Fig. 1.

Sox9^EGFP is expressed at 3 different levels in the small intestinal epithelium. A: Sox9^EGFP is expressed at variable levels, “HI,” “LO,” and “subLO,” in the crypts of the small intestine. HI levels are associated with postmitotic enteroendocrine cells, LO levels are associated with crypt-base columnar cells, “subLO” levels are associated with the transit-amplifying region of the crypt, and NEG levels are Sox9^EGFP negative. Images represent ×1,260 original magnification. B: flow cytometric analysis indicates distinct Sox9^EGFP expression levels. Gate parameters used to sort each population are indicated above each region of the histogram. C: postsort analysis indicates that single Sox9^EGFP-expressing cells have been isolated based on enhanced green fluorescent protein (EGFP) status. Images represent ×200 original magnification. The image exposures for Sox9^EGFPneg and Sox9^EGFsubLo panels were doubled to produce images that would allow visualization of EGFP expression in these 2 populations.