The Novel Role of Midbody-Associated mRNAs in Regulating Abscission

Abstract

Midbodies (MBs) have been shown to function during telophase as a recruiting hub, especially for ESCRT-III complex subunits, including CHMP4B, to regulate the abscission step of cytokinesis. However, the molecular machinery governing specific protein targeting and activation at the MB remains poorly understood. Until recently, it was thought that abscission regulating proteins, such as ESCRT-III complex subunits, accumulate at the MB by directly or indirectly binding to the MB resident protein, CEP55. However, recent studies have shown that depletion of CEP55 does not fully block ESCRT-III targeting to the MB, and cells in CEP55 knock-out mice divide normally. Additionally, since MBs are microtubule-rich, proteinaceous structures, it is conceptually hard to imagine how large protein complexes, such as the ESCRT-III complex, can successfully diffuse into the MB from the cytosol in a rapid and highly regulated manner. Here, we show that MBs contain mRNAs and that these MB-associated mRNAs can be locally translated, thus, resulting in the accumulation of abscission-regulating proteins. We also demonstrate that localized MB-associated translation of CHMP4B is required for it’s targeting to the abscission site. Finally, we demonstrate that 3’-UTR-dependent CHMP4B mRNA targeting to the MB is required for successful completion of cytokinesis. Based on all this data, we propose a novel method of regulating cytokinesis and abscission by MB-associated targeting and localized translation of selective mRNAs.

The biogenesis of large extracellular vesicles occurs in mitosis

“…As our lab recently discovered that the midbody and MBR are sites of active translation 52 , we sought to determine if common and commercial methods of isolating EVs also preserve translation capacity. Puromycin antibody labeling was used as a proxy for translation activity because the localization pattern is similar to HPG-Click-IT activity 52,88,89 . Here, cleared culture media was treated with puromycin for 10 minutes at 37°C.…”

Nuclear envelope budding: Getting large macromolecular complexes out of the nucleus

“…Alternatively, Pav may be organizing actin within NE buds to organize the megaRNPs within. Additionally, a recent study showed that MKLP1 (mammalian Pav ortholog) accumulates at the midbody (a transient structure during cytokinesis [ 84,85 ] where it regulates RNA localization and spatio‐temporal translation. Interestingly, the midbody contains RNPs and are a site of active translation.…”

An oocyte meiotic midbody cap is required for developmental competence in mice

“…Studies on MB functions have extended beyond regulatory functions of cytokinesis, and now indicate their signaling capabilities 9 and ribonucleoprotein (RNP) properties 13,[32][33][34][35] . An array of proteins involved in translation, translational regulation, and RNA molecules are enriched in mitotic MBs 33,34,36 .…”

“…Recent work attributes this ability to the RNAs that are potentially translated or used as templates to inhibit gene function after MBRs are internalized 12 . In somatic cells, MBs and MBRs are enriched with translational machinery and speci c transcripts that are recruited via their 3' untranslated region sequence, providing further explanation of how MBRs could act as signaling organelles 12,13 . Because oocytes must produce proteins critical for successful meiosis and early embryogenesis, we hypothesized that MBs would locally translate proteins.…”