOXIA INDUCES CHANGES IN TRANSLATABLE MESSENGER-RNA POPULATIONS IN TURTLE ORGANS - A POSSIBLE ADAPTIVE STRATEGY FOR ANAEROBIOSIS

The effects of anoxic submergence (16 h at 15 degrees C) on cellular m RNA contents were assessed in five organs of anoxia tolerant turtles T rachemys scripta elegans. Poly(A)(+) RNA was extracted from liver, red and white skeletal muscle, kidney and heart of control and anoxic tur tles, as well as from heart and kidney of turtles allowed 24 h aerobic recovery (at 15 degrees C) after anoxia exposure. Poly(A)+ RNA conten t increased by 30% in white muscle from anoxic turtles relative to con trol animals but was unchanged by metabolic state in other organs. Ext racted mRNA was translated in vitro in a wheat germ lysate system and the S-35-labelled polypeptides that were produced were separated by so dium dodecyl sulphate-polyacrylamide gel electrophoresis. Overall tran slational activity of the mRNA pool [cpm S-35-methionine incorporated per microgram poly(A)(+) RNA] was altered by anoxia exposure in three organs, increasing by 38 and 18% in liver and kidney and decreasing by 42% in red muscle. Anoxia exposure also led to qualitative changes in the protein products that resulted from in vitro translation. Sodium dodecyl sulphate polyacrylamide gel electrophoresis revealed the prese nce of a novel 19.5-kDa polypeptide in liver of anoxia-exposed animals as well as increased amounts of two other proteins at 28.6 and 79.9 k Da. In heart a new translation product of 26.8 kDa appeared in anoxia, and in kidney a 32.8-kDa polypeptide was produced during the aerobic recovery period after anoxia exposure. Anoxia stimulated the appearanc e of a 37.5-kDa protein in red skeletal muscle but anoxic red muscle a lso lost proteins of 40, 32, and 28.2 kDa that were present in aerobic controls. Anoxia exposure did not change the proteins produced by in vitro translation in white muscle. The results suggest that anoxia exp osure triggers rapid cellular responses in T. s. elegans that modify t ranslatable mRNA populations in organs, leading to new protein transcr ipts. This response may be one of the important molecular adaptations that support the natural anoxia tolerance of this species.