Isolation of yellow catfish β-actin promoter and generation of transgenic yellow catfish expressing enhanced yellow fluorescent protein.

Yellow catfish (Pelteobagrus fulvidraco Richardson) is one of the most important freshwater farmed species in China. However, its small size and slow growth rate limit its commercial value. Because genetic engineering has been a powerful tool to develop and improve fish traits for aquaculture, we performed transgenic research on yellow catfish in order to increase its size and growth rate. Performing PCR with degenerate primers, we cloned a genomic fragment comprising 5'-flanking sequence upstream of the initiation codon of β-actin gene in yellow catfish. The sequence is 1,017 bp long, containing the core sequence of proximal promoter including CAAT box, CArG motif and TATA box. Microinjecting the transgene construct Tg(beta-actin:eYFP) of the proximal promoter fused to enhanced yellow fluorescent protein (eYFP) reporter gene into zebrafish and yellow catfish embryos, we found the promoter could drive the reporter to express transiently in both embryos at early development. Screening the offspring of five transgenic zebrafish founders developed from the embryos microinjected with Tg(ycbeta-actin:mCherry) or 19 yellow catfish founders developed from the embryos microinjected with Tg(beta-actin:eYFP), we obtained three lines of transgenic zebrafish and one transgenic yellow catfish, respectively. Analyzing the expression patterns of the reporter genes in transgenic zebrafish (Tg(ycbeta-actin:mCherry)nju8/+) and transgenic yellow catfish (Tg(beta-actin:eYFP)nju11/+), we found the reporters were broadly expressed in both animals. In summary, we have established a platform to make transgenic yellow catfish using the proximal promoter of its own β-actin gene. The results will help us to create transgenic yellow catfish using "all yellow catfish" transgene constructs.