Loss of Mtmr2 and Mtmr2/Dlg1 interaction causes myelin outfoldings in vitro . Myelin outfoldings are rescued by MTMR2 replacement using LV transduction. A , Transduction of Mtmr2 -null Schwann cell/DRG neuron cocultures with a GFP LV. A′ , Inset, MBP-positive fibers with myelin outfoldings are indicated by arrowheads. B , Transduction of Mtmr2 -null Schwann cell/DRG neuron cocultures with FLAG-MTMR2 LV rescues myelin outfoldings. DAPI, 4′,6′-Diamidino-2-phenylindole. B′ , Inset. C , Electron microscopy on FLAG-MTMR2 LV transduced cocultures showing that myelin compaction is preserved on MTMR2 overexpression. At least 30 myelinated fibers were evaluated and compared with cultures infected with GFP alone. D , Quantification of MBP-positive fibers with myelin outfoldings in not transduced (NT) explants (75.5 ± 2.3; n = 6), transduced with GFP alone (76.5 ± 5.0; n = 4), and with FLAG-MTMR2 (10.7 ± 5.3; n = 9) ( p = 8.7 × 10 −6 ) (from at least 2 different experiments). E , Dlg1 coimmunoprecipitates with FLAG-MTMR2 but not with MTMR2 devoid of the PDZ-binding domain at the C terminus, termed FLAG-MTMR2ΔPDZBD. Input is the lysate. F , Western blot analysis showing similar level of expression of both FLAG-MTMR2 and FLAG-MTMR2ΔPDZBD on LV transduction of Mtmr2 -null DRG explants at MOI12.5. G , H , Examples of myelin-forming cocultures transduced with FLAG-MTMR2 or FLAG-MTMR2ΔPDZBD LV at MOI12.5. I , Quantification of MBP-positive fibers with myelin outfoldings on LV transduction of Mtmr2 -null explants with FLAG-MTMR2 (17.99 ± 2.20; n = 9) and FLAG-MTMR2ΔPDZBD (29.97 ± 1.76; n = 9) ( p = 0.00085); FLAG-MTMR2ΔPDZBD (29.97 ± 1.76; n = 9) and GFP (76.5 ± 5.0; n = 4) ( p = 0.00097) (2 different experiments). Error bars indicate SEM. ** p
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