Abstract
The Endosomal Sorting Complex Required for Transport (ESCRT) machinery facilitates topologically equivalent membrane remodelling and scission events in an ever-growing number of cellular processes, notably MVB biogenesis and endosomal sorting, enveloped viral budding and cytokinetic abscission. ESCRTs are recruited in a modular fashion to target membranes by site specific adaptor proteins, where they assemble within cytosol-filled membranous stalks to mediate bending and scission away from the cytoplasm.Cytokinesis is the process of separation of the cell cytosol into two daughter cells during cell division. During cytokinesis, the inward constriction of cell membrane eventually results in the formation of a thin protein rich stalk-like structure termed the midbody. Cytokinetic abscission is the final stage of cytokinesis during which the midbody is severed leading to the final resolution of daughter cells. The ESCRT machinery is central to cytokinetic abscission, during which it is recruited by the adaptor protein CEP55 to the midbody where it mediates the final severing event.
ESCRT-I is a heterotetramer comprised of TSG101, VPS28, VPS37A, B, C or D and MVB12A, MVB12 B or UBAP1. In this thesis, I identify UMAD1 by mass spectrometry and coprecipitation assays as another novel alternative MVB12 subunit of ESCRT-I, that is able to form a functional ESCRT-I complex and is involved in cytokinetic abscission. A direct interaction between the midbody adaptor protein CEP55 with TSG101 has been described, and coprecipitation assays have shown that TSG101 binds less well to CEP55 in the absence of UMAD1. Use of microscopy to more directly examine cytokinetic defects and differences in the time taken for abscission to occur have also provided evidence for both a generalised role for UMAD1 in mediating successful cytokinesis and also contribution specifically at the stage of abscission. We hypothesise that UMAD1 forms part of an ESCRT-I complex that contributes to abscission in one of two parallel partially redundant pathways, the other pathway being mediated by the ESCRT associated protein ALIX, which also interacts with CEP55. Consistent with this hypothesis are synergistic effects on abscission and cytokinetic defects upon co-depletion of UMAD1 with ALIX.
| Date of Award | 1 Jul 2020 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Juan Martin Serrano (Supervisor) & Monica Agromayor (Supervisor) |