Expression of genes by introduction of DNA into developing embryos can be used to analyze promoter elements that are developmentally regulated or to ectopically express proteins to test their function during development. Because of its large size and resilience to manipulation, theXenopusembryo is particularly suitable for studies utilizing microinjection, and there is a large body of literature describing successful promoter analysis and ectopic expression experiments. In this chapter, we will outline the fundamental methods and tools for expression of injected DNA in the early embryos ofXenopus. This chapter will not, however, attempt to review the recently developedXenopustransgenesis procedures (1 ,2 ). Although these transgenic methods offer significant advantages over the transient expression methods that we will describe below, the method is still under development and few examples of promoter analysis or of ectopic gene expression studies are yet available. Meanwhile, DNA expression from injected templates provides an efficient and simple method for gene analysis in the embryo.
