Two isoforms of hormone-sensitive lipase b are generated by alternative exons usage and transcriptional regulation by insulin in grass carp (Ctenopharyngodon idella)

The aim of this study was to investigate the gene structure of two hormone-sensitive lipase b (HSLb) isoforms and their transcriptional regulation by insulin in grass carp (Ctenopharyngodon idella). HSL is an important lipolytic enzyme responsible for the hydrolysis of triacylglycerols (TAGs). Two isoforms (HSLa and HSLb) have been cloned in fish, but information about their gene structure and function is very few. In this study, a novel grass carp HSLb isoform (HSLb2) were firstly isolated and characterized from grass carp, encoding peptides of 848 amino acid residues. HSLb2 comprises 13 coding exons and contains a different exon encoding six amino acids in the 5′-region compared to previous reported HSLb (HSLb1), revealing that alternative multiple exons usage (Exon b1 and Exon b2) results in a significant variation in the 5′-region of HSLb transcripts. Exon b2 is located close to the 3′ end of exon b1. Both HSLb2 and HSLb1 mRNAs were expressed in a wide range of tissues, but the abundance of each HSLb messenger RNA (mRNA) showed the tissue-dependent expression patterns. Incubation of hepatocytes with insulin in vitro reduced the mRNA levels of HSLb2 rather than HSLb1, suggesting two HSLb forms may serve somewhat different roles in the regulation of lipogenesis by insulin. To our knowledge, for the first time, the present study provides evidence that HSLb1 and HSLb2 are differentially expressed among tissues and also differentially regulated by insulin in vitro, which provide the groundwork to elucidate the gene structure and physiological function of HSL in fish.