The mouse Ptprr gene encodes two protein tyrosine phosphatases, PTP-SL and PTPBR7, that display distinct patterns of expression during neural development A. M. J. M. van den Maagdenberg, D. Ba Èchner, 1 J. T. G. Schepens, W. Peters, J. A. M. Fransen, B. Wieringa and W. J. A. J. Hendriks Department of Cell Biology, Institute of Cellular Signalling, University of Nijmegen, Adelbertusplein 1, 6525 EK Nijmegen, The Netherlands 1 Institute of Cellular Biochemistry, University Hospital Eppendorf, Hamburg, Germany Keywords: alternative promoters, cerebellum, endocytotic vesicles, protein isoforms, Purkinje cells, signal transduction, spinal ganglia 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-speci®c 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-speci®c transcript. In transient transfection experiments it is con®rmed 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. Introduction An important regulatory mechanism that is exploited for proper development and function of the central nervous system is reversible protein tyrosine phosphorylation (Walaas & Greengard, 1991; Gurd, 1997). For example, high levels of phosphotyrosine-containing proteins have been reported in the growth cones within the developing brain (Bixby & Jhabvala, 1993), and several neuronal receptor protein tyrosine kinases were shown to affect neuronal survival, differentiation and synaptic activity (Heumann, 1994; Gurd, 1997). Because protein tyrosine phosphatases (PTPases) together with protein tyrosine kinases coordinate the level of tyrosine phosphorylation, it is anticipated that also PTPases play an active role in brain development and function. In support of this view, various PTPases have been identi®ed that display restricted patterns of expression in the adult and developing nervous system, suggestive of specialized spatio-temporal functions in the brain (Stoker & Dutta, 1998). For example, STEP PTPases are expressed only within the striatal neurons of the basal ganglia and related structures receiving a dopamine input and projecting to the substantia nigra (Lombroso et al., 1993; Boulanger et al., 1995). The STEP (striatal-enriched phosphatase) family of PTPases comprises cytosolic as well as membrane-bound isoforms that all originate from a single gene by alternative splicing (Boulanger et al., 1995; Sharma & Lombroso, 1995; Bult et al., 1996). More direct, functional evidence for the importance of PTPases in neuronal developmental processes comes from studies in animals that carry mutations in neuronal PTPase genes (Desai et al., 1996; Krueger et al., 1996; Yeo et al., 1997). In certain Drosophila PTPase mutants, speci®c motor neurons of the central nervous system fail to migrate to their appropriate synaptic muscle targets due to premature axonal ending or bypassing (Desai et al., 1996; Krueger et al., 1996). In transgenic mice that contain a gene trap in the PTPase LAR gene, basal forebrain cholinergic neurons are reduced in size and cholinergic innervation of the dentate gyrus is decreased (Yeo et al., 1997). These data strongly suggest a regulatory function for PTPases in axonal path®nding and synapse formation. Recently, we described the cloning of a novel mouse brain PTPase, PTP-SL (STEP-like PTPase), that is homologous to the rat STEP family (Hendriks et al., 1995b). The gene encoding PTP-SL (Ptprr) was recently assigned to mouse chromosome region 8A2 (van den Maagdenberg et al., 1999). Others reported the cloning of a cDNA, termed PTPBR7 (brain PTPase clone number 7), that is partly identical to PTP-SL (Ogata et al., 1995). PTPBR7 cDNA encodes a receptor-type transmembrane PTPase that is expressed in the brain, especially in the habenula and the hippocampal region (Ogata et al., 1995). In the current study we show that PTP-SL and PTPBR7 transcripts are derived from the same single-copy gene (Ptprr). A promoter switch in the Ptprr gene occurs in Purkinje cells during cerebellar development that results in the replacement of the transmembrane PTPBR7 isoform by the vesicle-associated PTP-SL isoform. This transition coincides with a critical period of Correspondence: Dr W. J. A. J. Hendriks, as above. E-mail: w.hendriks@celbi.kun.nl Received 30 March 1999, revised 21 June 1999, accepted 22 June 1999 European Journal of Neuroscience, Vol. 11, pp. 3832±3844, 1999 Ó European Neuroscience Association