The proteomic response of cheliped myofibril tissue in the eurythermal porcelain crab Petrolisthes cinctipes to heat shock following acclimation to daily temperature fluctuations

The porcelain crab Petrolisthes cinctipes lives under rocks and in mussel beds in the mid-intertidal zone where it experiences immersion during high tide and saturating humid conditions in air during low tide, which can increase habitat temperature by up to 20 degrees C. To identify the biochemical changes affected by increasing temperature fluctuations and subsequent heat shock, we acclimated P. cinctipes for 30 days to one of three temperature regimes: (1) constant 10 degrees C, (2) daily temperature fluctuations between 10 and 20 degrees C ( 5 h up- ramp to 20 degrees C, 1 h down-ramp to 10 degrees C) and (3) 10-30 degrees C (up-ramp to 30 degrees C). After acclimation, animals were exposed to either 10 degrees C or a 30 degrees C heat shock to analyze the proteomic changes in claw muscle tissue. Following acclimation to 10- 30 degrees C (measured at 10 degrees C), enolase and ATP synthase increased in abundance. Following heat shock, isoforms of arginine kinase and glycolytic enzymes such as aldolase, triose phosphate isomerase and glyceraldehyde 3- phosphate dehydrogenase increased across all acclimation regimes. Full- length isoforms of hemocyanin increased abundance following acclimation to 10- 30 degrees C, but hemocyanin fragments increased after heat shock following constant 10 degrees C and fluctuating 10-20 degrees C, possibly playing a role as antimicrobial peptides. Following constant 10 degrees C and fluctuating 10- 20 degrees C, paramyosin and myosin heavy chain type-B increased in abundance, respectively, whereas myosin light and heavy chain decreased with heat shock. Actin- binding proteins, which stabilize actin filaments (filamin and tropomyosin), increased during heat shock following 10-30 degrees C; however, actin severing and depolymerization proteins (gelsolin and cofilin) increased during heat shock following 10-20 degrees C, possibly promoting muscle fiber restructuring. RAF kinase inhibitor protein and prostaglandin reductase increased during heat shock following constant 10 degrees C and fluctuating 10- 20 degrees C, possibly inhibiting an immune response during heat shock. The results suggest that ATP supply, muscle fiber restructuring and immune responses are all affected by temperature fluctuations and subsequent acute heat shock in muscle tissue. Furthermore, although heat shock after acclimation to constant 10 degrees C and fluctuating 10-30 degrees Cshowed the greatest effects on the proteome, moderately fluctuating temperatures (10-20 degrees C) broadened the temperature range over which claw muscle was able to respond to an acute heat shock with limited changes in the muscle proteome.