Plk4 Regulates Centriole Asymmetry and Spindle Orientation in Neural Stem Cells

Defects in mitotic spindle orientation (MSO) disrupt the organization of stem cell niches impacting tissue morphogenesis and homeostasis. Mutations in centrosome genes reduce MSO fidelity, leading to tissue dysplasia and causing several diseases such as microcephaly, dwarfism, and cancer. Whether these mutations perturb spindle orientation solely by affecting astral microtubule nucleation or whether centrosome proteins have more direct functions in regulatingMSO is unknown. To investigate this question, we analyzed the consequences of deregulating Plk4 (the master centriole duplication kinase) activity in Drosophila asymmetrically dividing neural stem cells. We found that Plk4 functions upstream of MSO control, orchestrating centriole symmetry breaking and consequently centrosome positioning. Mechanistically, we show that Plk4 acts through Spd2 phosphorylation, which induces centriole release from the apical cortex. Overall, this work not only reveals a role for Plk4 in regulating centrosome function but also links the centrosome biogenesis machinery with the MSO apparatus.ERC starting grant CentroStemCancer [242598]; Institut Curie; CNRS; NCI [P30CA23074]; NIGMS [R01 GM110166, GM126035]; FRM; IC; FRM installation grant; ATIP grantOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Genetic instability from a single S phase after whole-genome duplication

Diploid and stable karyotypes are associated with health and fitness in animals. By contrast, whole-genome duplications—doublings of the entire complement of chromosomes—are linked to genetic instability and frequently found in human cancers(1–3). It has been established that whole-genome duplications fuel chromosome instability through abnormal mitosis(4–8); however, the immediate consequences of tetraploidy in the first interphase are not known. This is a key question because single whole-genome duplication events such as cytokinesis failure can promote tumorigenesis(9). Here we find that human cells undergo high rates of DNA damage during DNA replication in the first S phase following induction of tetraploidy. Using DNA combing and single-cell sequencing, we show that DNA replication dynamics is perturbed, generating under- and over-replicated regions. Mechanistically, we find that these defects result from a shortage of proteins during the G1/S transition, which impairs the fidelity of DNA replication. This work shows that within a single interphase, unscheduled tetraploid cells can acquire highly abnormal karyotypes. These findings provide an explanation for the genetic instability landscape that favours tumorigenesis after tetraploidization

Clinical features and outcomes of elderly hospitalised patients with chronic obstructive pulmonary disease, heart failure or both

Background and objective: Chronic obstructive pulmonary disease (COPD) and heart failure (HF) mutually increase the risk of being present in the same patient, especially if older. Whether or not this coexistence may be associated with a worse prognosis is debated. Therefore, employing data derived from the REPOSI register, we evaluated the clinical features and outcomes in a population of elderly patients admitted to internal medicine wards and having COPD, HF or COPD + HF. Methods: We measured socio-demographic and anthropometric characteristics, severity and prevalence of comorbidities, clinical and laboratory features during hospitalization, mood disorders, functional independence, drug prescriptions and discharge destination. The primary study outcome was the risk of death. Results: We considered 2,343 elderly hospitalized patients (median age 81 years), of whom 1,154 (49%) had COPD, 813 (35%) HF, and 376 (16%) COPD + HF. Patients with COPD + HF had different characteristics than those with COPD or HF, such as a higher prevalence of previous hospitalizations, comorbidities (especially chronic kidney disease), higher respiratory rate at admission and number of prescribed drugs. Patients with COPD + HF (hazard ratio HR 1.74, 95% confidence intervals CI 1.16-2.61) and patients with dementia (HR 1.75, 95% CI 1.06-2.90) had a higher risk of death at one year. The Kaplan-Meier curves showed a higher mortality risk in the group of patients with COPD + HF for all causes (p = 0.010), respiratory causes (p = 0.006), cardiovascular causes (p = 0.046) and respiratory plus cardiovascular causes (p = 0.009). Conclusion: In this real-life cohort of hospitalized elderly patients, the coexistence of COPD and HF significantly worsened prognosis at one year. This finding may help to better define the care needs of this population

Identification des mécanismes moléculaires générant une instabilité génétique dans les cellules polyploïdes

La polyploïdie se caractérise par une duplication du génome entier. Elle inhibe efficacement la prolifération cellulaire et joue pourtant un rôle clé dans les étapes précoces de la tumorigénèse. Comment est-elle capable de promouvoir une instabilité génétique dans les cellules cancéreuses est une question en suspens. J'ai établi un système modèle affectant la cytocinèse pour étudier les conséquences de la polyploïdie dans les cellules souches neuronales (CSN) et dans le disque imaginal de l'aile de drosophile. Les cellules polyploïdes du disque sont rapidement éliminées, les CSN polyploïdes continuent de proliférer. Les CSN polyploïdes sont caractérisées par une instabilité génétique précoce et deux facteurs en sont responsables: les erreurs mitotiques et des dommages à l'ADN. Ces dommages sont issus en partie de l'incapacité des cellules à restreindre leur progression dans le cycle cellulaire après une réplication incomplète de l'ADN. J'ai trouvé que de multiples domaines nucléaires au sein de la même CSN polyploïde pouvaient présenter une asynchronie de leur progression dans le cycle cellulaire. Les domaines nucléaires en retard dans leur progression sont les cibles des lésions à l'ADN au moment de l'entrée en mitose. Les lésions sont réduites après surexpression de Chk1, une kinase de la voie ATR de réponse aux dommages à l'ADN. De plus, la prolifération incontrôlée des CSN polyploïdes génétiquement instables est responsable de leur potentiel tumorigénique dans les essais de transplantation. Mes résultats montrent que la tolérance à la polyploïdie dépend du tissu et qu'une série d'événements contribue à l'instabilité génétique dans les CSN polyploïdes.Polyploidy, which derives from whole-genome duplication events, is normally a potent inhibitor of cell proliferation, but plays important roles during the early steps of tumorigenesis. However, how the gain of multiple sets of chromosomes promotes the generation of unbalanced karyotypes typical of cancer cells remains to be investigated. Using a number of conditions that affect cytokinesis, I established a model system to study the consequences of polyploidy in the neural stem cells (NSCs) of Drosophila and in the wing disc (WD). Importantly, while polyploidy is rapidly eliminated from the WD, polyploid NSCs continue to proliferate. Polyploid NSCs are characterized by early-onset genetic instability and two sources account for the generation of unstable karyotypes: mitotic errors and high-levels of DNA damage. DNA damage in polyploid NSCs arises, at least in part, from the inability of polyploid cells to restrain cell cycle progression in response to incomplete DNA replication. Surprisingly, I found that multiple nuclear domains in the same polyploid NSC can exhibit asynchrony in cell cycle progression, with delayed nuclear domains experiencing acute DNA damage at mitotic entry. I show that DNA damage in polyploid NSCs can be reduced over-expressing Chk1, the main downstream kinase engaged by ATR in the DNA damage response. I also show that uncontrolled proliferation of genetically unstable polyploid NSCs holds tumorigenic potential in transplantation assays. Overall, my results show that the tolerance to polyploidy is tissue dependent and that a complex network of events contributes to the generation of unbalanced karyotypes in polyploid NSCs

Cell-Cycle Asynchrony Generates DNA Damage at Mitotic Entry in Polyploid Cells

International audienc

Chromosomes function as a barrier to mitotic spindle bipolarity in polyploid cells

International audiencePloidy variations such as genome doubling are frequent in human tumors and have been associated with genetic instability favoring tumor progression. How polyploid cells deal with increased centrosome numbers and DNA content remains unknown. Using Drosophila neuroblasts and human cancer cells to study mitotic spindle assembly in polyploid cells, we found that most polyploid cells divide in a multipolar manner. We show that even if an initial centrosome clustering step can occur at mitotic entry, the establishment of kinetochore-microtubule attachments leads to spatial chromosome configurations, whereby the final coalescence of supernumerary poles into a bipolar array is inhibited. Using in silico approaches and various spindle and DNA perturbations, we show that chromosomes act as a physical barrier blocking spindle pole coalescence and bipolarity. Importantly, microtubule stabilization suppressed multipolarity by improving both centrosome clustering and pole coalescence. This work identifies inhibitors of bipolar division in polyploid cells and provides a rationale to understand chromosome instability typical of polyploid cancer cells

Author Correction: Genetic instability from a single S phase after whole-genome duplication (Nature, (2022), 604, 7904, (146-151), 10.1038/s41586-022-04578-4)

In the version of this article initially published, the third sentence of the abstract, now reading “This is a key question because single whole-genome duplication events such as cytokinesis failure can promote tumorigenesis9 and DNA double-strand breaks10” was truncated and did not mention double-strand breaks or cite ref. 10 (Pedersen, R. S. et al. Profiling DNA damage response following mitotic perturbations. Nat. Commun. 7, 13887 (2016)). The reference has now been included in the HTML and PDF versions of the article

Genetic instability from a single S phase after whole-genome duplication

Diploid and stable karyotypes are associated with health and fitness in animals. By contrast, whole-genome duplications-doublings of the entire complement of chromosomes-are linked to genetic instability and frequently found in human cancers(1-3). It has been established that whole-genome duplications fuel chromosome instability through abnormal mitosis(4-8); however, the immediate consequences of tetraploidy in the first interphase are not known. This is a key question because single whole-genome duplication events such as cytokinesis failure can promote tumorigenesis(9). Here we find that human cells undergo high rates of DNA damage during DNA replication in the first S phase following induction of tetraploidy. Using DNA combing and single-cell sequencing, we show that DNA replication dynamics is perturbed, generating under- and over-replicated regions. Mechanistically, we find that these defects result from a shortage of proteins during the G1/S transition, which impairs the fidelity of DNA replication. This work shows that within a single interphase, unscheduled tetraploid cells can acquire highly abnormal karyotypes. These findings provide an explanation for the genetic instability landscape that favours tumorigenesis after tetraploidization

Follicular helper T cell signature of replicative exhaustion, apoptosis, and senescence in common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent primary antibody deficiency whereby follicular helper T (Tfh) cells fail to establish productive responses with B cells in germinal centers. Here, we analyzed the frequency, phenotype, transcriptome, and function of circulating Tfh (cTfh) cells in CVID patients displaying autoimmunity as an additional phenotype. A group of patients showed a high frequency of cTfh1 cells and a prominent expression of PD-1 and ICOS as well as a cTfh mRNA signature consistent with highly activated, but exhausted, senescent, and apoptotic cells. Plasmatic CXCL13 levels were elevated in this group and positively correlated with cTfh1 cell frequency and PD-1 levels. Monoallelic variants in RTEL1, a telomere length- and DNA repair-related gene, were identified in four patients belonging to this group. Their blood lymphocytes showed shortened telomeres, while their cTfh were more prone to apoptosis. These data point toward a novel pathogenetic mechanism in CVID, whereby alterations in DNA repair and telomere elongation might predispose to antibody deficiency. A Th1, highly activated but exhausted and apoptotic cTfh phenotype was associated with this form of CVID