Genomic Analysis of the Xenopus Organizer

Studies of the Xenopus organizer have laid the foundation for our understanding of the conserved signaling pathways that pattern vertebrate embryos during gastrulation. Here, we use this wealth of knowledge as leverage in the design and analysis of a genomic visualization of organizer-related gene transcription. Using ectopic expression of the two major activities of the organizer, BMP and Wnt inhibition, as well as endogenous tissues, we generate a focused set of samples that represent different aspects of organizer signaling. The genomic expression values of each sample are then measured with oligonucleotide arrays. From this data, genes regulated by organizer signaling are selected and then clustered by their patterns of regulation. A new GO biological process annotation of the Xenopus genome allows us to rapidly identify clusters that are highly enriched for known gastrula patterning genes. Within these clusters, we can predict the expression patterns of unknown genes with remarkable accuracy, leading to the discovery of new organizer-related gastrula stage expression patterns for 19 genes. Moreover, the patterns of gene response observed within these clusters allow us to parse apart the contributions of BMP and Wnt inhibition in organizer function. We find that the majority of gastrula patterning genes respond transcriptionally to these activities according to only a few stereotyped patterns, allowing us to describe suites of genes that are likely to share similar regulatory mechanisms. These suites of genes demonstrate a mechanism where BMP inhibition initiates the organizer program before gastrulation, and Wnt inhibition maintains and drives the organizer program during gastrulation.

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Hufton AL, Vinayagam A, Suhai S, Baker JC