Signals regulating differentiation and expression patterns of <i>Pax6</i> and <i>Fgf8</i> along the elongating neural axis.

<p>(A) Summary of cell populations, signal localisation and interactions at the caudal end of the E8-8.5 mouse embryo, RA retinoic acid, RAR, retinoic acid receptor, FGF, fibroblast growth factor, PS, primitive streak, S, somite, <i>Raldh2, Retinaldehyde dehydrogenase 2</i>; (B) <i>Pax6</i> is expressed in the neural tube (B′) in transverse section (TS), but not in (B″) preneural tube or (B‴) stem zone; (C) <i>Fgf8</i> is expressed in the stem zone, but not in the neural tube (C′) in TS or in (C″) preneural tube, stem zone expression in TS (C‴). Grey dashed lines in B′, B″, B‴, C′,C″, C‴ outline cell populations in which nuclei were assessed in FISH experiments. Scale bar = 50 microns, asterisk indicates position of the node in all embryo images.