Generation and Characterization of a Tissue-Specific Centrosome Indicator Mouse Line

Extra centrosomes delay DNA damage-driven tumorigenesis

Deregulated centrosome numbers are frequently found in human cancer and can promote malignancies in model organisms. Current research aims to clarify if extra centrosomes are cause or consequence of malignant transformation, and if their biogenesis can be targeted for therapy. Here, we show that oncogene-driven blood cancer is inert to genetic manipulation of centrosome numbers, whereas the formation of DNA damage-induced malignancies is delayed. We provide first evidence that this unexpected phenomenon is connected to extra centrosomes eliciting a pro-death signal engaging the apoptotic machinery. Apoptosis induction requires the PIDDosome multi-protein complex, as it can be abrogated by loss of any of its three components, Caspase-2, Raidd/Cradd, or Pidd1. BCL2 overexpression equally blocks cell death, documenting for the first time induction of mitochondrial apoptosis downstream of extra centrosomes. Our findings demonstrate context-dependent effects of centrosome amplification during transformation and ask to adjust current belief that extra centrosomes are intrinsically pro-tumorigenic.

Chromatin region binning of gene expression for improving embryo cell subtype identification

Mammalian embryonic development is a complex process, characterized by intricate spatiotemporal dynamics and distinct chromatin preferences. However, the quick diversification in early embryogenesis leads to significant cellular diversity and the sparsity of scRNA-seq data, posing challenges in accurately determining cell fate decisions. In this study, we introduce a chromatin region binning method using scChrBin, designed to identify chromatin regions that elucidate the dynamics of embryonic development and lineage differentiation. This method transforms scRNA-seq data into a chromatin-based matrix, leveraging genomic annotations. Our results showed that the scChrBin method achieves high accuracy, with 98.0% and 89.2% on two single-cell embryonic datasets, demonstrating its effectiveness in analyzing complex developmental processes. We also systematically and comprehensively analysis of these key chromatin binning regions and their associated genes, focusing on their roles in lineage and stage development. The perspective of chromatin region binning method enables a comprehensive analysis of transcriptome data at the chromatin level, allowing us to unveil the dynamic expression of chromatin regions across temporal and spatial development. The tool is available as an application at https://github.com/liameihao/scChrBin.

Centriole signaling restricts hepatocyte ploidy to maintain liver integrity

Hepatocyte polyploidization is a tightly controlled process that is initiated at weaning and increases with age. The proliferation of polyploid hepatocytes in vivo is restricted by the PIDDosome-P53 axis, but how this pathway is triggered remains unclear. Given that increased hepatocyte ploidy protects against malignant transformation, the evolutionary driver that sets the upper limit for hepatocyte ploidy remains unknown. Here we show that hepatocytes accumulate centrioles during cycles of polyploidization in vivo. The presence of excess mature centrioles containing ANKRD26 was required to activate the PIDDosome in polyploid cells. As a result, mice lacking centrioles in the liver or ANKRD26 exhibited increased hepatocyte ploidy. Under normal homeostatic conditions, this increase in liver ploidy did not impact organ function. However, in response to chronic liver injury, blocking centriole-mediated ploidy control leads to a massive increase in hepatocyte polyploidization, severe liver damage, and impaired liver function. These results show that hyperpolyploidization sensitizes the liver to injury, posing a trade-off for the cancer-protective effect of increased hepatocyte ploidy. Our results may have important implications for unscheduled polyploidization that frequently occurs in human patients with chronic liver disease.

PLK4 drives centriole amplification and apical surface area expansion in multiciliated cells

Multiciliated cells (MCCs) are terminally differentiated epithelia that assemble multiple motile cilia used to promote fluid flow. To template these cilia, MCCs dramatically expand their centriole content during a process known as centriole amplification. In cycling cells, the master regulator of centriole assembly Polo-like kinase 4 (PLK4) is essential for centriole duplication; however recent work has questioned the role of PLK4 in centriole assembly in MCCs. To address this discrepancy, we created genetically engineered mouse models and demonstrated that both PLK4 protein and kinase activity are critical for centriole amplification in MCCs. Tracheal epithelial cells that fail centriole amplification accumulate large assemblies of centriole proteins and do not undergo apical surface area expansion. These results show that the initial stages of centriole assembly are conserved between cycling cells and MCCs and suggest that centriole amplification and surface area expansion are coordinated events.

Every day, we inhale thousands of viruses, bacteria and pollution particles. To protect against these threats, cells in our airways produce mucus that traps inhaled particles before they reach the lungs. This mucus then needs to be removed to prevent it from becoming a breeding ground for microbes that may cause a respiratory infection. This is the responsibility of cells covered in tiny hair-like structures called cilia that move together to propel the mucus-trapped particles out of the airways.

These specialized cells can have up to 300 motile cilia on their surface, which grow from structures called centrioles that then anchor the cilia in place. Multiciliated cells are generated from precursor cells that only have two centrioles. Therefore, as these precursors develop, they must produce large numbers of centrioles, considerably more than other cells that only need a couple of extra centrioles during cell division. However, recent studies have questioned whether the precursors of multiciliated cells rely on the same regulatory proteins to produce centrioles as dividing cells.

To help answer this question, LoMastro et al. created genetically engineered mice that lacked or had an inactive form of PLK4, a protein which controls centriole formation in all cell types lacking multiple cilia. This showed that multiciliated cells also need this protein to produce centrioles. LoMastro et al. also found that multiciliated cells became larger while building centrioles, suggesting that this amplification process helps control the cell’s final size.

Defects in motile cilia activity can lead to fluid build-up in the brain, respiratory infections and infertility. Unfortunately, these disorders are difficult to diagnose currently and there is no cure. The findings of LoMastro et al. further our understanding of how motile cilia are built and maintained, and may help future scientists to develop better diagnostic tools and treatments for patients.

Transient genomic instability drives tumorigenesis through accelerated clonal evolution

In this study, Shoshani et al. tested the role of aneuploidy in tumor initiation and progression, and generated mice with random aneuploidies by transient induction of polo-like kinase 4 (Plk4), a master regulator of centrosome number. Their findings show how transient CIN generates cells with random aneuploidies from which ones that acquire a karyotype with specific chromosome gains are sufficient to drive cancer formation, and that distinct CIN mechanisms can lead to similar karyotypic cancer-causing outcomes.

Abnormal numerical and structural chromosome content is frequently found in human cancer. To test the role of aneuploidy in tumor initiation and progression, we generated mice with random aneuploidies by transient induction of polo-like kinase 4 (Plk4), a master regulator of centrosome number. Short-term chromosome instability (CIN) from transient Plk4 induction resulted in formation of aggressive T-cell lymphomas in mice with heterozygous inactivation of one p53 allele and accelerated tumor development in the absence of p53. Transient CIN increased the frequency of lymphoma-initiating cells with a specific karyotype profile, including trisomy of chromosomes 4, 5, 14, and 15 occurring early in tumorigenesis. Tumor development in mice with chronic CIN induced by an independent mechanism (through inactivation of the spindle assembly checkpoint) gradually trended toward a similar karyotypic profile, as determined by single-cell whole-genome DNA sequencing. Overall, we show how transient CIN generates cells with random aneuploidies from which ones that acquire a karyotype with specific chromosome gains are sufficient to drive cancer formation, and that distinct CIN mechanisms can lead to similar karyotypic cancer-causing outcomes.

Spatial Characterization of the Human Centrosome Proteome Opens Up New Horizons for a Small but Versatile Organelle

After a century of research, the human centrosome continues to fascinate. Based on immunofluorescence and confocal microscopy, an extensive inventory of the protein components of the human centrosome, and the centriolar satellites, with the important contribution of over 300 novel proteins localizing to these compartments is presented. A network of candidate centrosome proteins involved in ubiquitination, including six interaction partners of the Kelch-like protein 21, and an additional network of protein phosphatases, together supporting the suggested role of the centrosome as an interactive hub for cell signaling, is identified. Analysis of multi-localization across cellular organelles analyzed within the Human Protein Atlas (HPA) project shows how multi-localizing proteins are particularly overrepresented in centriolar satellites, supporting the dynamic nature and wide range of functions for this compartment. In summary, the spatial dissection of the human centrosome and centriolar satellites described here provides a comprehensive knowledgebase for further exploration of their proteomes.

Centrosome Amplification Is Sufficient to Promote Spontaneous Tumorigenesis in Mammals

Centrosome amplification is a common feature of human tumors, but whether this is a cause or a consequence of cancer remains unclear. Here, we test the consequence of centrosome amplification by creating mice in which centrosome number can be chronically increased in the absence of additional genetic defects. We show that increasing centrosome number elevated tumor initiation in a mouse model of intestinal neoplasia. Most importantly, we demonstrate that supernumerary centrosomes are sufficient to drive aneuploidy and the development of spontaneous tumors in multiple tissues. Tumors arising from centrosome amplification exhibit frequent mitotic errors and possess complex karyotypes, recapitulating a common feature of human cancer. Together, our data support a direct causal relationship among centrosome amplification, genomic instability, and tumor development.