Identification of a receptor-type protein tyrosine phosphatase expressed in postmitotic maturing neurons: its structure and expression in the central nervous system.

We have isolated a rat cDNA encoding a receptor-type protein-tyrosine-phosphatase (RTP) expressed in brain and kidney (RPTP-BK) and characterized its expression in the developing central nervous system. RPTP-BK has seven fibronectin type III-like repeats in the extracellular region and a unique catalytic phosphatase domain in the cytoplasmic region. Bacterial expression of its phosphatase domain showed that the dephosphorylation of phosphotyrosine residues was mediated by the cytoplasmic catalytic domain. Sequence comparison revealed that RPTP-BK is homologous with GLEPP1, a rabbit PTP expressed in renal glomerular epithelia, and has the same phosphatase domain as murine PTPphi expressed in macrophages. RPTP-BK has also significant homology with Drosophila DPTP10D in the phosphatase domain, whose expression is localized exclusively in growth cones of the embryonal brains. The gene for RPTP-BK is well conserved among other species, and the expression in the brain but not in the kidney is developmentally regulated during the neonatal stage. Hybridization in situ showed that RPTP-BK is highly expressed in the postmitotic maturing neurons of the olfactory bulb, developing neocortex, hippocampus and thalamus. Because the expression of RPTP-BK in the developing neocortex is correlated with the stage of axonogenesis in cortical neurons, RPTP-BK might be crucial in neural cell development of the mammalian central nervous system.