Characterization of chicken protein tyrosine phosphatase alpha and its expression in the central nervous system.

Protein tyrosine phosphorylation and dephosphorylation are important in cell proliferation, differentiation and functioning of the central nervous system. We have identified a cDNA clone encoding a new transmembrane protein tyrosine phosphatase from a chicken brain cDNA library. The predicted amino acid sequence contains two phosphatase tandem repeats in the intracellular domain and multiple glycosylation sites in the extracellular domain. Since its intracellular domain shares 94% identity with human PTP alpha, we call it chicken PTP alpha (ChPTP alpha). Antibodies specific to ChPTP alpha recognize two major protein bands at 130 and 85 kDa in immunoblot and immunoprecipitation. ChPTP alpha transcript and protein are found in many tissues, but they are particularly abundant in brain. To gain insight into the function of PTP alpha s, we investigated the cell-type specific localization of ChPTP alpha in cerebellum by in situ hybridization and immunostaining. Throughout development, the level of ChPTP alpha remains similar from embryonic day 7 to post-hatching day 14, but the abundance and distribution of cells expressing this protein vary systematically through this period. During development, ChPTP alpha appears in pre-migratory and migrating granule cells, and in Bergmann glia and their radial processes. By 2-weeks after hatching, ChPTP alpha disappears from all cells of the cerebellum except Bergmann glia. Our data, which show for the first time the temporal and spacial distribution of a PTP alpha, suggest that these transmembrane phosphatases are important in the differentiation and function of Bergmann glia and in the migration of granule cells, and thereby play a role in development of the cerebellum.