The goal of this work is to understand events in the early development of the amphibian, Xenopus laevis, at the molecular level. In order to analyse the role of posttranscriptional processes in the differential expression of genes, DNA and RNA molecules will be injected into oocytes and fertilized eggs of the frog to ask what sequences in a model transcript and what processing events control the efficiency of transfer to the cytoplasm and the stability of potential messenger RNA. To analyse the function of specific genes turned on in development it is necessary to develop new methods to interfere with the expression of specific genes. Genes will be overexpressed, or expressed in the inappropriate location by injection of DNA or RNA coding for the gene product. The possibility (and efficiency) of reducing specific gene expression by introducing an excess of antisense RNA complementary to a specific messenger RNA will be explored. These methods will be tested and optimised using model genes whose products can be easily assayed. Information from the work on RNA processing and stability will aid experimental design. Genes turned on in the developing embryo will be identified and described, then functionally analysed by examining the phenotype of embryos in which these genes are transiently over or underexpressed.