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PTPBR7 binding proteins in myelinating neurons of the mouse brain
Irene M Chesini1, Griet Debyser, Huib Croes
1Department of Cell Biology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Geert Grooteplein 28, 6525 GA Nijmegen, The Netherlands.
Abstract:
Mouse protein tyrosine phosphatase PTPBR7 is a receptor-like, transmembrane protein that is localized on the surface of neuronal cells. Its protein phosphatase activity is reduced upon multimerization, and PTPBR7-deficient mice display motor coordination defects. Extracellular molecules that may influence PTPBR7 activity, however, remain to be determined. We here show that the PTPBR7 extracellular domain binds to highly myelinated regions in mouse brain, in particular the white matter tracks in cerebellum. PTPBR7 deficiency does not alter this binding pattern, as witnessed by RAP in situ staining of Ptprr⁻/⁻ mouse brain sections. Additional in situ and in vitro experiments also suggest that sugar moieties of heparan sulphate and chondroitin sulphate glycosaminoglycans are not critical for PTPBR7 binding. Candidate binding proteins were affinity-purified exploiting the PTPBR7 extracellular domain and identified by mass spectrometric means. Results support the suggested link between PTPRR isoforms and cerebellar calcium ion homeostasis, and suggest an additional role in the process of cell-cell adhesion.
Insights
Mouse protein tyrosine phosphatase PTPBR7 binds to myelinated brain regions. Its deficiency causes motor coordination issues, but binding is unaffected by its absence, suggesting other factors influence its function.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- PTPBR7 is a neuronal transmembrane protein tyrosine phosphatase.
- PTPBR7 deficiency in mice leads to motor coordination deficits.
- The extracellular molecules influencing PTPBR7 activity are unknown.
Purpose of the Study:
- To identify extracellular binding partners of PTPBR7.
- To investigate the binding characteristics of the PTPBR7 extracellular domain in the mouse brain.
Main Methods:
- In situ hybridization and RAP staining on mouse brain sections.
- In vitro binding assays.
- Affinity purification and mass spectrometry for protein identification.
Main Results:
- The PTPBR7 extracellular domain binds to highly myelinated regions, particularly cerebellar white matter tracks.
- PTPBR7 deficiency does not affect this binding pattern.
- Heparan sulphate and chondroitin sulphate glycosaminoglycans are not critical for PTPBR7 binding.
- Mass spectrometry identified candidate binding proteins.
Conclusions:
- PTPBR7 interacts with specific brain regions, suggesting a role in white matter.
- The findings support a link between PTPRR isoforms, cerebellar calcium homeostasis, and cell-cell adhesion.
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