BET, a novel neuronal transmembrane protein with multiple EGF-like motifs.

Using the signal sequence trap method, we have identified a cDNA clone coding for a type I transmembrane protein, BET, with 10 epidermal growth factor (EGF) motifs in the extracellular domain. In situ hybridization revealed that the bet mRNA is specifically expressed in the mitral/tufted cells in the olfactory bulb, Purkinje cells in the cerebellum, and pyramidal cells in the hippocampus. Using polyclonal antibodies, we have demonstrated that the BET protein is highly glycosylated and is localized in patches in the dendrites and in the somata of neurons. Since the predicted structure of BET shares many similarities with the Notch ligands, this novel protein may play crucial roles in establishing the neuronal networks in the olfactory system, cerebellum, and hippocampus. BET is the first transmembrane protein containing only multiple EGF-like repeats specifically expressed in the brain.