SCHULTE, PM*; KEIR, K; University of British Columbia, Vancouver; University of British Columbia, Vancouver: The cystic fibrosis transmembrane conductance regulator and the evolution of euryhalinity in fish.

Fundulus heteroclitus, a euryhaline teleost fish, inhabits marshes, bays, and estuaries along the Atlantic Coast of North America. Increases in the glucocorticoid hormone cortisol are thought to be important in allowing transfer from FW to SW by causing upregulation of SW specific ion transporters, including the cystic fibrosis transmembrane conductance regulator (CFTR), an apical chloride channel. To investigate the mechanisms underlying this upregulation, we have sequenced the promoter of F. heteroclitus Cftr, and identified numerous putative glucocorticoid binding sites. However, tests of this promoter in cell culture and in transgenic fish indicated that these putative binding sites are non-functional. We also identified a putative osmotic responsive element (ORE), and functional assays of this element are ongoing. To investigate the evolution of euryhalinity, we have cloned the Cftr promoter from a number of species in the genus Fundulus, including freshwater-restricted and euryhaline representatives. The putative ORE differs between freshwater and euryhaline species, suggesting the possibility that variation in this promoter element may be involved in the evolution of euryhalinity.