Fig. 3.

Mesenchymal characters are concordant with those of epithelial tubes in the AFG. Histological sections of E13 epithelial tubes are shown at the axial levels indicated in Fig. 1A. (A) Sections shown in Fig. 2B were doubly stained for SOX9 (green) and α-SM (magenta). Mesenchymal tissues surrounding WT and ΔSOX2 trachea/bronchi comprise nearly complementary patches of SOX9-expressing cells and α-SM-expressing cells (broken double arrows). ΔSOX2 AFG tubes were also wrapped in SOX9- and α-SM-expressing mesenchymal tissues, albeit without their separation into patches (open arrowheads). In contrast, WT esophageal tissues lacked these cell types and only had distal α-SM-expressing cells (arrowheads). (B–D) Analogous sections of WT and ΔSOX2 AFG hybridized with mesenchyme-specific gene probes for Wnt4 (esophagus specific), Tbx4 (trachea/bronchus specific), and Hoxb6 (distal bronchus specific). Mesenchymal cells expressing these genes are indicated by open arrowheads. In ΔSOX2 AFG, Wnt4 expression was completely absent (B), epithelial tubes were all surrounded by Tbx4-expressing mesenchyme (C), and the posterior part of the tube was surrounded by Hoxb6-expressing mesenchyme, similar to the distal bronchi (D). Asterisk, an AFG-derived bronchiole-like tube. Scale bars: 100 µm.