Novel ubiquitous promoters and expression-vector optimization in ascidian embryos

Summary An expression system for transgenes is an important tool for gene function analyses. The present study describes a promoter sequence that can drive ubiquitous expression in ascidian development and optimization of a plasmid vector for maximizing transgene expression. Using the elongation factor 1-alpha promoter as a test ubiquitous promoter, we evaluated the sequence of the vector, polyadenylation signals, cleavage signals, and ribosome entry site sequences. In ascidian embryos, the most important sequence element for efficient expression was the polyadenylation signal. The polyadenylation signal sequence derived from SV40 and 3N-UTR of the C. intestinalis actin (CiAct) gene showed a similar effect on expression, while that derived from 3’-UTR of bovine growth hormone (bGH) lowered expression. Based on quantitative analysis, a polyadenylation signal sequence from C. intestinalis enhanced the expression of reporter genes more than the sequence from SV40. Thus, we proposed a new expression vector that was optimized for ascidian transgenesis. This was the first attempt to evaluate plasmid sequence elements systematically in ascidian embryogenesis. Our results should be useful not only for ascidian transgenesis but also for functional genomics of other organisms.