Isolation and characterization of somatolactin genes from two cold water marine teleosts, lumpfish (Cyclopterus lumpus) and halibut (Hippoglossus hippoglossus).

Somatolactin (SL) is a newly discovered pituitary hormone structurally related to both growth hormone and prolactin. We isolated the SL gene from two cold water marine teleosts, lumpfish (Cyclopterus lumpus) and halibut (Hippoglossus hippoglossus). The SL genes for lumpfish were isolated from a complementary DNA (cDNA) library by random gene tagging and sequencing. Two full-size clones of 1.2 (lfSL-6) and 1.6 (lfSL-9) kilobases (kb) were characterized. The SL genes for halibut were identified from its cDNA library using lumpfish SL gene as a probe. Two full-size SL clones of 1.1 and 1.6 kb were identified in halibut. All these clones encoded full-size SL (229 amino acids for lumpfish SL, 230 amino acids for halibut SL), including 7 cysteines and two and three potential glycosylation sites in halibut and lumpfish, respectively. The differences in length of these clones are attributed to their differences in 3' untranslated sequences. Although the halibut SL genes contain the consesus polyadenylation signal AATAAA, the lumpfish SL gene has the ATTAAA sequence in the larger clone (lfSL-9). None of the consensus or the alternative polyadenylation signals were found in the shorter clone (lfSL-6). Protein homology and DNA sequence alignments of SL genes from all five known marine fishes suggest that the SL gene sequence is highly conserved.