CDNA cloning of two types of growth hormone receptor in torafugu Takifugu rubripes: tissue distribution is possibly correlated to lipid accumulation patterns

Abstract

Growth hormone (GH) is an important hormone with primary roles in growth, lipid metabolism, osmoregulation, and immunity in fish, via the growth hormone receptor (GHR). We have cloned cDNAs from the torafugu pufferfish Takifugu rubripes encoding two distinct GHRs. Phylogenetic analysis of these GHRs together with their counterparts from other fish led to the identification of 1914- and 1695-bp cDNAs for torafugu GHR1 and GHR2, respectively. The deduced amino acid sequences of GHR1 and GHR2 showed 34% identity and, in comparison to torafugu GHR1, torafugu GHR2 lacked three extracellular cysteine and five intracellular tyrosine residues, suggesting that the two torafugu GHRs have different functions in GH/GHR signaling. Real-time PCR revealed that the transcript abundance of torafugu GHR1 and GHR2 tended to be high in fast muscle, slow muscle, and liver. Notably, the relative mRNA level of torafugu GHR1 was significantly higher in fast muscle, in comparison to the GHR1s from other fish reported to date where the highest relative mRNA levels have been found in the liver. Taken together with the well-known lipolytic effects of GH on fish liver, these expression patterns of torafugu GHRs suggest its liver-specific lipid accumulation.