Comparison of RPTP zeta/beta, phosphacan, and trkB mRNA expression in the developing and adult rat nervous system and induction of RPTP zeta/beta and phosphacan mRNA following brain injury.

The receptor protein tyrosine phosphatase (RPTP) zeta/beta and a major isoform, phosphacan, a chondroitin sulfate proteoglycan that contains the RPTP zeta/beta 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 RPTP zeta/beta 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 RPTP zeta/beta mRNAs in the developing peripheral and central nervous systems. Analysis with a probe specific for the catalytic TrkB isoform suggested that RPTP zeta/beta and non-catalytic trkB mRNAs were co-expressed in particular regions of the nervous system while the catalytic trkB and RPTP zeta/beta transcripts were also, but to a lesser extent. RPTP zeta/beta and phosphacan expression were extremely similar, differing particularly in the level of expression in the ventricular and subventricular zones, hippocampus, and ependyma. Furthermore, both RPTP zeta/beta and phosphacan mRNAs were found in several subsets of neurons as well as astrocytes. Following CNS injury, we observed robust induction of RPTP zeta/beta mRNA in areas of axonal sprouting, and of both RPTP zeta/beta 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.