Step-wise assembly, maturation and dynamic behavior of the human CENP-P/O/R/Q/U kinetochore sub-complex

Kinetochores are multi-protein megadalton assemblies that are required for attachment of microtubules to centromeres and, in turn, the segregation of chromosomes in mitosis. Kinetochore assembly is a cell cycle regulated multi-step process. The initial step occurs during interphase and involves loading of the 15-subunit constitutive centromere associated complex (CCAN), which contains a 5-subunit (CENP-P/O/R/Q/U) sub-complex. Here we show using a fluorescent three-hybrid (F3H) assay and fluorescence resonance energy transfer (FRET) in living mammalian cells that CENP-P/O/R/Q/U subunits exist in a tightly packed arrangement that involves multifold protein-protein interactions. This sub-complex is, however, not pre-assembled in the cytoplasm, but rather assembled on kinetochores through the step-wise recruitment of CENP-O/P heterodimers and the CENP-P, -O, -R, -Q and -U single protein units. SNAP-tag experiments and immuno-staining indicate that these loading events occur during S-phase in a manner similar to the nucleosome binding components of the CCAN, CENP-T/W/N. Furthermore, CENP-P/O/R/Q/U binding to the CCAN is largely mediated through interactions with the CENP-N binding protein CENP-L as well as CENP-K. Once assembled, CENP-P/O/R/Q/U exchanges slowly with the free nucleoplasmic pool indicating a low off-rate for individual CENP-P/O/R/Q/U subunits. Surprisingly, we then find that during late S-phase, following the kinetochore-binding step, both CENP-Q and -U but not -R undergo oligomerization. We propose that CENP-P/O/R/Q/U self-assembles on kinetochores with varying stoichiometry and undergoes a pre-mitotic maturation step that could be important for kinetochores switching into the correct conformation necessary for microtubule-attachment

CDK-dependent phosphorylation and nuclear exclusion coordinately control kinetochore assembly state

Accurate chromosome segregation requires assembly of the multiprotein kinetochore complex. Prior work has identified more than 100 different kinetochore components in human cells. However, little is known about the regulatory processes that specify their assembly upon mitotic entry and disassembly at mitotic exit. In this paper, we used a live-cell imaging–based assay to quantify kinetochore disassembly kinetics and systematically analyze the role of potential regulatory mechanisms in controlling kinetochore assembly state. We find that kinetochore assembly and disassembly was driven primarily by mitotic phosphorylation downstream of cyclin-dependent kinase (CDK). In addition, we demonstrate that nuclear exclusion of the Ndc80 complex helped restrict kinetochore formation to mitosis. Combining constitutive CDK-dependent phosphorylation of CENP-T and forced nuclear localization of the Ndc80 complex partially prevented kinetochore disassembly at mitotic exit and led to chromosome segregation defects in subsequent divisions. In total, we find that the coordinated temporal regulation of outer kinetochore assembly is essential for accurate cell division.Kinship Foundation. Searle Scholars ProgramLeukemia & Lymphoma Society of AmericaNational Institutes of Health (U.S.) (National Institute of General Medical Sciences (U.S.) Grant GM088313)Leukemia & Lymphoma Society of America (Special Fellows Award

How COVID-19 changed clinical research strategies: a global survey

Objective Clinical research has faced new challenges during the COVID-19 pandemic, leading to excessive operational demands affecting all stakeholders. We evaluated the impact of COVID-19 on clinical research strategies and compared different adaptations by regulatory bodies and academic research institutions in a global context, exploring what can be learned for possible future pandemics. Methods We conducted a cross-sectional online survey and identified and assessed different COVID-19-specific adaptation strategies used by academic research institutions and regulatory bodies. Results All 19 participating academic research institutions developed and followed similar strategies, including preventive measures, manpower recruitment, and prioritisation of COVID-19 projects. In contrast, measures for centralised management or coordination of COVID-19 projects, project preselection, and funding were handled differently amongst institutions. Regulatory bodies responded similarly to the pandemic by implementing fast-track authorisation procedures for COVID-19 projects and developing guidance documents. Quality and consistency of the information and advice provided was rated differently amongst institutions. Conclusion Both academic research institutions and regulatory bodies worldwide were able to cope with challenges during the COVID-19 pandemic by developing similar strategies. We identified some unique approaches to ensure fast and efficient responses to a pandemic. Ethical concerns should be addressed in any new decision-making process

Mild replication stress causes chromosome mis-segregation via premature centriole disengagement

Replication stress, a hallmark of cancerous and pre-cancerous lesions, is linked to structuralchromosomal aberrations. Recent studies demonstrated that it could also lead to numericalchromosomal instability (CIN). The mechanism, however, remains elusive. Here, we showthat inducing replication stress in non-cancerous cells stabilizes spindle microtubules andfavours premature centriole disengagement, causing transient multipolar spindles that lead tolagging chromosomes and micronuclei. Premature centriole disengagement depends on theG2 activity of the Cdk, Plk1 and ATR kinases, implying a DNA-damage induced deregulationof the centrosome cycle. Premature centriole disengagement also occurs spontaneously insome CIN+cancer cell lines and can be suppressed by attenuating replication stress. Finally,we show that replication stress potentiates the effect of the chemotherapeutic agent taxol, byincreasing the incidence of multipolar cell divisions. We postulate that replication stress incancer cells induces numerical CIN via transient multipolar spindles caused by prematurecentriole disengagement

How COVID-19 changed clinical research strategies: a global survey.

OBJECTIVE: Clinical research has faced new challenges during the COVID-19 pandemic, leading to excessive operational demands affecting all stakeholders. We evaluated the impact of COVID-19 on clinical research strategies and compared different adaptations by regulatory bodies and academic research institutions in a global context, exploring what can be learned for possible future pandemics. METHODS: We conducted a cross-sectional online survey and identified and assessed different COVID-19-specific adaptation strategies used by academic research institutions and regulatory bodies. RESULTS: All 19 participating academic research institutions developed and followed similar strategies, including preventive measures, manpower recruitment, and prioritisation of COVID-19 projects. In contrast, measures for centralised management or coordination of COVID-19 projects, project preselection, and funding were handled differently amongst institutions. Regulatory bodies responded similarly to the pandemic by implementing fast-track authorisation procedures for COVID-19 projects and developing guidance documents. Quality and consistency of the information and advice provided was rated differently amongst institutions. CONCLUSION: Both academic research institutions and regulatory bodies worldwide were able to cope with challenges during the COVID-19 pandemic by developing similar strategies. We identified some unique approaches to ensure fast and efficient responses to a pandemic. Ethical concerns should be addressed in any new decision-making process

F3H analysis of CENP-O class protein interactions.

<p>GFP-tagged CENP-O class proteins, CENP-K, -L, -N and -C (rows) were bound to ectopic chromosomes sites. When RFP-tagged CENP-O class proteins, CENP-K, -L, -N and -C (lines) were recruited to these proteins, this was visible by a yellow dot. Signal intensity at the nuclear spot was used an indicator for interaction strength. ++, +: strong interaction; +−: weak interaction; −: no interaction.</p