Improved cre reporter transgenic Xenopus.

We have produced and characterized improved transgenic reporter lines for detection of Cre recombinase activity during Xenopus development. Improvements include choice of fluorophores, which make these Cre reporter lines generally suitable for lineage tracing studies. We also include data for several new parameters affecting survival and transgenesis efficiency using the recently developed meganuclease method of frog transgenesis. These transgenic frogs express cyan fluorescent protein (CFP) under control of the ubiquitous promoter CMV, where CFP is replaced by DsRed2 (a red fluorescent protein) in the presence of Cre. Three independent, high expression, Cre-sensitive lines have been identified that maintain robust fluorophore expression across generations and lack DsRed2 expression in the absence of Cre. A novel use of these lines is to indelibly mark embryonic blastomeres by Cre mRNA injection for permanent fate mapping. Similarly, transgenically expressed Cre under control of tissue-specific promoters will allow detailed analysis of cell lineage relationships throughout embryogenesis, metamorphosis, and adulthood. 2009 Wiley-Liss, Inc.