Limits...
Rab8, POSH, and TAK1 regulate synaptic growth in a Drosophila model of frontotemporal dementia.

West RJ, Lu Y, Marie B, Gao FB, Sweeney ST - J. Cell Biol. (2015)

Bottom Line: Expression of Rab8 rescued overgrowth phenotypes generated by CHMP2B(Intron5).We identify novel roles for endosomal JNK-scaffold POSH (Plenty-of-SH3s) and a JNK kinase kinase, TAK1, in regulating growth activation in Rab8 mutants.Our data uncover Rab8, POSH, and TAK1 as regulators of synaptic growth responses and point to recycling endosome as a key compartment for synaptic growth regulation during neurodegenerative processes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology and Hull York Medical School, University of York, Heslington, York YO10 5DD, England, UK Department of Biology and Hull York Medical School, University of York, Heslington, York YO10 5DD, England, UK.

Show MeSH

Related in: MedlinePlus

Rab8 mutants reveal a role for the JNKKK TAK1 in synaptic overgrowth at the NMJ. (A and B) Loss of TAK1 function generated by Inhibition of TAK1 through panneuronal (n-Syb–Gal4) expression of a dominant-negative form of TAK1, knockdown by TAK1-RNAi, or use of a TAK1 loss-of-function allele completely alleviated synaptic overgrowth in a Rab8 mutant background. Correspondingly panneuronal expression of UAS-TAK1 promotes synaptic overgrowth, characterized by a significant increase in synaptic bouton number. Reduction of HRS function, using a heterozygous HRS loss-of-function allele HRSD28/+, in combination with Rab81/+ elicited a significant increase in synaptic bouton number. HRSD28/+ or Rab81/+ alone did not affect bouton number. Bar, 10 µm. ANOVA: F (d.f. 11) = 24.2733; P < 0.001 with post-hoc Dunnett’s comparison to wild-type control: ***, P < 0.001. Student’s t test comparison between genotypes: ###, P < 0.001; #, P < 0.05. Numbers above bars = n. Error bars show SEM.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4384727&req=5

fig8: Rab8 mutants reveal a role for the JNKKK TAK1 in synaptic overgrowth at the NMJ. (A and B) Loss of TAK1 function generated by Inhibition of TAK1 through panneuronal (n-Syb–Gal4) expression of a dominant-negative form of TAK1, knockdown by TAK1-RNAi, or use of a TAK1 loss-of-function allele completely alleviated synaptic overgrowth in a Rab8 mutant background. Correspondingly panneuronal expression of UAS-TAK1 promotes synaptic overgrowth, characterized by a significant increase in synaptic bouton number. Reduction of HRS function, using a heterozygous HRS loss-of-function allele HRSD28/+, in combination with Rab81/+ elicited a significant increase in synaptic bouton number. HRSD28/+ or Rab81/+ alone did not affect bouton number. Bar, 10 µm. ANOVA: F (d.f. 11) = 24.2733; P < 0.001 with post-hoc Dunnett’s comparison to wild-type control: ***, P < 0.001. Student’s t test comparison between genotypes: ###, P < 0.001; #, P < 0.05. Numbers above bars = n. Error bars show SEM.

Mentions: Having observed perturbed endosomal dynamics, HRS depletion, and elevated JNK signaling in Rab8 mutants, we asked whether POSH could provide a nexus linking these phenotypes with synaptic overgrowth. Here, we demonstrate an essential role for POSH in the regulation of synaptic growth in Rab8 mutants. Introducing POSH mutants into a Rab8 mutant background alleviates synaptic overgrowth (Fig. 7, A and B). Puncta of POSH, colocalizing with accumulations of P-MAD and the late endosomal marker spin (spinster; Sweeney and Davis, 2002) were observed in all larval axon bundles in Rab8 mutants, a phenotype not observed in wild type (Fig. 7, C and D). P-MAD accumulations were reversed by the introduction of POSH- mutants into a Rab8 mutant background (Fig. 7, C and D). If POSH is acting as a scaffold for JNK–AP-1 signaling and regulator of HRS abundance in the motor neuron, we would predict that the introduction of POSH- alleles into a Rab8 mutant would prevent transcriptional activation of the Puc-LacZ reporter and HRS down-regulation. Examining Puc-driven LacZ expression in a POSH/Rab8 mutant reduces transcriptional activation of the reporter dramatically compared with controls (Fig. 7 E). In addition, HRS levels are rescued to wild-type levels in a POSH/Rab8 mutant (Fig. 7 F). HRS is known to regulate TGF-β signaling (Jékely and Rørth, 2003), so we asked whether Dad-LacZ and P-MAD abundance are also rescued in POSH/Rab8 and we find that they are (Fig. 7, G and H). Overexpression of HRS in a Rab8 mutant background rescues synaptic overgrowth (Fig. 8) consistent with HRS regulating synaptic overgrowth via TGF-β receptor degradation (Rodal et al., 2011).


Rab8, POSH, and TAK1 regulate synaptic growth in a Drosophila model of frontotemporal dementia.

West RJ, Lu Y, Marie B, Gao FB, Sweeney ST - J. Cell Biol. (2015)

Rab8 mutants reveal a role for the JNKKK TAK1 in synaptic overgrowth at the NMJ. (A and B) Loss of TAK1 function generated by Inhibition of TAK1 through panneuronal (n-Syb–Gal4) expression of a dominant-negative form of TAK1, knockdown by TAK1-RNAi, or use of a TAK1 loss-of-function allele completely alleviated synaptic overgrowth in a Rab8 mutant background. Correspondingly panneuronal expression of UAS-TAK1 promotes synaptic overgrowth, characterized by a significant increase in synaptic bouton number. Reduction of HRS function, using a heterozygous HRS loss-of-function allele HRSD28/+, in combination with Rab81/+ elicited a significant increase in synaptic bouton number. HRSD28/+ or Rab81/+ alone did not affect bouton number. Bar, 10 µm. ANOVA: F (d.f. 11) = 24.2733; P < 0.001 with post-hoc Dunnett’s comparison to wild-type control: ***, P < 0.001. Student’s t test comparison between genotypes: ###, P < 0.001; #, P < 0.05. Numbers above bars = n. Error bars show SEM.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4384727&req=5

fig8: Rab8 mutants reveal a role for the JNKKK TAK1 in synaptic overgrowth at the NMJ. (A and B) Loss of TAK1 function generated by Inhibition of TAK1 through panneuronal (n-Syb–Gal4) expression of a dominant-negative form of TAK1, knockdown by TAK1-RNAi, or use of a TAK1 loss-of-function allele completely alleviated synaptic overgrowth in a Rab8 mutant background. Correspondingly panneuronal expression of UAS-TAK1 promotes synaptic overgrowth, characterized by a significant increase in synaptic bouton number. Reduction of HRS function, using a heterozygous HRS loss-of-function allele HRSD28/+, in combination with Rab81/+ elicited a significant increase in synaptic bouton number. HRSD28/+ or Rab81/+ alone did not affect bouton number. Bar, 10 µm. ANOVA: F (d.f. 11) = 24.2733; P < 0.001 with post-hoc Dunnett’s comparison to wild-type control: ***, P < 0.001. Student’s t test comparison between genotypes: ###, P < 0.001; #, P < 0.05. Numbers above bars = n. Error bars show SEM.
Mentions: Having observed perturbed endosomal dynamics, HRS depletion, and elevated JNK signaling in Rab8 mutants, we asked whether POSH could provide a nexus linking these phenotypes with synaptic overgrowth. Here, we demonstrate an essential role for POSH in the regulation of synaptic growth in Rab8 mutants. Introducing POSH mutants into a Rab8 mutant background alleviates synaptic overgrowth (Fig. 7, A and B). Puncta of POSH, colocalizing with accumulations of P-MAD and the late endosomal marker spin (spinster; Sweeney and Davis, 2002) were observed in all larval axon bundles in Rab8 mutants, a phenotype not observed in wild type (Fig. 7, C and D). P-MAD accumulations were reversed by the introduction of POSH- mutants into a Rab8 mutant background (Fig. 7, C and D). If POSH is acting as a scaffold for JNK–AP-1 signaling and regulator of HRS abundance in the motor neuron, we would predict that the introduction of POSH- alleles into a Rab8 mutant would prevent transcriptional activation of the Puc-LacZ reporter and HRS down-regulation. Examining Puc-driven LacZ expression in a POSH/Rab8 mutant reduces transcriptional activation of the reporter dramatically compared with controls (Fig. 7 E). In addition, HRS levels are rescued to wild-type levels in a POSH/Rab8 mutant (Fig. 7 F). HRS is known to regulate TGF-β signaling (Jékely and Rørth, 2003), so we asked whether Dad-LacZ and P-MAD abundance are also rescued in POSH/Rab8 and we find that they are (Fig. 7, G and H). Overexpression of HRS in a Rab8 mutant background rescues synaptic overgrowth (Fig. 8) consistent with HRS regulating synaptic overgrowth via TGF-β receptor degradation (Rodal et al., 2011).

Bottom Line: Expression of Rab8 rescued overgrowth phenotypes generated by CHMP2B(Intron5).We identify novel roles for endosomal JNK-scaffold POSH (Plenty-of-SH3s) and a JNK kinase kinase, TAK1, in regulating growth activation in Rab8 mutants.Our data uncover Rab8, POSH, and TAK1 as regulators of synaptic growth responses and point to recycling endosome as a key compartment for synaptic growth regulation during neurodegenerative processes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology and Hull York Medical School, University of York, Heslington, York YO10 5DD, England, UK Department of Biology and Hull York Medical School, University of York, Heslington, York YO10 5DD, England, UK.

Show MeSH
Related in: MedlinePlus