Fig. 7.

Pax8 and Nkx2-1 expression during mouse foregut morphogenesis. (A-D) IF staining of E7.5 and E7.75 embryos at the level of the forming foregut pocket shows strong Pax8 expression in the non-neuronal, ectodermal epithelium (ec, arrowheads) and in epithelial cells of the foregut endoderm (en, arrows). These embryos had a TS12 morphology and Nkx2-1 expression was not detectable at this stage. E-cadherin (cadherin 1) staining (red) is used to label epithelial structures in all panels. (E-H) Higher magnification views of foregut endoderm in E7.5-E7.75 embryos illustrate variable levels of Pax8 staining in endodermal cells (F). Confocal z-sections acquired at 50 µm intervals along the AP axis show anterior Pax8 expression (F) in both ventral and lateral foregut endoderm whereas posterior Pax8 expression (G) is limited to lateral endoderm. Note the complete absence of Nkx2-1 expression (H). (I-K) Confocal z-sections acquired at 30 µm intervals along the AP axis of E8.0 embryo foregut illustrate how the broad Pax8 expression domain in anterior ventral foregut endoderm (I) expands to gradually include more lateral domains at posterior locations (arrows in K). This embryo had a TS13 morphology. (L) Nkx2-1 expression was not detectable in E8.0 embryos. (M-P) Upon completion of embryo turning at E8.5, expression of both Pax8 (M-O) and Nkx2-1 (P) is detectable in ventral foregut endoderm of TS14 embryos. Confocal z-sections acquired at different levels along the AP axis show widespread persistence of Pax8 expression in the lateral foregut epithelium (arrows in M-O). (Q-T) Co-expression of Pax8 and Nkx2-1 in the morphologically distinct, ventral midline primordium of the thyroid of E9.0 (Q,R) and E9.5 (S,T) embryos. Scale bars: 50 µm.