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Epsin 1 Promotes Synaptic Growth by Enhancing BMP Signal Levels in Motoneuron Nuclei.

Vanlandingham PA, Fore TR, Chastain LR, Royer SM, Bao H, Reist NE, Zhang B - PLoS ONE (2013)

Bottom Line: Lqf-stimulated synaptic overgrowth is suppressed by genetic reduction of wit.Interestingly, lqf mutations reduce nuclear pMad levels without causing an apparent blockage of axonal transport itself.Finally, overexpression of Lqf significantly increases the number of multivesicular bodies (MVBs) in the synapse whereas lqf LOF reduces MVB formation, indicating that Lqf may function in signaling endosome recycling or maturation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Oklahoma, Norman, Oklahoma.

ABSTRACT
Bone morphogenetic protein (BMP) retrograde signaling is crucial for neuronal development and synaptic plasticity. However, how the BMP effector phospho-Mother against decapentaplegic (pMad) is processed following receptor activation remains poorly understood. Here we show that Drosophila Epsin1/Liquid facets (Lqf) positively regulates synaptic growth through post-endocytotic processing of pMad signaling complex. Lqf and the BMP receptor Wishful thinking (Wit) interact genetically and biochemically. lqf loss of function (LOF) reduces bouton number whereas overexpression of lqf stimulates bouton growth. Lqf-stimulated synaptic overgrowth is suppressed by genetic reduction of wit. Further, synaptic pMad fails to accumulate inside the motoneuron nuclei in lqf mutants and lqf suppresses synaptic overgrowth in spinster (spin) mutants with enhanced BMP signaling by reducing accumulation of nuclear pMad. Interestingly, lqf mutations reduce nuclear pMad levels without causing an apparent blockage of axonal transport itself. Finally, overexpression of Lqf significantly increases the number of multivesicular bodies (MVBs) in the synapse whereas lqf LOF reduces MVB formation, indicating that Lqf may function in signaling endosome recycling or maturation. Based on these observations, we propose that Lqf plays a novel endosomal role to ensure efficient retrograde transport of BMP signaling endosomes into motoneuron nuclei.

No MeSH data available.


Related in: MedlinePlus

Lqf is required for synaptic overgrowth and pMad retrograde transport in spinster mutants.(A–F) Representative images of bouton morphology and pMad levels at the NMJ (A, C, E) and motoneuron nuclei (B, D, F) in Drosophila 3rd instar larval NMJs from control larvae (CS, A–B), spin mutants (C–D) and spin;lqf double mutants (E–F). Synaptic boutons are overgrown in spin mutants (C), and this overgrowth is suppressed in the spin;lqf double mutants (E). (G) Quantification of synaptic bouton number in spin and spin;lqf mutants. Taken from three different animals for each genotype, n values represent the number of NMJs quantified. (H) Quantification of pMad intensity in boutons (white bars) and motoneuron nuclei (black bars). n = 5 NMJs from three larvae and 20 nuclei from five different larvae. Error bars represent SEM. *P<0.05, **P<0.01, ***P<0.001. One-way ANOVA with Tukey's Multiple Comparison Post test. Control (CS), spin (spin4/spin5), spin, lqf (spin4/spin5; lqfARI/lqf Df).
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pone-0065997-g004: Lqf is required for synaptic overgrowth and pMad retrograde transport in spinster mutants.(A–F) Representative images of bouton morphology and pMad levels at the NMJ (A, C, E) and motoneuron nuclei (B, D, F) in Drosophila 3rd instar larval NMJs from control larvae (CS, A–B), spin mutants (C–D) and spin;lqf double mutants (E–F). Synaptic boutons are overgrown in spin mutants (C), and this overgrowth is suppressed in the spin;lqf double mutants (E). (G) Quantification of synaptic bouton number in spin and spin;lqf mutants. Taken from three different animals for each genotype, n values represent the number of NMJs quantified. (H) Quantification of pMad intensity in boutons (white bars) and motoneuron nuclei (black bars). n = 5 NMJs from three larvae and 20 nuclei from five different larvae. Error bars represent SEM. *P<0.05, **P<0.01, ***P<0.001. One-way ANOVA with Tukey's Multiple Comparison Post test. Control (CS), spin (spin4/spin5), spin, lqf (spin4/spin5; lqfARI/lqf Df).

Mentions: There are multiple routes a cargo can take through the endocytic pathway following internalization. One of the best-characterized routes is trafficking to the lysosome, in which the cargo is first internalized by clathrin-mediated endocytosis and delivered to early endosomes. Endosomes containing cargo destined for lysosomes mature to become late endosomes/MVBs, which can fuse with lysosomes where the cargo is degraded [49]. In flies, the product of the spinster (spin) gene is shown to be involved in trafficking along the lysosomal degradation pathway [27]. Flies lacking spin display BMP signaling-dependent synaptic overgrowth [27]. We first examined bouton morphology in spin mutants (spin4/spin5) and in spin and lqf double mutants (spin4/spin5; lqfARI/lqf Df). spin mutants display overgrowth and hyperbranching of NMJs (Fig. 4A and B), similar to those publishes previously [27]. The spin; lqf double mutants show reduced synaptic growth similar to those seen in lqf (lqfARI/lqfFDD9) mutants (Fig. 4E and G), suggesting that overgrowth in spin mutants depends on Lqf.


Epsin 1 Promotes Synaptic Growth by Enhancing BMP Signal Levels in Motoneuron Nuclei.

Vanlandingham PA, Fore TR, Chastain LR, Royer SM, Bao H, Reist NE, Zhang B - PLoS ONE (2013)

Lqf is required for synaptic overgrowth and pMad retrograde transport in spinster mutants.(A–F) Representative images of bouton morphology and pMad levels at the NMJ (A, C, E) and motoneuron nuclei (B, D, F) in Drosophila 3rd instar larval NMJs from control larvae (CS, A–B), spin mutants (C–D) and spin;lqf double mutants (E–F). Synaptic boutons are overgrown in spin mutants (C), and this overgrowth is suppressed in the spin;lqf double mutants (E). (G) Quantification of synaptic bouton number in spin and spin;lqf mutants. Taken from three different animals for each genotype, n values represent the number of NMJs quantified. (H) Quantification of pMad intensity in boutons (white bars) and motoneuron nuclei (black bars). n = 5 NMJs from three larvae and 20 nuclei from five different larvae. Error bars represent SEM. *P<0.05, **P<0.01, ***P<0.001. One-way ANOVA with Tukey's Multiple Comparison Post test. Control (CS), spin (spin4/spin5), spin, lqf (spin4/spin5; lqfARI/lqf Df).
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Related In: Results  -  Collection

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pone-0065997-g004: Lqf is required for synaptic overgrowth and pMad retrograde transport in spinster mutants.(A–F) Representative images of bouton morphology and pMad levels at the NMJ (A, C, E) and motoneuron nuclei (B, D, F) in Drosophila 3rd instar larval NMJs from control larvae (CS, A–B), spin mutants (C–D) and spin;lqf double mutants (E–F). Synaptic boutons are overgrown in spin mutants (C), and this overgrowth is suppressed in the spin;lqf double mutants (E). (G) Quantification of synaptic bouton number in spin and spin;lqf mutants. Taken from three different animals for each genotype, n values represent the number of NMJs quantified. (H) Quantification of pMad intensity in boutons (white bars) and motoneuron nuclei (black bars). n = 5 NMJs from three larvae and 20 nuclei from five different larvae. Error bars represent SEM. *P<0.05, **P<0.01, ***P<0.001. One-way ANOVA with Tukey's Multiple Comparison Post test. Control (CS), spin (spin4/spin5), spin, lqf (spin4/spin5; lqfARI/lqf Df).
Mentions: There are multiple routes a cargo can take through the endocytic pathway following internalization. One of the best-characterized routes is trafficking to the lysosome, in which the cargo is first internalized by clathrin-mediated endocytosis and delivered to early endosomes. Endosomes containing cargo destined for lysosomes mature to become late endosomes/MVBs, which can fuse with lysosomes where the cargo is degraded [49]. In flies, the product of the spinster (spin) gene is shown to be involved in trafficking along the lysosomal degradation pathway [27]. Flies lacking spin display BMP signaling-dependent synaptic overgrowth [27]. We first examined bouton morphology in spin mutants (spin4/spin5) and in spin and lqf double mutants (spin4/spin5; lqfARI/lqf Df). spin mutants display overgrowth and hyperbranching of NMJs (Fig. 4A and B), similar to those publishes previously [27]. The spin; lqf double mutants show reduced synaptic growth similar to those seen in lqf (lqfARI/lqfFDD9) mutants (Fig. 4E and G), suggesting that overgrowth in spin mutants depends on Lqf.

Bottom Line: Lqf-stimulated synaptic overgrowth is suppressed by genetic reduction of wit.Interestingly, lqf mutations reduce nuclear pMad levels without causing an apparent blockage of axonal transport itself.Finally, overexpression of Lqf significantly increases the number of multivesicular bodies (MVBs) in the synapse whereas lqf LOF reduces MVB formation, indicating that Lqf may function in signaling endosome recycling or maturation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Oklahoma, Norman, Oklahoma.

ABSTRACT
Bone morphogenetic protein (BMP) retrograde signaling is crucial for neuronal development and synaptic plasticity. However, how the BMP effector phospho-Mother against decapentaplegic (pMad) is processed following receptor activation remains poorly understood. Here we show that Drosophila Epsin1/Liquid facets (Lqf) positively regulates synaptic growth through post-endocytotic processing of pMad signaling complex. Lqf and the BMP receptor Wishful thinking (Wit) interact genetically and biochemically. lqf loss of function (LOF) reduces bouton number whereas overexpression of lqf stimulates bouton growth. Lqf-stimulated synaptic overgrowth is suppressed by genetic reduction of wit. Further, synaptic pMad fails to accumulate inside the motoneuron nuclei in lqf mutants and lqf suppresses synaptic overgrowth in spinster (spin) mutants with enhanced BMP signaling by reducing accumulation of nuclear pMad. Interestingly, lqf mutations reduce nuclear pMad levels without causing an apparent blockage of axonal transport itself. Finally, overexpression of Lqf significantly increases the number of multivesicular bodies (MVBs) in the synapse whereas lqf LOF reduces MVB formation, indicating that Lqf may function in signaling endosome recycling or maturation. Based on these observations, we propose that Lqf plays a novel endosomal role to ensure efficient retrograde transport of BMP signaling endosomes into motoneuron nuclei.

No MeSH data available.


Related in: MedlinePlus