Expression Profile of Tumor Endothelial Marker 7 and a Putative Ligand in the Rat Spinal Cord and Dorsal Root Ganglion

STUDY DESIGN To analyze the expression profile of tumor endothelial marker 7 (TEM7) in the spinal cord and dorsal root ganglion (DRG). PURPOSE To investigate the expression profile of TEM7 in the spinal cord and DRG of adult and developing rats. OVERVIEW OF LITERATURE Tumor endothelial marker 7 (TEM7) is a putative transmembrane protein that is highly expressed in the tumor endothelium and in cerebellar neurons. METHODS In the present study, the expression profile of TEM7 in the spinal cord and DRG of the rat was investigated using in situ hybridization and immunohistochemical analysis. In addition, the secreted recombinant ectodomain of TEM7 was employed to label the expression of a putative ligand of TEM7 in the spinal cord and DRG. RESULTS Specific TEM7 mRNA localization was observed in the motor neurons of the spinal cord and sensory neurons of the DRG. Glial cells and vascular endothelial cells did not show hybridization signals. Immunohistochemical analysis with a specific polyclonal antibody revealed a similar localization profile for TEM7 mRNA expression. In the spinal cord, weak labeling was observed in the gray matter. The TEM7 ectodomain localized the expression of a putative ligand of TEM7 in the neurilemmal structures and perineurium of the spinal nerve roots. In the DRG, ligand labeling was observed in the endoneurium and perineurium of the spinal nerves, and extracellular matrix around the sensory neurons. A developmental study has shown that TEM7 mRNA expression in the motor neurons of the spinal cord and DRG increased with age during postnatal development. CONCLUSION These findings indicate that TEM7 plays a role as a transmembrane receptor in neuronal populations of the spinal cord and DRG.