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Disruption of Mtmr2 produces CMT4B1-like neuropathy with myelin outfolding and impaired spermatogenesis.

Bolino A, Bolis A, Previtali SC, Dina G, Bussini S, Dati G, Amadio S, Del Carro U, Mruk DD, Feltri ML, Cheng CY, Quattrini A, Wrabetz L - J. Cell Biol. (2004)

Bottom Line: We also identified a novel physical interaction in Schwann cells, between Mtmr2 and discs large 1 (Dlg1)/synapse-associated protein 97, a scaffolding molecule that is enriched at the node/paranode region.Dlg1 homologues have been located in several types of cellular junctions and play roles in cell polarity and membrane addition.We propose that Schwann cell-autonomous loss of Mtmr2-Dlg1 interaction dysregulates membrane homeostasis in the paranodal region, thereby producing outfolding and recurrent loops of myelin.

View Article: PubMed Central - PubMed

Affiliation: Dulbecco Telethon Institute, San Raffaele Scientific Institute, 20132 Milan, Italy. bolino.alessandra@hsr.it

ABSTRACT
Mutations in MTMR2, the myotubularin-related 2 gene, cause autosomal recessive Charcot-Marie-Tooth (CMT) type 4B1, a demyelinating neuropathy with myelin outfolding and azoospermia. MTMR2 encodes a ubiquitously expressed phosphatase whose preferred substrate is phosphatidylinositol (3,5)-biphosphate, a regulator of membrane homeostasis and vesicle transport. We generated Mtmr2- mice, which develop progressive neuropathy characterized by myelin outfolding and recurrent loops, predominantly at paranodal myelin, and depletion of spermatids and spermatocytes from the seminiferous epithelium, which leads to azoospermia. Disruption of Mtmr2 in Schwann cells reproduces the myelin abnormalities. We also identified a novel physical interaction in Schwann cells, between Mtmr2 and discs large 1 (Dlg1)/synapse-associated protein 97, a scaffolding molecule that is enriched at the node/paranode region. Dlg1 homologues have been located in several types of cellular junctions and play roles in cell polarity and membrane addition. We propose that Schwann cell-autonomous loss of Mtmr2-Dlg1 interaction dysregulates membrane homeostasis in the paranodal region, thereby producing outfolding and recurrent loops of myelin.

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Expression analysis in Mtmr2- sciatic nerve. (A–I) Immunohistochemical localization of Mtm1 in rat sciatic nerve using anti-Mtm1 polyclonal antibodies (A, D, and G). Mtm1 is located in the cytoplasm of myelin-forming Schwann cells, as shown by double staining with S100 (A–C); in axons, as shown by double staining with NF-M (D–F); and in non–myelin-forming Schwann cells, as revealed by double staining with GFAP (G–I). Immunohistochemical localization of Mtm1 was similar in sciatic nerves from control (J) and Mtmr2- (K) mice. (L–Q) Immunostaining for NF-L in mouse sciatic nerves from control (L–N) and Mtmr2- mice (O–Q). NF-H staining revealed all axons in normal (M) and mutant (P) mouse nerves. (R–W) Immunohistochemical localization of Mtmr1 in rat sciatic nerves using anti-Mtmr1 antibodies. Mtmr1 is localized in axons (R–T) and in the cytoplasm of non–myelin-forming Schwann cells (U–W). Mtmr1 was not detected in the cytoplasm of myelin-forming Schwann cells. No difference in Mtmr1 staining was observed between wild-type (X) and Mtmr2- (Y) sciatic nerves. (Z) Western blot analysis of P0, PMP-22, and MAG on sciatic nerve homogenates from normal and mutant animals. β-Tubulin was used to normalize loading. Bar: (A–F and L–T) 32 μm; (G–I and V and W) 20 μm; and (J, K, X, and Y) 25 μm.
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fig5: Expression analysis in Mtmr2- sciatic nerve. (A–I) Immunohistochemical localization of Mtm1 in rat sciatic nerve using anti-Mtm1 polyclonal antibodies (A, D, and G). Mtm1 is located in the cytoplasm of myelin-forming Schwann cells, as shown by double staining with S100 (A–C); in axons, as shown by double staining with NF-M (D–F); and in non–myelin-forming Schwann cells, as revealed by double staining with GFAP (G–I). Immunohistochemical localization of Mtm1 was similar in sciatic nerves from control (J) and Mtmr2- (K) mice. (L–Q) Immunostaining for NF-L in mouse sciatic nerves from control (L–N) and Mtmr2- mice (O–Q). NF-H staining revealed all axons in normal (M) and mutant (P) mouse nerves. (R–W) Immunohistochemical localization of Mtmr1 in rat sciatic nerves using anti-Mtmr1 antibodies. Mtmr1 is localized in axons (R–T) and in the cytoplasm of non–myelin-forming Schwann cells (U–W). Mtmr1 was not detected in the cytoplasm of myelin-forming Schwann cells. No difference in Mtmr1 staining was observed between wild-type (X) and Mtmr2- (Y) sciatic nerves. (Z) Western blot analysis of P0, PMP-22, and MAG on sciatic nerve homogenates from normal and mutant animals. β-Tubulin was used to normalize loading. Bar: (A–F and L–T) 32 μm; (G–I and V and W) 20 μm; and (J, K, X, and Y) 25 μm.

Mentions: To assess whether absence of Mtmr2 altered myelin protein levels, we performed Western blot analysis on sciatic nerve homogenates. PMP-22 (peripheral myelin protein 22) and P0 (myelin protein zero) levels were normal in Mtmr2- sciatic nerves (Fig. 5 Z), in keeping with the normal compaction and periodicity of myelin. On the other hand, the level of myelin-associated glycoprotein (MAG) was decreased in Mtmr2- sciatic nerves, an observation that is consistent with an alteration in noncompact myelin (mesaxonal loops, incisures, or paranodal loops; Fig. 5 Z). We also investigated whether expression of NF-L, an interactor of Mtmr2 in both axons and denervated Schwann cells (Previtali et al., 2003), was altered in sciatic nerves from Mtmr2- mice. The pattern and intensity of the NF-L immunostaining, as well as its level, were similar in mutant and wild-type nerves (Fig. 5, L–Q; and not depicted). NF-H immunostaining also appeared normal in mutant nerves (Fig. 5 P). Thus, loss of Mtmr2 does not seem to affect neurofilament expression or assembly in axons.


Disruption of Mtmr2 produces CMT4B1-like neuropathy with myelin outfolding and impaired spermatogenesis.

Bolino A, Bolis A, Previtali SC, Dina G, Bussini S, Dati G, Amadio S, Del Carro U, Mruk DD, Feltri ML, Cheng CY, Quattrini A, Wrabetz L - J. Cell Biol. (2004)

Expression analysis in Mtmr2- sciatic nerve. (A–I) Immunohistochemical localization of Mtm1 in rat sciatic nerve using anti-Mtm1 polyclonal antibodies (A, D, and G). Mtm1 is located in the cytoplasm of myelin-forming Schwann cells, as shown by double staining with S100 (A–C); in axons, as shown by double staining with NF-M (D–F); and in non–myelin-forming Schwann cells, as revealed by double staining with GFAP (G–I). Immunohistochemical localization of Mtm1 was similar in sciatic nerves from control (J) and Mtmr2- (K) mice. (L–Q) Immunostaining for NF-L in mouse sciatic nerves from control (L–N) and Mtmr2- mice (O–Q). NF-H staining revealed all axons in normal (M) and mutant (P) mouse nerves. (R–W) Immunohistochemical localization of Mtmr1 in rat sciatic nerves using anti-Mtmr1 antibodies. Mtmr1 is localized in axons (R–T) and in the cytoplasm of non–myelin-forming Schwann cells (U–W). Mtmr1 was not detected in the cytoplasm of myelin-forming Schwann cells. No difference in Mtmr1 staining was observed between wild-type (X) and Mtmr2- (Y) sciatic nerves. (Z) Western blot analysis of P0, PMP-22, and MAG on sciatic nerve homogenates from normal and mutant animals. β-Tubulin was used to normalize loading. Bar: (A–F and L–T) 32 μm; (G–I and V and W) 20 μm; and (J, K, X, and Y) 25 μm.
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Related In: Results  -  Collection

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fig5: Expression analysis in Mtmr2- sciatic nerve. (A–I) Immunohistochemical localization of Mtm1 in rat sciatic nerve using anti-Mtm1 polyclonal antibodies (A, D, and G). Mtm1 is located in the cytoplasm of myelin-forming Schwann cells, as shown by double staining with S100 (A–C); in axons, as shown by double staining with NF-M (D–F); and in non–myelin-forming Schwann cells, as revealed by double staining with GFAP (G–I). Immunohistochemical localization of Mtm1 was similar in sciatic nerves from control (J) and Mtmr2- (K) mice. (L–Q) Immunostaining for NF-L in mouse sciatic nerves from control (L–N) and Mtmr2- mice (O–Q). NF-H staining revealed all axons in normal (M) and mutant (P) mouse nerves. (R–W) Immunohistochemical localization of Mtmr1 in rat sciatic nerves using anti-Mtmr1 antibodies. Mtmr1 is localized in axons (R–T) and in the cytoplasm of non–myelin-forming Schwann cells (U–W). Mtmr1 was not detected in the cytoplasm of myelin-forming Schwann cells. No difference in Mtmr1 staining was observed between wild-type (X) and Mtmr2- (Y) sciatic nerves. (Z) Western blot analysis of P0, PMP-22, and MAG on sciatic nerve homogenates from normal and mutant animals. β-Tubulin was used to normalize loading. Bar: (A–F and L–T) 32 μm; (G–I and V and W) 20 μm; and (J, K, X, and Y) 25 μm.
Mentions: To assess whether absence of Mtmr2 altered myelin protein levels, we performed Western blot analysis on sciatic nerve homogenates. PMP-22 (peripheral myelin protein 22) and P0 (myelin protein zero) levels were normal in Mtmr2- sciatic nerves (Fig. 5 Z), in keeping with the normal compaction and periodicity of myelin. On the other hand, the level of myelin-associated glycoprotein (MAG) was decreased in Mtmr2- sciatic nerves, an observation that is consistent with an alteration in noncompact myelin (mesaxonal loops, incisures, or paranodal loops; Fig. 5 Z). We also investigated whether expression of NF-L, an interactor of Mtmr2 in both axons and denervated Schwann cells (Previtali et al., 2003), was altered in sciatic nerves from Mtmr2- mice. The pattern and intensity of the NF-L immunostaining, as well as its level, were similar in mutant and wild-type nerves (Fig. 5, L–Q; and not depicted). NF-H immunostaining also appeared normal in mutant nerves (Fig. 5 P). Thus, loss of Mtmr2 does not seem to affect neurofilament expression or assembly in axons.

Bottom Line: We also identified a novel physical interaction in Schwann cells, between Mtmr2 and discs large 1 (Dlg1)/synapse-associated protein 97, a scaffolding molecule that is enriched at the node/paranode region.Dlg1 homologues have been located in several types of cellular junctions and play roles in cell polarity and membrane addition.We propose that Schwann cell-autonomous loss of Mtmr2-Dlg1 interaction dysregulates membrane homeostasis in the paranodal region, thereby producing outfolding and recurrent loops of myelin.

View Article: PubMed Central - PubMed

Affiliation: Dulbecco Telethon Institute, San Raffaele Scientific Institute, 20132 Milan, Italy. bolino.alessandra@hsr.it

ABSTRACT
Mutations in MTMR2, the myotubularin-related 2 gene, cause autosomal recessive Charcot-Marie-Tooth (CMT) type 4B1, a demyelinating neuropathy with myelin outfolding and azoospermia. MTMR2 encodes a ubiquitously expressed phosphatase whose preferred substrate is phosphatidylinositol (3,5)-biphosphate, a regulator of membrane homeostasis and vesicle transport. We generated Mtmr2- mice, which develop progressive neuropathy characterized by myelin outfolding and recurrent loops, predominantly at paranodal myelin, and depletion of spermatids and spermatocytes from the seminiferous epithelium, which leads to azoospermia. Disruption of Mtmr2 in Schwann cells reproduces the myelin abnormalities. We also identified a novel physical interaction in Schwann cells, between Mtmr2 and discs large 1 (Dlg1)/synapse-associated protein 97, a scaffolding molecule that is enriched at the node/paranode region. Dlg1 homologues have been located in several types of cellular junctions and play roles in cell polarity and membrane addition. We propose that Schwann cell-autonomous loss of Mtmr2-Dlg1 interaction dysregulates membrane homeostasis in the paranodal region, thereby producing outfolding and recurrent loops of myelin.

Show MeSH
Related in: MedlinePlus