Fig. 8. MH precursors display altered molecular identities in ace and noi mutants. (A-H') Comparison of GFP protein (anti-GFP immunocytochemistry, brown staining) and pax6.1 RNA (ISH, blue staining) at the stages indicated in sagittal sections of her5PAC:egfp transgenic wild-type (A,C,E,G), ace (B,B',F,F',H,H') and noi (D) embryos. B', F' and H' are magnifications of the areas boxed in B, F and H. Note that GFP protein and pax6.1 expression are never co-expressed anteriorly in wild type (A,C,E,G) and noi (D), while extensive overlap between the two stainings is present in ace at the 15-, 20- and 30-somite stages (F',H',B'). (I-K,M-O) Comparison of GFP protein (anti-GFP immunocytochemistry, bottom panels, green staining) and fgfr3 (I-K) or otx2 (M-O) RNAs (in situ hybridisation, top panels, blue staining) at the stages indicated in her5PAC:egfp transgenic wild-type (I,M), ace (J,N) and noi (K,O) embryos. Top and bottom panels are bright-field and fluorescence views, respectively, of the same sagittal sections. Green arrowheads on the bright-field pictures point to the limits of GFP protein distribution. Note in ace that anterior GFP-positive cells do not co-express fgfr3 (J, compare with I), and that posterior MH cells are all otx2-positive (N, compare with M). By contrast, in noi, all the descendants of MH precursors express fgfr3 (K) but an otx2-negative territory is maintained within the caudal GFP-positive population (O). (L) Expression of fgfr3 revealed by whole-mount in situ hybridisation shows that MH precursors in noi are fgfr3-positive already at the 15-somite stage (bar, bottom panel, compare with wild-type sibling, top panel).

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