SPANINGS-PIERROT, C.; TOWLE, D.W.*; Univ. Montpellier II, France; Mt. Desert Island Biol. Lab., Salsbury Cove, ME: Ion Transporter Expression in Relation to Environmental Salinity in the Euryhaline Crab Pachygrapsus marmoratus

Changes in gene expression in gills of the hyper-/hypo-osmoregulating grapsid crab Pachygrapsus marmoratus following transfer from seawater (35 ppt) to low and high salinities (10 and 45 ppt) were investigated by measuring mRNA content for Na/K-ATPase alpha-subunit, Na/K/2Cl cotransporter, and V-type H-ATPase B-subunit by real-time quantitative PCR. In low salinity, Na/K-ATPase mRNA increased 6- to 20-fold in all tested gills, with significant enhancement in anterior gills 5 and 6 and posterior gill 9 24h after transfer from seawater and more rapid increases in posterior gills 7 and 8 4h after transfer. No differences in cotransporter mRNA expression occurred in anterior gills, but a slight increase was measured in posterior gills 6 to 48h after transfer. V-type H-ATPase expression increased 3-fold in posterior gill 7 within 2h and increased up to 10-fold in other gills after 48 h. Because enhanced expression of V-ATPase and Na/K-ATPase is induced by low salinity, these two transporters likely play critical roles in the active uptake of NaCl in P. marmoratus. Following transfer to high salinity, only posterior gill 7 exhibited a marked increase in Na/K-ATPase mRNA, doubling 4h after transfer and becoming 4-fold higher after 6h; slight increases in gills 8 and 9 and no changes in anterior gills were observed. Similar results were obtained for V-ATPase and cotransporter with a sharp increase (6- and 3-fold respectively) in gill 7 6h after transfer. The restricted response in ion transporter mRNA expression following transfer of P. marmoratus to high salinity suggests a high degree of gill specialization for hypo-osmoregulatory NaCl excretion. Supported by MDIBL and NSF (DBI-0100394).