Transgenic Xenopus laevis strain expressing cre recombinase in muscle cells.

For reproducible analyses of gene function in Xenopus, the use of transgenic strains is a promising approach but has limitations when investigating factors interfering with development. Therefore, inducible systems are attractive alternatives, and a binary system based on recombinases is a most versatile approach. We have shown previously that Cre and FLP recombinases are active in Xenopus laevis and can induce a silent reporter gene in a corresponding reporter strain. Here, we describe the establishment of the transgenic Xenopus laevis strain A7 expressing Cre recombinase under the control of the muscle-specific cardiac actin promoter. Upon crossing to several distinct reporter strains, A7 is able to induce EYFP, DsRed2, or LacZ reporter genes in a muscle-specific manner. This first Cre-expressing strain allows conditional activation of any gene of interest in muscle cells and, thus, opens up the use of recombinases as a new experimental strategy in Xenopus.