MICROGLIA-SPECIFIC LOCALIZATION OF A NOVEL CALCIUM-BINDING PROTEIN, IBA1

Recently it has been shown that mRNA of Iba1 (ionized calcium binding adaptor molecule 1), which was a novel calcium binding protein cDNA-cl oned by our group, is specifically expressed in microglia in cultures of rat brain cells [Imai et al. Biophys. Biochem. Res. Commun., 224 (1 996) 855-862]. In the present study, immunocytochemical and immunohist ochemical examinations demonstrated that Iba1 protein is expressed in microglia alone both in cultured brain cells and in the brain, respect ively. In a mixed cell culture of embryonic rat brain, immunocytochemi cally positive for Iba1 protein were the microglia but it was not dete ctable in neurons, astroglia, or oligodendroglia. Immunohistochemical staining of adult rat brain sections showed Iba1 protein to be specifi cally localised in ramified microglia. In addition, immunohistochemica l staining and immunoblot analysis of activated microglia in the facia l nucleus after facial nerve axotomy shows that expression of Iba1 pro tein was upregulated and peaked at 7 days. These results indicated tha t localisation of Iba1 protein is restricted to microglia both in vitr o and in vivo, and that Iba1 protein plays a role in regulating the fu nction of microglia, especially in the activated microglia. (C) 1998 E lsevier Science B.V. All rights reserved.