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The production of blood cells during steady-state and increased demand depends on the regulation of hematopoietic stem cell (HSC) self-renewal and differentiation. Similarly, the balance between self-renewal and differentiation of leukemia stem cells (LSCs) is crucial in the pathogenesis of leukemia. Here, we document that the TNF receptor superfamily member lymphotoxin-β receptor (LTβR) and its ligand LIGHT regulate quiescence and self-renewal of murine and human HSCs and LSCs. Cell-autonomous LIGHT/LTβR signaling on HSCs reduces cell cycling, promotes symmetric cell division and prevents primitive HSCs from exhaustion in serial re-transplantation experiments and genotoxic stress. LTβR deficiency reduces the numbers of LSCs and prolongs survival in a murine chronic myeloid leukemia (CML) model. Similarly, LIGHT/LTβR signaling in human G-CSF mobilized HSCs and human LSCs results in increased colony forming capacity in vitro. Thus, our results define LIGHT/LTβR signaling as an important pathway in the regulation of the self-renewal of HSCs and LSCs., Regulation of self-renewal is critical during steady state and stress in haematpoietic stem cells (HSCs), and underlies leukaemia pathology. Here, the authors show that LIGHT and its receptor LTβR promote quiescence and self-renewal of HSCs and that LTβR deficiency promotes survival in a mouse leukaemia model.

Stem cells including cancer stem cells (CSC) divide symmetrically or asymmetrically. Usually symmetric cell division makes two daughter cells of the same fate, either as stem cells or more differentiated progenies; while asymmetric cell division (ACD) produces daughter cells of different fates. In this review, we first provide an overview of ACD, and then discuss more molecular details of ACD using the well- characterized Drosophila neuroblast system as an example. Aiming to explore the connections between cell heterogeneity in cancers and the critical need of ACD for self-renewal and generating cell diversity, we then examine how cell division symmetry control impacts common features associated with CSCs, including niche competition, cancer dormancy, drug resistance, epithelial-mesenchymal transition (EMT) and its reverse process mesenchymal-epithelial transition (MET), and cancer stem cell plasticity. As CSC may underlie resistance to therapy and cancer metastasis, understanding how cell division mode is selected and executed in these cells will provide possible strategies to target CSC.

Glioblastoma (GBM) is a malignant tumor with a high recurrence rate and has very poor prognosis in humans. The median survival is still

Stomatal differentiation manifests via several rounds of asymmetric cell division and a single symmetric cell division: the former, formative divisions amplify the number of epidermal cells, and the latter is essential for creating a functional guard cell pair. These cell division patterns are coordinated with progressive fate specification and cell-state transitional steps, which rely on the transcriptional regulation by a set of cell type-specific basic helix loop helix (bHLH) transcription factors. It has been proposed that the mechanisms underlying cell-fate decision and cell cycle progression are interconnected in a wide range of developmental processes. This review highlights the recent findings on how cell cycle regulators are transcriptionally regulated and contributing to each step of stomatal lineage progression.

Sensory experience influences proliferation and differentiation of oligodendrocyte progenitor cells (OPCs). Enhanced sensorimotor experience promoted the lineage progression of OPCs and myelination in the gray matter and white matter (WM) of sensorimotor cortex. In the visual cortex, reduced experience reportedly delayed the maturation of myelination in the gray matter, but whether and how such experience alters the subcortical WM is unclear. Here we investigated if binocular enucleation from the onset of eye opening (i.e., P15) affects the cell state of OPCs in mouse primary visual cortex (V1). Proliferative cells in the WM declined nearly half over 3 days from postnatal day (P) 25. A 3-day BrdU-labeling showed gradual decline in proliferation rates from P19 to P28. Binocular enucleation resulted in an increase in the cycling state of the OPCs that were proliferated from P22 to P25 but not before or after this period. This increase in proliferative OPCs was not associated with lineage progression toward differentiated oligodendrocytes. Proliferative OPCs arose mostly due to symmetric cell division but also asymmetric formation of proliferative and quiescent OPCs. By P30, almost all the proliferated cells exited the cell cycle. Maturing oligodendrocytes among the proliferated cells increased at this age, but most of them disappeared over 25 days. The cell density of the maturing oligodendrocytes was unaffected by binocular enucleation, however. These data suggest that binocular enucleation transiently elevates proliferative OPCs in the subcortical WM of V1 during a specific period of the fourth postnatal week without subsequently affecting the number of maturing oligodendrocytes several days later., Highlights • Binocular enucleation increased proliferative OPCs during P22-25 in the V1 WM. • Proliferative OPCs decrease in half from P25 over 3 days. • P22-25 proliferated cells nearly all exited the cell cycle by P30. • Some P22-25 proliferated OPCs matured over 5 days but disappeared over 25 days. • Visual loss did not influence oligodendrocyte maturation or its disappearance.

Industrial bioreactors use microbial organisms as living factories to produce a wide range of commercial products. For most applications, yields eventually become limited by the proliferation of "escape mutants" that acquire a growth advantage by losing the ability to make product. The goal of this work is to use mathematical models to determine whether this problem could be addressed in continuous flow bioreactors that include a "stem cell" population that multiplies rapidly and could be used to compete against the emergence of cheater mutants. In this system, external stimuli can be used to induce stem cell multiplication through symmetric cell division, or to limit stem cell multiplication and induce higher production through an asymmetric cell division that produces one stem cell and one new product-producing "factory cell". Our results show product yields from bioreactors with microbial stem cells can be increased by 18% to 127% over conventional methods, and sensitivity analysis shows that yields could be improved over a broad range of parameter space.

Asymmetric cell division (ACD) is an important physiological event in the development of various organisms and maintenance of tissue homeostasis. ACD produces two different cells in a single cell division: a stem/progenitor cell and differentiated cell. Although the balance between self-renewal and differentiation is precisely controlled, disruptions to ACD and/or enhancements in the self-renewal division (symmetric cell division: SCD) of stem cells resulted in the formation of tumors in Drosophila neuroblasts. ACD is now regarded as one of the characteristics of human cancer stem cells, and is a driving force for cancer cell heterogeneity. We recently reported that MYCN controls the balance between SCD and ACD in human neuroblastoma cells. In this mini-review, we discuss the mechanisms underlying MYCN-mediated cell division fate.

Coordination between cell differentiation and proliferation during development requires the balance between asymmetric and symmetric modes of cell division. However, the cellular intrinsic cue underlying the binary choice between these two division modes remains elusive. Here we show evidence inCaenorhabditis elegansthat the invariable lineage of the division modes is programmed by the balance between antagonizing complexes of partitioning-defective (PAR) proteins. By uncoupling unequal inheritance of PAR proteins from that of fate determinants during zygote division, we demonstrated that changes in the balance between PAR-2 and PAR-6 are sufficient to re-program the division modes from symmetric to asymmetric andvice versain two-cell stage embryos. The division mode adopted occurs independently of asymmetry in cytoplasmic fate determinants, cell-size asymmetry, and cell-cycle asynchrony between the sister cells. We propose that the balance between antagonizing PAR proteins represents an intrinsic self-organizing cue for binary specification of the division modes during development.

During neural development, stem and precursor cells can divide either symmetrically or asymmetrically. The transition between symmetric and asymmetric cell divisions is a major determinant of precursor cell expansion and neural differentiation, but the underlying mechanisms that regulate this transition are not well understood. Here, we identify the Sonic hedgehog (Shh) pathway as a critical determinant regulating the mode of division of cerebellar granule cell precursors (GCPs). Using partial gain and loss of function mutations within the Shh pathway, we show that pathway activation determines spindle orientation of GCPs, and that mitotic spindle orientation correlates with the mode of division. Mechanistically, we show that the phosphatase Eya1 is essential for implementing Shh-dependent GCP spindle orientation. We identify atypical protein kinase C (aPKC) as a direct target of Eya1 activity and show that Eya1 dephosphorylates a critical threonine (T410) in the activation loop. Thus, Eya1 inactivates aPKC, resulting in reduced phosphorylation of Numb and other components that regulate the mode of division. This Eya1-dependent cascade is critical in linking spindle orientation, cell cycle exit and terminal differentiation. Together these findings demonstrate that a Shh-Eya1 regulatory axis selectively promotes symmetric cell divisions during cerebellar development by coordinating spindle orientation and cell fate determinants.

Live-cell imaging has revolutionized our understanding of dynamic cellular processes in bacteria and eukaryotes. While similar techniques have recently been applied to the study of halophilic archaea, our ability to explore the cell biology of thermophilic archaea is limited, due to the technical challenges of imaging at high temperatures. Here, we report the construction of the Sulfoscope, a heated chamber that enables live-cell imaging on an inverted fluorescent microscope. Using this system combined with thermostable fluorescent probes, we were able to image Sulfolobus cells as they divide, revealing a tight coupling between changes in DNA compaction, segregation and cytokinesis. By imaging deletion mutants, we observe important differences in the function of the two ESCRTIII proteins recently implicated in cytokinesis. The loss of CdvB1 compromises cell division, causing occasional division failures and fusion of the two daughter cells, whereas the deletion of cdvB2 leads to a profound loss of division symmetry, generating daughter cells that vary widely in size and eventually generating ghost cells. These data indicate that DNA separation and cytokinesis are coordinated in Sulfolobus, as is the case in eukaryotes, and that two contractile ESCRTIII polymers perform distinct roles to ensure that Sulfolobus cells undergo a robust and symmetrical division. Taken together, the Sulfoscope has shown to provide a controlled high temperature environment, in which cell biology of Sulfolobus can be studied in unprecedent details.

Multicellularity evolved independently in multiple lineages, yielding organisms with a wide range of adult sizes. Building an intact soma is not a trivial task, when dividing cells accumulate damage. Here, we study ‘ontogenetic management strategies’, i.e. rules of dividing, differentiating and killing somatic cells, to examine two questions. First, do these rules evolve differently for organisms differing in the target mature body size, and second, how well a strategy evolved in small-bodied organisms performs if implemented in a large body – and vice versa (‘large’-evolved strategies in small bodies). We model the growth and mature lifespan of an organism starting from a single cell and optimize, using a genetic algorithm, trait combinations across a range of target sizes, with seven evolving traits: 1) probability of asymmetric division, 2) probability of differentiation (per symmetric cell division), 3) Hayflick limit, 4) damage response threshold, 5) damage response strength, 6) number of differentiation steps, 7) division propensity of cells relative to ‘stemness’. Some, but not all traits, evolve differently depending on body size: large-bodied organisms perform best with a smaller probability of differentiation, a larger number of differentiation steps on the way to form a tissue, and a higher threshold of cellular damage to trigger cell death, than small organisms. Strategies evolved in large organisms are more robust: they maintain high performance across a wide range of body sizes, while those that evolved in smaller organisms fail when attempting to create a large body. This highlights an asymmetry: under various risks of developmental failure and cancer, it is easier for a lineage to become miniaturized (should selection otherwise favour this) than to increase in size.

The bacterial cell cycle consists of a series of genetically coordinated biochemical and biophysical events. In Caulobacter crescentus, CtrA is an essential cell cycle regulator that modulates many cell cycle processes. In the present study, the role of the CtrA was investigated in Rhodobacter sphaeroides 2.4.1 by employing genetic, molecular, and bioinformatic approaches. Examination of the ctrA-null mutant revealed that the loss of CtrA did not affect growth characteristics and cell morphology in R. sphaeroides when grown under aerobic or photosynthetic growth conditions but slower growth was noticed in the anaerobic-dark-DMSO condition. Phylogenetic analyses demonstrated that CtrA has diversified its role in major lineages of α-Proteobacteria and has possibly been involved in adaptation to variable lifestyles. Analysis of the CtrA binding sites in the R. sphaeroides genome suggests that CtrA may regulate 127 genes involving different cellular processes. Protein homology searches revealed that only a small number of ctrA-regulated genes are homologous across C. crescentus, R. capsulatus, and R. sphaeroides. Comparison of the functions of putative ctrA-regulated genes in C. crescentus, R. capsulatus, and R. sphaeroides revealed that all three species possessed broad pathway control across a variety of cluster of orthologous gene functions (COGs). However, interestingly, it seems that the essentiality of CtrA in C. crescentus may depend more on the selective control that it exerts on a few critical cell cycle genes and pathways that are not controlled by CtrA in a similar fashion in R. capsulatus and R. sphaeroides.

Summary Radial glia-like (RGL) stem cells persist in the adult mammalian hippocampus, where they generate new neurons and astrocytes throughout life. The process of adult neurogenesis is well documented, but cell-autonomous factors regulating neuronal and astroglial differentiation are incompletely understood. Here, we evaluate the functions of the transcription factor zinc-finger E-box binding homeobox 1 (ZEB1) in adult hippocampal RGL cells using a conditional-inducible mouse model. We find that ZEB1 is necessary for self-renewal of active RGL cells. Genetic deletion of Zeb1 causes a shift toward symmetric cell division that consumes the RGL cell and generates pro-neuronal progenies, resulting in an increase of newborn neurons and a decrease of newly generated astrocytes. We identify ZEB1 as positive regulator of the ets-domain transcription factor ETV5 that is critical for asymmetric division., Graphical abstract, Highlights • The stem cell transcription factor, ZEB1, demarcates active from quiescent RGL cells • ZEB1 drives the self-renewal of RGL cells by promoting asymmetric cell division • Loss of Zeb1 causes increased neurogenesis and decreased astrogliogenesis • ZEB1 induces Etv5 expression to regulate asymmetric cell division, Gupta et al. show that the stem cell transcription factor, ZEB1, labels activated hippocampal stem cells and regulates their self-renewal and astroglial fate specification. Mechanistically, ZEB1 promotes asymmetric cell divisions and induces the expression of ETV5, a transcriptional regulator of asymmetric divisions and astroglial lineage commitment.

Coordination between cell differentiation and proliferation during development requires the balance between asymmetric and symmetric modes of cell division. However, the cellular intrinsic cue underlying the choice between these two division modes remains elusive. Here, we show evidence in Caenorhabditis elegans that the invariable lineage of the division modes is specified by the balance between antagonizing complexes of partitioning-defective (PAR) proteins. By uncoupling unequal inheritance of PAR proteins from that of fate determinants during cell division, we demonstrate that changes in the balance between PAR-2 and PAR-6 can be sufficient to re-program the division modes from symmetric to asymmetric and vice versa in two daughter cells. The division mode adopted occurs independently of asymmetry in cytoplasmic fate determinants, cell-size asymmetry, and cell-cycle asynchrony between sister cells. We propose that the balance between PAR proteins represents an intrinsic self-organizing cue for the specification of the two division modes during development.

Cancer stem-like cells (CSC) drive cancer progression and recurrence. Self-renewal expansion of CSC is achieved through symmetric cell division, yet how external stimuli affect intracellular regulatory programs of CSC division modes and stemness remains obscure. Here, we report that the hTERThigh prostate cancer cells exhibit CSC properties, including a stem cell–associated gene expression signature, long-term tumor-propagating capacity and epithelial-to-mesenchymal transition. In promoting the self-renewal symmetric division of hTERThigh prostate cancer cells, WNT3a dramatically decreased the ratio of hTERThigh prostate cancer cells undergoing asymmetric division. Increased WNT/β-catenin signal activation was also detected in hTERThigh prostate cancer cells. hTERT-mediated CSC properties were at least partially dependent on β-catenin. These findings provide novel cellular and molecular mechanisms for the self-renewal of CSC orchestrated by tumor microenvironmental stimuli and intracellular signals. Cancer Res; 77(9); 2534–47. ©2017 AACR.

Longitudinal bone growth in children is sustained by growth plates, narrow discs of cartilage that provide a continuous supply of chondrocytes for endochondral ossification1. However, it remains unknown how this supply is maintained throughout childhood growth. Chondroprogenitors in the resting zone are thought to be gradually consumed as they supply cells for longitudinal growth1,2, but this model has never been proved. Here, using clonal genetic tracing with multicolour reporters and functional perturbations, we demonstrate that longitudinal growth during the fetal and neonatal periods involves depletion of chondroprogenitors, whereas later in life, coinciding with the formation of the secondary ossification centre, chondroprogenitors acquire the capacity for self-renewal, resulting in the formation of large, stable monoclonal columns of chondrocytes. Simultaneously, chondroprogenitors begin to express stem cell markers and undergo symmetric cell division. Regulation of the pool of self-renewing progenitors involves the hedgehog and mammalian target of rapamycin complex 1 (mTORC1) signalling pathways. Our findings indicate that a stem cell niche develops postnatally in the epiphyseal growth plate, which provides a continuous supply of chondrocytes over a prolonged period. Clonal genetic tracing is used to demonstrate that, in mice, longitudinal bone growth during fetal and neonatal periods relies on the gradual consumption of chondroprogenitors, whereas in adults, a stem cell niche is formed allowing renewing of chondroprogenitors and leading to formation of large, stable monoclonal columns of chondrocytes.

During neural development, stem and precursor cells can divide either symmetrically or asymmetrically. The transition between symmetric and asymmetric cell divisions is a major determinant of precursor cell expansion and neural differentiation, but the underlying mechanisms that regulate this transition are not well understood. Here, we identify the Sonic hedgehog (Shh) pathway as a critical determinant regulating the mode of division of cerebellar granule cell precursors (GCPs). Using partial gain and loss of function mutations within the Shh pathway, we show that pathway activation determines spindle orientation of GCPs, and that mitotic spindle orientation directly correlates with the mode of division. Mechanistically, we show that the phosphatase Eya1 is essential for implementing Shh-dependent GCP spindle orientation. We identify atypical protein kinase C (aPKC) as a direct target of Eya1 activity and show that Eya1 dephosphorylates Threonine (T410) in the activation loop of this polarity complex component. Thus, Eya1 inactivates the cell polarity complex, resulting in reduced phosphorylation of Numb and other components that regulate the mode of division. This Eya1-dependent cascade is critical in linking spindle orientation, cell cycle exit and terminal differentiation. Together these findings demonstrate that a Shh-Eya1 regulatory axis selectively promotes symmetric cell divisions during cerebellar development by coordinating spindle orientation and cell fate determinants.Summary statementBiological responses to Shh signaling are specified by the magnitude of pathway activation and the cellular context. This study shows that potent Shh signaling regulates mitotic orientation and symmetric division of cerebellar granule cell precursors in a process that requires the phosphatase Eya1 and unequal distribution of cell fate determinants to daughter cells.

Summary Cancer is believed to arise from stem cells, but mechanisms that limit the acquisition of mutations and tumor development have not been well defined. We show that a +4 stem cell (SC) in the gastric antrum, marked by expression of Cck2r (a GPCR) and Delta-like ligand 1 (DLL1), is a label-retaining cell that undergoes predominant asymmetric cell division. This +4 antral SC is Notch1low/ Numb+ and repressed by signaling from gastrin-expressing endocrine (G) cells. Chemical carcinogenesis of the stomach is associated with loss of G cells, increased symmetric stem cell division, glandular fission, and more rapid stem cell lineage tracing, a process that can be suppressed by exogenous gastrin treatment. This hormonal suppression is associated with a marked reduction in gastric cancer mutational load, as revealed by exomic sequencing. Taken together, our results show that gastric tumorigenesis is associated with increased symmetric cell division that facilitates mutation and is suppressed by GPCR signaling.

Mitotic spindle orientation must be tightly regulated during development and adult tissue homeostasis. It determines cell-fate specification and tissue architecture during asymmetric and symmetric cell division, respectively. Here, we uncover a novel role for Ephrin–Eph intercellular signaling in controlling mitotic spindle alignment in Drosophila optic lobe neuroepithelial cells through aPKC activity–dependent myosin II regulation. We show that conserved core components of the mitotic spindle orientation machinery, including Discs Large1, Mud/NuMA, and Canoe/Afadin, mislocalize in dividing Eph mutant neuroepithelial cells and produce spindle alignment defects in these cells when they are down-regulated. In addition, the loss of Eph leads to a Rho signaling–dependent activation of the PI3K–Akt1 pathway, enhancing cell proliferation within this neuroepithelium. Hence, Eph signaling is a novel extrinsic mechanism that regulates both spindle orientation and cell proliferation in the Drosophila optic lobe neuroepithelium. Similar mechanisms could operate in other Drosophila and vertebrate epithelia., Our laboratory was supported by the Spanish grants from the Ministerio de Economia y Competitividad (BFU2012-33020 and BFU2015-64251) and by the European Regional Development Fund. The Instituto de Neurociencias in Alicante is a “Severo Ochoa” Center of Excellence.

Hutchinson-Gilford progeria syndrome (HGPS) is the result of a defective form of the lamin A protein called progerin. While progerin is known to disrupt the properties of the nuclear lamina, the underlying mechanisms responsible for the pathophysiology of HGPS remain less clear. Previous studies in our laboratory have shown that progerin expression in murine epidermal basal cells results in impaired stratification and halted development of the skin. Stratification and differentiation of the epidermis is regulated by asymmetric stem cell division. Here, we show that expression of progerin impairs the ability of stem cells to maintain tissue homeostasis as a result of altered cell division. Quantification of basal skin cells showed an increase in symmetric cell division that correlated with progerin accumulation in HGPS mice. Investigation of the mechanisms underlying this phenomenon revealed a putative role of Wnt/beta-catenin signaling. Further analysis suggested an alteration in the nuclear translocation of beta-catenin involving the inner and outer nuclear membrane proteins, emerin and nesprin-2. Taken together, our results suggest a direct involvement of progerin in the transmission of Wnt signaling and normal stem cell division. These insights into the molecular mechanisms of progerin may help develop new treatment strategies for HGPS.

The cancer stem cell (CSC) model has emerged as a prominent paradigm for explaining tumour heterogeneity. CSCs in tumour recurrence and drug resistance have also been implicated in a number of studies. In fact, CSCs are often identified by their expression of drug-efflux proteins which are also highly expressed in normal stem cells. Similarly, pro-survival or proliferation signalling often exhibited by stem cells is regularly reported as being upregulated by CSC. Here we review evidence suggesting that many aspects of CSCs are more readily described by clonal evolution. As an example, cancer cells often exhibit copy number gains of genes involved in drug-efflux proteins and pro-survival signalling. Consequently, clonal selection for stem cell traits may result in cancer cells developing "stemness" traits which impart a fitness advantage, without strictly following a CSC model. Finally, since symmetric cell division would give rise to more cells than asymmetric division, it is expected that more advanced tumours would depart from a CSC. Collectively, these observations suggest clonal evolution may explain many aspects of the CSC.

Cell division is a fundamental but complex process that gives rise to two daughter cells. It includes an ordered set of events, altogether called “the cell cycle”, that culminate with cytokinesis, the final stage of mitosis leading to the physical separation of the two daughter cells. Symmetric cell division equally partitions cellular components between the two daughter cells, which are therefore identical to one another and often share the same fate. In many cases, however, cell division is asymmetrical and generates two daughter cells that differ in specific protein inheritance, cell size, or developmental potential. The budding yeast Saccharomyces cerevisiae has proven to be an excellent system to investigate the molecular mechanisms governing asymmetric cell division and cytokinesis. Budding yeast is highly polarized during the cell cycle and divides asymmetrically, producing two cells with distinct sizes and fates. Many components of the machinery establishing cell polarization during budding are relocalized to the division site (i.e., the bud neck) for cytokinesis. In this review we recapitulate how budding yeast cells undergo polarized processes at the bud neck for cell division.

Controlled cell division is central to the growth and development of all multicellular organisms. Within the proliferating zone of the Arabidopsis root, regular symmetric divisions give rise to patterns of parallel files of cells, the genetic basis of which remains unclear. We found that genotypes impaired in the TONNEAU1a (TON1a) gene display misoriented symmetric divisions in the epidermis and have no division defects in the underlying cortical tissue. The TON1a gene encodes a microtubule-associated protein. We show that in the ton1a mutant, epidermal and cortical cells do not form narrow, ring-like preprophase bands (PPBs), which are plant-specific, cytoskeletal structures that predict the position of the division plane before mitosis. The results indicate that in the cortex but not in the epidermis, division plane positioning and patterning can proceed correctly in the absence of both a functional TON1a and PPB formation. Differences between tissues in how they respond to the signals that guide symmetric division orientation during patterning might provide the basis for organised organ growth in the absence of cell movements., Summary: Adjacent tissues have different requirements for the precise positioning of the division plane, which is mediated at the intracellular level by the preprophase band that controls the pattern of cell division.

International audience; Stem cells can be maintained through symmetric cell divisions (SCDs) and asymmetric cell divisions (ACDs). How and when these divisions occur in vivo in vertebrates is poorly understood. Here, we developed a clonogenic cell tracing method that demonstrates the asymmetric distribution of transcription factors along with old and new DNA in mouse muscle stem cells during skeletal muscle regeneration. Combining single-cell tracking and artificial niches ex vivo, we show how cells switch from ACDs to SCDs, suggesting that they are not engaged in an obligate mode of cell division. Further, we generated SNAP-tagged histone H3-reporter mice and find that, unlike fly germline stem cells, differential fate outcomes are associated with a symmetric distribution of the H3.1 and H3.3 histone variants in mouse muscle stem cells. This versatile and efficient H3-SNAP labeling system will allow an investigation of mechanisms underlying the maintenance of epigenomic identity and plasticity in a variety of tissues.; Les cellules souches peuvent être maintenues par des divisions cellulaires symétriques (DCS) et des divisions cellulaires asymétriques (DCA). On comprend mal comment et quand ces divisions se produisent in vivo chez les vertébrés. Ici, nous avons développé une méthode de traçage cellulaire clonogène qui démontre la distribution asymétrique des facteurs de transcription ainsi que de l'ADN ancien et nouveau dans les cellules souches de muscles de souris pendant la régénération des muscles squelettiques. En combinant le traçage d'une seule cellule et des niches artificielles ex vivo, nous montrons comment les cellules passent des ACD aux SCD, ce qui suggère qu'elles ne sont pas engagées dans un mode de division cellulaire obligatoire. En outre, nous avons généré des souris indicatrices d'histone H3 marquées par SNAP et nous avons découvert que, contrairement aux cellules souches germinales de mouches, les résultats différentiels du destin sont associés à une distribution symétrique des variantes d'histone H3.1 et H3.3 dans les cellules souches musculaires de souris. Ce système de marquage H3-SNAP polyvalent et efficace permettra d'étudier les mécanismes sous-jacents au maintien de l'identité et de la plasticité épigénomiques dans une variété de tissus.

The normal intestinal epithelium is continuously regenerated at a rapid rate from actively cycling Lgr5-expressing intestinal stem cells (ISCs) that reside at the crypt base. Recent mathematical modeling based on several lineage-tracing studies in mice shows that the symmetric cell division-dominant neutral drift model fits well with the observed in vivo growth of ISC clones and suggests that symmetric divisions are central to ISC homeostasis. However, other studies suggest a critical role for asymmetric cell division in the maintenance of ISC homeostasis in vivo. Here, we show that the stochastic branching and Moran process models with both a symmetric and asymmetric division mode not only simulate the stochastic growth of the ISC clone in silico but also closely fit the in vivo stem cell dynamics observed in lineage-tracing studies. In addition, the proposed model with highest probability for asymmetric division is more consistent with in vivo observations reported here and by others. Our in vivo studies of mitotic spindle orientations and lineage-traced progeny pairs indicate that asymmetric cell division is a dominant mode used by ISCs under normal homeostasis. Therefore, we propose the asymmetric cell division-dominant neutral drift model for normal ISC homeostasis.NEW & NOTEWORTHY The prevailing mathematical model suggests that intestinal stem cells (ISCs) divide symmetrically. The present study provides evidence that asymmetric cell division is the major contributor to ISC maintenance and thus proposes an asymmetric cell division-dominant neutral drift model. Consistent with this model, in vivo studies of mitotic spindle orientation and lineage-traced progeny pairs indicate that asymmetric cell division is the dominant mode used by ISCs under normal homeostasis.

International audience; The orientation of the mitotic spindle (MS) is tightly regulated, but the molecular mechanisms are incompletely understood. Here we report a novel role for the multifunctional adaptor protein ALG-2-interacting protein X (ALIX) in regulating MS orientation in addition to its well-established role in cytokinesis. We show that ALIX is recruited to the pericentriolar material (PCM) of the centrosomes and promotes correct orientation of the MS in asymmetrically dividing Drosophila stem cells and epithelial cells, and symmetrically dividing Drosophila and human epithelial cells. ALIX-deprived cells display defective formation of astral microtubules (MTs), which results in abnormal MS orientation. Specifically, ALIX is recruited to the PCM via Drosophila Spindle defective 2 (DSpd-2)/Cep192, where ALIX promotes accumulation of γ-tubulin and thus facilitates efficient nucleation of astral MTs. In addition, ALIX promotes MT stability by recruiting microtubule-associated protein 1S (MAP1S), which stabilizes newly formed MTs. Altogether, our results demonstrate a novel evolutionarily conserved role of ALIX in providing robustness to the orientation of the MS by promoting astral MT formation during asymmetric and symmetric cell division.

Symmetric cell division (SD) and asymmetric cell division (ASD) were the unique characteristics of stem cells and the mechanisms underlying stem cell renewal. While recent studies have identified the presence of SD and ASD in lung cancer stem cells (CSCs), the mechanisms regulating SD and ASD in cancer state have not been elucidated, mostly due to the lack of stable cellular models of SD and ASD in CSC research. In this study, the interaction between Zeb1, an Epithelial-Mesenchymal Transition (EMT) factor shown to regulate CSCs self-renew, and Numb, which regulates SD and ASD in the normal neural stem cell was investigated using the stable mouse Lewis lung adenocarcinoma SD (LLC-SD) and ASD (LLC-ASD) lines established from our previous study. The most significant finding derived from this line of research is that we have identified and molecularly ordered the axis of Zeb1-miR-31-Numb that regulates the SD, a mechanism of CSC self-renewal that has not been previously described. More specifically, the expression of Zeb1 and Numb were both significantly higher in LLC-SD than LLC-ASD cells. Silencing of Zeb1 or Numb expression lead to decreased ratio of SD and weakened single-cell cloning formation, tumor growth and tumor metastasis, respectively. The rescure experiments have molecularly ordered the regulation of Numb by Zeb1, indirectly mediated by miR-31. Moreover, we also provided preliminary evidence supporting the clinical relevance of our finding. In summary, our study provides a new insight for the self-renew of lung CSCs in which SD is regulated by the axis of Zeb1-miR-31-Numb.

Recently, several reports showed that about 80 % of mid-log phase Mycobacterium smegmatis, Mycobacterium marinum, and Mycobacterium bovis BCG cells divide symmetrically with 5–10 % deviation in the septum position from the median. However, the mode of cell division of the pathogenic mycobacterial species, Mycobacterium tuberculosis, remained unclear. Therefore, in the present study, using electron microscopy, fluorescence microscopy of septum- and nucleoid-stained live and fixed cells, and live cell time-lapse imaging, we show the occurrence of asymmetric cell division with unusually deviated septum/constriction in 20 % of the 15 % septating M. tuberculosis cells in the mid-log phase population. The remaining 80 % of the 15 % septating cells divided symmetrically but with 2–5 % deviation in the septum/constriction position, as reported for M. smegmatis, M. marinum, and M. bovis BCG cells. Both the long and the short portions of the asymmetrically dividing M. tuberculosis cells with unusually deviated septum contained nucleoids, thereby generating viable short and long cells from each asymmetric division. M. tuberculosis short cells were acid fast positive and, like the long cells, further readily underwent growth and division to generate micro-colony, thereby showing that they were neither mini cells, spores nor dormant forms of mycobacteria. The freshly diagnosed pulmonary tuberculosis patients’ sputum samples, which are known for the prevalence of oxidative stress conditions, also contained short cells at the same proportion as that in the mid-log phase population. The probable physiological significance of the generation of the short cells through unusually deviated asymmetric cell division is discussed.

BACKGROUND: Formation of stomatal complexes in Poaceae is the outcome of three asymmetric and one symmetric cell division occurring in particular leaf protodermal cells. In this definite sequence of cell division events, the generation of subsidiary cells is of particular importance and constitutes an attractive model for studying local intercellular stimulation. In brief, an induction stimulus emitted by the guard cell mother cells (GMCs) triggers a series of polarization events in their laterally adjacent protodermal cells. This signal determines the fate of the latter cells, forcing them to divide asymmetrically and become committed to subsidiary cell mother cells (SMCs). SCOPE: This article summarizes old and recent structural and molecular data mostly derived from Zea mays, focusing on the interplay between GMCs and SMCs, and on the unique polarization sequence occurring in both cell types. Recent evidence suggests that auxin operates as an inducer of SMC polarization/asymmetric division. The intercellular auxin transport is facilitated by the distribution of a specific transmembrane auxin carrier and requires reactive oxygen species (ROS). Interestingly, the local differentiation of the common cell wall between SMCs and GMCs is one of the earliest features of SMC polarization. Leucine-rich repeat receptor-like kinases, Rho-like plant GTPases as well as the SCAR/WAVE regulatory complex also participate in the perception of the morphogenetic stimulus and have been implicated in certain polarization events in SMCs. Moreover, the transduction of the auxin signal and its function are assisted by phosphatidylinositol-3-kinase and the products of the catalytic activity of phospholipases C and D. CONCLUSION: In the present review, the possible role(s) of each of the components in SMC polarization and asymmetric division are discussed, and an overall perspective on the mechanisms beyond these phenomena is provided.

Background: The stem cell factor receptor (SCFR) has been demonstrated to be expressed in the neural retina of mice, rat, and human for decades. Previous reports indicate that SCFR correlates with glia differentiation of late retinal progenitor cells, retinal vasculogenesis, and homeostasis of the blood-retinal barrier. However, the role of SCF/SCFR signaling in the growth and development of the neural retina (NR), especially in the early embryonic stage, remains poorly understood. Methods: Human optic cup (OC) cultures were generated from human embryonic stem cells (hESCs) with SFEBq method. The angle between retinal pigment epithelium (RPE) and NR, the axial length of OC, and the length of the ciliary marginal zone (CMZ) were measured. Proliferation, mechanical dynamic, and cellular migration were assessed with BrdU labeling and quantitative immunofluorescence. Findings: We show that the SCF/SCFR signaling orchestrates invagination of the NR via regulation of symmetric cell division, cytoskeleton dynamic, and apical constriction of retinal progenitor cells in the CMZ. Furthermore, activation of SCF/SCFR signaling enhances neurogenesis in the central-most NR via accelerating the migration of immature ganglion cells. Interpretation: Our study reveals an important role of SCF/SCFR signaling in controlling ciliary marginal cellular behaviors during early morphogenesis and neurogenesis of the human embryonic NR, providing a new potential therapeutic target for human congenital eye diseases such as anophthalmia, microphthalmia, and congenital high myopia. Funding Statement: This study was supported by the National Key R&D program of China (2018YFA01017302), National Basic Research Program of China (2013CB967002) and National Natural Science Foundation of China (81873688). Declaration of Interests: All authors declare no competing interests. Ethics Approval Statement: All experiments were performed in accordance with the guidelines of the Ethics Committee of Southwest Hospital, The Army Medical University.

How cells ensure symmetric inheritance Parental histones with modifications are recycled to newly replicated DNA strands during genome replication, but do the two sister chromatids inherit modified histones equally? Yu et al. and Petryk et al. found in mouse and yeast, respectively, that modified histones are segregated to both DNA daughter strands in a largely symmetric manner (see the Perspective by Ahmad and Henikoff). However, the mechanisms ensuring this symmetric inheritance in yeast and mouse were different. Yeasts use subunits of DNA polymerase to prevent the lagging-strand bias of parental histones, whereas in mouse cells, the replicative helicase MCM2 counters the leading-strand bias. Science , this issue p. 1386 , p. 1389 ; see also p. 1311

Emerging data implicates ubiquitination, a post-translational modification, in regulating essential cellular events, one of them being mitosis. In this review we discuss how various E3 ligases modulate the cortical proteins such as dynein, LGN, NuMa, Gα, along with polymerization, stability, and integrity of spindles. These are responsible for regulating symmetric cell division. Some of the ubiquitin ligases regulating these proteins include PARK2, BRCA1/BARD1, MGRN1, SMURF2, and SIAH1; these play a pivotal role in the correct positioning of the spindle apparatus. A direct connection between developmental or various pathological disorders and the ubiquitination mediated cortical regulation is rather speculative, though deletions or mutations in them lead to developmental disorders and disease conditions.

The mechanisms of asymmetric organ development have been under intensive investigation for years, yet the proposed mechanisms remain controversial (1-3). The female Bruchus quadrimaculatus beetle insect develops two black-colored spots bilaterally located on each upper elytra wing by an unknown mechanism. Fifty percent of the P (for piebald, two colors) gene homozygous mutant insects, described in 1925, had a normal left elytrum (with two black spots) and an abnormal right elytrum (with two red spots) and the balance supported the converse lateralized pigment arrangement (4). Rather than supporting the conventional morphogen model for the wings pigmentation development, their biological origin is explained here with the somatic strand-specific epigenetic imprinting and selective sister chromatid segregation (SSIS) mechanism (5). We propose that the P gene product performs the selective sister chromatid segregation function to produce symmetric cell division of a specific cell during embryogenesis to result in the bilateral symmetric development of elytra black color spots and that the altered chromatid segregation pattern of the mutant causes asymmetric cell division to confer the piebald phenotype.

Glioblastoma is an aggressive primary malignancy of the brain with almost 100% recurrence rate. Our lab and others have shown that GBM contains a subpopulation of glioma stem cells (GSCs) that may drive the therapeutic resistance capabilities of recurrent GBM. We have shown that the GSC population expands following administration of temozolomide (TMZ). While it has been suggested that this expansion relies solely on Darwinian selection, we and others have demonstrated that cellular plasticity-driven expansion of therapy resistance GSCs post-therapy may play a role in disease recurrence. GSCs can divide in three ways: (1) asymmetric division, which produces one GSC and one differentiated cancer cell, (2) symmetric division that promotes self-renewal by forming two daughter GSCs or (3) symmetric division that supports differentiation by forming two mature cancer cells. Here, we show that symmetric self-renewing cell division—where one GSC gives rise to two daughter GSCs—occurs at a rate of 24% in GBM cells treated with control vehicle, yet at a rate of 54% following TMZ therapy (p

Primary microcephaly (MCPH) is an autosomal recessive disorder characterized by congenital reduction of head circumference. Here, we identified compound heterozygous mutations c.731 C > T (p.Ser 244 Leu) and c.2413 G > T (p.Glu 805 X) in the WDR62/MCPH2 gene, which encodes the mitotic centrosomal protein WDR62, in two siblings in a Japanese family with microcephaly using whole-exome sequencing. However, the molecular and cellular pathology of microcephaly caused by WDR62/MCPH2 mutation remains unclear. To clarify the physiological role of WDR62, we used the CRISPR/Cas9 system and single-stranded oligonucleotides as a point-mutation-targeting donor to generate human cell lines with knock-in of WDR62/MCPH2 c.731 C > T (p.Ser 244 Leu) missense mutation. In normal metaphase, the mitotic spindle forms parallel to the substratum to ensure symmetric cell division, while WDR62/MCPH2-mutated cells exhibited a randomized spindle orientation caused by the impaired astral microtubule assembly. It was shown that a mitotic kinase, Polo-like kinase 1 (PLK1), is required for the maintenance of spindle orientation through astral microtubule development. In this study, we demonstrated that WDR62 is a PLK1 substrate that is phosphorylated at Ser 897, and that this phosphorylation at the spindle poles promotes astral microtubule assembly to stabilize spindle orientation. Our findings provide insights into the role of the PLK1-WDR62 pathway in the maintenance of proper spindle orientation.

A general view is that Schizosaccharomyces pombe undergoes symmetric cell division with two daughter cells inheriting equal shares of the content from the mother cell. Here we show that CTP synthase, a metabolic enzyme responsible for the de novo synthesis of the nucleotide CTP, can form filamentous cytoophidia in the cytoplasm and nucleus of S. pombe cells. Surprisingly, we observe that both cytoplasmic and nuclear cytoophidia are asymmetrically inherited during cell division. Our time-lapse studies suggest that cytoophidia are dynamic. Once the mother cell divides, the cytoplasmic and nuclear cytoophidia independently partition into one of the two daughter cells. Although the two daughter cells differ from one another morphologically, they possess similar chances of inheriting the cytoplasmic cytoophidium from the mother cell, suggesting that the partition of cytoophidium is a stochastic process. Our findings on asymmetric inheritance of cytoophidia in S. pombe offer an exciting opportunity to study the inheritance of metabolic enzymes in a well-studied model system.

Stem cells subserve repair functions for the lifetime of the organism but, as a consequence of this responsibility, are candidate cells for accumulating numerous genetic and/or epigenetic aberrations leading to malignant transformation. However, given the importance of this guardian role, stem cells likely harbor some process for maintaining their precious genetic code such as non-random segregation of chromatid strands as predicted by the Immortal Strand Hypothesis (ISH). Discerning such non-random chromosomal segregation and asymmetric cell division in normal or cancer stem cells has been complicated by methodological shortcomings but also by differing division kinetics amongst tissues and the likelihood that both asymmetric and symmetric cell divisions, dictated by local extrinsic factors, are operant in these cells. Recent data suggest that cancer stem cells demonstrate a higher incidence of symmetric versus asymmetric cell division with both daughter cells retaining self-renewal characteristics, a profile which may underlie poorly differentiated morphology and marked clonal diversity in tumors. Pathways and targets are beginning to emerge which may provide opportunities for preventing such a predilection in cancer stem cells and that will hopefully translate into new classes of chemotherapeutics in oncology. Thus, although the existence of the ISH remains controversial, the shift of cell division dynamics to symmetric random chromosome segregation/self-renewal, which would negate any likelihood of template strand retention, appears to be a surrogate marker for the presence of highly malignant tumorigenic cell populations.

In the mouse the first Hematopoietic Stem Cell (HSC) is detected by transplantation at embryonic day E10.5. HSC emerge in the Aorta-Gonad-Mesonephros Region and migrate to the Fetal Liver (FL) where they supposedly expand dramatically (about 20-fold) between day E12.5-E15.5. HSC then migrate to the Bone Marrow (BM), where they predominantly reside in adult life. We recently reported that lifelong hematopoiesis is established by hundreds of blood precursors throughout mouse ontogeny (Ganuza et al., NCB 2017). Our novel non-invasive approach (based on the inducible multi-color ROSA26Confetti reporter) has allowed us to re-interrogate the clonal dynamics of blood precursors during steady-state without perturbing embryogenesis or using transplantation as a read-out for HSC potential. Here, we applied this approach to interrogate the clonal dynamics of embryonic (E14-E19) and neonatal (P1-P21) hematopoietic precursors. Towards this, Confetti labeling of blood progenitors at discrete stages of development was induced by treating ROSA26(+/Confetti) Ubiquitin(+/ERT2-Cre) (UbiqERT2-Cre) embryos or neonates with tamoxifen at E12-E14, E15-E17, P1, P8-P9, P14-15 or P21-P22. In contrast to previous dogma, we failed to detect a 20-fold expansion in the number of blood precursors during the presumed FL expansion period. Rather, between E11.5 and E15.5 we observed a three-fold expansion in blood precursors that contribute to adult peripheral blood. This was followed by a two-fold expansion in these same precursors between E15.5 and P1 and a 1.5-fold expansion between P1 and P8. These results contribute to our understanding of the precise developmental windows (and presumably niches) that support the symmetric cell division of HSCs.

Summary The metabolic properties of leukemia-initiating cells (LICs) in distinct bone marrow niches and their relationships to cell-fate determinations remain largely unknown. Using a metabolic imaging system with a highly responsive genetically encoded metabolic sensor, SoNar, we reveal that SoNar-high cells are more glycolytic, enriched for higher LIC frequency, and develop leukemia much faster than SoNar-low counterparts in an MLL-AF9-induced murine acute myeloid leukemia model. SoNar-high cells mainly home to and locate in the hypoxic endosteal niche and maintain their activities through efficient symmetric division. SoNar can indicate the dynamics of metabolic changes of LICs in the endosteal niche. SoNar-high human leukemia cells or primary samples have enhanced clonogenic capacities in vitro or leukemogenesis in vivo. PDK2 fine-tunes glycolysis, homing, and symmetric division of LICs. These findings provide a unique angle for the study of metabolisms in stem cells, and may lead to development of novel strategies for cancer treatment.

© 2019 Elsevier Inc. The nature of cell-state transitions during the transit-amplifying phases of many developmental processes—hematopoiesis in particular—is unclear. Here, we use single-cell RNA sequencing to demonstrate a continuum of transcriptomic states in committed transit-amplifying erythropoietic progenitors, which correlates with a continuum of proliferative potentials in these cells. We show that glucocorticoids enhance erythrocyte production by slowing the rate of progression through this developmental continuum of transit-amplifying progenitors, permitting more cell divisions prior to terminal erythroid differentiation. Mechanistically, glucocorticoids prolong expression of genes that antagonize and slow induction of genes that drive terminal erythroid differentiation. Erythroid progenitor daughter cell pairs have similar transcriptomes with or without glucocorticoid stimulation, indicating largely symmetric cell division. Thus, the rate of progression along a developmental continuum dictates the absolute number of erythroid cells generated from each transit-amplifying progenitor, suggesting a paradigm for regulating the total output of differentiated cells in numerous other developmental processes. Li et al. utilize single-cell RNA-seq and functional assays to demonstrate erythropoiesis progresses through a continuum of both transcriptomic and phenotypic states. Perturbation of developmental progression through this continuum with glucocorticoid steroids reveals differentiation speed can be uncoupled from cell-cycle progression, generating greater numbers of erythrocytes.

Substantial evidence supports the concept that cancers are organized in a cellular hierarchy with cancer stem cells (CSC) at the apex. To date, the primary evidence for CSCs derives from transplantation assays, which have known limitations. In particular, they are unable to report on the fate of cells within the original human tumor. Because of the difficulty in measuring tumor characteristics in patients, cellular organization and other aspects of cancer dynamics have not been quantified directly, although they likely play a fundamental role in tumor progression and therapy response. As such, new approaches to study CSCs in patient-derived tumor specimens are needed. In this study, we exploited ultradeep single-molecule genomic data derived from multiple microdissected colorectal cancer glands per tumor, along with a novel quantitative approach to measure tumor characteristics, define patient-specific tumor profiles, and infer tumor ancestral trees. We show that each cancer is unique in terms of its cellular organization, molecular heterogeneity, time from malignant transformation, and rate of mutation and apoptosis. Importantly, we estimate CSC fractions between 0.5% and 4%, indicative of a hierarchical organization responsible for long-lived CSC lineages, with variable rates of symmetric cell division. We also observed extensive molecular heterogeneity, both between and within individual cancer glands, suggesting a complex hierarchy of mitotic clones. Our framework enables the measurement of clinically relevant patient-specific characteristics in vivo, providing insight into the cellular organization and dynamics of tumor growth, with implications for personalized patient care. Cancer Res; 73(1); 41–49. ©2012 AACR.

Objective: Stem-like cancer cells contribute to cancer initiation and maintenance. Stem cells can self-renew by asymmetric cell division (ACD). ACD with non-random chromosomal cosegregation (ACD-NRCC) is one possible self-renewal mechanism. There is a paucity of evidence supporting ACD-NRCC in human cancer. Our aim was to investigate ACD-NRCC and its potential interactions with the cancer niche (microenvironment) in gastrointestinal cancers. Design: We used DNA double and single labeling approaches with FACS to isolate live cells undergoing ACD-NRCC. Results: Gastrointestinal cancers contain rare subpopulations of cells capable of ACD-NRCC. ACD-NRCC was detected preferentially in subpopulations of cells previously suggested to be stem-like/tumor-initiating cancer cells. ACD-NRCC was independent of cell-to-cell contact, and was regulated by the cancer niche in a heat-sensitive paracrine fashion. Wnt pathway genes and proteins are differentially expressed in cells undergoing ACD-NRCC vs. symmetric cell division. Blocking the Wnt pathway with IWP2 (WNT antagonist) or siRNA-TCF4 resulted in suppression of ACD-NRCC. However, using a Wnt-agonist did not increase the relative proportion of cells undergoing ACD-NRCC. Conclusion: Gastrointestinal cancers contain subpopulations of cells capable of ACD-NRCC. Here we show for the first time that ACD-NRCC can be regulated by the Wnt pathway, and by the cancer niche in a paracrine fashion. However, whether ACD-NRCC is exclusively associated with stem-like cancer cells remains to be determined. Further study of these findings might generate novel insights into stem cell and cancer biology. Targeting the mechanism of ACD-NRCC might engender novel approaches for cancer therapy.

Airway basal cells are quiescent at steady state but robustly activate and proliferate to repair damaged epithelium in response to injury. However little is known about the molecular mechanisms underlying this process. We previously reported that the TAM receptor tyrosine kinase Axl negatively regulates epithelial differentiation of human lung tissue-derived multi-potent cells in vitro (Eur Respir J 2013 42:P3138 ). To investigate the role of Axl kinase in regulation of airway stem cell function in vivo , we firstly determined cell-types expressing Axl in murine airway epithelium. Histological examination revealed that Axl kinase was expressed by basal cells but not by other luminal cells such as secretory cells and ciliated cells. qRT-PCR confirmed this exclusive expression of Axl mRNA in basal cells. Next, we sought to define the function of Axl on airway basal cells in response to injury. Intra-nasal administration of H1N1/PR8 influenza A virus increased Ki67+ cycling airway basal cells and this increase was attenuated in Axl-deficient mice. We also observed that basal cells undergoing asymmetric cell division increased in Axl-deficient mice during the influenza-induced injury. Consistently, basal cell spheroids at a 2-cell stage generated from trachea of Axl-deficient mice showed more differentiating phenotypes ex vivo compared to wild-type mice. Consequently ciliated cells regeneration was more evident in a resolution phase of the in vivo influenza-injury model. Taken together these data suggest that Axl regulates basal cell expansion by promoting cell cycle re-entry and symmetric cell division in response to injury.

Source at http://dx.doi.org/10.1016/j.jtbi.2016.11.030 A model of haematopoiesis that links self-organisation with symmetric and asymmetric cell division is presented in this paper. It is assumed that all cell divisions are completely random events, and that the daughter cells resulting from symmetric and asymmetric stem cell divisions are, in general, phenotypically identical, and still, the haematopoietic system has the flexibility to self-renew, produce mature cells by differentiation, and regenerate undifferentiated and differentiated cells when necessary, due to self-organisation. As far as we know, no previous model implements symmetric and asymmetric division as the result of self-organisation. The model presented in this paper is inspired by experiments on the Drosophila germline stem cell, which imply that under normal conditions, the stem cells typically divide asymmetrically, whereas during regeneration, the rate of symmetric division increases. Moreover, the model can reproduce several of the results from experiments on female Safari cats. In particular, the model can explain why significant fluctuation in the phenotypes of haematopoietic cells was observed in some cats, when the haematopoietic system had reached normal population level after regeneration. To our knowledge, no previous model of haematopoiesis in Safari cats has captured this phenomenon.

Evidence is presented for dynamic cortical association of dynein and dynactin in mammalian cells and its regulation by Plk1, astral microtubules, and the cell cycle. The asymmetric spindle positioning in LLC-Pk1 cells and its correction by dynein and dynactin provide a new system for analysis of spindle position and symmetric cell division., In cultured mammalian cells, how dynein/dynactin contributes to spindle positioning is poorly understood. To assess the role of cortical dynein/dynactin in this process, we generated mammalian cell lines expressing localization and affinity purification (LAP)–tagged dynein/dynactin subunits from bacterial artificial chromosomes and observed asymmetric cortical localization of dynein and dynactin during mitosis. In cells with asymmetrically positioned spindles, dynein and dynactin were both enriched at the cortex distal to the spindle. NuMA, an upstream targeting factor, localized asymmetrically along the cell cortex in a manner similar to dynein and dynactin. During spindle motion toward the distal cortex, dynein and dynactin were locally diminished and subsequently enriched at the new distal cortex. At anaphase onset, we observed a transient increase in cortical dynein, followed by a reduction in telophase. Spindle motion frequently resulted in cells entering anaphase with an asymmetrically positioned spindle. These cells gave rise to symmetric daughter cells by dynein-dependent differential spindle pole motion in anaphase. Our results demonstrate that cortical dynein and dynactin dynamically associate with the cell cortex in a cell cycle–regulated manner and are required to correct spindle mispositioning in LLC-Pk1 epithelial cells.

Glial cells are essential for the development and function of the nervous system. In the mammalian brain, vast numbers of glia of several different functional types are generated during late embryonic and early foetal development. However, the molecular cues that instruct gliogenesis and determine glial cell type are poorly understood. During post-embryonic development, the number of glia in the Drosophila larval brain increases dramatically, potentially providing a powerful model for understanding gliogenesis. Using glial-specific clonal analysis we find that perineural glia and cortex glia proliferate extensively through symmetric cell division in the post-embryonic brain. Using pan-glial inhibition and loss-of-function clonal analysis we find that Insulin-like receptor (InR)/Target of rapamycin (TOR) signalling is required for the proliferation of perineural glia. Fibroblast growth factor (FGF) signalling is also required for perineural glia proliferation and acts synergistically with the InR/TOR pathway. Cortex glia require InR in part, but not downstream components of the TOR pathway, for proliferation. Moreover, cortex glia absolutely require FGF signalling, such that inhibition of the FGF pathway almost completely blocks the generation of cortex glia. Neuronal expression of the FGF receptor ligand Pyramus is also required for the generation of cortex glia, suggesting a mechanism whereby neuronal FGF expression coordinates neurogenesis and cortex gliogenesis. In summary, we have identified two major pathways that control perineural and cortex gliogenesis in the post-embryonic brain and have shown that the molecular circuitry required is lineage specific.

In Escherichia coli, the pole-to-pole oscillation of the Min proteins directs septum formation to midcell, which is required for symmetric cell division. In vitro, protein waves emerge from the self-organization of MinD, a membrane-binding ATPase, and its activator MinE. For wave propagation, the proteins need to cycle through states of collective membrane binding and unbinding. Although MinD presumably undergoes cooperative membrane attachment, it is unclear how synchronous detachment is coordinated. We used confocal and single-molecule microscopy to elucidate the order of events during Min wave propagation. We propose that protein detachment at the rear of the wave, and the formation of the E-ring, are accomplished by two complementary processes: first, local accumulation of MinE due to rapid rebinding, leading to dynamic instability; and second, a structural change induced by membrane-interaction of MinE in an equimolar MinD-MinE (MinDE) complex, which supports the robustness of pattern formation.

Stem cells use asymmetric and symmetric cell division to generate progeny. Symmetric cell division is defined as the generation of daughter cells that are destined to acquire the same fate. Stem cells divide asymmetrically to generate one daughter with a stem-cell fate and one daughter with different fate. Disruption of the machinery that regulates asymmetric division may be a reason for the generation of cancer. The asymmetric mechanism is maintained by cell polarity factors, cell fate determinants, and the spindle apparatus. The mutation or dysregulation of these factors may change stem cells from asymmetric to symmetric cell division, then leading to tumorigenesis. Therefore, further study is needed on the mechanisms of stem cell control between asymmetric and symmetric cell division, as well as the relationships among stem cells, cancer stem cells, and tumor cells. It may bring us a new approach for the resistance, recurrence, and metastasis of tumors.

We describe the use of DNA transposons as tools for carrying out functional screenings in murine embryonic stem (ES) cell-derived neural stem (NS) cells. NS cells are a new type of stem cells featuring radial glial properties, that undergoes symmetric cell division for an indefinite number of passages, expanding as a monolayer. In this model, the previously unreported Sleeping Beauty transposase M3A achieves an optimal blend of clone generation efficiency and low redundancy of integrations per clone, compared to the SB100X Sleeping Beauty variant and to the piggyBac transposon. The technology described here makes it possible to randomly trap genes in the NS cell genome and modify their expression or tag them with fluorescent markers and selectable genes, allowing recombinant cells to be isolated and expanded clonally. This approach will facilitate the identification of novel determinants of stem cell biology and neural cell fate specification in NS cells.