Function and regulation domains of a newly isolated putative β-actin promoter from pacific white shrimp

Current development of transgenic shrimp research has been hampered due to the lack of the suitable promoters and efficient transfection methods for crustaceans. A 1642 bp sequence, containing 5'-upstream sequence, exon 1, intron 1 and partial exon 2, which is responsible for transcriptional initiation of the newly reported shrimp β-actin (actinT1), has been isolated from the Pacific white shrimp (Litopenaeus vannamei) and named as SbaP. To determine its function and potential application in marine biotechnology, the sequence and functional domains were examined by constitutive expression of the luciferase reporter gene. We have identified 5' regions that play a central role in the expression of the β-actin gene. The proximal promoter (-1642/-1325) contains two highly conserved transcriptional sites, CCAAT box and CArG motif. Two negative (-1140/-924, -222/-21) and one positive (-810/-425) regulatory elements have been identified in intron1. Transient transfection assay with a construct containing proximal promoter and enhancer (SbaPΔ-222/+1Δ-1325/-924) regions of the shrimp β-actin coupled with luciferase and EGFP (enhanced green fluorescent protein) showed that the promoter was not only functional in sf21 cells, but promoter activity was more than 8-fold higher than a viral-origin promoter (ie1, white spot syndrome virus immediate early gene promoter). Furthermore, SbaPΔ-222/+1Δ-1325/-924 drove a successful expression of luciferase injection assay in vivo injection and also showed higher promoter activity than the ie1 promoter, suggesting that the expression vectors constructed with SbaPΔ-222/+1Δ-1325/-924 have important potential in gene transfer studies for shrimp and other crustacean species.