Molecular profiling of the mature Organiser (Hensen's node) as a stem zone.

We report that four genes are upregulated when the chick Hensen's node becomes a stem zone (contributing cells to make the entire notochord and medial somitic mesoderm, without recruitment of cells from the surrounding epiblast), and that they remain expressed in the mature node throughout axial elongation. Methods:The Organiser was labelled at the end of gastrulation and the embryos let to develop 8-10 somites. Fluorescent cells remaining in the Organiser were separated from their neighbours (adjacent neural plate, emerging presomitic mesoderm) either manually, from live embryos (M series), or by laser-capture microdissection from paraffin sections of embryos fixed with modified methacarn.