Intrinsic genomic features of individual chromosomes can contribute to chromosome-specific aneuploidy. Centromeres are key elements for the maintenance of chromosome segregation fidelity via a specialized chromatin marked by CENP-A wrapped by repetitive DNA. These long stretches of repetitive DNA vary in length among human chromosomes. Using CENP-A genetic inactivation in human cells, we directly interrogate if differences in the centromere length reflect the heterogeneity of centromeric DNA-dependent features and whether this, in turn, affects the genesis of chromosome-specific aneuploidy. Using three distinct approaches, we show that mis-segregation rates vary among different chromosomes under conditions that compromise centromere function. Whole-genome sequencing and centromere mapping combined with cytogenetic analysis, small molecule inhibitors, and genetic manipulation revealed that inter-chromosomal heterogeneity of centromeric features, but not centromere length, influences chromosome segregation fidelity. We conclude that faithful chromosome segregation for most of human chromosomes is biased in favor of centromeres with high abundance of DNA-dependent centromeric components. These inter-chromosomal differences in centromere features can translate into non-random aneuploidy, a hallmark of cancer and genetic diseases.

IntroductionIn multiple sclerosis (MS), tissue damage occurs in both the white and grey matter. [1][2][3][4] Extensive loss of axons in the white matter and injury to neuronal cell bodies, located in the cortex and deep grey matter, are evident from an early stage. Perhaps appropriately, much of the research before the turn of the century had been focussed on inflammation and demyelination due to their dominance in MS compared to other neurodegenerative disorders. 5 On the other hand, whilst neurodegeneration in MS was documented over a century ago, only limited research has been carried out on the neuronal compartments in MS. 3,6 The multifocality of grey matter and white matter pathology and chronicity of the disease mean that there is likely to be more than one degenerative stimulus leading to the common pathway of axon degeneration through calcium overload in the axoplasm. 7,8 Inflammation and axon degeneration in MS Inflammation is the most consistent characteristic associated with axonal injury at all stages of MS. [9][10][11] Neuropathological examinations of post-mortem cases of recent-onset fulminant MS reveal extensive tissue injury associated with infiltration of lymphocytes and monocytes, activation of microglia, deposition of immunoglobulins and complement, and a hypoxia-like insult. 12,13 T cells and antibodies directed against neuronal components, such as neurofascin-186 in the nodes of Ranvier, and intracellular antigens such as neurofilament-light and neurofilament-medium, may directly injure axons. 14,15 These inflammatory insults disrupt myelin, injure oligodendrocytes and astrocytes and also damage axons. Inflammation also disrupts the blood-brain barrier, particularly in relapsing-remitting MS (RRMS), as indicated by gadolinium-enhancing lesions on magnetic resonance imaging. 16,17 Currently available MS therapies effectively deal with the gadolinium-enhancing active MS lesions as well as their clinical correlate -relapses. 17 These agents therefore limit any fixed neurological deficits resulting from incompletely recovered relapses. In contrast to the effectiveness of disease-modifying therapies for relapsing MS, these agents do not The central role of mitochondria in axonal degeneration in multiple sclerosisGraham R Campbell, Joseph T Worrall and Don J Mahad Abstract: Neurodegeneration in multiple sclerosis (MS) is related to inflammation and demyelination. In acute MS lesions and experimental autoimmune encephalomyelitis focal immune attacks damage axons by injuring axonal mitochondria. In progressive MS, however, axonal damage occurs in chronically demyelinated regions, myelinated regions and also at the active edge of slowly expanding chronic lesions. How axonal energy failure occurs in progressive MS is incompletely understood. Recent studies show that oligodendrocytes supply lactate to myelinated axons as a metabolic substrate for mitochondria to generate ATP, a process which will be altered upon demyelination. In addition, a number of studies have identified mitochondrial abnormaliti...

SummaryA common assumption is that human chromosomes carry equal chances of mis-segregation during compromised cell division. Human chromosomes vary in multiple parameters that might generate bias, but technological limitations have precluded a comprehensive analysis of chromosome-specific aneuploidy. Here, by imaging specific centromeres coupled with high-throughput single-cell analysis as well as single-cell sequencing, we show that aneuploidy occurs non-randomly following common treatments to elevate chromosome mis-segregation. Temporary spindle disruption leads to elevated mis-segregation and aneuploidy of a subset of chromosomes, particularly affecting chromosomes 1 and 2. Unexpectedly, we find that a period of mitotic delay weakens centromeric cohesion and promotes chromosome mis-segregation and that chromosomes 1 and 2 are particularly prone to suffer cohesion fatigue. Our findings demonstrate that inherent properties of individual chromosomes can bias chromosome mis-segregation and aneuploidy rates, with implications for studies on aneuploidy in human disease.

SummaryIn animals, the protein kinase C (PKC) family has expanded into diversely regulated subgroups, including the Rho family-responsive PKN kinases. Here, we describe knockouts of all three mouse PKN isoforms and reveal that PKN2 loss results in lethality at embryonic day 10 (E10), with associated cardiovascular and morphogenetic defects. The cardiovascular phenotype was not recapitulated by conditional deletion of PKN2 in endothelial cells or the developing heart. In contrast, inducible systemic deletion of PKN2 after E7 provoked collapse of the embryonic mesoderm. Furthermore, mouse embryonic fibroblasts, which arise from the embryonic mesoderm, depend on PKN2 for proliferation and motility. These cellular defects are reflected in vivo as dependence on PKN2 for mesoderm proliferation and neural crest migration. We conclude that failure of the mesoderm to expand in the absence of PKN2 compromises cardiovascular integrity and development, resulting in lethality.

Summary: Recurrent patterns of chromosomal changes (aneuploidy) are widespread in cancer. These patterns are mainly attributed to selection processes due to an assumption that human chromosomes carry equal chance of being mis-segregated into daughter cells when fidelity of cell division is compromised. Human chromosomes vary widely in size, gene density and other parameters that might generate bias in mis-segregation rates, however technological limitations have precluded a systematic and high throughput analysis of chromosome-specific aneuploidy. Here, using fluorescence In-Situ hybridization (FISH) imaging of specific centromeres coupled with high-throughput single cell analysis, as well as single-cell sequencing we show that human chromosome mis-segregation is non-random.Merotelic kinetochore attachment induced by nocodazole washout leads to elevated aneuploidy of a subset of chromosomes, and high rates of anaphase lagging of chromosomes 1 and 2. Mechanistically, we show that these chromosomes are prone to cohesion fatigue that results in anaphase lagging upon release from nocodazole or Eg5 inhibition. Our findings suggest that inherent properties of specific chromosomes can influence chromosome mis-segregation and aneuploidy, with implications for studies on aneuploidy in human disease.