HENRY, R.P.*; SMITH, C.; Auburn University; University of New Hampshire: CARBONIC ANHYDRASE REPRESSOR IN THE SINUS GLAND OF THE EURYHALINE GREEN CRAB CARCINUS MAENAS

The enzyme carbonic anhydrase (CA) is a central component of the molecular mechanism of low salinity adaptation in the euryhaline green crab, Carcinus maenas. There is a 10-fold induction of CA activity in the posterior, ion transporting gills of blue crabs in response to transfer from high (32 ppt) to low (15 ppt) salinity. Recent evidence has indicated that CA induction is under inhibitory control by a repressor compound found in the eyestalk. Eyestalk ablation (ESA) results in a doubling of CA activity and expression in the absence of low salinity exposure, and ESA potentiates normal CA induction in low salinity. Furthermore, injection of eyestalk extracts from high salinity adapted crabs inhibits salinity-stimulated CA induction. The putative CA repressor is acid- and heat-stable for short periods of time (2 min) but loses its potency after being boiled for more than 5 min. Injection of sinus gland extract inhibits low salinity CA induction, but injections of the remaining medullary tissue of the eyestalk has no effect. This suggests the putative CA repressor is an inhibitory neuropeptide, produced in the X-organ and stored in the sinus gland. The repressor is also present in the hemolymph of crabs acclimated to high salinity, but it is absent from eyestalk-ablated crabs and crabs that have been acclimated to 10 ppt for one week. This compound is effective at the transcriptional level, inhibiting the increase in CA RNA normally seen in response to low salinity exposure. HPLC fractionation of sinus gland extract is currently under way to identify the peak containing the CA repressor activity. Supported by NSF 02-0003 to RPH, and by the Thomas H. Maren Foundation.