Optimized conditions for transgenesis of the ascidian Ciona using square wave electroporation

The protochordate Ciona has recently become an important model organism for the study of developmental gene regulation, in part because transient transgenic embryos can be produced rapidly and reliably using electroporation. Published methods are currently for the use of electroporation devices delivering exponentially decaying pulses. However, some workers have advocated the use of square wave electroporation devices for eukaryotic transgenics. This paper presents results of experiments to find optimal conditions for the use of square-wave electroporation in the ascidian Ciona. In the present analysis, a single pulse of 90 msec duration at 63-75 V/cm was found to give an optimal balance of a high proportion of cells transformed with the transgene, and a low level of abnormal development. Forty micrograms of DNA per electroporation is sufficient for effective visualization of reporter gene expression, although doses up to 100 μg provide higher proportions of transformed cells. In side-by-side comparison with exponential pulse electroporation, square wave pulses give similar penetrance of transgene expression, along with lower proportions of embryos with abnormal development at higher amounts of input DNA.