Fig. 1. Expression of BMPs and Noggin at the time of fusion of the primary palate. (A-D) Expression of Bmp2, (E-H) expression of Bmp4, (I-L) expression of Bmp7, (M,N,P,Q) expression of Noggin. Plane of section for midsagittal sections (B,F,J,N,O) is the broken line in (A), plane of section for frontal sections is the broken line in B. (O) Expression of Shh. Bottom row was photographed in brightfield; silver grains appear black on a white background. (A,C) Expression of Bmp2 is high in the facial mesenchyme at the zone of fusion (arrows in A). Some epithelial signal can also be seen in (D). (E,G,H) Bmp4 is expressed primarily in epithelium in the maxilla and frontonasal mass. (I,K) Bmp7 is expressed in all epithelia at high levels as well as the inferior mesenchyme of the frontonasal mass (arrows). (M) Noggin is expressed at the caudal edge of the frontonasal mass at stage 24, including the lateral corners (globular processes, arrow); however, at stage 28 expression is lost at the corners (arrow, P). (F,N) Sagittal sections close to the midline show that Noggin and Bmp4 distinguish the frontonasal mass epithelium from that of stomodeal and general surface epithelium, whereas Shh is expressed in stomodeal epithelium up to the edge of the oral epithelium (O). The edges of the Noggin expression domain in relation to those of Bmp4 and Shh are indicated by arrowheads (F,O). (D,H,L) Higher-power views of the region of contact between the frontonasal mass and maxillary prominence highlight epithelial expression of all three Bmps and no expression of Noggin (Q). Scale bars: 500 µm for dark field images;100 µm for brightfield images. Abbreviations: fnm, frontonasal mass; lnp, lateral nasal prominence; md, mandibular prominence; mx, maxillary prominence.

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