Cloning, characterization and neuronal expression profiles of tumor endothelial marker 7 in the rat brain

Tumor endothelial marker7 (TEM7) is a putative transmembrane protein that is highly expressed in the tumor endothelium. In the present study, the expression profile of TEM7 was investigated in TEM7-transfected human embryonic kidney (HEK) 293 cells and the rat brain. The extracellular secretion of the recombinant N-terminal ectodomain of TEM7, not full-length TEM7, was observed in the transiently transfected HEK 293 cells. The full-length TEM7 was found inside and membrane part of cells as demonstrated by confocal microscopy. In situ hybridization study revealed that TEM7 mRNA expressions were localized to specific neuronal areas, such as cerebellar Purkinje cells, the layer IV and V of cerebral cortex, hippocampal pyramidal cells and hypothalamic magnocellular nuclei. Immunohistochemical investigation of TEM expression with specific antibodies against TEM7 further supported the spatial expression patterns of TEM7 mRNA. The temporal expression of TEM7 mRNA in the cerebellar Purkinje cells demonstrated a postnatal developmental regulation of TEM7 expression. Our results indicate that TEM7 plays a role as a transmembrane receptor in some neuronal populations of the vertebrate brains.