The mouse Ptprr gene encodes two protein tyrosine phosphatases, PTP‐SL and PTPBR7, that display distinct patterns of expression during neural development

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Abstract
The protein tyrosine phosphatases PTP‐SL and PTPBR7 differ only in the length of their N‐terminal domain. We show here that PTP‐SL and PTPBR7 are isoforms derived from a single gene (Ptprr) through developmentally regulated use of alternative promoters. Isoform‐specific reverse transcriptase‐polymer chain reaction (RT‐PCR) and RNA in situ hybridization experiments reveal that 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 cells has ceased and is replaced by the PTP‐SL‐specific transcript. In transient transfection experiments it is confirmed that PTPBR7 is a type I transmembrane protein tyrosine phosphatase (PTPase). PTP‐SL, however, appears to be a cytosolic membrane‐associated PTPase that is located at perinuclear vesicular structures that partly belong to the endosomal compartment. Thus, during maturation of Purkinje cells, a gene‐promoter switch results in the replacement of a receptor‐type PTPase by a cytosolic vesicle‐associated isoform.