Neuroendocrine Control of Salinity-Mediated Carbonic Anhydrase Expression in the Gills of Euryhaline Crustaceans

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This study will examine mechanisms of how organisms sense environmental changes, and how they adapt to cope with these changes by turning on specific genes that give them new physiological abilities. The focus is on crustaceans. Euryhaline crustaceans are those that tolerate a wide range of salt concentrations in water, from the open ocean to freshwater rivers. In general, they do so by taking up salts (sodium and chloride), thus maintaining constant concentrations of vital blood salts. The molecular basis of this ability is a suite of transport proteins that are expressed in the gill. A number of proteins have been identified that are responsible for the transport of individual ions. The mechanism of transport usually involves the uptake of a vital ion in exchange for the ionic form of a waste product (e.g., Na+/H+ and Cl-/HCO3- exchange). The waste products are produced from the reaction of CO2 and water, which is catalyzed by the enzyme carbonic anhydrase (CA). Because H+ and HCO3- are used in exchange for cations and anions in general, CA is believed to be a central support enzyme in the overall mechanism of ion uptake. Furthermore, the expression of CA is up-regulated when these organisms are exposed to low salinity. Preliminary evidence indicates that the regulatory mechanism is present only in euryhaline species and that it is under inhibitory control by a CA repressor (believed to be a neuropeptide) found in the major endocrine system of crustaceans, the X-organ/sinus gland complex. This peptide will be identified by HPLC, and its action on CA expression investigated through the use of quantitative PCR and reporter enzyme assays. This research also has broader impacts, because estuaries are highly productive environments, and one species being studied is economically important (e.g., Callinectes sapidus) whereas the other (Carcinus maenas) is an invasive species that has been both ecologically and economically disruptive. The project will also involve the training of undergraduate students, graduate students, and postdoctoral associates in all phases of the research.