Expression of receptor protein tyrosine phosphatase δ, PTPδ, in mouse central nervous system.

Protein tyrosine phosphate δ (PTPδ), one of the receptor type IIa protein tyrosine phosphates, is known for its roles in axon guidance, synapse formation, cell adhesion, and tumor suppression. Alternative splicing of this gene generates at least four (A-D) isoforms; however, the major isoform in vivo is yet to be determined. The protein localization has neither been revealed. We have generated anti-mouse PTPδ-specific monoclonal antibody and analyzed the protein expression in wild-type and Ptpδ knockout mice. Immunoblot analysis of various organs revealed that neuronal tissues express both C-and D-isoforms of PTPδ, whereas non-neuronal tissues express only C-isoform. Immunohistochemistry of wild-type or Ptpδ heterozygous sections showed that olfactory bulb, cerebral cortex, hippocampus, cerebellum, and several nuclei in brain stem exhibit moderate to strong positive signals. These signals were absent in Ptpδ knockout specimens. Higher magnification revealed differences between expression patterns of PTPδ mRNA and its protein product. In hippocampus, weak mRNA expression in CA1 stratum pyramidale but strong immunostaining in the stratum lacunosum moleculare was observed, suggesting the axonal expression of PTPδ in the entorhinal cortical afferents. Olfactory mitral cells exhibited mRNA expression in cell bodies and protein localization in their dendritic fields, glomerular and external plexiform layers. Nissl staining showed that the external plexiform layer was reduced in Ptpδ knockout mice. Golgi-impregnation confirmed the poor dendritic growth of homozygous mitral cells. These results suggest that PTPδ may localize in axons as well as in dendrites to regulate their elaboration in the central nervous system.