Representative immunofluorescent staining of frozen serial sections of the adult colonic mucosa for the detection of the α6A and α6B splice variants and proliferation markers. (A) Expression of the A variant showing a predominant distribution in the lower half of the glands (g), the region containing the progenitor cells as confirmed by immunodetection with Ki67 (B) and Rbm19 (C). (D, E) The B variant was detected in the upper half of the glands and at the surface (s) epithelium. (F-I) Higher magnification of the lower gland region stained for the detection of α6B (F), α6A (G), Ki67 (H) and Rbm19 (I) showed that in the colon, α6B is absent from the lower crypt while both α6A and the proliferative zone extend to the bottom of the glands. Red-brown signal: Evan's blue counter stain. Magnifications: A-D: scale bars in A and D = 50 μm; E-I: scale bar in E = 25 μm.