The synthesis of a small heat shock/alpha-crystallin protein in Artemia and its relationship to stress tolerance during development

Fertilized oocytes of the brine shrimp Artemia franciscana undergo either o voviviparous or oviparous development, yielding Gee swimming larvae (naupli i) or encysted gastrulae (cysts), respectively. Encystment is followed by d iapause, wherein metabolism is greatly reduced; the resulting cysts are ver y resistant to extreme stress, including desiccation and long-term anoxia. The synthesis of p26, a small heat shock/alpha-crystallin protein produced only in oviparously developing Artemia, is shown in this paper to be transc riptionally regulated. A p26 mRNA of about 0.7 kb was detected on Northern blots in the second day after oocyte fertilization. It peaked as embryos en cysted and declined rapidly when activated cysts resumed development. The a ppearance of p26 protein, as indicated by immunoprobing of Western blots, f ollowed mRNA by 1 day; it also increased as encystment occurred hut remaine d constant during postgastrula development of cysts. However, p26 underwent a marked reduction during emergence of nauplii and could not be detected i n cell-free extracts of second-instar larvae, p26 entered nuclei of encysti ng embryos soon after synthesis and was localized therein as late as instar II, when it was restricted to a small set of salt gland nuclei. First-inst ar larvae derived from cysts were more thermotolerant than larvae that had developed ovoviviparously, but synthesis of p26 was not induced by heat und er the experimental conditions employed. Additionally, transformed bacteria synthesizing p26 were more thermotolerant than bacteria that lacked the pr otein. The results support the proposal that p26, a developmentally regulat ed protein synthesized during embryo encystment, has chaperone activity in vivo and protects the proteins of encysted Artemia from stress-induced dena turation. (C) 1999 Academic Press.