Fig. 4. 129/Sv-Rac1Leu61 crypts in adult chimeric mice are elongated and show increased proliferation. (A-C) Sections from an adult Rac1Leu61 chimeric jejunum. (A) X-Gal genotyping of 129/Sv and B6-ROSA26 epithelial cells. The broken line indicates the location of crypt-villus junctions. (B) Same section as in A stained with mouse anti-c-Myc, Cy3-labeled sheep anti-mouse Ig and bis-benzimide. Cytoplasmic c-Myc staining (red) is more prominent in the 129/Sv villus epithelium (arrowhead) compared with crypt (arrows) epithelium. (C) High-power view of the 129/Sv and adjacent B6 crypts noted in B. The arrowhead highlights the modest increase in c-Myc staining in the upper part of the 129/Sv-Rac1Leu61 crypt compared with the neighboring B6-ROSA26 crypt. (D,E) Section from a normal 9-month-old chimera. (D) X-Gal genotyping. (E) Section stained with the same reagents as in B. Asterisks in B,E indicate Cy3-positive lymphocytes in the lamina propria that react with the mouse secondary antibody. This lamina propria staining can be used as a reference internal control: even with the increased exposure in E, no epithelial c-Myc staining is detectable in the normal chimera. (F,G) X-Gal plus Hematoxylin and Eosin (F), or nuclear Fast Red (G) stained sections. The arrow in F denotes a 129/Sv crypt that appears elongated when compared to a neighboring B6-ROSA26 crypt (arrowhead). In G, arrowheads point to some of the increased M-phase cells present in a 129/Sv crypt. (H) Quantitative morphometric studies reveal a 2.5-fold increase in mitotic index in 129/Sv-Rac1Leu61 crypts. See text for definition of the mitotic index. Scale bars: 25 µm.