Leukocytecommonantigen-related(LAR)class protein tyrosine phosphatases (PTPs) are critical for axonal guidance; however, their relation to specific guidance cues is poorly defined. We here show that PTP-3, a LAR homolog in Caenorhabditis elegans, is involved in axon guidance regulated by Semaphorin-2A-signaling. PTPδ, one of the vertebrate LAR class PTPs, participates in the Semaphorin-3A (Sema3A)-induced growthconecollapseresponseofprimarycultured dorsal rootganglionneuronsfromMusmusculusembryos.Invivo,however,the contribution of PTPδ in Sema3A-regualted axon guidance was minimal. Instead, PTPδ played a major role in Sema3A-dependent cortical dendritic growth. Ptpδ-/-and Sema3a-/-mutant mice exhibited poor arborization of basal dendrites of cortical layerVneurons. This phenotype was observed in both male and female mutants. The double-heterozygous mutants, Ptpδ-/-; Sema3a-/-, also showed a similar phenotype, indicating the geneticinteraction.InPtpδ-/-brains, Fynand Srckinaseswerehyper phosphorylatedat theirC-terminal Tyr527 residues. Sema3A-stimulation induced dephosphorylation of Tyr527 in the dendrites of wild-type cortical neurons but not of Ptpδ-/-. Arborization of cortical basal dendrites was reduced in Fyn-/- as well as in Ptpδ-/-; Fyn-/- double-heterozygous mutants. Collectively, PTPδ mediates Sema3A-signaling through the activation of Fyn by C-terminal dephosphorylation.
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