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Interspecific- and acclimation-induced variation in levels of heat-shock proteins 70 (hsp70) and 90 (hsp90) and heat-shock transcription factor-1 (HSF1) in congeneric marine snails (genus Tegula): implications for regulation of hsp gene expression

Lars Tomanek^* and George N. Somero

Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950-3094, USA

View larger version (47K): [in a new window]   Fig. 1. The regulatory model of transcriptional activation leading to the de novo synthesis of heat-shock proteins (hsps). Under non-stressful conditions, heat-shock factor-1 (HSF1) monomers are associated with a chaperone complex that consists at least of hsp70, hsp90 and hsp40 (for references, see text). During thermal stress, the chaperones dissociate from the complex and bind to unfolded proteins. Dissociation of the complex thus frees HSF1 monomers, which are then able to move into the nucleus and bind to the heat-shock element (HSE). HSF1 trimers bound to the HSE become hyper-phosphorylated (P) before they are transcriptionally competent. As hsp levels increase, their binding to HSF1 triggers its dissociation from the HSE, leading to a decrease in hsp gene transcription (diamond-shaped ends indicate this inhibitory effect).

View larger version (50K): [in a new window]   Fig. 2. Western blots of hsp70 isoforms, hsp90 and heat-shock factor-1 (HSF1) in a field-acclimatized (F) group of three Tegula congeners and after 30–34 days of laboratory-acclimation to 13, 18 or 23°C. Lanes contain equal amounts of protein (5 µg for hsp70 blots and 25 µg for hsp90 and HSF1 blots). A known amount of an hsp70, hsp90 or HSF1 standard (Std; see text) was loaded on each gel.

View larger version (26K): [in a new window]   Fig. 3. Endogenous levels of hsp72 in three Tegula congeners field-acclimatized (July 1997) and laboratory-acclimated to 13, 18 or 23°C for 30–34 days. Long lines indicate pairwise comparisons within species among treatments; short lines indicate comparisons within treatments among species. Ref. refers to the group with which all other groups along a line are compared. **P<0.05; NS, not significant. Values are means +1 S.E.M. (N=5 for all data points except for T. brunnea at 18°C, for which N=4).

View larger version (27K): [in a new window]   Fig. 4. Endogenous levels of hsp74 in three Tegula congeners field-acclimatized (July 1997) and laboratory-acclimated to 13, 18 or 23°C for 30–34 days. Values are means +1 S.E.M. (N=5 for all data points). For further details, see Fig. 3.

View larger version (24K): [in a new window]   Fig. 5. Ratios of hsp72 to hsp74 levels in three Tegula congeners field-acclimatized (July 1997) and laboratory-acclimated to 13, 18 or 23°C for 30–34 days. Values are means +1 S.E.M. (N=5 for all data points except for T. brunnea at 18°C, for which N=4). For further details, see Fig. 3.

View larger version (28K): [in a new window]   Fig. 6. Sum of hsp72 and hsp74 levels in three Tegula congeners field-acclimatized (July 1997) and laboratory-acclimated to 13, 18 or 23°C for 30–34 days. Values are means +1 S.E.M. (N=5 for all data points except for T. brunnea at 18°C, for which N=4). For further details, see Fig. 3.

View larger version (27K): [in a new window]   Fig. 7. Endogenous levels of hsp90 in three Tegula congeners field-acclimatized (July 1997) and laboratory-acclimated to 13, 18 or 23°C for 30–34 days. Values are means +1 S.E.M. (N=5 for all data points). For further details, see Fig. 3.

View larger version (27K): [in a new window]   Fig. 8. Endogenous levels of heat-shock transcription factor-1 (HSF1) in three Tegula congeners field-acclimatized (July 1997) and laboratory-acclimated to 13, 18 or 23°C for 30–34 days. Values are means +1 S.E.M. N=5 for all data points except for T. funebralis under field conditions (N=4), at 13°C (N=3) and 18°C (N=4) and for T. montereyi at 18°C (N=4) and 23°C (N=4). For further details, see Fig. 3.

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