Autophagy involves engulfment of cytoplasmic contents by double-membraned autophagosomes, which ultimately fuse with lysosomes to enable degradation of their substrates. We recently proposed that the tubular-vesicular recycling endosome membranes was a core platform on which the critical early events of autophagosome formation occurred, including LC3-membrane conjugation to autophagic precursors. Here we report that the release of autophagosome precursors from recycling endosomes is mediated by DNM2-dependent scission of these tubules. This process is regulated by DNM2 binding to LC3, and is increased by autophagy-inducing stimuli. This scission is defective in cells expressing a centronuclear myopathy-causing DNM2 mutant. This mutant has an unusual mechanism as it depletes normal-functioning DNM2 from autophagosome formation sites on recycling endosomes by causing increased binding to an alternative plasma membrane partner, ITSN1. This “scission” step is thus critical for autophagosome formation, is defective in a human disease, and influences the way we consider how autophagosomes are formed.