A study of somatolactin actions by ectopic expression in transgenic zebrafish larvae

Somatolactin (SL) is a fish-specific hormone that belongs to the prolactin (PRL) and GH family. Recently, two forms of SL, SLα and SLβ, have been found in some species, and may have different actions and functions. To investigate the role of SL in fish growth and metabolism, we generated transgenic fish founders with ectopic expression of SLα and SLβ to study the physiological functions and actions of these SLs among several marker genes. We fused the cDNAs encoding the precursor SLs in frame to a zebrafish β-actin gene promoter to generate transgenic zebrafish lines that were coinjected with a green fluorescent protein (GFP) driven by the same promoter. The transgenic zebrafish were selected based on GFP expression and confirmed by genomic PCR, Southern blot analysis, and transgene expression. Investigations into the expression of marker genes in larvae on different pathways using real-time PCR have provided a general understanding of the actions of SLs. This study found that the overexpression of SLα and SLβ in vivo significantly enhanced the transcription of IGFs, insulin, leptin, sterol regulatory element binding protein 1, and fatty acid synthase, as well as the expression level of vitellogenin and proopiomelanocortin, while causing reduced levels of catalase and glutathione S-transferase in the larvae of transgenic zebrafish.