Metal ion-responsive transgenic Xenopus laevis as an environmental monitoring animal

Tet-On binary systems for tissue-specific and inducible transgene expression

Tissue-specific and inducible control of transgene expression is a cornerstone of modern studies in developmental biology. Even though such control of transgene expression has been accomplished in Xenopus, no general or widely available set of transgenic lines have been produced akin to those found in mouse and zebrafish. Here, I describe the design and characterization of transgenic lines in Xenopus constituting the Tet-On binary transgene expression system comprising two components: (1) rtTA transgenic lines, i.e., lines harboring the doxycycline- (Dox-) dependent transgenic transcription factor rtTA under control of a tissue-specific promoter and (2) transgenic promoter (TRE) transgenic lines, i.e., lines harboring a gene of interest (hereafter called the transgene) under control of a promoter (TRE). In double transgenic animals, i.e., embryos or tadpoles harboring both the rtTA and TRE components, transgene expression remains off the absence of Dox. Addition of Dox to the rearing water causes a conformational change in rtTA allowing it to bind the TRE promoter and induce transgene expression. Tissue specificity of transgene expression is determined by the promoter regulating rtTA expression, and inducibility is determined by the addition of Dox to the rearing water. Deposition of rtTA and TRE transgenic lines enabling tissue-specific inducible control of transgene expression into the Xenopus stock center will provide a powerful and flexible resource for studies in developmental biology.

Transgenesis procedures in Xenopus

Stable integration of foreign DNA into the frog genome has been the purpose of several studies aimed at generating transgenic animals or producing mutations of endogenous genes. Inserting DNA into a host genome can be achieved in a number of ways. In Xenopus, different strategies have been developed which exhibit specific molecular and technical features. Although several of these technologies were also applied in various model organizms, the attributes of each method have rarely been experimentally compared. Investigators are thus confronted with a difficult choice to discriminate which method would be best suited for their applications. To gain better understanding, a transgenesis workshop was organized by the X-omics consortium. Three procedures were assessed side-by-side, and the results obtained are used to illustrate this review. In addition, a number of reagents and tools have been set up for the purpose of gene expression and functional gene analyses. This not only improves the status of Xenopus as a powerful model for developmental studies, but also renders it suitable for sophisticated genetic approaches. Twenty years after the first reported transgenic Xenopus, we review the state of the art of transgenic research, focusing on the new perspectives in performing genetic studies in this species.

Go with the glow: fluorescent proteins to light transgenic organisms

Once a biological novelty known for their role in bioluminescence, fluorescent proteins (FPs) from marine invertebrates have revolutionized the life sciences. Organisms from all kingdoms have been transformed with the Aequorea victoria green fluorescent protein (GFP), and biotechnology has been advanced by the use of FPs. This article reviews the current uses of FPs in whole transgenic organisms and genomics and looks beyond GFP to the complete color palette and spectral properties afforded by FPs from other marine organisms. Coupled with electronic devices for visualizing and quantifying FPs, recently cloned FP genes might be useful for the ecological monitoring of transgenic organisms in the environment. Therefore, this review also addresses the in vivo labeling of organisms with an emphasis on plants.