ROYAL, TD; KELLEY, KM; California State Univ., Long Beach; California State Univ., Long Beach: Molecular and Physiological Characterization of an Insulin-like Growth Factor-binding Protein in a Chondrichthyean Fish

Studies in fishes have demonstrated that insulin-like growth factor-binding proteins (IGFBPs) are differentially regulated by a variety of hormones and under different physiological circumstances. For example, stressful situations induce peaks in circulating concentrations of glucocorticoids in parallel with alterations in plasma IGFBP levels: a 30 kDa IGFBP, believed to be the counterpart of mammalian IGFBP-1, is increased, while a 40-45 kDa IGFBP, believed to be the counterpart of mammalian IGFBP-3, is decreased. Glucocorticoid treatments of fish indicate the same direct effects on IGFBPs, and these occur with an inhibition of somatic growth. To date, there have been no studies of IGFBPs in chondrichthyean fish species. We have therefore initiated an effort to clone and study IGFBPs from elasmobranchs, including the round stingray (Urobatis halleri), to determine the degree to which these proteins have conserved primary sequences and physiological actions. A partial 522-bp cDNA was isolated from U. halleri liver that encodes 174 residues from part of the variable mid-region to the C-terminus of vertebrate IGFBP-3. Sequence identities were highest in the C-terminus (60-75%) and, interestingly, were not greater among the fish (tilapia, zebrafish) as compared against chicken, mouse, and human. Studies on the expression of IGFBP-3 mRNA in U. halleri in liver, which produces a 45 kDa IGFBP, and in fish subjected to stress will be discussed [Support in part from NSF grant IBN-0115975 and California Sea Grant #R/F-192]