Biochemical and Biophysical Research Communications
In vivo expression of Osterix in mature granule cells of adult mouse olfactory bulb
Highlights
► Osterix is expressed in the mouse olfactory bulb as well as bone. ► Osx-expressing cells exist in the mature interneuron region of the granule cell layer of the adult mouse olfactory bulb. ► The Osx-expression in mature interneurons may suggest that Osx is a new marker for mature neuroblasts.
Introduction
The olfactory bulb (OB), which is located in the rostral part of the mouse brain, is the first relay station in the olfactory system and recognizes odorants via a complex pathway [1]. The OB is organized into the main olfactory bulb (MOB), which plays a role in odor recognition, and the accessory olfactory bulb, which is positioned in the dorsal-posterior region of the OB and is associated with lactation and mating [1]. The structure of the MOB consists of five layers: the glomerular layer (GL), the external plexiform layer (EPL), the mitral cell layer (MCL), the inner plexiform layer (IPL), and the granule cell layer (GCL) [1]. Odorants are recognized in the olfactory epithelium after being inhaled through the naris, and then the biomolecular signals are converted into neurochemical signals [2]. These signals are recognized by specific olfactory receptors in the olfactory nerve layer and they are then delivered to the GL through unbranched axons. Next, the signals are transported from the GL to the GCL, after which they arrive at the olfactory cortex, where the odorant signals are recognized by the central nervous system [2]. Through the course of this pathway, signal transport in connection with olfaction occurs continuously during the mouse life cycle. In the adult brain, neurogenesis occurs in the subgranular zone of the dentate gyrus and in the subventricular zone (SVZ) of the lateral ventricles [3], [4]. Neuroblasts that are produced in the SVZ migrate to the OB via the rostral migratory stream (RMS), where they mature into interneurons [3], [5], [6]. New OB interneurons, which are continually generated, replace old neurons throughout the life cycle [7], [8]. However, the function of this continual replacement remains unclear.
Osterix (Osx), which is a zinc finger-containing transcription factor, plays an important role in osteoblasts for bone formation [9], [10], [11]. The Osx gene is first expressed in differentiating chondrocytes and in the surrounding perichondrium at embryonic day 13.5 and is continuously found in adult bone [11]. Human specificity protein-7 (Sp7) is a homologue of mouse Osx with 95% identity [12]. Sp7 mRNA in human adult tissues is detected in nonskeletal tissues including the brain, placenta, and lungs, as well as the skeletal tissue [12]. Osx/Sp7 is homologous with the motifs present in the Sp family and the Krüppel-like transcription factor family. Several studies have reported that the Sp family functions in neurogenesis as well as in skeletogenesis. Sp4, which is involved in the development of the central nervous system, regulates dendritic patterning during maturation of the cerebellum [13]. In Sp4 null mutant mice, the density of dentate granule cells is decreased and the width of the dentate gyrus and the molecular layer is reduced [14]. The levels of Sp3 and Sp4 are increased in the brain of Alzheimer’s disease patients, indicating that Sp proteins may have the potential to regulate neuronal signaling [15]. Sp8 regulates the patterning of the midbrain and the hindbrain during embryonic and postnatal stages [16]. Sp8 also contributes to the diversity of OB interneurons by modulating the survival, migration, and molecular specificity of neuroblast/interneurons [17]. However, the function of Osx/Sp7 in nonskeletal tissues is still unknown. In this study, the pattern of Osx expression was analyzed for the first time in nonskeletal tissues of adult mice. Osx was significantly expressed in the mouse OB, as well as in bone. The results of this study suggest that Osx may play a critical role in the development of the OB and in the olfactory system.
Section snippets
Antibodies
Mouse anti-Osx was purchased from Abcam (Cambridge, UK). Mouse anti-NeuN and anti-microtubule-associated protein 2 (MAP2) were purchased from Molecular Probes (Oregon, USA) and Sigma (St. Louis, USA), respectively. Mouse anti-GABA and goat anti-calretinin (CR) were purchased from Abcam and Santa Cruz (EU), respectively. Alexa 488 and Alexa 568 goat anti-rabbit secondary antibodies were purchased from Molecular Probes.
Reverse transcriptase-polymerase chain reaction (RT-PCR)
An analysis of mRNA expression was conducted using the Mouse MTC Panel I
Osx mRNA expression in nonskeletal tissues
Osx, which is known to be a bone-specific transcription factor, has only been studied in bone to date [9], [10], [11], [19]. In order to examine Osx expression in other tissues of adult mice, RT-PCR was conducted using the Mouse MTC Panel I generated from tissues of adult mice. Osx was significantly expressed in the brain as well as in bone (Fig. 1A). However, Osx expression was not observed in other nonskeletal tissues, including the spleen, lung, and liver. The mRNA expression of Osx was
Acknowledgments
We thank Dr. Benoit de Crombrugghe (University of Texas M.D. Anderson Cancer Center) for providing Osx+/− mice. This work was supported by Basic Science Research Program through The National Research Foundation of Korea (NRF) funded by The Ministry of Education, Science and Technology (2009-0071230 and 2010-0008391) and the research promoting grant from The Keimyung University Dongsan Medical Center in 2007.
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