Fig. 5. Effect of exogenous BMP2 and epithelial stripping on programmed cell death and the effect of BMP2 on Noggin expression. Embryos in (A-I,K,L) were treated with 0.84 mg ml^–1 BMP2. Embryo in J was treated with Nile Blue Sulfate and the epithelium was stripped. (A,D,G,J) High power views of the globular process on the treated side. (A-C) Four hours after the bead was implanted, there is very little cell death induced around the bead (A,B). Noggin expression is increased in the epithelium and in the mesenchyme in an adjacent section (arrowhead, C). (D,E) TUNEL-reacted sections show increase in programmed cell death in the epithelium of the frontonasal mass (arrowheads) and in the mesenchyme lateral to the bead. (F) Expression of Noggin is increased in the epithelium extending up into the nasal pit and maxillary epithelia (arrowheads). A gradient of increased Noggin expression with lower expression near the bead and higher expression further from the bead (arrow). This pattern is complementary to the programmed cell death shown in E. The peak increase in programmed cell death is seen at 12 hours (G,H) and a decrease in size of the globular process is already evident (arrowhead). (I) Areas of lower Noggin expression partly overlap areas of cell death medial to the bead. (K) TUNEL reaction is nearly absent on the right-hand side, 24 hours after bead implantation. (L) Noggin expression remains high in the epithelium and in the mesenchyme on the treated side of the frontonasal mass. (J) TUNEL reaction on an embryo 10 hours after frontonasal mass epithelium was stripped. There is increased programmed cell death in a localized region of the globular process (arrow). Scale bars: 100 µm for A,D,G,J; 500 µm for B,C,E,F,H,I,K,L. Abbreviations: b, bead; epi, epithelium; fnm, frontonasal mass; lnp, lateral nasal prominence; md, mandibular prominence; mx, maxillary prominence.

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