Meeting Abstract

P1.142  Sunday, Jan. 4  A carbonic anhydrase repressor found in the sinus gland acts at the level of mRNA expression in the euryhaline green crab, Carcinus maenas HENRY, R.P.; Auburn University henryrp@auburn.edu

The enzyme carbonic anhydrase (CA) is known to be a central molecular component of branchial ion uptake mechanisms in crustacean gills. Cytoplasmic CA catalyzes the conversion of respiratory CO2 and water to protons and bicarbonate ions, which then serve as counterions for the active uptake of cations (Na)and anions (Cl), respectively. In the euryhaline decapod, Carcinus maenas,CA activity is induced up to 12 fold in the posterior, ion-transporting gills, upon exposure to low salinity (15 ppt). CA induction is believed to be under transcriptional regulation (i.e., gene activation followed by synthesis of new enzyme). mRNA for the cytoplasmic isoform (CAc) increases 10 fold after 6 hr of low salinity exposure and 100 fold after 24 hr. This precedes the initial induction of CA activity, which takes place at 48-72 hr post-transfer. CA gene activation appears to be under the control of a repressor found in the sinus gland (SG). Injection of SG extract, twice per day over a 4 day period, into crabs transferred from 32 to 15 ppt, results in an approximate 50% inhibition in the induction of CA activity. Injection of extract of the surrounding medullary tissue of the eyestalk has no effect. Hourly injections of SG extract for the initial 6 hours of low salinity transfer inhibits the initial 10 fold increase in CAc mRNA by up to 70%. These results indicate that the putative CA repessor acts at the level of gene expression to maintain low, baseline concentrations of CAc mRNA and hence baseline levels of CA activity in high salinity. Supported by NSF IBN 02-30005.