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The nuclear import of Frizzled2-C by Importins-beta11 and alpha2 promotes postsynaptic development.

Mosca TJ, Schwarz TL - Nat. Neurosci. (2010)

Bottom Line: The mechanism of nuclear import is unknown and the developmental consequences of this translocation are uncertain.We found that Fz2-C localization to muscle nuclei required the nuclear import factors Importin-beta11 and Importin-alpha2 and that this pathway promoted the postsynaptic development of the subsynaptic reticulum (SSR), an elaboration of the postsynaptic plasma membrane. importin-beta11 (imp-beta11) and dfz2 mutants had less SSR, and some boutons lacked the postsynaptic marker Discs Large.Thus, Wnt-activated growth of the postsynaptic membrane is mediated by the synapse-to-nucleus translocation and active nuclear import of Fz2-C via a selective Importin-beta11/alpha2 pathway.

View Article: PubMed Central - PubMed

Affiliation: The F.M. Kirby Neurobiology Center, Children's Hospital Boston, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts, USA.

ABSTRACT
Synapse-to-nucleus signaling is critical for synaptic development and plasticity. In Drosophila, the ligand Wingless causes the C terminus of its Frizzled2 receptor (Fz2-C) to be cleaved and translocated from the postsynaptic density to nuclei. The mechanism of nuclear import is unknown and the developmental consequences of this translocation are uncertain. We found that Fz2-C localization to muscle nuclei required the nuclear import factors Importin-beta11 and Importin-alpha2 and that this pathway promoted the postsynaptic development of the subsynaptic reticulum (SSR), an elaboration of the postsynaptic plasma membrane. importin-beta11 (imp-beta11) and dfz2 mutants had less SSR, and some boutons lacked the postsynaptic marker Discs Large. These developmental defects in imp-beta11 mutants could be overcome by expression of Fz2-C fused to a nuclear localization sequence that can bypass Importin-beta11. Thus, Wnt-activated growth of the postsynaptic membrane is mediated by the synapse-to-nucleus translocation and active nuclear import of Fz2-C via a selective Importin-beta11/alpha2 pathway.

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Wnt Pathway Components are Properly Localized in Importin Mutants(a–r) Representative confocal images of the NMJ at muscles 6 and 7 in the indicated genotypes, and immunostained as indicated, with anti-HRP (magenta) to mark the neuronal endings. Neither importin mutant prevented Wingless ligand localization to synaptic boutons, dGRIP localization to synapses, or Frizzled2 receptor localization to the synapse. Antibodies to the N-terminal (Fz2-N) and C terminus (Fz2-C; data not shown) gave equivalent results. (s–x) Single confocal slices through the equator of individual third-instar muscle nuclei in the indicated genotypes and stained with the DFz2-N antibody (green) and an antibody to Lamin C (magenta) to mark the nuclear envelope. Perinuclear staining in each genotype indicates endocytosis and trafficking of the DFz2 receptor to the nuclear envelope. In all images, scale bar = 10 µm. Genotypes: Wild-type, (y,w; FRT42D; +; +), imp-β1170 / Df (y,w; imp-β1170 / Df; +; +), imp-α2D14 (y,w; imp-α2D14; +; +).
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Figure 3: Wnt Pathway Components are Properly Localized in Importin Mutants(a–r) Representative confocal images of the NMJ at muscles 6 and 7 in the indicated genotypes, and immunostained as indicated, with anti-HRP (magenta) to mark the neuronal endings. Neither importin mutant prevented Wingless ligand localization to synaptic boutons, dGRIP localization to synapses, or Frizzled2 receptor localization to the synapse. Antibodies to the N-terminal (Fz2-N) and C terminus (Fz2-C; data not shown) gave equivalent results. (s–x) Single confocal slices through the equator of individual third-instar muscle nuclei in the indicated genotypes and stained with the DFz2-N antibody (green) and an antibody to Lamin C (magenta) to mark the nuclear envelope. Perinuclear staining in each genotype indicates endocytosis and trafficking of the DFz2 receptor to the nuclear envelope. In all images, scale bar = 10 µm. Genotypes: Wild-type, (y,w; FRT42D; +; +), imp-β1170 / Df (y,w; imp-β1170 / Df; +; +), imp-α2D14 (y,w; imp-α2D14; +; +).

Mentions: The absence of nuclear Fz2-C localization need not be, a priori, a direct defect in nuclear import; mislocalization or loss of expression of Wnt signaling components in imp-β11 or imp-α2 could reduce nuclear Fz2-C as a secondary consequence. Therefore, we examined Wingless, Fz2 and dGRIP, a scaffold protein11, 14 at the fly NMJ and found no detectable change in their localization or levels of expression in either imp-β11 or imp-α2 (Fig. 3a–r). Therefore, the lack of nuclear Fz2-C in the importin mutants cannot be accounted for by the loss of upstream components of the pathway.


The nuclear import of Frizzled2-C by Importins-beta11 and alpha2 promotes postsynaptic development.

Mosca TJ, Schwarz TL - Nat. Neurosci. (2010)

Wnt Pathway Components are Properly Localized in Importin Mutants(a–r) Representative confocal images of the NMJ at muscles 6 and 7 in the indicated genotypes, and immunostained as indicated, with anti-HRP (magenta) to mark the neuronal endings. Neither importin mutant prevented Wingless ligand localization to synaptic boutons, dGRIP localization to synapses, or Frizzled2 receptor localization to the synapse. Antibodies to the N-terminal (Fz2-N) and C terminus (Fz2-C; data not shown) gave equivalent results. (s–x) Single confocal slices through the equator of individual third-instar muscle nuclei in the indicated genotypes and stained with the DFz2-N antibody (green) and an antibody to Lamin C (magenta) to mark the nuclear envelope. Perinuclear staining in each genotype indicates endocytosis and trafficking of the DFz2 receptor to the nuclear envelope. In all images, scale bar = 10 µm. Genotypes: Wild-type, (y,w; FRT42D; +; +), imp-β1170 / Df (y,w; imp-β1170 / Df; +; +), imp-α2D14 (y,w; imp-α2D14; +; +).
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Related In: Results  -  Collection

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Figure 3: Wnt Pathway Components are Properly Localized in Importin Mutants(a–r) Representative confocal images of the NMJ at muscles 6 and 7 in the indicated genotypes, and immunostained as indicated, with anti-HRP (magenta) to mark the neuronal endings. Neither importin mutant prevented Wingless ligand localization to synaptic boutons, dGRIP localization to synapses, or Frizzled2 receptor localization to the synapse. Antibodies to the N-terminal (Fz2-N) and C terminus (Fz2-C; data not shown) gave equivalent results. (s–x) Single confocal slices through the equator of individual third-instar muscle nuclei in the indicated genotypes and stained with the DFz2-N antibody (green) and an antibody to Lamin C (magenta) to mark the nuclear envelope. Perinuclear staining in each genotype indicates endocytosis and trafficking of the DFz2 receptor to the nuclear envelope. In all images, scale bar = 10 µm. Genotypes: Wild-type, (y,w; FRT42D; +; +), imp-β1170 / Df (y,w; imp-β1170 / Df; +; +), imp-α2D14 (y,w; imp-α2D14; +; +).
Mentions: The absence of nuclear Fz2-C localization need not be, a priori, a direct defect in nuclear import; mislocalization or loss of expression of Wnt signaling components in imp-β11 or imp-α2 could reduce nuclear Fz2-C as a secondary consequence. Therefore, we examined Wingless, Fz2 and dGRIP, a scaffold protein11, 14 at the fly NMJ and found no detectable change in their localization or levels of expression in either imp-β11 or imp-α2 (Fig. 3a–r). Therefore, the lack of nuclear Fz2-C in the importin mutants cannot be accounted for by the loss of upstream components of the pathway.

Bottom Line: The mechanism of nuclear import is unknown and the developmental consequences of this translocation are uncertain.We found that Fz2-C localization to muscle nuclei required the nuclear import factors Importin-beta11 and Importin-alpha2 and that this pathway promoted the postsynaptic development of the subsynaptic reticulum (SSR), an elaboration of the postsynaptic plasma membrane. importin-beta11 (imp-beta11) and dfz2 mutants had less SSR, and some boutons lacked the postsynaptic marker Discs Large.Thus, Wnt-activated growth of the postsynaptic membrane is mediated by the synapse-to-nucleus translocation and active nuclear import of Fz2-C via a selective Importin-beta11/alpha2 pathway.

View Article: PubMed Central - PubMed

Affiliation: The F.M. Kirby Neurobiology Center, Children's Hospital Boston, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts, USA.

ABSTRACT
Synapse-to-nucleus signaling is critical for synaptic development and plasticity. In Drosophila, the ligand Wingless causes the C terminus of its Frizzled2 receptor (Fz2-C) to be cleaved and translocated from the postsynaptic density to nuclei. The mechanism of nuclear import is unknown and the developmental consequences of this translocation are uncertain. We found that Fz2-C localization to muscle nuclei required the nuclear import factors Importin-beta11 and Importin-alpha2 and that this pathway promoted the postsynaptic development of the subsynaptic reticulum (SSR), an elaboration of the postsynaptic plasma membrane. importin-beta11 (imp-beta11) and dfz2 mutants had less SSR, and some boutons lacked the postsynaptic marker Discs Large. These developmental defects in imp-beta11 mutants could be overcome by expression of Fz2-C fused to a nuclear localization sequence that can bypass Importin-beta11. Thus, Wnt-activated growth of the postsynaptic membrane is mediated by the synapse-to-nucleus translocation and active nuclear import of Fz2-C via a selective Importin-beta11/alpha2 pathway.

Show MeSH
Related in: MedlinePlus