A TYROSINE KINASE-LIKE MOLECULE IS LOCALIZED IN THE NUCLEAR-MEMBRANE OF NEURONS - HIPPOCAMPAL BEHAVIOR UNDER STRESS

Protein tyrosine kinases play important roles in the development of th e mammalian nervous system during embryogenesis and in the maintenance of function of the adult brain. Using a semi-nested PCR technique bas ed on a short amino acid motif of protein tyrosine kinases, we isolate d a human genomic DNA encoding a peptide whose sequence was related to known mammalian protein tyrosine kinases. The expression was examined by Northern blot analysis, and transcripts were detected almost exclu sively in the brain. The corresponding cDNA was sequenced, and it was revealed that the gene designated as byk coded for a receptor-like mol ecule with a motif of protein tyrosine kinase. Immunohistochemical ana lysis demonstrated that the Byk protein was expressed in neurons and w as located in the nuclear envelope. To understand the physiological si gnificance of the Byk protein, we investigated the behavior of this mo lecule in the hippocampus after ischemia. Byk-like immunoreactivity di sappeared from the neurons in the fields CA1 through CA3 and the denta te gyrus of the hippocampus following 20 min of ischemia. After recirc ulation of blood flow, neurons in the CA3 field and the dentate gyrus re-expressed Byk-like antigen but CA1 neurons did not. Interestingly, Byk-like immunoreactivity was detected in microglial cells and astrocy tes in the CA1 field that were activated after ischemia. Byk could be a new tool to study the neuron-glia and glia-glia interactions.