A flk-1 promoter/enhancer reporter transgenic Xenopus laevis generated using the Sleeping Beauty transposon system: an in vivo model for vascular studies.

We have used the Sleeping Beauty (SB) transposable element to generate transgenic Xenopus laevis with expression of green fluorescent protein (GFP) in vascular endothelial cells using the frog flk-1 promoter. This is the first characterization of a SB-generated transgenic Xenopus that has tissue-restricted expression. We demonstrate that the transgene integrated into single genomic loci in two independent founder lines and is transmitted through the germline at the expected Mendelian frequencies. Transgene integration occurred through a noncanonical transposition process possibly reflecting Xenopus-specific interactions with the SB system. The transgenic animals express GFP in the same spatial and temporal pattern as the endogenous flk-1 gene throughout development and into adulthood. Overexpression of xVEGF122 in the transgenic animals disrupts vascular development that is visualized by fluorescent microscopy. These studies demonstrate the convenience of the SB system for generating transgenic animals and the utility of the xflk-1:GFP transgenic line for in vivo studies of vascular development.