Genetic manipulation of circadian rhythms in Xenopus

Xenopus laevis retina is an important experimental model system for the study of circadian oscillator mechanisms, as light input pathways, central oscillator mechanisms, and multiple output pathways are all contained within this tissue. These retinas continue to exhibit robust circadian rhythms even after being maintained in culture for many days. The usefulness of this system has been improved even further by the development of a technique for simple genetic manipulation of these animals, which is complemented by expanded genomics resources (Xenopus genome project, microarray, etc.). By taking advantage of the transgenic technique in Xenopus described in this article, many types of analysis can be done on the primary transgenic animals within a couple of weeks after transgenesis. The availability of many cell-type-specific promoters and well-characterized cell types within the Xenopus retina provides the advantage of cell-specific modification of clock function using this method; in other words, contributions of different cell types within the circadian system can be analyzed independently by "molecular dissociation" of these cells. This article describes both how this transgenic technique is useful and various considerations that should be taken into account when these types of experiments are planned and interpreted. Application of these new techniques to studies of clock function provide an opportunity to rapidly assess gene expression and/or function in the context of the intact retina.