False-Positive β-Galactosidase Staining in Osteoclasts by Endogenous Enzyme: Studies in Neonatal and Month-Old Wild-Type Mice

• Published in: Connective Tissue Research Vol. 47; no. 4; pp. 229 - 234
• Main Authors: Odgren, Paul R., MacKay, Carole A., Mason-Savas, April, Yang, Meiheng, Mailhot, Geneviève, Birnbaum, Mark J.
• Format: Journal Article
• Language: English
• Published: England Informa UK Ltd 2006; Taylor & Francis
• Subjects: Acid Phosphatase - metabolism; Animals; Animals, Newborn; beta-Galactosidase - metabolism; Bone and Bones - enzymology; Escherichia coli; False Positive Reactions; Gene Targeting; Histochemistry; Histocytochemistry - methods; Isoenzymes - metabolism; LacZ; Mice; Mice, Inbred C57BL; Osteoclast Gene Expression; Osteoclasts - cytology; Osteoclasts - enzymology; Tartrate-Resistant Acid Phosphatase; Transgene Detection
• ISSN: 0300-8207; 1521-0456; 1607-8438
• DOI: 10.1080/03008200600860086

Escherichia coli β-galactosidase (β-gal), encoded by the lacZ gene, has become an essential tool in studies of gene expression and function in higher eukaryotes. lac-Z is widely used as a marker gene to detect expression of transgenes or Cre recombinase driven by tissue-specific promoters. The timing and location of promoter activity is easily visualized in whole embryos or specific tissues using the cleavable, chromogenic substrate, 5-bromo-4-chloro-3-indolyl-D-galactopyranoside (X-gal). The tissue specificity of promoters in transgenic constructs is routinely tested by using a promoter of choice to drive lacZ. Alternatively, the targeted expression of Cre recombinase to perform in vivo recombination of loxP sites can be visualized by β-gal staining in mice carrying a Cre-activated lacZ transgene, such as the ROSA26 strain. In the course of our investigations, we examined β-gal activity in bone tissue from genetically normal mice using standard detection methodology and found very high endogenous activity in bone-resorbing osteoclasts. This was true in frozen, paraffin, and glycol methacrylate sections. X-gal staining colocalized with the osteoclast marker, tartrate-resistant acid phosphatase (TRAP). β-gal activity was present in osteoclasts in long bones, in the mandible, and in both neonatal and more mature animals. We present this brief article as a caution to those testing genetic models of skeletal gene expression using β-gal as a marker gene.