Fig. 6. Bts1 is necessary to the expression of pax2.1 and its dependent cascade in the MHD. (A-D) pax2.1 expression revealed by whole-mount in situ hybridisation (purple) at 90% epiboly (B) or tail bud (A,C,D) after injection of MO^bts1 (A-C) or the mismatch control MO^bts14 (D). All injections were made at the 16-cell stage into one central blastomere. (C) A biotinylated control MO of unrelated sequence co-injected as a tracer (turquoise staining) to monitor the exact distribution of targeted cells (turquoise arrows) compared with pax2.1-expressing cells (purple arrows); the area shown is a high magnification of the domain indicated by the black arrow in the inset. (D) nls-lacZ RNA used as a tracer to reveal the targeted area (brown staining). (A) Whole-mount views; (B-D) flat-mounts, anterior towards the top; arrows point to injected areas (affected and unaffected expression are indicated by filled and open arrows, respectively). Note that the injection of MO^bts1, but not MO^bts14, strongly diminishes the number of pax2.1-positive cells from the onset of pax2.1 expression (B), and that cells maintaining pax2.1 expression have not been targeted by the injection (C). (E-H) Expression of her5 (E, tail bud), fgf8 (F, tail bud), wnt1 (G, one to two somites) and eng2 (H, three somites) upon injection of MO^bts1 (conditions as in D). Note that these expression are unaffected. (I-N) Expression of pax2.1 (I,J), eng3 (K,L) and pax5 (M,N) at the five-somite stage upon injection of control MO or MO^bts1, as indicated. (I,J) Dorsal views, anterior towards the top; (K-N) Optical coronal sections, dorsal towards the top. Note that at five somites, the pax2.1-dependent markers eng3 and pax5 are also affected.

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