EXPRESSION CLONING OF A CDNA-ENCODING A FISH PROLACTIN RECEPTOR

By using an expression cloning strategy, we isolated a single positive clone encoding a tilapia prolactin (PRL) receptor, Tilapia PRL(188) was used to screen a freshwater tilapia kidney expression library transfected in COS cells, The tilapia PRL receptor is a mature protein of 606 amino acids, The extracellular domain is devoid of the tandem repeat units present in birds and has two pairs of cysteine residues, a Trp-Ser-Xaa-Trp-Ser motif, and two potential N-glycosylation sites, The cytoplasmic domain contains 372 amino acids, including box 1, a sequence previously shown to be important for signal transduction in mammalian species, Thus, the general structure is similar to the long form of mammalian PRL receptors; however, amino acid comparisons reveal a rather low identity (approximate to 37%). Northern blot analysis shows the existence of a single transcript in osmoregulatory tissues and reproductive organs, This localization is in agreement with known functions of PRL in teleosts.