JAYASUNDARA, N.*; SPANINGS-PIERROT, C.; TOWLE, D.W.; College of the Atlantic; Universite Montpellier II; Mount Desert Island Biological Laboratory: Quantitative analysis of hsp70 mRNA expression under salinity stress in the euryhaline shore crab Pachygrapsus marmoratus

Marbled rock crabs (Pachygrapsus marmoratus) are subjected to physiological stress due to large and rapid fluctuations in seawater salinity, conditions that we hypothesized might elicit changes in the gene expression of heat shock proteins (hsps) in gills, the most important osmoregulatory organs. We identified and sequenced an hsp70 cDNA from Pachygrapsus and quantitated hsp70 mRNA expression in anterior and posterior gills under low (10 ppt) and high (45 ppt) salinity at different time intervals following transfer from normal seawater (32 ppt). Real-time PCR analysis showed that hsp70 mRNA is expressed equally under control conditions in anterior (G5, G6) and posterior (G7, G8, G9) gills. Following transfer to low salinity, hsp70 expression increased about 2-fold in G5, G6 and G9 at 24 and 48 h. However, in G7 and G8 it started to increase by 3- to 4-fold within the first 6 h and slightly decreased by 48 h. Following transfer to high salinity, G5, G6, and G9 did not show any significant change. However, G8 showed a 2-fold increase within 4 h and by 48 h decreased gradually to the level observed under control conditions. In G7, hsp70 expression increased about 3-fold within 4 h and about 4-fold in 6 h, then slightly decreased at 24 and 48 h to a level that was still twice the amount expressed in controls. The expression of arginine kinase (AK), a putative housekeeping gene, showed nearly equal levels at all times. These results confirm that hsp70 is highly expressed under salinity-stressed conditions and that posterior gills, gill 7 in particular, play an important role in osmoregulatory adjustments of Pachygrapsus marmoratus. Supported by NSF (IBN-0340622).