News & Views

Common fragile sites (CFSs) are chromosomal regions that are prone to form breaks or gaps during mitosis, in particular following replication stress. The mechanisms modulating CFS expression and promoting safe chromatid transmission to daughter cells are not clear. Now CFS expression is shown to reflect the activity of the MUS81–EME1 resolvase complex which cooperates with the dissolving action of the BLM helicase to prevent uncontrolled chromosome breakage and to promote genome integrity.

Multiple activities cooperate to determine the architecture of the mitotic spindle. Kip3 is a kinesin-8 motor protein in budding yeast that acts as a microtubule depolymerase. Now Kip3 is shown to also crosslink and slide antiparallel microtubules, providing additional insights into how kinesin-8 motors control spindle integrity.

Senescence, a cell-autonomous tumour suppressor mechanism, also has pro-tumorigenic effects on neighbouring pre-malignant cells through the senescence-associated secretory phenotype (SASP). The SASP is now shown to be regulated by inflammasomes and to induce paracrine senescence in healthy cells, indicating that senescence may also represent a non-cell-autonomous tumour suppressor mechanism linked to innate immunity.

Fetal haematopoietic stem cells (HSCs) self-renew extensively to build the blood system from scratch. The protein Lin28b negatively regulates the microRNA let-7 to keep levels of its target Hmga2 high, hence conferring high self-renewal potential to fetal HSCs. This regulatory circuit can be experimentally modulated to boost the lower self-renewal activity of quiescent adult HSCs.

Cell morphological plasticity is controlled by intracellular signalling pathways. By combining large-scale imaging with quantitative analysis, an RNA interference (RNAi) screen in Drosophila melanogaster haemocytes reveals that most targeted genes regulate transitions between discrete shapes. Loss of gene function changes shape frequencies or reduces diversity, rather than producing new morphologies.

Disseminated tumour cells (DTCs) can adopt a state of long-term dormancy. However, when and why they emerge from quiescence has remained unclear. Distinct microvascular niches are now shown to regulate this process. Mature blood vessels produce signals that sustain tumour cell quiescence, whereas sprouting microvasculature provides stimuli that reactivate DTCs, leading to metastatic relapse.

The substrates of mammalian ULK1/2 and its yeast homologue Atg1 in autophagy have remained elusive. The class III phosphatidylinositol 3-kinase component Beclin-1 has now been identified as a physiological substrate of the ULK kinases in autophagy following amino acid starvation, therefore suggesting a critical molecular link between the upstream kinases and the autophagy core machinery.

Addition of a specific set of transcription factors reprograms somatic cell nuclei to a pluripotent state. Sequential addition of these factors, rather than the simultaneous exposure used in standard protocols, improves reprogramming efficiency. This sequential method favours a transition through a state with enhanced mesenchymal characteristics before driving an epithelial transformation on the way to the pluripotent state.

Identification and characterization of a third type of adipocyte known as brite (brown-in-white) adipocytes has drawn considerable attention, as these cells are thought to regulate energy expenditure and may help combat obesity. Remarkably, white adipocytes can adopt the characteristics of brite adipocytes following cold stimulation, and this process is reversible in vivo.

Autophagy contributes to lipid catabolism through direct mobilization and breakdown of cellular lipid stores. Two recent studies reveal the regulatory mechanisms activated by cells during starvation to ensure that the cellular compartments involved in autophagic lipid catabolism are ready to receive, process and use these lipids. The regulators represent attractive therapeutic targets to help fight lipid-excess-associated diseases.

Cancer-associated fibroblasts (CAFs) may contribute to tissue tension and cancer progression by increasing extracellular matrix (ECM) deposition and remodelling. However, how CAFs become activated and their roles in tumour mechanics have remained unclear. YAP is now identified as a tension-stimulated CAF activator that promotes malignancy through a mechanically reinforced feed-forward loop.

How different integrin receptors for the same extracellular ligand transduce distinct cellular responses is unclear. The characterization of the class-specific adhesomes of β₁ and α_V integrins now shows that whereas α_V integrins promote unbranched actin polymerization, β₁ integrins induce myosin-II-dependent contractility, and both integrin subtypes synergistically mediate rigidity sensing.

Although myelination largely occurs during early postnatal life, myelinating oligodendrocytes are still generated in the adult brain. Myelin turnover in the adult is necessary for proper neuronal function and is gravely compromised in myelin disorders. The lineage relationship between adult neural stem cells and adult-born oligodendrocytes has been clarified, highlighting molecular pathways that could potentially be targeted to favour de novo myelination in pathological situations.

Sorting nexin proteins (SNXs) and the cargo-selective retromer complex play key roles in receptor recycling from endosomes to the cell surface. A global proteomics analysis reveals a collection of cell surface proteins that rely on SNX27 and the retromer complex for their cell surface localization at steady state.

FOXO transcription factors promote longevity from worms to mammals, but the mechanisms by which FOXO extends lifespan have remained elusive. In the nematode Caenorhabditis elegans, FOXO is now shown to recruit the nucleosome remodelling complex SWI/SNF to its target genes, which is essential for FOXO to elicit stress resistance and longevity.

To ensure proper attachment of all chromosomes to the spindle, PLK1 has to associate with kinetochores during prometaphase and must be released from these sites before sister chromatid separation can begin. The monoubiquitylation of PLK1 by the ubiquitin ligase CUL3–KLHL22 is now identified as a critical step in promoting the release of PLK1 from kinetochores, pushing non-proteolytic ubiquitylation into the limelight of cell division research.

How application of force affects actin remodelling during mechanotransduction has remained unclear. Mechanical manipulation of the cell cortex is now shown to trigger actin monomer release from filaments, which in turn activates formin-dependent actin filament elongation. This force-sensitive actin polymerization does not require GTPases or membrane receptors, but it involves actin itself.

The recruitment of the silencing complex Polycomb group (PcG) to its target sites in mammalian cells has remained elusive. A prevalent model proposes that the PRC1 component is recruited through recognition of methylated H3K27 found at target sites occupied by the PRC2 component. However, mounting evidence suggests that PRC2-independent mechanisms of PRC1 recruitment exist. Three studies describe that the histone demethylase Kdm2b binds to unmethylated CpG islands and recruits a subset of PRC1 complexes to chromatin in pluripotent stem cells.

α-catenin exists as part of the cadherin–catenin adhesion complex as well as in a cytoplasmic pool. However, which of these pools is responsible for its biological impact remains controversial. A structure-function analysis in Drosophila melanogaster illuminates how the molecular properties of α-catenin translate into functional outcomes in an intact organism.

Centrosomes play an important role in Drosophila melanogaster stem cells, where the different size and activity of the two centrosomes help these cells divide asymmetrically. The molecular basis of the centrosome asymmetry has remained unclear, but new work highlights the centrosomal protein Centrobin as a key player in this process.