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Fig. 4. Comparison of the expression patterns of Xotch, chd and shh. In situ hybridisation of (A,D,G,J) Xotch, (B,E,H,K) chd and (C,F,I,L) shh. (A-C) Vegetal view of an early gastrula, stage 10.25, dorsal side up, showing (A) the distribution of Xotch mRNA in the dorsal marginal zone, (B) the expression of chd in the organiser and (C) shh transcripts, first seen at this stage in the organiser and found in a subdomain of the chd territory. (D-F) Vibratome section in the sagittal plane of an early gastrula showing (D) the expression of Xotch in the epithelial and subepithelial layers of the organiser, (E) the expression of chd in the epithelial and subepithelial layers and in the deep zone of the organiser and (F) a patch of cells expressing shh in the subepithelial layer of the organiser, with some faint staining in the epithelial layer. The arrowheads in D,E,F point to the dorsal blastoporal groove. Distinctions in the cellular composition of the gastrula organiser followed the criteria of Hausen and Riebesell (Hausen and Riebesell, 1991). (G) Late gastrula/early neurula embryo, dorsal view, anterior up, showing the distribution of Xotch transcripts. Interestingly, we observed asymmetries in several embryos, with higher levels of Xotch mRNA on the right side. The yellow line indicates the plane of section shown in J. (H) Dorsal view of a late gastrula, anterior up, showing the expression of chd in the involuted cells. (I) Dorsal view of a late gastrula, anterior up, showing the expression of shh in the dorsal midline. (J) Transverse vibratome section at the level of the posterior trunk of the same embryo as in G. Xotch transcripts are found in proneural domains (p) of the neural plate, presomitic mesoderm (s) and in the developing floor plate (f) but are not found in the notochord (n). Notice higher levels of Xotch mRNA in the proneural and presomitic domains on the right side. More anterior sections also showed the presence of Xotch transcripts in prospective floor plate cells, although at lower levels, and their absence from the notochord (not shown). (K) Sagittal section of the same embryo shown in H, anterior to the left; the blastopore is at the right margin. Chd transcripts are distributed along the notochord. (L) Sagittal section of the same embryo shown in I, anterior to the left; the blastopore is at the right margin. Shh transcripts are found in the three dorsal midline layers, in a dorsal to ventral gradient. |
