Osterix (Osx) has been identified as an osteoblast-specific transcription factor that is required for skeletogenesis. Here, we examined the expression of Osx in non-skeletal tissues. Together with a high expression in bones, Osx was expressed in the mouse brain, and its expression gradually increased during postnatal developmental periods. Specific-expression of Osx was observed primarily in the olfactory bulb (OB), with little in the cerebral cortex and the cerebellum. Osx expression was examined in the OB of Osx heterozygous mice with a LacZ knock-in in the Osx locus, which resulted in strong X-gal staining in the OB. X-gal-positive cells were located in the mitral and granule cell layers of the adult mouse OB, which was confirmed by immunohistochemical analysis with anti-Osx antibody. Osx expression overlapped extensively with NeuN, a marker of mature neuron, indicating that the Osx-positive cells were mature interneurons of the granule cell layer in the adult mouse OB. This is the first study to examine the in vivo expression of Osx in the mouse OB, and this finding may indicate a new function of Osx as a marker for mature neuroblasts in the OB. (C) 2011 Elsevier Inc. All rights reserved.