Comparison of RPTPζ/β, phosphacan, and trkB mRNA expression in the developing and adult rat nervous system and induction of RPTPζ/β and phosphacan mRNA following brain injury

The receptor protein tyrosine phosphatase (RPTP)ζ/β and a major isoform, phosphacan, a chondroitin sulfate proteoglycan that contains the RPTPζ/β extracellular domain but not the transmembrane and intracellular phosphatase domains, are expressed abundantly in the nervous system, primarily by astroglia. Because of similarities in the expression patterns of RPTPζ/β and the receptor tyrosine kinase TrkB, we investigated whether RNAs encoding these proteins were co-localized during development, which would suggest that these molecules might functionally interact in vivo. By in-situ hybridization, we noted extensive areas of overlap in the expression of trkB and RPTPζ/β mRNAs in the developing peripheral and central nervous systems. Analysis with a probe specific for the catalytic TrkB isoform suggested that RPTPζ/β and non-catalytic trkB mRNAs were co-expressed in particular regions of the nervous system while the catalytic trkB and RPTPζ/β transcripts were also, but to a lesser extent. RPTPζ/β and phosphacan expression were extremely similar, differing particularly in the level of expression in the ventricular and subventricular zones, hippocampus, and ependyma. Furthermore, both RPTPζ/β and phosphacan mRNAs were found in several subsets of neurons as well as astrocytes. Following CNS injury, we observed robust induction of RPTPζ/β mRNA in areas of axonal sprouting, and of both RPTPζ/β and phosphacan mRNAs in areas of glial scarring, implying that the encoded proteins and the cell adhesion molecules and extracellular matrix proteins to which they bind may contribute to recovery from injury and perhaps regulation of axonal regrowth in the nervous system.