FGF and Nodal signaling are required for posterior neural tissue formation.

<p>A) Schematic representation of b6.5 lineage history with representation of embryos, cell lineage and gene expression at different stages. The different tissues and precursors are color coded: vegetal cells in grey, anterior (a-line) ectoderm in white, posterior (b-line) ectoderm in yellow, dorsal tail epidermis in green and dorsal tail nerve cord in purple. Embryos are in animal view (top row) or lateral view (bottom row) with anterior to the left. B) Expression of early and late b6.5 lineage markers when FGF-Erk and Nodal signaling pathways are disrupted. <i>Msxb</i> which is normally expressed in the four daughter cells of the b6.5 blastomere (Bi) is not expressed in U0126-treated (Biv) and SB431542-treated (Bvii) embryos. Animal views of <i>Msxb</i> at early gastrula stages (stages 10/11) (Bi, iv, vii). Schematic animal views of stage 10 embryos are depicted as insets in <i>Msxb</i> panels: anterior ectoderm in white, posterior ectoderm in yellow and gene expression in blue. Expression of <i>Klf1/2/4</i> is lost in tail dorsal midline for both treatments (Bv and Bviii). The dorsal tail nerve cord marker <i>KH.C7.391</i> is suppressed (Bvi and Bix). Lateral view with dorsal to the top and anterior to the left (Bii, iii, v, vi, viii and ix) at stage 19. Control DMSO-treated embryos (Bi-iii), U0126-treated embryos (Biv-vi) and SB431542-treated embryos (Bvii-ix). White arrows and arrowheads indicate sites with a loss of expression. C) Gene interactions revealed by loss-of-function data.