Expression of a truncated receptor protein tyrosine phosphatase kappa in the brain of an adult transgenic mouse

Receptor protein tyrosine phosphatases (RPTPs) comprise a family of proteins that feature intracellular phosphatase domains and an ectodomain with putative ligand-binding motifs. Several RPTPs are expressed in the brain, including RPTP-κ which participates in homophilic cell–cell interactions in vitro [Y.-P. Jiang, H. Wang, P. D'Eustachio, J.M. Musacchio, J. Schlessinger, J. Sap, Cloning and characterization of R-PTP-κ, a new member of the receptor protein tyrosine phosphatase family with a proteolytically cleaved cellular adhesion molecule-like extracellular region, Mol. Cell. Biol. 13 (1993) 2942–2951; J. Sap, Y.-P. Jiang, D. Friedlander, M. Grumet, J. Schlessinger, Receptor tyrosine phosphatase R-PTP-κ mediates homophilic binding, Mol. Cell. Biol. 14 (1994) 1–9]. The homology of RPTP-κ's ectodomain to neural cell adhesion molecules indicates potential roles in developmental processes such as axonal growth and target recognition, as has been demonstrated for certain Drosophila RPTPs. The brain distribution of RPTP-κ-expressing cells has not been determined, however. In a gene-trap mouse model with a β-gal+neo (β-geo) insertion in the endogenous RPTP-κ gene, the consequent loss of RPTP-κ's enzymatic activity does not produce any obvious phenotypic defects [W.C. Skarnes, J.E. Moss, S.M. Hurtley, R.S.P. Beddington, Capturing genes encoding membrane and secreted proteins important for mouse development, Proc. Natl. Acad. Sci. U.S.A. 92 (1995) 6592–6596]. Nevertheless, since the transgene's expression is driven by the endogenous RPTP-κ promoter, distribution of the truncated RPTP-κ/β-geo fusion protein should reflect the regional and cellular expression of wild-type RPTP-κ, and thus may identify sites where RPTP-κ is important. Towards that goal, we have used this mouse model to map the distribution of the truncated RPTP-κ/β-geo fusion protein in the adult mouse brain using β-galactosidase as a marker enzyme. Visualization of the β-galactosidase activity revealed a non-random pattern of expression, and identified cells throughout the CNS that display RPTP-κ promoter activity. Several neural systems highly expressed the transgene—most notably cortical, olfactory, hippocampal, hypothalamic, amygdaloid and visual structures. These well-characterized brain regions may provide a basis for future studies of RPTP-κ function.