Quiescent gemmules of the freshwater sponge, Spongilla lacustris (Linnaeus, 1759), contain remarkably high levels of Hsp70 stress protein and hsp70 stress gene mRNA

Abstract

With the onset of changing environmental conditions in autumn, the freshwater sponge Spongilla lacustris (Linnaeus, 1759) produces resistant stages (gemmules) which are in the state of quiescence. Gemmules stored at 8 degrees C remained quiescent; however, germination occurred within 24 hr after the water temperature was increased to 22.5 degrees C. Sponges hatched through the micropyle and subsequently built new spicules and a new canal system. The molecular and biochemical mechanisms which enable the gemmules to survive long periods of adverse conditions are not known. For the first time we focused on the role of the stress protein Hsp70 and the expression of hsp70 mRNA in S. lacustris during the development of gemmules in the state of quiescence into growing sponges. The partial sequence of hsp70 seems to be a true hsp gene since transcription could be clearly enhanced by temperature elevation. The results showed a large pool of cellular Hsp70 and hsp70 mRNA in gemmules during the state of quiescence. Within hours after a temperature trigger, the Hsp70 level decreased slowly and reached approximately the level of an adult sponge. Hsp70 presumably allows gemmules to stabilize their proteins and membranes during dormancy from autumn to spring when water temperatures change.