Anoxia induces changes in translatable mRNA populations in turtle organs: a possible adaptave strategy for anaerobiosis
Abstract:
The effects of anoxic submergence (16 h at 15°C) on cellular mRNA contents were assessed in five organs of anoxia tolerant turtles Trachemys scripta elegans. Poly(A)+ RNA was extracted from liver, red and white skeletal muscle, kidney and heart of control and anoxic turtles, as well as from heart and kidney of turtles allowed 24 h aerobic recovery (at 15°C) after anoxia exposure. Poly(A)+ RNA content increased by 30 % in white muscle from anoxic turtles relative to control animals but was unchanged by metabolic state in other organs. Extracted mRNA was translated in vitro in a wheat germ lysate system and the 35S-labelled polypeptides that were produced were separated by SDS-polyacrylamide gel electrophoresis. Overall translational activity of the mRNA pool [cpm 35S-methionine incorporated per microgram poly(A)+ RNA] was altered by anoxia exposure in 3 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. SDS-PAGE revealed the presence 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 kDa. 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 appearance of a 37.5 kDa protein in red skeletal muscle but anoxic red muscle also 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 exposure triggers rapid cellular responses in T. s. elegans that modify translatable mRNA populations in organs, leading to new protein transcripts. This response may be one of the important molecular adaptations that support the natural anoxia tolerance of this species.