825V Poster - 13. Neural development and physiology
Wednesday April 06, 4:00 PM - 7:00 PM

Authors:
Caitlin O'Brien ^1,2; Susan Younger ^1,2; Lily Jan ^1,2; Yuh Nung Jan ^1,2

Affiliations:
1) Howard Hughes Medical Institute; 2) University of California San Francisco

Keywords:
e. neuronal morphogenesis; i. cellular organelles

Membrane trafficking pathways are essential to sculpting neuronal morphology. The closely related GARP (Golgi-Associated Retrograde Protein) and EARP (Endosome-Associated Recycling Protein) complexes are conserved membrane tethers that function in the secretory and endolysosomal pathways. These complexes share the proteins Vps51, Vps52, and Vps53, and each contain a complex-specific protein: Vps54 in GARP and Vps50 in EARP. Several mutations in the core components (Vps51 and Vps53) are associated with neurodevelopmental disorders, but a precise role for these complexes in neurodevelopment is still unclear. We generated CRISPR knockout Drosophila of the shared component Vps53, and the complex-specific components Vps50 and Vps54 (also known as scattered). We find that both complexes are required for dendrite morphogenesis at a specific time during development. Larval neurons are largely spared, but alterations in endolysosomes and dendrite morphology emerge during remodeling of peripheral sensory neurons during pupation. We also observe accumulation of sterol specifically in GARP-, but not EARP-deficient neurons. Previous studies of GARP-deficient cells found that sterol accumulates in lysosomes. To our surprise, we find that sterols accumulate at the trans-Golgi network (TGN), not in lysosomes, in Vps54^KO/KO Drosophila neurons. As sterol auxotrophs, Drosophila obtain sterol from dietary sources only and therefore may utilize additional mechanisms to transfer sterol from the endolysosomal to the secretory pathway after uptake. Targeting genes that regulate sterols and related lipids at the TGN can modulate the Vps54^KO/KO phenotype. Specifically, overexpressing the oxysterol binding protein (Osbp), which transfers sterol between the endolysosomal and secretory pathways at multiple membrane contact sites, exacerbates the dendrite regrowth defect of Vps54^KO/KO neurons, while a null allele of Osbp partially rescues it. This suggests that the activity of Osbp may be upregulated in Vps54^KO/KO neurons and that the accumulation of excess sterol at the TGN is, at least in part, responsible for inhibiting dendrite regrowth. These studies begin to functionally distinguish the GARP and EARP complexes in neurodevelopment and indicate that both membrane trafficking and lipid transfer pathways are essential for proper dendrite growth.