Biogenesis of the Drosophila omegasome requires Zonda

MELANI, MARIANA

Conferencia; 59th Annual Drosophila Research Conference; 2018

Omegasomes are the first distinguishable autophagy-specific membranous structure that forms when the nucleation complex (VPS34, BECN1/ATG6, ATG14 and VPS15) mediates local deposition of phospatidylinositol-3-phospate (PI3P) in a specific domain of the ER. The molecules and mechanisms that mediate targeting of this complex and the localized deposition of PI3P remain however poorly defined. We found that Zonda, a transmembrane immunophilin is required for Vps34-mediated PI3P deposition and omegasome formation. Upon starvation, Zonda nucleates in endoplasmic reticulum-associated foci with the characteristic shape and size of mammalian omegasomes. Moreover, these Zonda-labelled structures colocalize with omegasome markers GFP-DFCP1 and GFP-2xFYVE and contain phagophore markers ATG5 and ATG8 inside. Zonda-labelled omegasomes require initiation complex components (Atg1, Atg13 and Atg17), but not nucleation complex components (Vps34, Vps15, Atg6 or Atg14). Zonda interacts physically with ATG1 through its kinase domain, as well as with ATG6 and Vps34, suggesting this immunophilin could act as a platform on the ER to bridge these two complexes together. Moreover, Zonda overexpression is sufficient to trigger omegasomes formation that fully develop into autophagosomes and degradative autolysosomes as evaluated by transmission electron microscopy as well as several autophagic markers. We propose that Zonda is an early component of the autophagy cascade necessary for Vps34-dependent PI3P deposition and omegasome formation.