Co-induction of hepatic IGF-I and progranulin mRNA by growth hormone in tilapia, Oreochromis mossambiccus

Abstract

Like IGF-I, progranulin (pgrn) is a growth factor involved in tumorigenesis and wound healing. We report here the identification and characterization of pgrn cDNA in tilapia and the regulation of its expression by growth hormone (GH). The tilapia pgrn cDNA was cloned by RT-PCR amplification, using gene specific oligonucleotides as amplification primers. The cDNA contains an open reading frame encoding a peptide of 206 amino acid residues (aa) that contains a presumptive signal peptide (23 aa) and two repeat units of granulin (grn, 51 and 52 aa, respectively) franked by a GAP of 49 aa and the carboxyl terminus with 31 aa. The two predicted grn peptides are arranged in tandem repeats interrupted by a GAP peptide. RT-PCR analysis revealed that high levels of prgn mRNA were present in several tissues such as spleen, gastric cecum, intestine, fat tissue, gill, kidney, eye and pancreas, and lower levels in liver, muscle, heart, brain, skin and stomach. Administration of a single dose (500 ng/g body weight) of recombinant seabream growth hormone (rbGH) by intraperitoneal (ip) injection into one-month-old tilapia resulted in an obvious increase of IGF-I and pgrn mRNA (2.7-fold and 2.5-fold, respectively) in the liver at three hours post-GH treatment. The peptide levels of pgrn in the liver of GH-treated fish also were substantially induced over controls at 12 h post-GH treatment as detected by western immuno-blot analysis. The co-induction of IGF-I and pgrn following GH treatment may suggest the involvement of pgrn in GH regulated growth in tilapia.