Expression of a member of tumor necrosis factor receptor superfamily, TROY, in the developing olfactory system

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Abstract
TROY is a recently identified member of the tumor necrosis factor (TNF) receptor superfamily. We have previously reported that TROY induces the activation of nuclear factor κB via TNF receptor‐associated factor 2, 5, and 6, and is strongly expressed in the developing central nervous system, including the olfactory bulb. In this study, we investigated the detailed cellular characterization of TROY‐expressing cells in the developing olfactory system of mice using in situ hybridization and immunohistochemistry. Both mRNA and protein of TROY were first detected in the olfactory nerve layer (ONL) of the olfactory bulb at embryonic day 13.5. During late embryogenesis, TROY expression was most intense in the inner ONL (ONL‐i). In the postnatal olfactory bulb, TROY‐expressing cells were also detected in the glomerular layer (GL), in addition to the ONL‐i. The double‐immunofluorescence method demonstrated that TROY was expressed in olfactory ensheathing cells (OECs) of the ONL‐i, which were positive for neuropeptide Y (NPY), but neither S‐100 nor p75 low‐affinity nerve growth factor receptor. Some TROY‐expressing cells in the ONL‐i were observed with the astrocyte‐like phenotype (GFAP+/NPY−). In addition, TROY was also detected in GFAP+ glial cells of the GL. Thus, TROY was expressed in some specific subsets of glial cells in the olfactory bulb, including OECs, suggesting that TROY may play some roles in the developing and adult olfactory system.