Juliane Da Graça
Award winner 2025

Summary of the work

Autophagy is a cellular process initiated by the de novo formation of a double membrane vesicle called autophagosome, which emanate from a transient structure termed phagophore. Phagophore biogenesis requires phase transition and occurs at the immediate vicinity of endoplasmic reticulum (ER) subdomains which can be engaged in membrane tethering with other organelles such as mitochondria and plasma membrane. Recently, we demonstrated a dynamic recruitment of early endosomal membranes toward sites of phagophore biogenesis. Our present work shows that the number of endosomes-ER contact sites (EERCS) increases during acute response of starvation and are mobilized in early steps of autophagy pathway. To relevantly tackle the implication of EERCS during phagophore biogenesis, we optimized different cutting-edge technologies specific for contact sites studies (i.e. expansion microscopy, machine learning-based analysis, split-turboID, biochemical purification). Deeper analyzes on the nature and the dynamics of EERCS unveiled their implication in the creation of a local environment with specific biochemical properties. These include phase transition and Ca2+ confined release, events that could support de novo membrane generation. Here, we identify a novel role for ER-endosomes membrane contact sites during early response to nutrients deprivation. We propose that dynamic mobilization of EERCS enable transient confinement of cytoplasm which in turns favors the local enrichment of proteins, lipids and ions required for  phagophore biogenesis initiation.