JAYASUNDARA, N.*; SPANINGS-PIERROT, C.; TOWLE, D.W.; MDI Bio. Lab., Salsbury Cove, ME; Universite Montpellier, France; MDI Bio. Lab., Salsbury Cove, ME: Salinity-induced changes in isoform-specific Na⁺+K⁺-ATPase gene expression in the European shore crab Pachygrapsus marmoratus

The grapsid crab P. marmoratus is strongly euryhaline, regulating hemolymph osmolality by absorbing NaCl across the gills from low salinity and excreting NaCl into high salinity. Gene transcript levels measured in gills by quantitative PCR show significant changes with environmental salinity. Beginning within 2 hours after transfer of crabs from 36 to 10 ppt salinity, Na⁺+K⁺-ATPase α-subunit mRNA increases 8-to-20-fold in all analyzed gills and remains high for at least 48 hours. However, transfer from 36 to 45 ppt induces Na⁺+K⁺-ATPase α-subunit mRNA expression only in gill 7, increasing 10-fold by 6 hours, suggesting that gill 7 may be specialized for NaCl excretion. A closer examination of α-subunit transcripts demonstrated the presence of two isoforms, which we have labeled C and D, identical to each other except that the D isoform contains an in-frame insert of 81 nucleotides near the 5� end, resulting in the encoding of 27 additional amino acids. Transcriptional response to salinity change is exhibited primarily by the C isoform, which is present at particularly low levels in animals acclimated to 36 ppt but becomes strongly induced upon salinity change. The expression of the D isoform is also enhanced but only modestly. Analysis of genomic DNA indicates that both C and D isoforms are encoded at the genomic level and are likely not the result of alternative splicing. Supported by NSF IBN-0340622.