Two-dimensional gel analysis of the heat-shock response in marine snails (genus Tegula): interspecific variation in protein expression and acclimation ability

Abstract

The degree to which temperature acclimation modifies the acute synthesis of the entire heat-shock protein (Hsp) complement is still unknown, but it may constitute an important mechanism for understanding the differences in acclimation ability among closely related ectothermic species that occupy widely varying thermal environments. In general, eurythermal (heat-tolerant) species modify physiological function in response to an increase in acclimation temperature to a greater extent than stenothermal (heat-sensitive) species. In the present work I used 35S-labelled amino acids and two-dimensional gel electrophoresis to test this assumption for how acclimation affects acute Hsp expression (referred to as phenotypic plasticity) in two heat-sensitive, low-intertidal to subtidal zone turban snails, Tegula brunnea and T. montereyi, in comparison to a heat-tolerant, mid- to low-intertidal zone congener, T. funebralis. I was able (i) to detect the synthesis of over 30 proteins in gill tissue, primarily in the 70 kDa range, in response to an increase in temperature (13 degrees C, 24 degrees C, 27 degrees C and 30 degrees C), (ii) to assess the effect of acclimation (13 degrees C vs 22 degrees C) on acute Hsp synthesis, and (iii) to compare this effect among the three Tegula congeners. After increasing acclimation temperature from 13 degrees C to 22 degrees C, synthesis of the most highly expressed Hsps decreased more in T. brunnea and T. montereyi than in T. funebralis. Two highly expressed proteins of molecular mass 71 and 74 kDa, however, were also synthesized constitutively at 13 degrees C and changed with increasing acclimation temperature in all three species. Although similar in phenotypic plasticity, T. brunnea and T. montereyi synthesized either a 76 or a 72 kDa cluster of proteins, respectively, and differed in how acclimation affected the acute synthesis of several 77 kDa proteins. Thus, in Tegula, the effect of acclimation on Hsp expression is (i) Hsp-specific, (ii) dependent on a protein's expression pattern (constitutive and inducible vs only inducible), (iii) and is actually limited in the more eurythermal mid- to low-intertidal congener. These results contradict the general assumption that greater heat tolerance correlates with an increased ability to modify physiological function in response to acclimation.