Exit from mitosis in animal cells is substantially delayed when spindle assembly is inhibited, spindle bipolarity is disrupted, or when a monopolar spindle is formed. These observations have led to the proposal that animal cells have a ‘spindle assembly’ checkpoint for the metaphase-anaphase transition that monitors bipolar spindle organization. However, the existence of such a checkpoint is uncertain because perturbations in spindle organization can produce unattached kinetochores, which by themselves are known to delay anaphase onset. In this study we have tested if cells monitor bipolar spindle organization, independent of kinetochore attachment, by analyzing the duration of mitosis in sea urchin zygotes and vertebrate somatic cells containing multipolar spindles in which all kinetochores are attached to spindle poles. We found that sea urchin zygotes containing tripolar or tetrapolar spindles progressed from nuclear envelope breakdown to anaphase onset with normal timing. We also found that the presence of supernumerary, unpaired spindle poles did not greatly prolong mitosis. Observation of untreated PtK1 cells that formed tripolar or tetrapolar spindles revealed that they progressed through mitosis, on average, at the normal rate. More importantly, the interval between the bipolar attachment of the last monooriented chromosome and anaphase onset was normal. Thus, neither of these cell types can detect the presence of gross aberrations in spindle architecture that inevitably lead to aneuploidy. We conclude that animal cells do not have a checkpoint for the metaphase-anaphase transition that monitors defects in spindle architecture independent of the checkpoint that monitors kinetochore attachment to the spindle. For dividing cells in which spindle microtubule assembly is not experimentally compromised, we propose that the completion of kinetochore attachment is the event which limits the time of the metaphase-anaphase transition.
Special Issue: Cell Biology of Lipids
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Lipids are the main component of cellular membranes, but have key roles in many essential cellular processes, as well as structural and signalling functions. Our 2022 special issue showcases the diversity of current research in lipid cell biology.
The special issue includes an interview with Guest Editor James Olzmann. James has also contributed to this lipid droplet wall poster from our sponsor, Cayman Chemical.
Propose a new Workshop
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Our Workshops bring together leading experts and early-career researchers from a range of scientific backgrounds. Applications are now open to propose Workshops for 2024, one of which will be held in a Global South country.
We’re hiring: Community Manager, preLights
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We are seeking to appoint a new Community Manager to run our preprint highlighting service, preLights. Launched in 2018, this initiative has gained significant attention from researchers and the publishing industry. We are now looking for the right person to join us for the next phase of community building and the site’s growth and development. Please see the full job description for further details.
The application deadline is 20 May 2022.
Essay series: Equity, diversity and inclusion in cell biology
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The JCS Essay Series is an initiative to help showcase and provide a platform for voices in the field of cell biology. The first topic we covered was 'Equity, diversity and inclusion in cell biology', and the winning and runner up essays are now available to read.
FocalPlane Network launched
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We are excited to announce the launch of the FocalPlane Network, an international directory of microscopists. The idea behind the FocalPlane Network is to facilitate promotion and networking as well as assist those seeking conference speakers, committee members, reviewers or collaborators. We hope that it will help promote diversity in the community. Find out more and join the Network here.
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