Expression of Lgr5-GFP at crypt bottoms. (a) Lgrf-5 is shown in green, with a counterstain for DNA in red to outline crypts and villi. (b) Lgr5 marks cycling crypt base columnar cells. Lgr5 expression appears in brown, in between the white/blue Paneth cells at crypt bottoms. (c) Schematic of crypt architecture. Reproduced, with permission from Elsevier, from Barker N, Clevers H: Gastroenterology 2007, 133:1755-1760.