Long-term anoxia in encysted embryos of the crustacean, Artemia franciscana: viability, ultrastructure, and stress proteins

Cells of encysted embryos of Artemia franciscana, the brine shrimp, are amo ng the most resistant of all animal cells to extremes of environmental stre ss. We focus here on their ability to survive continuous anoxia for periods of years, during which their metabolic rate is undetectable. We asked whet her their impressive tolerance was reflected in changes at the ultrastructu ral level. The ultrastructure of encysted embryos previously experiencing 3 8 days and 3.3 years of anoxia was com pared with those not undergoing anox ia (controls). Rough endoplasmic reticulum was abundant in anoxic embryos, in spite of the absence of protein biosynthesis in their cells. Other cytop lasmic changes had occurred in the anoxic cells, but overall their structur e was remarkably intact, in view of their 3 years of continuous anoxia. A m ajor difference was the presence of abundant electron-dense granules in the nuclei of anoxic embryos; these were present but rare in nuclei of control s. Biochemical fractionation and Western immunoblotting confirmed previous observations that substantial amounts of the small heat shock/alpha-crystal lin protein (p26) translocated into nuclei of anoxic embryos. We have no ev idence that the dense granules contain this protein, but that remains a pos sibility. In contrast, and contrary to expectation, proteins of the hsp70 a nd 90 families did not undergo anoxia-induced nuclear translocation, an unu sual result since such translocations have been widely observed in cells fr om a variety of organisms.