Aneuploidy causes premature differentiation of neural and intestinal stem cells

Arsenic impairs Drosophila neural stem cell mitotic progression and sleep behavior in a tauopathy model

Despite established exposure limits, arsenic remains the most significant environmental risk factor detrimental to human health and is associated with carcinogenesis and neurotoxicity. Arsenic compromises neurodevelopment, and it is associated with peripheral neuropathy in adults. Exposure to heavy metals, such as arsenic, may also increase the risk of neurodegenerative disorders. Nevertheless, the molecular mechanisms underlying arsenic-induced neurotoxicity remain poorly understood. Elucidating how arsenic contributes to neurotoxicity may mitigate some of the risks associated with chronic sublethal exposure and inform future interventions. In this study, we examine the effects of arsenic exposure on Drosophila larval neurodevelopment and adult neurologic function. Consistent with prior work, we identify significant developmental delays and heightened mortality in response to arsenic. Within the developing larval brain, we identify a dose-dependent increase in brain volume. This aberrant brain growth is coupled with impaired mitotic progression of the neural stem cells (NSCs), progenitors of the neurons and glia of the central nervous system. Live imaging of cycling NSCs reveals significant delays in cell cycle progression upon arsenic treatment, leading to genomic instability. In adults, chronic arsenic exposure reduces neurologic function, such as locomotion. Finally, we show arsenic selectively impairs circadian rhythms in a humanized tauopathy model. These findings inform mechanisms of arsenic neurotoxicity and reveal sex-specific and genetic vulnerabilities to sublethal exposure.

Simple aneuploidy evades p53 surveillance and promotes niche factor-independent growth in human intestinal organoids

Aneuploidy is nearly ubiquitous in tumor genomes, but the role of aneuploidy in the early stages of cancer evolution remains unclear. Here, by inducing heterogeneous aneuploidy in non-transformed human colon organoids (colonoids), we investigated how the effects of aneuploidy on cell growth and differentiation may promote malignant transformation. Previous work implicated p53 activation as a downstream response to aneuploidy induction. We found that simple aneuploidy, characterized by 1-3 gained or lost chromosomes, resulted in little or modest p53 activation and cell cycle arrest when compared with more complex aneuploid cells. Single-cell RNA sequencing analysis revealed that the degree of p53 activation was strongly correlated with karyotype complexity. Single-cell tracking showed that cells could continue to divide despite the observation of one to a few lagging chromosomes. Unexpectedly, colonoids with simple aneuploidy exhibited impaired differentiation after niche factor withdrawal. These findings demonstrate that simple aneuploid cells can escape p53 surveillance and may contribute to niche factor-independent growth of cancer-initiating colon stem cells.

Apoptotic signaling: Beyond cell death

Apoptosis is the best described form of regulated cell death, and was, until relatively recently, considered irreversible once particular biochemical points-of-no-return were activated. In this manuscript, we examine the mechanisms cells use to escape from a self-amplifying death signaling module. We discuss the role of feedback, dynamics, propagation, and noise in apoptotic signaling. We conclude with a revised model for the role of apoptosis in animal development, homeostasis, and disease.

Loss-of-function of kinesin-5 KIF11 causes microcephaly, chorioretinopathy, and developmental disorders through chromosome instability and cell cycle arrest

Kinesin motors play a fundamental role in development by controlling intracellular transport, spindle assembly, and microtubule organization. In humans, patients carrying mutations in KIF11 suffer from an autosomal dominant inheritable disease called microcephaly with or without chorioretinopathy, lymphoedema, or mental retardation (MCLMR). While mitotic functions of KIF11 proteins have been well documented in centrosome separation and spindle assembly, cellular mechanisms underlying KIF11 dysfunction and MCLMR remain unclear. In this study, we generate KIF11-inhibition chick and zebrafish models and find that KIF11 inhibition results in microcephaly, chorioretinopathy, and severe developmental defects in vivo. Notably, loss-of-function of KIF11 causes the formation of monopolar spindle and chromosome misalignment, which finally contribute to cell cycle arrest, chromosome instability, and cell death. Our results demonstrate that KIF11 is crucial for spindle assembly, chromosome alignment, and cell cycle progression of progenitor stem cells, indicating a potential link between polyploidy and MCLMR. Our data have revealed that KIF11 inhibition cause microcephaly, chorioretinopathy, and development disorders through the formation of monopolar spindle, polyploid, and cell cycle arrest.

Aneuploidy-induced cellular behaviors: Insights from Drosophila

A balanced gene complement is crucial for proper cell function. Aneuploidy, the condition of having an imbalanced chromosome set, alters the stoichiometry of gene copy numbers and protein complexes and has dramatic consequences at the cellular and organismal levels. In humans, aneuploidy is associated with different pathological conditions including cancer, microcephaly, mental retardation, miscarriages, and aging. Over the last century, Drosophila has provided a valuable system for studying the consequences of systemic aneuploidies. More recently, it has contributed to the identification and molecular dissection of aneuploidy-induced cellular behaviors and their impact at the tissue and organismal levels. In this perspective, we review this active field of research, first by comparing knowledge from yeast, mouse, and human cells, then by highlighting the contributions of Drosophila. The aim of these discussions was to further our understanding of the functional interplay between aneuploidy, cell physiology, and tissue homeostasis in human development and disease.

Differential effects of aneuploidy on growth and differentiation in human intestinal stem cells

Aneuploidy, a near ubiquitous genetic feature of tumors, is a context-dependent driver of cancer evolution; however, the mechanistic basis of this role remains unclear. Here, by inducing heterogeneous aneuploidy in non-transformed human colon organoids (colonoids), we investigate how the effects of aneuploidy on cell growth and differentiation may promote malignant transformation. Single-cell RNA sequencing reveals that the gene expression signature across over 100 unique aneuploid karyotypes is enriched with p53 responsive genes. The primary driver of p53 activation is karyotype complexity. Complex aneuploid cells with multiple unbalanced chromosomes activate p53 and undergo G1 cell-cycle arrest, independent of DNA damage and without evidence of senescence. By contrast, simple aneuploid cells with 1-3 chromosomes gained or lost continue to proliferate, demonstrated by single cell tracking in colonoids. Notably, simple aneuploid cells exhibit impaired differentiation when niche factors are withdrawn. These findings suggest that while complex aneuploid cells are eliminated from the normal epithelium due to p53 activation, simple aneuploid cells can escape this checkpoint and may contribute to niche factor-independent growth of cancer-initiating cells.

Analysis of Bub3 and Nup75 in the Drosophila male germline lineage

Extensive communication at the stem cell-niche interface and asymmetric stem cell division is key for the homeostasis of the Drosophila male germline stem cell system. To improve our understanding of these processes, we analysed the function of the mitotic checkpoint complex (MCC) component Bub3 and the nucleoporin Nup75, a component of the nuclear pore complex realizing the transport of signalling effector molecules to the nucleus, in the Drosophila testis. By lineage-specific interference, we found that the two genes control germline development and maintenance. Bub3 is continuously required in the germline, as its loss results in the beginning in an over-proliferation of early germ cells and later on in loss of the germline. The absence of the germline lineage in such testes has dramatic cell non-autonomous consequences, as cells co-expressing markers of hub and somatic cyst cell fates accumulate and populate in extreme cases the whole testis. Our analysis of Nups showed that some of them are critical for lineage maintenance, as their depletion results in the loss of the affected lineage. In contrast, Nup75 plays a role in controlling proliferation of early germ cells but not differentiating spermatogonia and seems to be involved in keeping hub cells quiescent. In sum, our analysis shows that Bub3 and Nup75 are required for male germline development and maintenance.

Regulation of intestinal stem cell activity by a mitotic cell cycle regulator Polo in Drosophila

Maintaining a definite and stable pool of dividing stem cells plays an important role in organ development. This process requires an appropriate progression of mitosis for proper spindle orientation and polarity to ensure the ability of stem cells to proliferate and differentiate correctly. Polo-like kinases (Plks)/Polo are the highly conserved serine/threonine kinases involved in the initiation of mitosis as well as in the progression of the cell cycle. Although numerous studies have investigated the mitotic defects upon loss of Plks/Polo in cells, little is known about the in vivo consequences of stem cells with abnormal Polo activity in the context of tissue and organism development. The current study aimed to investigate this question using the Drosophila intestine, an organ dynamically maintained by the intestinal stem cells (ISCs). The results indicated that the polo depletion caused a reduction in the gut size due to a gradual decrease in the number of functional ISCs. Interestingly, the polo-deficient ISCs showed an extended G2/M phase and aneuploidy and were subsequently eliminated by premature differentiation into enterocytes (ECs). In contrast, the constitutively active Polo (poloT182D) suppressed ISC proliferation, induced abnormal accumulation of β-tubulin in cells, and drove ISC loss via apoptosis. Therefore, Polo activity should be properly maintained for optimal stem cell function. Further analysis suggested that polo was a direct target gene of Sox21a, a Sox transcription factor that critically regulates stem cell activity. Together, this study provided a novel perspective on the correlation between the progression of mitosis and the ISC function in Drosophila.

Genome-Wide Expression Analysis of Long Noncoding RNAs and Their Target Genes in Metafemale Drosophila

Aneuploidy is usually more detrimental than altered ploidy of the entire set of chromosomes. To explore the regulatory mechanism of gene expression in aneuploidy, we analyzed the transcriptome sequencing data of metafemale Drosophila. The results showed that most genes on the X chromosome undergo dosage compensation, while the genes on the autosomal chromosomes mainly present inverse dosage effects. Furthermore, long noncoding RNAs (lncRNAs) have been identified as key regulators of gene expression, and they are more sensitive to dosage changes than mRNAs. We analyzed differentially expressed mRNAs (DEGs) and differentially expressed lncRNAs (DELs) in metafemale Drosophila and performed functional enrichment analyses of DEGs and the target genes of DELs, and we found that they are involved in several important biological processes. By constructing lncRNA-mRNA interaction networks and calculating the maximal clique centrality (MCC) value of each node in the network, we also identified two key candidate lncRNAs (CR43940 and CR42765), and two of their target genes, Sin3A and MED1, were identified as inverse dosage modulators. These results suggest that lncRNAs play an important role in the regulation of genomic imbalances. This study may deepen the understanding of the gene expression regulatory mechanisms in aneuploidy from the perspective of lncRNAs.

XLF/Cernunnos loss impairs mouse brain development by altering symmetric proliferative divisions of neural progenitors

XLF/Cernunnos is a component of the ligation complex used in classical non-homologous end-joining (cNHEJ), a major DNA double-strand break (DSB) repair pathway. We report neurodevelopmental delays and significant behavioral alterations associated with microcephaly in Xlf-/- mice. This phenotype, reminiscent of clinical and neuropathologic features in humans deficient in cNHEJ, is associated with a low level of apoptosis of neural cells and premature neurogenesis, which consists of an early shift of neural progenitors from proliferative to neurogenic divisions during brain development. We show that premature neurogenesis is related to an increase in chromatid breaks affecting mitotic spindle orientation, highlighting a direct link between asymmetric chromosome segregation and asymmetric neurogenic divisions. This study reveals thus that XLF is required for maintaining symmetric proliferative divisions of neural progenitors during brain development and shows that premature neurogenesis may play a major role in neurodevelopmental pathologies caused by NHEJ deficiency and/or genotoxic stress.

Illuminati: a form of gene expression plasticity in Drosophila neural stem cells

While testing for genome instability in Drosophila as reported by unscheduled upregulation of UAS-GFP in cells that co-express GAL80 and GAL4, we noticed that, as expected, background levels were low in most developing tissues. However, GFP-positive clones were frequent in the larval brain. Most of these clones originated from central brain neural stem cells. Using imaging-based approaches and genome sequencing, we show that these unscheduled clones do not result from chromosome loss or mutations in GAL80. We have named this phenomenon 'Illuminati'. Illuminati is strongly enhanced in brat tumors and is also sensitive to environmental conditions such as food content and temperature. Illuminati is suppressed by Su(var)2-10, but it is not significantly affected by several modifiers of position effect variegation or Gal4::UAS variegation. We conclude that Illuminati identifies a previously unknown type of functional instability that may have important implications in development and disease.

Nondiploid cancer cells: Stress, tolerance and therapeutic inspirations

Aberrant ploidy status is a prominent characteristic in malignant neoplasms. Approximately 90% of solid tumors and 75% of haematopoietic malignancies contain aneuploidy cells, and 30%-60% of tumors undergo whole-genome doubling, indicating that nondiploidy might be a prevalent genomic aberration in cancer. Although the role of aneuploid and polyploid cells in cancer remains to be elucidated, recent studies have suggested that nondiploid cells might be a dangerous minority that severely challenges cancer management. Ploidy shifts cause multiple fitness coasts for cancer cells, mainly including genomic, proteotoxic, metabolic and immune stresses. However, nondiploid comprises a well-adopted subpopulation, with many tolerance mechanisms evident in cells along with ploidy shifts. Aneuploid and polyploid cells elegantly maintain an autonomous balance between the stress and tolerance during adaptive evolution in cancer. Breaking the balance might provide some inspiration for ploidy-selective cancer therapy and alleviation of ploidy-related chemoresistance. To understand of the complex role and therapeutic potential of nondiploid cells better, we reviewed the survival stresses and adaptive tolerances within nondiploid cancer cells and summarized therapeutic ploidy-selective alterations for potential use in developing future cancer therapy.

Regulation and coordination of the different DNA damage responses in Drosophila

Cells have evolved mechanisms that allow them to respond to DNA damage to preserve genomic integrity and maintain tissue homeostasis. These responses include the activation of the cell cycle checkpoints and the repair mechanisms or the induction of apoptosis that eventually will eliminate damaged cells. These “life” vs. “death” decisions differ depending on the cell type, stages of development, and the proliferation status of the cell. The apoptotic response after DNA damage is of special interest as defects in its induction could contribute to tumorigenesis or the resistance of cancer cells to therapeutic agents such as radiotherapy. Multiples studies have elucidated the molecular mechanisms that mediate the activation of the DNA damage response pathway (DDR) and specifically the role of p53. However, much less is known about how the different cellular responses such as cell proliferation control and apoptosis are coordinated to maintain tissue homeostasis. Another interesting question is how the differential apoptotic response to DNA damage is regulated in distinct cell types. The use of Drosophila melanogaster as a model organism has been fundamental to understand the molecular and cellular mechanisms triggered by genotoxic stress. Here, we review the current knowledge regarding the cellular responses to ionizing radiation as the cause of DNA damage with special attention to apoptosis in Drosophila: how these responses are regulated and coordinated in different cellular contexts and in different tissues. The existence of intrinsic mechanisms that might attenuate the apoptotic pathway in response to this sort of DNA damage may well be informative for the differences in the clinical responsiveness of tumor cells after radiation therapy.

An interplay between cellular growth and atypical fusion defines morphogenesis of a modular glial niche in Drosophila

Neural stem cells (NSCs) live in an intricate cellular microenvironment supporting their activity, the niche. Whilst shape and function are inseparable, the morphogenetic aspects of niche development are poorly understood. Here, we use the formation of a glial niche to investigate acquisition of architectural complexity. Cortex glia (CG) in Drosophila regulate neurogenesis and build a reticular structure around NSCs. We first show that individual CG cells grow tremendously to ensheath several NSC lineages, employing elaborate proliferative mechanisms which convert these cells into syncytia rich in cytoplasmic bridges. CG syncytia further undergo homotypic cell-cell fusion, using defined cell surface receptors and actin regulators. Cellular exchange is however dynamic in space and time. This atypical cell fusion remodels cellular borders, restructuring the CG syncytia. Ultimately, combined growth and fusion builds the multi-level architecture of the niche, and creates a modular, spatial partition of the NSC population. Our findings provide insights into how a niche forms and organises while developing intimate contacts with a stem cell population.

The spindle assembly checkpoint and the spatial activation of Polo kinase determine the duration of cell division and prevent tumor formation

The maintenance of a restricted pool of asymmetrically dividing stem cells is essential for tissue homeostasis. This process requires the control of mitotic progression that ensures the accurate chromosome segregation. In addition, this event is coupled to the asymmetric distribution of cell fate determinants in order to prevent stem cell amplification. How this coupling is regulated remains poorly described. Here, using asymmetrically dividing Drosophila neural stem cells (NSCs), we show that Polo kinase activity levels determine timely Cyclin B degradation and mitotic progression independent of the spindle assembly checkpoint (SAC). This event is mediated by the direct phosphorylation of Polo kinase by Aurora A at spindle poles and Aurora B kinases at centromeres. Furthermore, we show that Aurora A-dependent activation of Polo is the major event that promotes NSC polarization and together with the SAC prevents brain tumor growth. Altogether, our results show that an Aurora/Polo kinase module couples NSC mitotic progression and polarization for tissue homeostasis.

Traip controls mushroom body size by suppressing mitotic defects

Microcephaly is a failure to develop proper brain size and neuron number. Mutations in diverse genes are linked to microcephaly, including several with DNA damage repair (DDR) functions; however, it is not well understood how these DDR gene mutations limit brain size. One such gene is TRAIP, which has multiple functions in DDR. We characterized the Drosophila TRAIP homolog nopo, hereafter traip, and found that traip mutants (traip-) have a brain-specific defect in the mushroom body (MB). traip- MBs were smaller and contained fewer neurons, but no neurodegeneration, consistent with human primary microcephaly. Reduced neuron numbers in traip- were explained by premature loss of MB neuroblasts (MB-NBs), in part via caspase-dependent cell death. Many traip- MB-NBs had prominent chromosome bridges in anaphase, along with polyploidy, aneuploidy or micronuclei. Traip localization during mitosis is sufficient for MB development, suggesting that Traip can repair chromosome bridges during mitosis if necessary. Our results suggest that proper brain size is ensured by the recently described role for TRAIP in unloading stalled replication forks in mitosis, which suppresses DNA bridges and premature neural stem cell loss to promote proper neuron number.

Effects of aneuploidy on cell behaviour and function

Aneuploidy, a genomic alternation characterized by deviations in the copy number of chromosomes, affects organisms from early development through to aging. Although it is a main cause of human pregnancy loss and a hallmark of cancer, how aneuploidy affects cellular function has been elusive. The last two decades have seen rapid advances in the understanding of the causes and consequences of aneuploidy at the molecular and cellular levels. These studies have uncovered effects of aneuploidy that can be beneficial or detrimental to cells and organisms in an environmental context-dependent and karyotype-dependent manner. Aneuploidy also imposes general stress on cells that stems from an imbalanced genome and, consequently, also an imbalanced proteome. These insights provide the fundamental framework for understanding the impact of aneuploidy in genome evolution, human pathogenesis and drug resistance.

Interaction of Male Specific Lethal complex and genomic imbalance on global gene expression in Drosophila

The inverse dosage effect caused by chromosome number variations shows global consequences in genomic imbalance including sexual dimorphism and an X chromosome-specific response. To investigate the relationship of the MSL complex to genomic imbalance, we over-expressed MSL2 in autosomal and sex chromosomal aneuploids, and analyzed the different transcriptomes. Some candidate genes involved in regulatory mechanisms have also been tested during embryogenesis using TSA-FISH. Here we show that the de novo MSL complex assembled on the X chromosomes in females further reduced the global expression level on the basis of 2/3 down-regulation caused by the inverse dosage effect in trisomy through epigenetic modulations rather than induced dosage compensation. Plus, the sexual dimorphism effect in unbalanced genomes was further examined due to the pre-existing of the MSL complex in males. All these results demonstrate the dynamic functions of the MSL complex on global gene expression in different aneuploid genomes.

Understanding microcephaly through the study of centrosome regulation in Drosophila neural stem cells

Microcephaly is a rare, yet devastating, neurodevelopmental condition caused by genetic or environmental insults, such as the Zika virus infection. Microcephaly manifests with a severely reduced head circumference. Among the known heritable microcephaly genes, a significant proportion are annotated with centrosome-related ontologies. Centrosomes are microtubule-organizing centers, and they play fundamental roles in the proliferation of the neuronal progenitors, the neural stem cells (NSCs), which undergo repeated rounds of asymmetric cell division to drive neurogenesis and brain development. Many of the genes, pathways, and developmental paradigms that dictate NSC development in humans are conserved in Drosophila melanogaster. As such, studies of Drosophila NSCs lend invaluable insights into centrosome function within NSCs and help inform the pathophysiology of human microcephaly. This mini-review will briefly survey causative links between deregulated centrosome functions and microcephaly with particular emphasis on insights learned from Drosophila NSCs.

WDR62 localizes katanin at spindle poles to ensure synchronous chromosome segregation

Mutations in the WDR62 gene cause primary microcephaly, a pathological condition often associated with defective cell division that results in severe brain developmental defects. The precise function and localization of WDR62 within the mitotic spindle is, however, still under debate, as it has been proposed to act either at centrosomes or on the mitotic spindle. Here we explored the cellular functions of WDR62 in human epithelial cell lines using both short-term siRNA protein depletions and long-term CRISPR/Cas9 gene knockouts. We demonstrate that WDR62 localizes at spindle poles, promoting the recruitment of the microtubule-severing enzyme katanin. Depletion or loss of WDR62 stabilizes spindle microtubules due to insufficient microtubule minus-end depolymerization but does not affect plus-end microtubule dynamics. During chromosome segregation, WDR62 and katanin promote efficient poleward microtubule flux and favor the synchronicity of poleward movements in anaphase to prevent lagging chromosomes. We speculate that these lagging chromosomes might be linked to developmental defects in primary microcephaly.

Drosophila Tubulin-Specific Chaperone E Recruits Tubulin around Chromatin to Promote Mitotic Spindle Assembly

Proper assembly of mitotic spindles requires microtubule nucleation not only at the centrosomes but also around chromatin. In this study, we found that the Drosophila tubulin-specific chaperone dTBCE is required for the enrichment of tubulin in the nuclear space after nuclear envelope breakdown and for subsequent promotion of spindle microtubule nucleation. These events depend on the CAP-Gly motif found in dTBCE and are regulated by Ran and lamin proteins. Our data suggest that during early mitosis, dTBCE and nuclear pore proteins become enriched in the nucleus, where they interact with the Ran GTPase to promote dynamic tubulin enrichment. We propose that this novel mechanism enhances microtubule nucleation around chromatin, thereby facilitating mitotic spindle assembly.

Understanding How Genetic Mutations Collaborate with Genomic Instability in Cancer

Chromosomal instability is the process of mis-segregation for ongoing chromosomes, which leads to cells with an abnormal number of chromosomes, also known as an aneuploid state. Induced aneuploidy is detrimental during development and in primary cells but aneuploidy is also a hallmark of cancer cells. It is therefore believed that premalignant cells need to overcome aneuploidy-imposed stresses to become tumorigenic. Over the past decade, some aneuploidy-tolerating pathways have been identified through small-scale screens, which suggest that aneuploidy tolerance pathways can potentially be therapeutically exploited. However, to better understand the processes that lead to aneuploidy tolerance in cancer cells, large-scale and unbiased genetic screens are needed, both in euploid and aneuploid cancer models. In this review, we describe some of the currently known aneuploidy-tolerating hits, how large-scale genome-wide screens can broaden our knowledge on aneuploidy specific cancer driver genes, and how we can exploit the outcomes of these screens to improve future cancer therapy.

Mms19 promotes spindle microtubule assembly in Drosophila neural stem cells

Mitotic divisions depend on the timely assembly and proper orientation of the mitotic spindle. Malfunctioning of these processes can considerably delay mitosis, thereby compromising tissue growth and homeostasis, and leading to chromosomal instability. Loss of functional Mms19 drastically affects the growth and development of mitotic tissues in Drosophila larvae and we now demonstrate that Mms19 is an important factor that promotes spindle and astral microtubule (MT) growth, and MT stability and bundling. Mms19 function is needed for the coordination of mitotic events and for the rapid progression through mitosis that is characteristic of neural stem cells. Surprisingly, Mms19 performs its mitotic activities through two different pathways. By stimulating the mitotic kinase cascade, it triggers the localization of the MT regulatory complex TACC/Msps (Transforming Acidic Coiled Coil/Minispindles, the homolog of human ch-TOG) to the centrosome. This activity of Mms19 can be rescued by stimulating the mitotic kinase cascade. However, other aspects of the Mms19 phenotypes cannot be rescued in this way, pointing to an additional mechanism of Mms19 action. We provide evidence that Mms19 binds directly to MTs and that this stimulates MT stability and bundling.

Maternal sevoflurane exposure affects differentiation of hippocampal neural stem cells by regulating miR-410-3p and ATN1

BACKGROUND

Currently, numerous animal studies have shown that exposure to commonly used general anesthetics during pregnancy may cause neurocognitive impairment in the offspring. Reportedly, exposure to sevoflurane during mid-trimester of pregnancy can inhibit proliferation of neural stem cells (NSCs) and lead to early apoptosis. Whether exposure to sevoflurane during pregnancy affects the differentiation of NSCs remains unclear.

METHODS

In the present study, pregnant rats were exposed to 3% sevoflurane once for 2 h on gestational day 14 (G14) or 3 times for 2 h on G13, G14, and G15. Next, the differentiation of NSCs was measured using neuron marker β-tubulin III and astrocyte marker glial fibrillary acidic protein (GFAP) in fetal brain tissues 24 h and 72 h after anesthesia and in hippocampus on postnatal day 28. Primary cultured rat NSCs were exposed to 4.1% sevoflurane to explore the mechanism.

RESULTS

The results showed that during mid-trimester, multiple exposures to sevoflurane can cause premature differentiation of NSCs in developing brains of offspring and lead to long-term neuron reduction and astrocyte proliferation in hippocampus. The data from the present study indicated that repeated exposure to sevoflurane downregulated atrophin-1 (ATN1) expression and caused early differentiation of NSCs. Overexpression of ATN1 via lentivirus transfection attenuated the influence of sevoflurane. Using dual luciferase assay, ATN1 was found to be a target gene of microRNA-410-3p (miR-410-3p). MiR-410-3p suppression via lentivirus transfection recovered the ATN1 expression and differentiation of NSCs.

CONCLUSIONS

The results from the present study demonstrated that repeated exposure to sevoflurane leads to early differentiation of NSCs and long-term effects via the miR-410-3p/ATN1 pathway.

Targeting MAD2 modulates stemness and tumorigenesis in human Gastric Cancer cell lines

Rationale: Gastric cancer (GC) is a solid tumor that contains subpopulations of cancer stem cells (CSCs), which are considered drivers of tumor initiation and metastasis; responsible for therapeutic resistance; and promoters of tumor relapse. The balance between symmetric and asymmetric division is crucial for stem cell maintenance. The objective of this study is to evaluate the role of MAD2, a key protein for proper mitotic checkpoint activity, in the tumorigenesis of GC.

Methods: Gastric cancer stem cells (GCSCs) were obtained from MKN45, SNU638 and ST2957 cell lines. Pluripotency and stemness markers were evaluated by RT-qPCR and autofluorescence and membrane markers by flow cytometry. Relevant signal transduction pathways were studied by WB. We analysed cell cycle progression, migration and invasion after modulation of MAD2 activity or protein expression levels in these in vitro models. In vivo assays were performed in a nude mouse subcutaneous xenograft model.

Results: We found that NANOG, CXCR4 and autofluorescence are common and consistent markers for the GCSCs analysed, with other markers showing more variability. The three main signalling pathways (Wnt/β-catenin; Hedgehog and Notch) were activated in GCSCs. Downregulation of MAD2 in MKN45^CSCs decreased the expression of markers CXCR4, CD133, CD90, LGR5 and VIM, without affecting cell cycle profile or therapy resistance. Moreover, migration, invasion and tumor growth were clearly reduced, and accordingly, we found that metalloprotease expression decreased. These results were accompanied by a reduction in the levels of transcription factors related with epithelial-to-mesenchymal transition.

Conclusions: We can conclude that MAD2 is important for GCSCs stemness and its downregulation in MKN45^CSCs plays a central role in GC tumorigenesis, likely through CXCR4-SNAI2-MMP1. Thus, its potential use in the clinical setting should be studied as its functions appear to extend beyond mitosis.

A somatic evolutionary model of the dynamics of aneuploid cells during hematopoietic reconstitution

Aneuploidy is a feature of many cancers. Recent studies demonstrate that in the hematopoietic stem and progenitor cell (HSPC) compartment aneuploid cells have reduced fitness and are efficiently purged from the bone marrow. However, early phases of hematopoietic reconstitution following bone marrow transplantation provide a window of opportunity whereby aneuploid cells rise in frequency, only to decline to basal levels thereafter. Here we demonstrate by Monte Carlo modeling that two mechanisms could underlie this aneuploidy peak: rapid expansion of the engrafted HSPC population and bone marrow microenvironment degradation caused by pre-transplantation radiation treatment. Both mechanisms reduce the strength of purifying selection acting in early post-transplantation bone marrow. We explore the contribution of other factors such as alterations in cell division rates that affect the strength of purifying selection, the balance of drift and selection imposed by the HSPC population size, and the mutation-selection balance dependent on the rate of aneuploidy generation per cell division. We propose a somatic evolutionary model for the dynamics of cells with aneuploidy or other fitness-reducing mutations during hematopoietic reconstitution following bone marrow transplantation. Similar alterations in the strength of purifying selection during cancer development could help explain the paradox of aneuploidy abundance in tumors despite somatic fitness costs.

The Kinase Activity of Drosophila BubR1 Is Required for Insulin Signaling-Dependent Stem Cell Maintenance

As a core component of the mitotic checkpoint complex, BubR1 has a modular organization of molecular functions, with KEN box and other motifs at the N terminus inhibiting the anaphase-promoting complex/cyclosome, and a kinase domain at the C terminus, whose function remains unsettled, especially at organismal levels. We generate knock-in BubR1 mutations in the Drosophila genome to separately disrupt the KEN box and the kinase domain. All of the mutants are homozygously viable and fertile and show no defects in mitotic progression. The mutants without kinase activity have an increased lifespan and phenotypic changes associated with attenuated insulin signaling, including reduced InR on the cell membrane, weakened PI3K and AKT activity, and elevated expression of dFoxO targets. The BubR1 kinase-dead mutants have a reduced cap cell number in female germaria, which can be rescued by expressing a constitutively active InR. We conclude that one major physiological role of BubR1 kinase in Drosophila is to modulate insulin signaling.

Long noncoding RNA SAM promotes myoblast proliferation through stabilizing Sugt1 and facilitating kinetochore assembly

The functional study of lncRNAs in skeletal muscle satellite cells (SCs) remains at the infancy stage. Here we identify SAM (Sugt1 asssociated muscle) lncRNA that is enriched in the proliferating myoblasts. Global deletion of SAM has no overt effect on mice but impairs adult muscle regeneration following acute damage; it also exacerbates the chronic injury-induced dystrophic phenotype in mdx mice. Consistently, inducible deletion of SAM in SCs leads to deficiency in muscle regeneration. Further examination reveals that SAM loss results in a cell-autonomous defect in the proliferative expansion of myoblasts. Mechanistically, we find SAM interacts and stabilizes Sugt1, a co-chaperon protein key to kinetochore assembly during cell division. Loss of SAM or Sugt1 both disrupts kinetochore assembly in mitotic cells due to the mislocalization of two components: Dsn1 and Hec1. Altogether, our findings identify SAM as a regulator of SC proliferation through facilitating Sugt1 mediated kinetochore assembly during cell division.

Long noncoding RNA SAM (Sugt1 associated muscle) is upregulated in the proliferating myoblast cells. Here the authors investigate SAM knockout mice and suggest that SAM binds and stabilizes Sugt1, a co-chaperone protein that regulates kinetochore assembly.

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

Ploidy 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.

Centrosomes: The good and the bad for brain development

Centrosomes nucleate and organise the microtubule cytoskeleton in animal cells. These membraneless organelles are key structures for tissue organisation, polarity and growth. Centrosome dysfunction, defined as deviation in centrosome numbers and/or structural integrity, has major impact on brain size and functionality, as compared with other tissues of the organism. In this review, we discuss the contribution of centrosomes to brain growth during development. We discuss in particular the impact of centrosome dysfunction in Drosophila and mammalian neural stem cell division and fitness, which ultimately underlie brain growth defects.

Cohesin controls intestinal stem cell identity by maintaining association of Escargot with target promoters

Intestinal stem cells (ISCs) maintain regenerative capacity of the intestinal epithelium. Their function and activity are regulated by transcriptional changes, yet how such changes are coordinated at the genomic level remains unclear. The Cohesin complex regulates transcription globally by generating topologically-associated DNA domains (TADs) that link promotor regions with distant enhancers. We show here that the Cohesin complex prevents premature differentiation of Drosophila ISCs into enterocytes (ECs). Depletion of the Cohesin subunit Rad21 and the loading factor Nipped-B triggers an ISC to EC differentiation program that is independent of Notch signaling, but can be rescued by over-expression of the ISC-specific escargot (esg) transcription factor. Using damID and transcriptomic analysis, we find that Cohesin regulates Esg binding to promoters of differentiation genes, including a group of Notch target genes involved in ISC differentiation. We propose that Cohesin ensures efficient Esg-dependent gene repression to maintain stemness and intestinal homeostasis.

Altering microtubule dynamics is synergistically toxic with spindle assembly checkpoint inhibition

Chromosomal instability (CIN) is a hallmark feature of cancer cells. In this study, Schukken and colleagues screen for compounds that selectively target CIN cells and identify an inhibitor of Src kinase to be selectively toxic for CIN cells.

Chromosomal instability (CIN) and aneuploidy are hallmarks of cancer. As most cancers are aneuploid, targeting aneuploidy or CIN may be an effective way to target a broad spectrum of cancers. Here, we perform two small molecule compound screens to identify drugs that selectively target cells that are aneuploid or exhibit a CIN phenotype. We find that aneuploid cells are much more sensitive to the energy metabolism regulating drug ZLN005 than their euploid counterparts. Furthermore, cells with an ongoing CIN phenotype, induced by spindle assembly checkpoint (SAC) alleviation, are significantly more sensitive to the Src kinase inhibitor SKI606. We show that inhibiting Src kinase increases microtubule polymerization rates and, more generally, that deregulating microtubule polymerization rates is particularly toxic to cells with a defective SAC. Our findings, therefore, suggest that tumors with a dysfunctional SAC are particularly sensitive to microtubule poisons and, vice versa, that compounds alleviating the SAC provide a powerful means to treat tumors with deregulated microtubule dynamics.

The Mitotic Apparatus and Kinetochores in Microcephaly and Neurodevelopmental Diseases

Regulators of mitotic division, when dysfunctional or expressed in a deregulated manner (over- or underexpressed) in somatic cells, cause chromosome instability, which is a predisposing condition to cancer that is associated with unrestricted proliferation. Genes encoding mitotic regulators are growingly implicated in neurodevelopmental diseases. Here, we briefly summarize existing knowledge on how microcephaly-related mitotic genes operate in the control of chromosome segregation during mitosis in somatic cells, with a special focus on the role of kinetochore factors. Then, we review evidence implicating mitotic apparatus- and kinetochore-resident factors in the origin of congenital microcephaly. We discuss data emerging from these works, which suggest a critical role of correct mitotic division in controlling neuronal cell proliferation and shaping the architecture of the central nervous system.

Ionizing radiation reduces larval brain size by inducing premature differentiation of Drosophila neural stem cells

DNA damaging agents, such as ionizing radiation (IR), induce cell cycle arrest, senescence, differentiation, or cell death of stem cells, which may affect tissue homeostasis. The specific response of stem cells upon irradiation seems to vary depending on the cell type and their developmental stages. Drosophila larval brain contains neural stem cells called neuroblasts (NBs) and maintaining an appropriate number of NBs is critical to maintain brain size. Irradiation of larvae at early larval stage results in microcephaly, whereas the DNA damage response of NBs that could explain this small brain size is not clearly understood. We observed that the irradiation of larvae in the second instar retarded brain growth, accompanied by fewer NBs. The IR-induced microcephaly does not seem to result from apoptosis since the irradiated larval brain was not stained with activated Caspase nor was the microcephaly affected by the ectopic expression of the apoptosis inhibitor. When analyzed for the percentage of mitotic cells, irradiated NBs recovered their proliferative potential within 6 h post-irradiation after transient cell cycle arrest. However, IR eventually reduced the proliferation of NBs at later time points and induced the premature differentiation of NBs. In summary, IR-induced microcephaly occurs by NB loss due to premature differentiation, rather than apoptotic cell death.

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

Polyploidy arises from the gain of complete chromosome sets [1], and it is known to promote cancer genome evolution. Recent evidence suggests that a large proportion of human tumors experience whole-genome duplications (WGDs), which might favor the generation of highly abnormal karyotypes within a short time frame, rather than in a stepwise manner [2-6]. However, the molecular mechanisms linking whole-genome duplication to genetic instability remain poorly understood. Using repeated cytokinesis failure to induce polyploidization of Drosophila neural stem cells (NSCs) (also called neuroblasts [NBs]), we investigated the consequences of polyploidy in vivo. Surprisingly, we found that DNA damage is generated in a subset of nuclei of polyploid NBs during mitosis. Importantly, our observations in flies were confirmed in mouse NSCs (mNSCs) and human cancer cells after acute cytokinesis inhibition. Interestingly, DNA damage occurs in nuclei that were not ready to enter mitosis but were forced to do so when exposed to the mitotic environment of neighboring nuclei within the same cell. Additionally, we found that polyploid cells are cell-cycle asynchronous and forcing cell-cycle synchronization was sufficient to lower the levels of DNA damage generated during mitosis. Overall, this work supports a model in which DNA damage at mitotic entry can generate DNA structural abnormalities that might contribute to the onset of genetic instability.

Endoplasmic reticulum and Golgi stress in microcephaly

Microcephaly is a neurodevelopmental condition characterized by a small brain size associated with intellectual deficiency in most cases and is one of the most frequent clinical sign encountered in neurodevelopmental disorders. It can result from a wide range of environmental insults occurring during pregnancy or postnatally, as well as from various genetic causes and represents a highly heterogeneous condition. However, several lines of evidence highlight a compromised mode of division of the cortical precursor cells during neurogenesis, affecting neural commitment or survival as one of the common mechanisms leading to a limited production of neurons and associated with the most severe forms of congenital microcephaly. In this context, the emergence of the endoplasmic reticulum (ER) and the Golgi apparatus as key guardians of cellular homeostasis, especially through the regulation of proteostasis, has raised the hypothesis that pathological ER and/or Golgi stress could contribute significantly to cortical impairments eliciting microcephaly. In this review, we discuss recent findings implicating ER and Golgi stress responses in early brain development and provide an overview of microcephaly-associated genes involved in these pathways.

A Double-Edged Sword: Aneuploidy is a Prevalent Strategy in Fungal Adaptation

Aneuploidy, a deviation from a balanced genome by either gain or loss of chromosomes, is generally associated with impaired fitness and developmental defects in eukaryotic organisms. While the general physiological impact of aneuploidy remains largely elusive, many phenotypes associated with aneuploidy link to a common theme of stress adaptation. Here, we review previously identified mechanisms and observations related to aneuploidy, focusing on the highly diverse eukaryotes, fungi. Fungi, which have conquered virtually all environments, including several hostile ecological niches, exhibit widespread aneuploidy and employ it as an adaptive strategy under severe stress. Gambling with the balance between genome plasticity and stability has its cost and in fact, most aneuploidies have fitness defects. How can this fitness defect be reconciled with the prevalence of aneuploidy in fungi? It is likely that the fitness cost of the extra chromosomes is outweighed by the advantage they confer under life-threatening stresses. In fact, once the selective pressures are withdrawn, aneuploidy is often lost and replaced by less drastic mutations that possibly incur a lower fitness cost. We discuss representative examples across hostile environments, including medically and industrially relevant cases, to highlight potential adaptive mechanisms in aneuploid yeast.

Polarity signaling ensures epidermal homeostasis by coupling cellular mechanics and genomic integrity

Epithelial homeostasis requires balanced progenitor cell proliferation and differentiation, whereas disrupting this equilibrium fosters degeneration or cancer. Here we studied how cell polarity signaling orchestrates epidermal self-renewal and differentiation. Using genetic ablation, quantitative imaging, mechanochemical reconstitution and atomic force microscopy, we find that mammalian Par3 couples genome integrity and epidermal fate through shaping keratinocyte mechanics, rather than mitotic spindle orientation. Par3 inactivation impairs RhoA activity, actomyosin contractility and viscoelasticity, eliciting mitotic failures that trigger aneuploidy, mitosis-dependent DNA damage responses, p53 stabilization and premature differentiation. Importantly, reconstituting myosin activity is sufficient to restore mitotic fidelity, genome integrity, and balanced differentiation and stratification. Collectively, this study deciphers a mechanical signaling network in which Par3 acts upstream of Rho/actomyosin contractility to promote intrinsic force generation, thereby maintaining mitotic accuracy and cellular fitness at the genomic level. Disturbing this network may compromise not only epidermal homeostasis but potentially also that of other self-renewing epithelia.

Many developing tissues require Par-driven polarization, but its role in mammalian tissue maintenance is unclear. Here, the authors show that in mouse epidermis, Par3 governs tissue homeostasis not via orientation of cell division but by coupling cell mechanics with mitotic accuracy and genome integrity.

Tissue stem cells: the new actors in the aneuploidy field

The development of multicellular organisms and the maintenance of its tissues relies on mitosis. However, this process represents a major challenge for genomic stability as each time a cell division occurs there are multiple steps where errors can lead to an abnormal chromosomal content in daughter cells - aneuploidy. Aneuploidy was first postulated to act as a tumour promoting agent over one century ago. Since then, we have learned to appreciate the complexity involving the cellular responses to aneuploidy and to value the importance of models where aneuploidy is induced in vivo and in a cell-type specific manner. Recent data suggests that stem cells evolved a distinct response to aneuploidy, being able to survive and proliferate as aneuploid. Since stem cells are the main cells responsible for tissue renewal, it is of the utmost importance to place the spotlight on stem cells within the aneuploidy field. Here, we briefly review some of the biological mechanisms implicated in aneuploidy, the relationship between aneuploidy and tissue pathologies, and summarize the most recent findings in Drosophila on how tissue stem cells respond to aneuploidy. Once we understand how stem cell behavior is impacted by aneuploidy, we might be able to better describe the complicated link between aneuploidy and tumourigenesis.

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 regulating MSO 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.

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Drosophila Plk4 mutant NSCs show defects in centriole asymmetry and spindle positioning

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Apical centriole anchoring requires the PCM protein Spd-2 and the APC/C activator Fzr

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Movement of the centriole toward the basal side of the cell requires Plk4 activity

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At the mother centriole, Plk4 phosphorylates Spd2 to trigger PCM shedding and Fzr loss

Loss of a proteostatic checkpoint in intestinal stem cells contributes to age-related epithelial dysfunction

A decline in protein homeostasis (proteostasis) has been proposed as a hallmark of aging. Somatic stem cells (SCs) uniquely maintain their proteostatic capacity through mechanisms that remain incompletely understood. Here, we describe and characterize a ‘proteostatic checkpoint’ in Drosophila intestinal SCs (ISCs). Following a breakdown of proteostasis, ISCs coordinate cell cycle arrest with protein aggregate clearance by Atg8-mediated activation of the Nrf2-like transcription factor cap-n-collar C (CncC). CncC induces the cell cycle inhibitor Dacapo and proteolytic genes. The capacity to engage this checkpoint is lost in ISCs from aging flies, and we show that it can be restored by treating flies with an Nrf2 activator, or by over-expression of CncC or Atg8a. This limits age-related intestinal barrier dysfunction and can result in lifespan extension. Our findings identify a new mechanism by which somatic SCs preserve proteostasis, and highlight potential intervention strategies to maintain regenerative homeostasis.

Protein homeostasis maintenance (proteostasis) is critical for cell function, but declines during aging. Here the authors detail a proteostatic checkpoint in Drosophila intestinal stem cells coordinating cell cycle arrest with protein aggregate clearance, along with its role in aging related intestinal dysfunction.

Approaches towards Longevity: Reprogramming, Senolysis, and Improved Mitotic Competence as Anti-Aging Therapies

Mainstream approaches that are currently used as anti-aging therapies primarily explore the senescence and epigenetic drift aging hallmarks and they are at two ends of the spectrum. While senolytic therapies include either the selective elimination of senescent cells or the disruption of their secretome with the use of drugs or natural compounds, cellular reprogramming uses genetic manipulation to revert cells all the way back to pluripotency. Here, we describe the progress that has been made on these therapies, while highlighting the major challenges involved. Moreover, based on recent findings elucidating the impact of mitotic shutdown and aneuploidy in cellular senescence, we discuss the modulation of mitotic competence as an alternative strategy to delay the hallmarks of aging. We propose that a regulated rise in mitotic competence of cells could circumvent certain limitations that are present in the senolytic and reprogramming approaches, by acting to decelerate senescence and possibly restore the epigenetic landscape.

Induced aneuploidy in neural stem cells triggers a delayed stress response and impairs adult life span in flies

Studying aneuploidy during organism development has strong limitations because chronic mitotic perturbations used to generate aneuploidy usually result in lethality. We developed a genetic tool to induce aneuploidy in an acute and time-controlled manner during Drosophila development. This is achieved by reversible depletion of cohesin, a key molecule controlling mitotic fidelity. Larvae challenged with aneuploidy hatch into adults with severe motor defects shortening their life span. Neural stem cells, despite being aneuploid, display a delayed stress response and continue proliferating, resulting in the rapid appearance of chromosomal instability, a complex array of karyotypes, and cellular abnormalities. Notably, when other brain-cell lineages are forced to self-renew, aneuploidy-associated stress response is significantly delayed. Protecting only the developing brain from induced aneuploidy is sufficient to rescue motor defects and adult life span, suggesting that neural tissue is the most ill-equipped to deal with developmental aneuploidy.

The diverse consequences of aneuploidy

Aneuploidy, or imbalanced chromosome number, has profound effects on eukaryotic cells. In humans, aneuploidy is associated with various pathologies, including cancer, which suggests that it mediates a proliferative advantage under these conditions. Here, we discuss physiological changes triggered by aneuploidy, such as altered cell growth, transcriptional changes, proteotoxic stress, genomic instability and response to interferons, and how cancer cells adapt to the changing aneuploid genome.

Aneuploidy in intestinal stem cells promotes gut dysplasia in Drosophila

Aneuploidy is associated with different human diseases including cancer. However, different cell types appear to respond differently to aneuploidy, either by promoting tumorigenesis or causing cell death. We set out to study the behavior of adult Drosophila melanogaster intestinal stem cells (ISCs) after induction of chromosome missegregation either by abrogation of the spindle assembly checkpoint or through kinetochore disruption or centrosome amplification. These conditions induce moderate levels of aneuploidy in ISCs, and we find no evidence of apoptosis. Instead, we observe a significant accumulation of ISCs associated with increased stem cell proliferation and an excess of enteroendocrine cells. Moreover, aneuploidy causes up-regulation of the JNK pathway throughout the posterior midgut, and specific inhibition of JNK signaling in ISCs is sufficient to prevent dysplasia. Our findings highlight the importance of understanding the behavior of different stem cell populations to aneuploidy and how these can act as reservoirs for genomic alterations that can lead to tissue pathologies.

Inactivation of PLK4-STIL Module Prevents Self-Renewal and Triggers p53-Dependent Differentiation in Human Pluripotent Stem Cells

Centrioles account for centrosomes and cilia formation. Recently, a link between centrosomal components and human developmental disorders has been established. However, the exact mechanisms how centrosome abnormalities influence embryogenesis and cell fate are not understood. PLK4-STIL module represents a key element of centrosome duplication cycle. We analyzed consequences of inactivation of the module for early events of embryogenesis in human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). We demonstrate that blocking of PLK4 or STIL functions leads to centrosome loss followed by both p53-dependent and -independent defects, including prolonged cell divisions, upregulation of p53, chromosome instability, and, importantly, reduction of pluripotency markers and induction of differentiation. We show that the observed loss of key stem cells properties is connected to alterations in mitotic timing and protein turnover. In sum, our data define a link between centrosome, its regulators, and the control of pluripotency and differentiation in PSCs.

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Blocking of PLK4-STIL module in hESCs/hiPSCs leads to:

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Centrosome loss, prolonged and error-prone mitosis;

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p53-dependent differentiation;

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Reduction of pluripotency linked to altered protein turnover

Live imaging of heart tube development in mouse reveals alternating phases of cardiac differentiation and morphogenesis

During vertebrate heart development, two progenitor populations, first and second heart fields (FHF, SHF), sequentially contribute to longitudinal subdivisions of the heart tube (HT), with the FHF contributing the left ventricle and part of the atria, and the SHF the rest of the heart. Here, we study the dynamics of cardiac differentiation and morphogenesis by tracking individual cells in live analysis of mouse embryos. We report that during an initial phase, FHF precursors differentiate rapidly to form a cardiac crescent, while limited morphogenesis takes place. In a second phase, no differentiation occurs while extensive morphogenesis, including splanchnic mesoderm sliding over the endoderm, results in HT formation. In a third phase, cardiac precursor differentiation resumes and contributes to SHF-derived regions and the dorsal closure of the HT. These results reveal tissue-level coordination between morphogenesis and differentiation during HT formation and provide a new framework to understand heart development.

We all start life as a single cell, which – over the course of nine months – multiplies to generate the billions of cells that can be found in a newborn. As an embryo develops, the cells need to achieve two major tasks: they need to diversify into different types of cells, such as blood cells or muscle cells, and they need to organize themselves in space to form tissues and organs.

The heart of an embryo, for example, first forms a simple structure called the heart tube that can pump blood and later develops into the four chambers that we see in adults. The tube is made up of cells from two different origins, known as the first and second heart fields. Unlike other organs, the heart has to start beating while it is still developing, and until now, it was unclear how the heart manages this difficult task.

Here, Ivanovich et al. studied mouse embryos grown outside the womb by using a combination of advanced microscopy and genetic labeling to track how single cells turn into beating cells and move while the heart forms. The results showed that specializing into beating cells and forming the heart tube shape happened during alternating phases. The first heart-field cells turned into beating cells and began to contract at an early stage before the heart tube was formed. Next, the cells of the second heart field did not instantly develop into beating cells, but instead, helped the first heart-field cells to acquire the shape of a heart tube. Once this was completed, the second heart-field cells started to specialize into beating cells and created the additional parts of the more complex adult heart.

This research shows that the second heart field plays an active role in helping the heart tube form. The alternating phases of cell specialization and tissue formation allow the heart to become active whilst it is still developing. A better insight into how the heart forms may help us to create new treatments for various genetic heart conditions. The methods used here could also help to study how cells build other organs.

CIN and Aneuploidy: Different Concepts, Different Consequences

Chromosomal instability (CIN) and aneuploidy are similar concepts but not synonymous. CIN is the process that leads to chromosome copy number alterations, and aneuploidy is the result. While CIN and resulting aneuploidy often cause growth defects, they are also selected for in cancer cells. Although such contradicting fates may seem paradoxical at first, they can be better understood when CIN and aneuploidy are assessed separately, taking into account the in vitro or in vivo context, the rate of CIN, and severity of the aneuploid karyotype. As CIN can only be measured in living cells, which proves to be technically challenging in vivo, aneuploidy is more frequently quantified. However, CIN rates might be more predictive for tumor outcome than assessing aneuploidy rates alone. In reviewing the literature, we therefore conclude that there is an urgent need for new models in which we can monitor chromosome mis-segregation and its consequences in vivo. Also see the video abstract here: https://youtu.be/fL3LxZduchg.