Cautious use of fli1a:EGFP transgenic zebrafish in vascular research.

Integration of exogenous sequence into an intact genome may cause some artificial phenotype or unspecific observations. We noticed that there is unspecific vascular expression when using fli1a:EGFP transgenic embryos for whole-mount in situ hybridization (WISH) experiments. We therefore tested whether the residual vector sequence contained in the fli1a:EGFP transgene or the integration of transgene into the genome may cause this expression 'noise' and/or deregulation of gene expression at a genome-wide level. RNA probes were synthesized using two different methods, i.e. vector-based and PCR-based. The vector-based dnmt3 probe showed unspecific vascular expression in fli1a:EGFP embryos, but not in wildtype embryos, by WISH. Moreover, we also found that compared to that in wildtype, there were alterations in gene expression at whole-genome level in the fli1a:EGFP embryos. Our finding that the vector sequence contained in the fli1a:EGFP genome causes unspecific vascular expression by WISH and the genome-wide expression profiling is altered in fli1a:EGFP embryos strongly argue that extra caution should be taken for data interpretation when using transgenics, such as fli1a:EGFP, in developmental biology studies.