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. 2020 Mar 6;9:e54224. doi: 10.7554/eLife.54224

Figure 3. Re-expression of presynaptic PTP σ rescues postsynaptic LTP in the hippocampus through mechanisms independent of the extracellular region of PTPσ.

(A) Diagram depicting re-expression of WT and mutant PTPσ proteins in the CA3 region of the hippocampus by local injection of AAV(php.eB)-eIF1a-Ptprs (WT and mutants), followed by measurement of TBS-LTP. (B) Diagram depicting the domain structures of PTPσ and extracellular and cytoplasmic regions/domains involved in protein-protein interactions or tyrosine phosphatase activity. The first three Ig domains are important for trans-synaptic adhesions with Slitrk1, TrkC, CSPG/HSPG or SALM5, and the residues Y224 and K68/K69/K71/K72 are important for Slitrk1 and CSPG/HSPG interactions, respectively. (C) Specific PTPσ mutants used in our experiments, with point mutations or small deletions in the extracellular domains. All binding partners of PTPσ affected by the mutations/deletions are also indicated. (D) Expression levels and sizes of PTPσ mutants, revealed by immunoblot analysis of HEK293T cell lysates using two independent PTPσ antibodies targeting the N-terminal region (~Ig1-2) and C-terminus (last 30 residues) that can detect all PTPσ mutants, except for PTPσ-ΔIg12, which is not detected by the N-terminal antibody. (E) Rescue of TBS-LTP at SC-CA1 synapses by re-expression of WT PTPσ as well as mutant PTPσ (lacking CSPG/HSPG and Slitrk1 interactions) in the CA3 region of Emx1-Cre;Ptprsfl/fl mice (P28–32) through local injection of AAV-eIF1a-Ptprs-WT/mut. In control experiments, AAV-hSyn-eGFP was injected into the CA3 region of both Ptprsfl/fl (WT) and Emx1-Cre;Ptprsfl/fl mice. (n = 14 slices from four mice [WT-eGFP], 13, 5 [cKO-eGFP], 14, 6 [cKO-PTPσ-WT], 11, 4 [cKO-PTPσ−4A], and 11, 4 [cKO-PTPσ-Y224S], *p<0.05, **p<0.01, ns, not significant, one-way ANOVA with Dunnett’s test). (F) Full and partial rescue of TBS-LTP at SC-CA1 synapses by re-expression of mutant PTPσ lacking Ig1+2 (ΔIg12), Ig3 (ΔIg3), or FNIII1+2 (ΔFN12) domains in the CA3 region of Emx1-Cre;Ptprsfl/fl mice (P28–32) by local injection of AAV-eEF1-Ptprs. Note that expression of PTPσ-ΔIg3 induces a partial rescue. Control virus (AAV-eIF1a-eGFP) was injected into the CA3 region of both Ptprsfl/fl (control) and Emx1-Cre;Ptprsfl/fl mice. (n = 12 slices from four mice [WT-eGFP], 13, 4 [cKO-eGFP], 16, 5 [cKO-PTPσ-ΔIg12], 20, 6 [cKO-PTPσ-ΔIg3], and 13, 5 [cKO-PTPσ-ΔFn12], *p<0.05, **p<0.01, ns, not significant, one-way ANOVA with Dunnett’s test).

Figure 3.

Figure 3—figure supplement 1. PTPσ adhesions with known postsynaptic partners, and identification of the amino acid residues involved in the interactions.

Figure 3—figure supplement 1.

(A) PTPσ adhesions with known postsynaptic partners based on reported complex structures and molecular modeling of the SALM5-PTPσ complex. (B) Amino acid residues involved in the interactions between PTPσ and PTPσ-binding postsynaptic adhesion molecules based on reported or modeled complex structures. Note that IL1RAPL1 and IL-1RAcP have been shown to interact with PTPδ but not PTPσ (Yamagata et al., 2015; Yoshida et al., 2012; Yoshida et al., 2011).