Protein tyrosine phosphatase that negatively regulates oligodendrocyte precursor proliferation in the embryonic spinal cord. Required for normal differentiation of the precursor cells into mature, fully myelinating oligodendrocytes. May play a role in protecting oligondendrocytes against apoptosis. May play a role in the establishment of contextual memory, probably via the dephosphorylation of proteins that are part of important signaling cascades. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate The carbonic-anhydrase like domain interacts with CNTN1 (contactin) (PubMed:20133774, PubMed:21969550). Interaction with PTN promotes formation of homooligomers; oligomerization impairs phosphatase activity (By similarity). Interacts (via chondroitin sulfate chains) with MDK (via C-terminal); this interaction is inhibited by PTN; this interaction promotes neuronal migration (By similarity). A secreted form is apparently generated by shedding of the extracellular domain. Detected in neurons and astrocytes in the central nervous system (CNS). Detected in the hippocampus and in brain cortex. No visible phenotype. Mice are born at the expected Mendelian rate, are viable and fertile (PubMed:11003666). Embryonic mutant mice show increased levels of oligodendrocyte precursor cells in the spinal cord, combined with impaired differentiation of the precursor cells into mature, fully myelinating oligodendrocytes (PubMed:21969550). Mutant mice show slightly increased susceptibility to experimental autoimmune encephalomyelitis (EAE) and strongly reduced recovery. Contrary to wild-type, mutant mice remain paralyzed and display increased levels of apoptotic oligodendrocytes in the spinal cord (PubMed:12355066). Besides, mutant mice display impaired contextual fear memory, probably due to impaired dephosphorylation of proteins that are part of important signaling cascades (PubMed:16513268). Belongs to the protein-tyrosine phosphatase family. Receptor class 5 subfamily.