Production and Purification of Recombinant Somatolactin and its Effects on Insulin-like Growth Factors Gene Expression in Tilapia Hepatocytes

Jianpeng Peng,Anji Lian

doi:10.4172/2150-3508.1000166

Abstract

Somatolactin (SL), the member of the growth hormone (GH)/prolactin (PRL) family, is fish-specific pituitary hormone with diverse functions. However, little is known about its biological function in fish hepatocytes. Using tilapia as a model, SLtranscripts were shown to be widely expressed in various extrapituitary tissues with the relatively high expression level in liver. To explore the biological action of SL in hepatocytes, we produced and purified recombinant tilapia SL protein which could induce pigment aggregation in tilapia melanophores. Further, the antiserum for the SL was produced and its specificity was confirmed by antiserum preabsorption. During 4 week starvation, hepatic SL transcripts in starved fish were significantly higher than the control fish starting on the 1st week of starvation until 4th week. After re-feeding, the SL transcripts level returned to normal. Using primary cultures of tilapia hepatocytes, insulin-like growth factors (IGF1 and IGF2) gene expression were elevated by static incubation with recombinant tilapia SL. In contrast, removal endogenous SL by immunoneutralization using SL antiserum was shown to inhibit IGF1 and IGFgene expression. These findings, taken together, provide evidence for the first time that SL may serve as a novel regulator in fish stimulating IGF1 and IGF gene expression in hepatocytes.

Highlights

Somatolactin (SL), a member of the growth hormone (GH)/ prolactin (PRL) family, is fish-specific hormone as the gene has been lost in tetrapods during the period of land invasion [1]
Our results demonstrated for the first time that SL could serve as a novel stimulator for insulin-like growth factors (IGFs) gene expression in tilapia hepatocytes
SL is a pituitary hormone unique to fish models, SL transcripts have been detected in extrapituitary tissues, e.g., in liver of tilapia observed in our present study, grass carp [34] and goldfish [35] and SL receptor was most highly expressed in liver of Tilapia [36] and Salmon [37]

Summary

Introduction

Somatolactin (SL), a member of the growth hormone (GH)/ prolactin (PRL) family, is fish-specific hormone as the gene has been lost in tetrapods during the period of land invasion [1]. Injection of coho salmon SL stimulated IGF gene expression [26] and over-expression SL could increase IGF1 and IGF2 mRNA levels in zebrafish embryo [27], whereas intraperitioneal injection of a single dose of SL to juvenile gilthead sea bream did not modify the circulating amount of IGF1 [28]. These findings raise the possibility that IGF gene expression may be under SL control in fish. No information is available regarding the biological actions of SL on IGF gene expression in fish hepatocytes

Methods

Results

Conclusion