Microarray Analysis of Somitogenesis Reveals Novel Targets of Different WNT Signaling Pathways in the Somitic Mesoderm

WNT signaling plays a major role in patterning the dermomyotome of the somitic mesoderm. However, knowledge of downstream target genes and their regulation is limited. To identify new genes involved in the development and early patterning of the somite, we performed a comparison of gene expression by microarray between the presomitic mesoderm and the 5 most recently formed somites of the mouse at embryonic day 9.5. We identified 207 genes upregulated and 120 genes downregulated in somite formation. Expression analysis and functional categorization of these genes demonstrate this to be a diverse pool that provides a valuable resource for studying somite development. Thus far, we have found three genes expressed in the dermomyotome of the early somite. Consistent with their expression patterns, these genes are transcriptional targets of WNT signals, but display differential activation by different WNTs. We further demonstrate that 1 of these genes, Troy, is a direct target of canonical WNT signaling, while the other 2 genes, Selp and Arl4, are not. Thus, our microarray study using microdissected tissues not only provides global information on gene expression during somite development, it also provides novel targets to study the inductive signaling pathways that direct somite patterning.