The Midbody (MB) & Midbody Remnant (MBR)
Ahna giving a public talk about the history of the midbody and current research in the Skop Lab
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The midbody is a unique structure assembled at the end of mitosis. After the chromosomes separate in anaphase, the acto-myosin ring constricts the antiparallel microtubules known as the central spindle into an intercellular bridge. The 1-2um midbody (MB) occupies the center of the bridge, and has a core of electron-dense material (in electron micrographs) called the MB matrix coating the region of microtubule overlap. The matrix has an unusual property in that it is impenetrable to antibodies such as anti-tubulin, and thus has been called the ‘dark zone’. A surprising finding was that abscission does not pinch directly through the center of this 'dark zone', but bilaterally flanking this region, releasing the MB as an extracellular vesicle (midbody remnant or MBR) containing the matrix. It is striking that the midbody resembles an extracellular vesicle, vehicles once thought to be involved in selective elimination of cellular debris, but are now appreciated as critical mediators of intercellular communication. The functional importance of post-mitotic MBR signaling is now established, but central questions remain: Is MBR signaling a fundamental and generalizable mode of intercellular communication? What is the mechanism(s) of informational transfer? Does the mysterious MB matrix play a role in post-mitotic signaling function?
Midbody dysregulation in cancer and neurodegenerative diseases. The midbody has long been considered a vestigial ‘garbage can’ of the cell, and research focus as a potential target for therapeutics has accordingly been lacking. Despite this history, mutations in several critical midbody proteins have been linked to diseases including MARCH syndrome, Hodgkin’s Lymphoma, Spinocerebellar ataxia type 2, microcephaly, glioma, lung cancer, and breast cancer—all having phenotypes associated with abnormal cytokinesis, ranging from bi-nucleate cells, abscission defects or over-proliferation. The variety of pathologies are vast and include ovarian and testicular hypoplasia/fertility associated with microcephaly; tumors of glia, lung or breast cancer; bi-nucleate neurons, cerebellar hypoplasia, hydranencephaly as seen in MARCH syndrome; and importantly, progressive neurodegeneration with pathologic aggregation of RNA granules as seen in several neurodegenerative diseases. Our lab focuses on several areas and we use mammalian cell culture and stem cells to address these questions:
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The Midbody Remnant (MBR)
The midbody remnant (MBR) is a large extracellular vesicle formed during the final stages of cell division[1]. Once thought to be cellular debris, recent research has revealed that MBRs play crucial roles in cell signaling, proliferation, and fate determination[2][4]. The MBR contains a unique assembly of ribonucleoproteins, mRNAs, and cellular machinery capable of active protein translation[2]. This RNA-rich cargo includes transcripts involved in cell fate, oncogenesis, and pluripotency. Interestingly, MBRs can be released into the extracellular space, internalized by other cells, or degraded through autophagy, potentially serving as a novel mode of intercellular communication. The fate and function of MBRs have significant implications for cellular processes, differentiation, and even cancer progression.
Recent papers on the MBR from the Skop lab include:
1. Patel S., et al. (2024) Extracellular vesicles, including large translating vesicles called midbody remnants, are released during the cell cycle. Molecular Biology of the Cell
2. Park S, et al. (2023) The mammalian midbody and midbody remnant are assembly sites for RNA and localized translation. Developmental Cell.
3. Park S, et al. (2023) A protocol for isolating and imaging large extracellular vesicles or midbody remnants from mammalian cell culture. STAR Protocols.
4. Jung GI, et al. (2023) An oocyte meiotic midbody cap is required for developmental competence in mice. Nature Communications.
5. Skop AR, Liu H, Yates J 3rd, Meyer BJ, Heald R. Dissection of the mammalian midbody proteome reveals conserved cytokinesis mechanisms. Science
Recent papers on the MBR from the Skop lab include:
1. Patel S., et al. (2024) Extracellular vesicles, including large translating vesicles called midbody remnants, are released during the cell cycle. Molecular Biology of the Cell
2. Park S, et al. (2023) The mammalian midbody and midbody remnant are assembly sites for RNA and localized translation. Developmental Cell.
3. Park S, et al. (2023) A protocol for isolating and imaging large extracellular vesicles or midbody remnants from mammalian cell culture. STAR Protocols.
4. Jung GI, et al. (2023) An oocyte meiotic midbody cap is required for developmental competence in mice. Nature Communications.
5. Skop AR, Liu H, Yates J 3rd, Meyer BJ, Heald R. Dissection of the mammalian midbody proteome reveals conserved cytokinesis mechanisms. Science
Cytokinesis
Cell division is required for the propagation of all living things. A critical phase of cell division occurs just after segregation of the duplicated genome, when the chromosomes, cytoplasm and organelles are partitioned to two daughter cells in a process termed cytokinesis. In animal cells, cytokinesis is driven by a cortical contraction that physically pinches the cell into two, and requires coordination of the mitotic spindle, actin cytoskeleton and plasma membrane. Failures in cytokinesis can cause cell death and age-related disorders, or lead to a genome amplification characteristic of many cancers. Although cytokinesis has been studied for over 125 years, little is known about the molecular factors and mechanisms involved. We are particularly interested in understanding how the cleavage furrow is established, how the completion of cytokinesis is achieved and what roles the spindle midzone and midbody play in cell division. My laboratory integrates multiple approaches in both mammalian and C. elegans systems to identify and characterize conserved factors, taking advantage of proteomics, functional genomics, genetics, cell biology and video-microscopy techniques.
We have characterized the function of an RNA Binding Protein, ATX-2/Ataxin-2, in cytokinesis. When mutated in humans, leads to neurodegenerative disease. We have been looking into the role of midbody associated mRNAs in cytokinesis and their post-mitotic function.
We identified novel ATX-2 interacting proteins in a temperature sensitive suppressor screen (Gnazzo, et al, 2017)
Our lab recently identified that the conserved RNA-Binding Protein (RBP), ATX-2, regulates cytokinesis by regulating the targeting of ZEN-4 to the spindle midzone through a conserved translation regulator, PAR-5/14-3-3sigma (Gnazzo, et al, 2016).
We have found that the anterior PAR proteins are necessary during cytokinesis (Pittman & Skop, 2012).
We published the mitotic spindle proteome (Bonner, 2011). This proteome was isolated from CHO cell mitotic spindles. The RNAi screen of the mitotic spindle proteome identifies an ER resident protein as playing a role in cytokinesis (Bonner et al, 2013).
We characterized, RACK-1, a midbody-associated protein, as playing an essential role in regulating RAB-11 endosomal trafficking during cytokinesis in the early embryo. (Ai et al, 2009). RACK-1 is also necessary for cell polarity (Ai et al, 2011).
Cell Polarity
Cell polarity is crucial for generating diversity throughout development. In the C. elegans embryo, polarity is determined by opposing PAR protein complexes that create distinct anterior and posterior domains. Actin dynamics are also critical for establishing and maintaining both cortical and cytoplasmic differences. Current models for the role of PAR proteins in polarity suggest that PAR-dependent membrane recycling is required to generate or possibly maintain a plasma membrane domain and boundary, yet the links between the PAR proteins, endocytic machinery and the actin cytoskeleton during development have not been made. We are currently trying to identify factors that play a key role in maintaining polarity factors in a fluid and dynamic membrane throughout development. Factors that regulate cell polarity are important for the development of all organisms, tissues and stem cells and identifying proteins that maintain polarized distributions in specific membrane domains are enormously important for our understanding of diverse developmental events.
We identified Dynamin/DYN-1 as playing a necessary role in the maintenance of anterior cell polarity (Nakayama, Shivas, et al, 2009).
We have identified the Arp2/3 complex as a factor necessary for early endosome dynamics and the maintenace of PAR asymmetry (Shivas & Skop, 2012).
We have found that the anterior PAR proteins are necessary during cytokinesis (Pittman & Skop, 2012).
RACK-1 is necessary for cell polarity (Ai et al, 2011).
Cell Polarity review (Shivas, Morrison, et al, 2010)
To account for the scientific and medical profit obtained through experiments performed using HeLa cells, our lab has pledged to make donations to the Henrietta Lacks Foundation for all HeLa cell lines we created in the past and those that we create in the future. We encourage other labs to do the same. Make a donation to the Henrietta Lacks Foundation. We are indebted to Henrietta Lacks and her family for her cells that we use routinely in our lab.
Read more about Henrietta Lacks:
NYTimes Article 8-7-2003
Wikipedia
Johns Hopkins University Article
Smithsonian
The Immortal Life of Henrietta Lacks
Read more about Henrietta Lacks:
NYTimes Article 8-7-2003
Wikipedia
Johns Hopkins University Article
Smithsonian
The Immortal Life of Henrietta Lacks
