Fig. 5. Loss of Sox17 function elevates apoptosis but does not affect the initial formation of anterior definitive endoderm. (A-I) Whole-mount TUNEL staining (brown) of the mutant embryos at early neural plate (A, anterior view), late neural-plate to early head-fold [anterolateral (B), posterior (C), sagittal section (D) and transverse sections (E,F)] and early somite stages [anterior (G), posteroventral (H) and transverse section (I)]. Mutant embryos do not show any more TUNEL-positive cells than do the normal (+/+ and +/–) embryos prior to the neural plate stage (A). However, at the late neural plate to early somite stages, more TUNEL-positive cells are found in the prospective foregut endoderm (B,E-G; arrows in D,I). By contrast, no increase in apoptosis is found in the posterior endoderm (C,D,H). In H, the broken red lines indicate the border between anterior and posterior gut segments. The broken arrows in B,G show the plane of sectioning (D,E,I); the broken rectangle (E) marks the area shown in the magnified view (F). (J,K) Cer1 expression in the anterior definitive endoderm of the normal and mutant embryos at early- to late-bud stage (J, lateral view) and at late neural-plate stage (K, lateral view). Proper expression of Cer1 was found in the prospective foregut endoderm of the normal (+/+ and +/–) and null mutant embryos. Scale bars: 10 µm.
