Nucleotide Sequence and Growth Hormone-Regulated Expression of Salmon Insulin-Like Growth Factor I mRNA

Abstract

Protein and cDNA sequence analysis have revealed that the insulin-like growth factor (IGF-I) has been highly conserved among several mammalian species. Using the combined techniques of polymerase chain reaction and molecular cloning, we have now obtained the cDNA sequence encoding preproIGF-I from a teleost species, Oncorhynchus kisutch (coho salmon). The 2020 nucleotide (nt) cloned cDNA sequence contains a 528 nt open reading frame encoding 176 amino acids in preproIGF-I and 175 nt and 1317 nt of flanking 5'- and 3'-untranslated regions, respectively. The deduced amino acid sequence of salmon IGF-I is highly conserved relative to its mammalian homologues and there are only 14 amino acid differences out of 70 between salmon and human IGF-I. Interestingly, the C-terminal E domain of salmon proIGF-I, which is presumed to be proteolytically cleaved during biosynthesis, also shows striking amino acid sequence homology with its mammalian counterpart, except for an internal 27 residue segment that is unique to salmon proIGF-I. Northern analysis revealed that salmon preproIGF-I mRNA consists predominantly of a single 3900 nt sized band although minor bands were also observed after prolonged autoradiographic exposure. The RNA analysis also revealed that the level of preproIGF-I mRNA is increased 6-fold in liver RNA isolated from salmon injected with bovine GH, as compared to untreated controls. These results demonstrate that the primary structure and regulated expression of IGF-I by GH have been conserved in teleosts.

Purification, amino acid sequence and characterisation of kangaroo IGF-I

“…The difference of Glu at position 20 also occurs in IGF-I from several species of fish including salmon (Cao et al 1989), barramundi (Kinhult 1996) and sea-bream (Duguay et al 1996). This change is not seen in IGF-I from all other species of fish characterised, with IGF-I from carp (Liang et al 1996) and shark (Duguay et al 1995) containing Asp, a similarly charged amino acid, at position 20.…”

“…IGF proteins or cDNA transcripts have been described in the chicken (Dawe et al 1988, Kallincos et al 1990, several species of fish (Cao et al 1989, Duguay et al 1995, 1996, Moriyama et al 1995, Liang et al 1996, Kinhult 1996 and the frog, Xenopus laevis (Kajimoto & Rotwein 1990). N-Terminal protein sequencing and the cDNA-deduced amino acid sequences indicate that there is a high degree of conservation of IGF structure throughout vertebrate evolution.…”

Insulin-like growth factor-I stimulates gonadotrophin production from eel pituitary cells: a possible metabolic signal for induction of puberty

“…In this study we used mammalian (human recombinant) IGF-I, since a high degree of molecular conservation has been shown for IGF-I from teleosts to mammals (Cao et al 1989, and review by Upton et al 1997). Moreover, mammalian IGF-I has been shown to be biologically active in the eel in two experimental situations.…”

Primary cultured hepatocytes of the bony fish, Oreochromis mossambicus, the tilapia: a valid tool for physiological studies on IGF-I expression in liver

“…IGF-I sequences are highly conserved throughout evolution (Reinecke & Collet 1998). IGF-I cDNA sequences have recently been characterised in several bony fish species: Oncorhynchus kisutch (Cao et al 1989), O. mykiss (Shamblott & Chen 1992), Oreochromis mossambicus , Chen et al 1998, Cyprinus carpio (Hashimoto et al 1997), Cottus scorpius (Loffing-Cueni et al 1998) and Lates calcarifer (Kinhult-Stahlbom et al 1999). These showed about 80% sequence homology to each other, and approximately 45% to the human IGF-I sequence.…”

“…Evidence for a potential GH-dependency of liver IGF-I expression, however, is conflicting. In salmonids, injections of bovine GH increased IGF-I mRNA and serum IGF-I levels (Cao et al 1989, Shamblott et al 1995. In contrast, no significant increase in the amount of liver IGF-I mRNA was achieved after intraperitoneal administration of recombinant seabream GH in barramundi (Kinhult-Stahlbom et al 1999).…”