is required for axial elongation and segmentation in vertebrate embryos.

During vertebrate embryonic development, the formation of axial structures is driven by a population of stem-like cells that reside in a region of the tailbud called the chordoneural hinge (CNH). We have compared the mouse CNH transcriptome with those of surrounding tissues and shown that the CNH and tailbud mesoderm are transcriptionally similar, and distinct from the presomitic mesoderm. Amongst CNH-enriched genes are several that are required for axial elongation, including , , and , and androgen/oestrogen receptor nuclear signalling components such as We show that the pattern and duration of tailbud expression is conserved in mouse, zebrafish and chicken embryos, and that is required for axial elongation and somitogenesis in zebrafish embryos. The axial truncation phenotype of morphant embryos can be explained by much reduced expression of (), which is required for axial progenitor maintenance. Posterior segmentation defects in the morphants (including misexpression of genes such as , and ) appear to result, in part, from lost expression of the segmentation clock gene, .