21-P050 The role of Alsin, a guanine exchange factor for Rab5 GTPase, in early Xenopus development

and the activated signalling pathways investigated. To ensure equivalent activation of downstream pathways by each ligand, phosphorylated-smad2 levels were assayed by Western blot. Up to 100-fold higher concentrations of Xnr1 than ActivinA were required to induce equivalent levels of phosphorylation of smad2. The expression of well-known downstream targets of Activin and Xnr1 was assayed by quantitative PCR to confirm appropriate pathway activation. Affymetrix Microarrays were then performed at three developmental timepoints to identify highly differentially regulated novel genes, which were then validated by examining their expression patterns in gastrulation stage embryos. Initial experiments to overexpress and knockdown these genes are currently being performed.