The mouse Ptprr gene encodes two protein tyrosine phosphatases, PTP-SL andPTPBR7, that display distinct patterns of expression during neural development

The protein tyrosine phosphatases PTP-SL and PTPBR7 differ only in the leng th of their N-terminal domain. We show here that PTP-SL and PTPBR7 are isof orms derived from a single gene (Ptprr) through developmentally regulated u se of alternative promoters. Isoform-specific reverse transcriptase-polymer chain reaction (RT-PCR) and RNA in situ hybridization experiments reveal t hat PTPBR7 is expressed during early embryogenesis in spinal ganglia cells as well as in developing Purkinje cells. Post-natally, PTPBR7 is expressed in various regions of the adult mouse brain, but expression in Purkinje cel ls has ceased and is replaced by the PTP-SL-specific transcript. In transie nt transfection experiments it is confirmed that PTPBR7 is a type I transme mbrane protein tyrosine phosphatase (PTPase). PTP-SL, however, appears to b e a cytosolic membrane-associated PTPase that is located at perinuclear ves icular structures that partly belong to the endosomal compartment. Thus, du ring maturation of Purkinje cells, a gene-promoter switch results in the re placement of a receptor-type PTPase by a cytosolic vesicle-associated isofo rm.