Fig. 4. Differentiation, proliferation and Mist1 expression in the gastric unit. (A) Expression of Mist1 in the neck and base of wild-type animals was assessed: blue, nuclei (bisbenzimide); green, neck cells (GSII); red, ZCs (GIF); purple, poyclonal rabbit anti-Mist1. Upper: GSII, GIF and Mist1. Lower: same field with bisbenzimide, GIF and Mist1. Note how only cells that also express GIF (i.e. ZCs or transitional cells) express nuclear Mist1 and that almost all mature ZCs express Mist1. Two TZ cells are indicated with negative nuclei (although quantification showed that half of transitional cells are Mist1-positive). A single apparently negative ZC is marked by an arrow (these cells are rare). (B) Expression from the Mist1 promoter in the Mist1^-/- mice. Labeling and layout as in A, except: purple, expression of nuclear lacZ `knocked in' to Mist1 promoter (anti-ß-galactosidase antibody). Note how Mist1 promoter activity is first detectable in a subset (promoter-positive cells are labeled `1,3,4') of the four GIF^Hi cells at the transition between the neck and base zones and is not detectable in neck cells or the earlier transition cell with equal levels of mucous and zymogenic granules (TZ1). (C) Brdu immunolabeling in representative gastric units at 90 minute timepoint. Labeling as in A, except: purple, polyclonal goat anti-Brdu. Note single positive cell in isthmus or pit region of wild type and Mist1^-/- (arrows) and early neck cell of Mist1^-/- mouse. Transitional cells with negative nuclei are also indicated. (D) Brdu pulse-chase experiments. All animals were injected with Brdu concomitantly and sacrificed on different days. Note that the day 9 timepoint comprised only one genotype: Mist1^-/-.