The heat shock response of the cryptobiotic brine shrimp Artemia — II. Heat shock proteins

Abstract

1. 1.The synthesis of heat shock protein (hsps) and heat shock-related proteins has been examined in cysts and nauplius larvae of Artemia exposed to different temperatures. 2. 2.One dimensional SDS-PAGE analysis of proteins from larvae of between 24 and 72 h of development shows a temperature-dependent increase in the synthesis of two proteins, p68 and p89 between 28 and 40°C. A 5 min heat shock at 40°C is sufficient to enhance the subsequent expression of p68 and p89 while 45 min to 1 h at this temperature causes the strong repression of non-hsp synthesis. 3. 3.Cysts synthesise p68 and p89 appreciably at 28°C but enhance this synthesis up to 40°C. However normal protein synthesis is not repressed relative to hsp synthesis until 47°C, in agreement with the known thermotolerance of the cysts. 4. 4.Two-dimensional IEF/SDS-PAGE analysis coupled to immunoblotting with an anti-chick hsp70 antibody shows p68 to consist of inducible hsp68 and hsp70 and constitutively synthesised heat shock cognate (hsc70) forms. The hsp68 isoforms are absent from cysts but are induced upon heat shock. Larvae appear constitutively to express some hsp68 isoforms but these are enhanced considerably by heat. The p70 proteins show a variable pattern of stage-specific and heat activation. 5. 5.Further heat-inducible species, p74 and p45 isoforms probably arise through proteolytic degradation of p89 and p68/p70 respectively. The p45 proteins cross-react with anti-chick hsp70. 6. 6.A low molecular weight hsp, hsp31, is constitutively synthesised by cysts but is strictly heat inducible in larvae. Its behaviour thus mirrors the constitutive and inducible thermotolerance of cysts and larvae respectively and it may therefore have a role to play in this phenomenon. It may also be related to artemin, the abundant cyst-specific 19S protein particle which appears to characterise the crytobiotic state.