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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 positively regulates multivesicular body (MVB) formation.(A–C) Ultrastructure of 3rd instar NMJs from the indicated genotypes. Control (A) and lqf mutant (B) boutons display a typical vesicle size and distribution. Overexpression of Lqf (C) results in an increased vesicle size and more MVBs that are also increased in size compared to control synapses. Lqf levels do not affect non-multivesicular endosome diameter. Scale bars are 500 µm. (D–F) Quantification of multivesicular bodies (MVBs) and endosomes in A–C. MVB number (D), diameter (E) and endosome diameter (F) have significant differences among control and lqf mutants and Lqf overexpression. Error bars represent SEM. *P<0.05, ***P<0.001. (E) Unpaired t-test, p = 0.0470. (F) One-way ANOVA, p = <0.001. Control (CS), lqf (lqfARI/lqfFDD9), LqfO/E (ElavC155-Gal4/+; UAS-Lqf/+).
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pone-0065997-g005: Lqf positively regulates multivesicular body (MVB) formation.(A–C) Ultrastructure of 3rd instar NMJs from the indicated genotypes. Control (A) and lqf mutant (B) boutons display a typical vesicle size and distribution. Overexpression of Lqf (C) results in an increased vesicle size and more MVBs that are also increased in size compared to control synapses. Lqf levels do not affect non-multivesicular endosome diameter. Scale bars are 500 µm. (D–F) Quantification of multivesicular bodies (MVBs) and endosomes in A–C. MVB number (D), diameter (E) and endosome diameter (F) have significant differences among control and lqf mutants and Lqf overexpression. Error bars represent SEM. *P<0.05, ***P<0.001. (E) Unpaired t-test, p = 0.0470. (F) One-way ANOVA, p = <0.001. Control (CS), lqf (lqfARI/lqfFDD9), LqfO/E (ElavC155-Gal4/+; UAS-Lqf/+).

Mentions: We next examined the ultrastructure of endosomes at NMJs of larva either deficient of Lqf (Fig. 5B) or overexpressing Lqf (Fig. 5C). We first quantified the number and size of MVBs, a population of endosomes that form downstream of early endosomes (reviewed in [49], [50]). Whereas the MVB subset of endosomes can be observed, albeit infrequently, in control NMJs, the presence of MVBs at NMJs in the lqf mutant is rare (Fig. 5B,D), a finding consistent with a recent report in lqf mutant fat cells [51]. Conversely, overexpression of Lqf leads to a dramatic increase in both the number and size of MVBs in NMJs (Fig. 5C, D, E). We then quantified the diameter of non-multivesicular endosomes, and detected a slight, but non-significant decrease in lqf mutant NMJs (Fig. 5F). We also detected an increase in endosome size in larvae with Lqf overexpression compared to control NMJs (Fig. 5F). Together, our data along with those of Csikos and colleagues [51] suggest a functional role for Lqf in late stages of endocytic trafficking and MVB formation.


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 positively regulates multivesicular body (MVB) formation.(A–C) Ultrastructure of 3rd instar NMJs from the indicated genotypes. Control (A) and lqf mutant (B) boutons display a typical vesicle size and distribution. Overexpression of Lqf (C) results in an increased vesicle size and more MVBs that are also increased in size compared to control synapses. Lqf levels do not affect non-multivesicular endosome diameter. Scale bars are 500 µm. (D–F) Quantification of multivesicular bodies (MVBs) and endosomes in A–C. MVB number (D), diameter (E) and endosome diameter (F) have significant differences among control and lqf mutants and Lqf overexpression. Error bars represent SEM. *P<0.05, ***P<0.001. (E) Unpaired t-test, p = 0.0470. (F) One-way ANOVA, p = <0.001. Control (CS), lqf (lqfARI/lqfFDD9), LqfO/E (ElavC155-Gal4/+; UAS-Lqf/+).
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pone-0065997-g005: Lqf positively regulates multivesicular body (MVB) formation.(A–C) Ultrastructure of 3rd instar NMJs from the indicated genotypes. Control (A) and lqf mutant (B) boutons display a typical vesicle size and distribution. Overexpression of Lqf (C) results in an increased vesicle size and more MVBs that are also increased in size compared to control synapses. Lqf levels do not affect non-multivesicular endosome diameter. Scale bars are 500 µm. (D–F) Quantification of multivesicular bodies (MVBs) and endosomes in A–C. MVB number (D), diameter (E) and endosome diameter (F) have significant differences among control and lqf mutants and Lqf overexpression. Error bars represent SEM. *P<0.05, ***P<0.001. (E) Unpaired t-test, p = 0.0470. (F) One-way ANOVA, p = <0.001. Control (CS), lqf (lqfARI/lqfFDD9), LqfO/E (ElavC155-Gal4/+; UAS-Lqf/+).
Mentions: We next examined the ultrastructure of endosomes at NMJs of larva either deficient of Lqf (Fig. 5B) or overexpressing Lqf (Fig. 5C). We first quantified the number and size of MVBs, a population of endosomes that form downstream of early endosomes (reviewed in [49], [50]). Whereas the MVB subset of endosomes can be observed, albeit infrequently, in control NMJs, the presence of MVBs at NMJs in the lqf mutant is rare (Fig. 5B,D), a finding consistent with a recent report in lqf mutant fat cells [51]. Conversely, overexpression of Lqf leads to a dramatic increase in both the number and size of MVBs in NMJs (Fig. 5C, D, E). We then quantified the diameter of non-multivesicular endosomes, and detected a slight, but non-significant decrease in lqf mutant NMJs (Fig. 5F). We also detected an increase in endosome size in larvae with Lqf overexpression compared to control NMJs (Fig. 5F). Together, our data along with those of Csikos and colleagues [51] suggest a functional role for Lqf in late stages of endocytic trafficking and MVB formation.

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