Receptor tyrosine phosphatase-delta is a hemophilic, neurite-promoting cell adhesion molecule for CNS neurons

Appropriate regulation of tyrosine phosphorylation is essential for axon gr owth and guidance; evidence from invertebrates indicates that receptor-type tyrosine phosphatases (RPTPs) are required for correct axon growth during CNS development. One vertebrate RPTP, PTP-delta, is highly expressed in bra in and has a cell adhesion moleculelike extracellular domain (ECD) comprisi ng three immunoglobulin repeats and eight fibronectin type III repeats. Usi ng fluorescent beads (Covaspheres) coated with the PTP-delta ECD, as well a s insect cells expressing PTP-delta on their surfaces, we show that PTP-del ta is a hemophilic cell adhesion molecule. A variety of chick neurons adher e strongly to an Fc fusion protein containing the PTP-delta ECD. Additional ly, substrate-bound PTP-delta ECD fusion protein strongly promotes neurite outgrowth from forebrain neurons; this effect is separable from ifs effect on adhesion. Our results indicate that PTP-delta is a neurite-promoting cel l adhesion molecule for CNS neurons.