The nuclear envelope (NE) is central to the architecture of eukaryotic cells, both as a physical barrier separating the nucleus from the cytoplasm and as gate-keeper of selective transport between... Show moreThe nuclear envelope (NE) is central to the architecture of eukaryotic cells, both as a physical barrier separating the nucleus from the cytoplasm and as gate-keeper of selective transport between them. However, in open mitosis, the NE fragments to allow for spindle formation and segregation of chromosomes, resulting in intermixing of nuclear and cytoplasmic soluble fractions. Recent studies have shed new light on the mechanisms driving reinstatement of soluble proteome homeostasis following NE reformation in daughter cells. Here, we pro-vide an overview of how mitotic cells confront this challenge to ensure continuity of basic cellular functions across generations and elaborate on the implications for the proteasome - a macromolecular machine that functions in both cytoplas-mic and nuclear compartments. Show less
Jongsma, M.L.M.; Bakker, J.; Cabukusta, B.; Liv, N.; Elsland, D. van; Fermie, J.; ... ; Neefjes, J. 2020
The endolysosomal system fulfils a myriad of cellular functions predicated on regulated membrane identity progressions, collectively termed maturation. Mature or "late" endosomes are designated by... Show moreThe endolysosomal system fulfils a myriad of cellular functions predicated on regulated membrane identity progressions, collectively termed maturation. Mature or "late" endosomes are designated by small membrane-bound GTPases Rab7 and Arl8b, which can either operate independently or collaborate to form a joint compartment. Whether, and how, Rab7 and Arl8b resolve this hybrid identity compartment to regain functional autonomy is unknown. Here, we report that Arl8b employs its effector SKIP to instigate inactivation and removal of Rab7 from select membranes. We find that SKIP interacts with Rab7 and functions as its negative effector, delivering the cognate GAP, TBC1D15. Recruitment of TBC1D15 to SKIP occurs via the HOPS complex, whose assembly is facilitated by contacts between Rab7 and the KMI motif of SKIP. Consequently, SKIP mediates reinstatement of single identity Arl8b sub-compartment through an ordered Rab7-to-Arl8b handover, and, together with Rab7's positive effector RILP, enforces spatial, temporal and morphological compartmentalization of endolysosomal organelles. Show less
Jongsma, M.L.M.; Bakker, J.; Cabukusta, B.; Liv, N.; Elsland, D. van; Fermie, J.; ... ; Neefjes, J. 2020
The endolysosomal system fulfils a myriad of cellular functions predicated on regulated membrane identity progressions, collectively termed maturation. Mature or "late" endosomes are designated by... Show moreThe endolysosomal system fulfils a myriad of cellular functions predicated on regulated membrane identity progressions, collectively termed maturation. Mature or "late" endosomes are designated by small membrane-bound GTPases Rab7 and Arl8b, which can either operate independently or collaborate to form a joint compartment. Whether, and how, Rab7 and Arl8b resolve this hybrid identity compartment to regain functional autonomy is unknown. Here, we report that Arl8b employs its effector SKIP to instigate inactivation and removal of Rab7 from select membranes. We find that SKIP interacts with Rab7 and functions as its negative effector, delivering the cognate GAP, TBC1D15. Recruitment of TBC1D15 to SKIP occurs via the HOPS complex, whose assembly is facilitated by contacts between Rab7 and the KMI motif of SKIP. Consequently, SKIP mediates reinstatement of single identity Arl8b sub-compartment through an ordered Rab7-to-Arl8b handover, and, together with Rab7's positive effector RILP, enforces spatial, temporal and morphological compartmentalization of endolysosomal organelles. Show less