Expression of hypoxia-inducible, membrane-bound carbonic anhydrase isozyme XII in mouse tissues.

Carbonic anhydrase (CA) XII is a membrane-associated enzyme that has been demonstrated to be normally expressed in some human tissues, to be upregulated in some cancers, and to be a hypoxia-inducible gene product. In mouse, CA XII has been recently localized in the kidney. In the present study, we investigated CA XII gene and protein expression in other mouse tissues, with the kidney serving as a positive control for the reagents. The expression of CA XII mRNA was examined using polymerase chain reaction (PCR) amplification of commercial cDNAs produced from selected mouse tissues. A strong positive signal for CA XII mRNA was detected in the kidney, and weak signals were obtained in the testis and lung. Heart, spleen, liver, and skeletal muscle were negative. Immunohistochemical staining was performed using a mouse CA XII-specific antibody and biotin-streptavidin complex method. The results showed high expression of CA XII in the kidney, as expected. It was also highly expressed in the surface epithelial cells of the colon, whereas it was absent in the stomach, proximal small intestine, pancreas, liver, heart, and skeletal muscle. The maturing sperm cells showed a weak staining in a pattern that most probably indicates expression in the developing acrosomal membrane. The high expression in the kidney and colon suggests a role for CA XII in the maintenance of body ion and pH homeostasis in the mouse. However, the present findings demonstrated that CA XII has a very limited distribution in mouse tissues outside these two organs.