The BLOC-1 Subunit Pallidin Facilitates Activity-Dependent Synaptic Vesicle Recycling

Abstract

Membrane trafficking pathways must be exquisitely coordinated at synaptic terminals to maintain functionality, particularly during conditions of high activity. We have generated null mutations in the Drosophila homolog of pallidin, a central subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), to determine its role in synaptic development and physiology. We find that Pallidin localizes to presynaptic microtubules and cytoskeletal structures, and that the stability of Pallidin protein is highly dependent on the BLOC-1 components Dysbindin and Blos1. We demonstrate that the rapidly recycling vesicle pool is not sustained during high synaptic activity in pallidin mutants, leading to accelerated rundown and slowed recovery. Following intense activity, we observe a loss of early endosomes and a concomitant increase in tubular endosomal structures in synapses without Pallidin. Together, our data reveal that Pallidin subserves a key role in promoting efficient synaptic vesicle recycling and re-formation through early endosomes during sustained activity.

A Presynaptic Glutamate Receptor Subunit Confers Robustness to Neurotransmission and Homeostatic Potentiation

“…Third-instar larvae were dissected in ice cold 0 Ca 2+ HL-3 and immunostained as described (Chen et al, 2017). The following antibodies were used: mouse anti-Synapsin, 3C11 (1:10; Developmental Studies Hybridoma Bank; DSHB); mouse anti-Bruchpilot (BRP), (nc82; 1:100; DSHB); affinity-purified rabbit anti-GluRIII (1:2000; (Marrus et al, 2004)); rabbit anti-GFP (1:1000; A-11122; Invitrogen) and rat anti-DKaiR1D (1:1000).…”

“…Third-instar larval brain and muscle tissue extracts (50 animals of each genotype) were prepared and used for immunoblotting as previously described (Chen et al, 2017). DKaiR1D (1:1000) and α-Tubulin (1:2000; JLA20, DSHB) primary antibodies were used with a 1:5000 dilution of horseradish peroxidase-conjugated anti-rat or anti-mouse secondary antibodies (Jackson ImmunoResearch).…”

“…All dissections and recordings were performed as previously described (Chen et al, 2017). Larvae were incubated with or without philanthotoxin-433 (Sigma; 20 μM) and resuspended in HL-3 for 10 mins, as described (Dickman and Davis, 2009; Frank et al, 2006).…”

Pallidin is a novel interacting protein for cytohesin‐2 and regulates the early endosomal pathway and dendritic formation in neurons

“…In neurons, BLOC‐1 is implicated in the biogenesis and release of synaptic vesicles in presynaptic terminals (Newell‐Litwa et al . ; Di Giovanni and Sheng ; Chen et al ., ). In addition, neurons from pallid mutant mice show impaired neurite outgrowth (Ghiani et al .…”

Neurodevelopmental disease mechanisms, primary cilia, and endosomes converge on the BLOC‐1 and BORC complexes

“…Dysbindin‐null mice sandy ( Bloc1s8 sdy/sdy ) lacking dysbindin polypeptide also express reduced levels of Bloc1s5, Bloc1s6, and Snapin (Li et al, ; Starcevic and Dell'Angelica, ; Feng et al, ). This interdependency of BLOC‐1 subunits for stability appears to be universal, as evidenced by reduced pallidin expression in Drosophila Bloc1s1/blos1 andBloc1s8/dysbindin mutants (Chen et al, ). Similarly, dysbindin is reduced in null mouse models of Bloc1s3 ( Bloc1s3 rp/rp ), Bloc1s5 ( Bloc1s5 mu/mu ), and Bloc1s6 ( Bloc1s6 pa/pa ) (Li et al, ; Starcevic and Dell'Angelica, ; Feng et al, ).…”