2.1. The Function of the Atg Proteins. Autophagosomes are formed by expansion and sealing of a small cistern known as the phagophore or isolation membrane ( Figure 1 ). Once complete, they deliver their cargo into the hydrolytic lumen of lysosomes for degradation. A diverse set of components are involved in the biogenesis of autophagosomes, which primarily includes the proteins encoded by the autophagyrelated genes (ATG). Most ATG genes have initially been identified and characterized in yeast. Subsequent studies in higher eukaryotes have revealed that these key factors are highly conserved. To date, 36 Atg proteins have been identified and 16 are part of the core Atg machinery essential for all autophagy-related pathways [7] . Upon autophagy induction, these proteins associate following a hierarchical order [8, 9] to first mediate the formation of the phagophore and then to expand it into an autophagosome [10, 11] . While their molecular functions and their precise contribution during the biogenesis of double-membrane vesicles remain largely unknown, they have been classified in 4 functional groups of genes: (1) the Atg1/ULK complex, (2) the phosphatidylinositol 3-kinase (PI3K) complex, (3) the Atg9 trafficking system, and (4) the two parallel ubiquitinlike conjugation systems ( Figure 1 ).