Changing intracellular compartmentalization of β‐galactosidase in the ROSA26 reporter mouse during embryonic development: A light‐ and electron‐microscopic study

The beta-geo (LacZ) reporter gene encodes for β-galactosidase (β-gal) in all cells of the ROSA26 mouse during embryonic development. As such, β-gal activity constitutes an excellent marker for in situ labeling of expressing cells. However, the intracellular distribution of β-gal differs between cells, and changes during embryonic development. Therefore, we studied LacZ-encoded β-gal using light and electron microscopy in the heart, lung, liver, and small intestine on days 13 and 16 of gestation, and the kidney on day 16 of gestation in ROSA26 mice. The Bluo-gal method was carried out under standardized conditions, including fixation, washing, and incubation procedures. Intracellular β-gal staining is encountered in a combination of membranous compartments, including the nuclear envelope, the endoplasmic reticulum, and the plasma membrane. Its exact localization depends on the cell type and is regulated during development. Therefore, one must take the compartmental transition of intracellular β-gal staining into consideration when interpreting results obtained from experiments using ROSA26 mice. © 2004 Wiley-Liss, Inc.