Microtubules do not promote mitotic slippage when the spindle assembly checkpoint cannot be satisfied

© 2008 Brito et al. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Journal of Cell Biology 182 (2009): 623-629, doi:10.1083/jcb.200805072.When the spindle assembly checkpoint (SAC) cannot be satisfied, cells exit mitosis via mitotic slippage. In microtubule (MT) poisons, slippage requires cyclin B proteolysis, and it appears to be accelerated in drug concentrations that allow some MT assembly. To determine if MTs accelerate slippage, we followed mitosis in human RPE-1 cells exposed to various spindle poisons. At 37°C, the duration of mitosis in nocodazole, colcemid, or vinblastine concentrations that inhibit MT assembly varied from 20 to 30 h, revealing that different MT poisons differentially depress the cyclin B destruction rate during slippage. The duration of mitosis in Eg5 inhibitors, which induce monopolar spindles without disrupting MT dynamics, was the same as in cells lacking MTs. Thus, in the presence of numerous unattached kinetochores, MTs do not accelerate slippage. Finally, compared with cells lacking MTs, exit from mitosis is accelerated over a range of spindle poison concentrations that allow MT assembly because the SAC becomes satisfied on abnormal spindles and not because slippage is accelerated.This research was supported by The National Institutes of Health (GMS 40198 to C.L. Rieder) and a doctoral research fellowship (SFRH/ BD/13663/2003) from Fundacao para a Ciencia e a Tecnologia (to D.A. Brito)

Cells satisfy the mitotic checkpoint in Taxol, and do so faster in concentrations that stabilize syntelic attachments

© The Authors, 2009 . This article is distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License. The definitive version was published in Journal of Cell Biology 186 (2009): 675-684, doi:10.1083/jcb.200906150.To determine why the duration of mitosis (DM) is less in Taxol than in nocodazole or Eg5 inhibitors we studied the relationship between Taxol concentration, the DM, and the mitotic checkpoint. We found that unlike for other spindle poisons, in Taxol the DM becomes progressively shorter as the concentration surpasses ~0.5 µM. Studies on RPE1 and PtK2 expressing GFP/cyclin B or YFP/Mad2 revealed that cells ultimately satisfy the checkpoint in Taxol and do so faster at concentrations >0.5 µM. Inhibiting the aurora-B kinase in Taxol-treated RPE1 cells accelerates checkpoint satisfaction by stabilizing syntelic kinetochore attachments and reduces the DM to ~1.5 h regardless of drug concentration. A similar stabilization of syntelic attachments by Taxol itself appears responsible for accelerated checkpoint satisfaction at concentrations >0.5 µM. Our results provide a novel conceptual framework for how Taxol prolongs mitosis and caution against using it in checkpoint studies. They also offer an explanation for why some cells are more sensitive to lower versus higher Taxol concentrations.This work was supported by National Institutes of Health GMS grant 40198 to C.L. Rieder

Comment on "A centrosome-independent role for gamma-TuRC proteins in the spindle assembly checkpoint"

Müller et al. (Reports, 27 October 2006, p. 654) showed that inhibition of the γ-tubulin ring complex (γ-TuRC) activates the spindle assembly checkpoint (SAC), which led them to suggest that γ-TuRC proteins play molecular roles in SAC activation. Because γ-TuRC inhibition leads to pleiotropic spindle defects, which are well known to activate kinetochore-derived checkpoint signaling, we believe that this conclusion is premature

Carbapenemase-producing organisms: a global scourge

The dramatic increase in the prevalence and clinical impact of infections caused by bacteria producing carbapenemases is a global health concern. Carbapenemase production is especially problematic when encountered in members of the family Enterobacteriaceae. Due to their ability to readily spread and colonize patients in healthcare environments, preventing the transmission of these organisms is a major public health initiative and coordinated international effort are needed. Central to the treatment and control of carbapenemase-producing organisms (CPOs) are phenotypic (growth-/biochemical-dependent) and nucleic acid–based carbapenemase detection tests that identify carbapenemase activity directly or their associated molecular determinants. Importantly, bacterial isolates harboring carbapenemases are often resistant to multiple antibiotic classes, resulting in limited therapy options. Emerging agents, novel antibiotic combinations and treatment regimens offer promise for management of these infections. This review highlights our current understanding of CPOs with emphasis on their epidemiology, detection, treatment, and control

Ownership of Automobile as Prima Facie Evidence of Responsibility for Negligence of Person Operating It

Generally speaking, absent statutory change, an owner of an automobile is responsible for injuries resulting from its negligent operation by another, only if it is shown that, at the time of the injury, the relationship of principal and agent or master and servant existed between the owner and the operator, and that the operator was then acting in the scope of his employment. Ordinary human experience and knowledge show clearly that in the great majority of cases automobiles are operated by their owners or by some servant or agent on the owner\u27s business. It is equally apparent that in the cases where this is false, the knowledge of the facts and the ability to show them are peculiarly in the cognizance of the owner. Understanding this, the great majority of the courts of the United States recognixe that it is desirable and fair to aid the plaintiff in establishing his case by giving him the assistance of some sort of a presumption of the agency of the driver and that he was in the scope of his employment-either from ownership of the automobile alone, or from ownership plus some other related fact.Generally speaking, absent statutory change, an owner of an automobile is responsible for injuries resulting from its negligent operation by another, only if it is shown that, at the time of the injury, the relationship of principal and agent or master and servant existed between the owner and the operator, and that the operator was then acting in the scope of his employment. Ordinary human experience and knowledge show clearly that in the great majority of cases automobiles are operated by their owners or by some servant or agent on the owner\u27s business. It is equally apparent that in the cases where this is false, the knowledge of the facts and the ability to show them are peculiarly in the cognizance of the owner. Understanding this, the great majority of the courts of the United States recognize that it is desirable and fair to aid the plaintiff in establishing his case by giving him the assistance of some sort of a presumption of the agency of the driver and that he was in the scope of his employment-either from ownership of the automobile alone, or from ownership plus some other related fact

The need for conducting randomized trials in a pandemic to provide high quality evidence: overcoming the challenges

This presentation discusses: The polarization of COVID-19 Background randomized controlled trials (RCTs) vs observational studies Why we need RCTs in pandemics/epidemics for multiple types of interventions Outline challenges from an example RCT in the COVID-19 era Overcoming challenges in conducting randomized trials during a pandemi