Daughter Cell Fate Research Articles

All are equal, but some are more equal than others: Epigenetic regulation of germline stem cell fate in <i>Drosophila</i> <i>melanogaster</i>

Adult stem cells are capable of both symmetric and asymmetric cell divisions. Asymmetric cell division allows self-renewal and gives rise to intermediate cells that ultimately differentiate into specific cell types. Consequently, adult stem cells play a key role in development and tissue homeostasis during the life span of an organism. Typically, adult stem cell divisions are regulated through coordination between non-autonomous signaling from the niche and cell-autonomous influences from stem cell-intrinsic factors. Although localized distribution of proteins, RNA and organelles during cell division contributes significantly to the differences between fates of daughter cells, recent studies have also implicated epigenetic factors in this process. A number of epigenetic modifications remain associated with the chromosomes during mitosis and serve as a template to reestablish fates after mitosis. Whether the distribution of epigenetic modifications is random on each chromatid or there is a bias in their distribution is therefore under extensive investigation. The nonrandom distribution of epigenetic modifications on mitotic chromosomes provides an attractive possible explanation of how bias is generated during chromatid segregation. In Drosophila male germline stem cells, the histone modifications present in the stem cells are distinct from those in the differentiating daughter cells. These modifications help to retain pre-existing histones in the mother cell while imparting newly synthesized histones to the daughter cell. Importantly, the retention of pre-existing histones in the stem cells is a prerequisite to maintain their ability to self-renew. Here we summarize recent studies that focus on the role of different epigenetic modifications in the regulation of asymmetric adult germline stem cell divisions in Drosophila. We further describe how epigenetic modifications potentially lead to variations in the otherwise equivalent chromatids, and discuss the role of biased chromatid segregation in asymmetric cell divisions.

The Spindle Orientation Machinery Beyond Mitosis: When Cell Specialization Demands Polarization.

Mitosis is a process requiring strict spatial organization of cellular components. In particular, the orientation of the mitotic spindle with respect to the tissue defines the division plane. In turn, the orientation of cell division can regulate tissue morphology or the fate of daughter cells. While we have learned much about the mechanisms of mitotic spindle orientation, recent studies suggest that the proteins implicated can also play important roles in post-mitotic cells. Interestingly, post-mitotic protein function often involves polarizing the cell cytoskeleton during differentiation, mirroring its ability to orient the mitotic spindle during division. This review focuses on alternative functions of the spindle orientation machinery after division, when the cell undergoes a specialization process associated with differentiation or mature function, and discusses diseases associated to those alternative functions.

Molecular mechanisms of asymmetric divisions in mammary stem cells.

Stem cells have the remarkable ability to undergo proliferative symmetric divisions and self-renewing asymmetric divisions. Balancing of the two modes of division sustains tissue morphogenesis and homeostasis. Asymmetric divisions of Drosophila neuroblasts (NBs) and sensory organ precursor (SOP) cells served as prototypes to learn what we consider now principles of asymmetric mitoses. They also provide initial evidence supporting the notion that aberrant symmetric divisions of stem cells could correlate with malignancy. However, transferring the molecular knowledge of circuits underlying asymmetry from flies to mammals has proven more challenging than expected. Several experimental approaches have been used to define asymmetry in mammalian systems, based on daughter cell fate, unequal partitioning of determinants and niche contacts, or proliferative potential. In this review, we aim to provide a critical evaluation of the assays used to establish the stem cell mode of division, with a particular focus on the mammary gland system. In this context, we will discuss the genetic alterations that impinge on the modality of stem cell division and their role in breast cancer development.

Protein S Regulates Neural Stem Cell Quiescence and Neurogenesis.

Neurons are continuously produced in brains of adult mammalian organisms throughout life-a process tightly regulated to ensure a balanced homeostasis. In the adult brain, quiescent Neural Stem Cells (NSCs) residing in distinct niches engage in proliferation, to self-renew and to give rise to differentiated neurons and astrocytes. The mechanisms governing the intricate regulation of NSC quiescence and neuronal differentiation are not completely understood. Here, we report the expression of Protein S (PROS1) in adult NSCs, and show that genetic ablation of Pros1 in neural progenitors increased hippocampal NSC proliferation by 47%. We show that PROS1 regulates the balance of NSC quiescence and proliferation, also affecting daughter cell fate. We identified the PROS1-dependent downregulation of Notch1 signaling to correlate with NSC exit from quiescence. Notch1 and Hes5 mRNA levels were rescued by reintroducing Pros1 into NCS or by supplementation with purified PROS1, suggesting the regulation of Notch pathway by PROS1. Although Pros1-ablated NSCs show multilineage differentiation, we observed a 36% decrease in neurogenesis, coupled with a similar increase in astrogenesis, suggesting PROS1 is instructive for neurogenesis, and plays a role in fate determination, also seen in aged mice. Rescue experiments indicate PROS1 is secreted by NSCs and functions by a NSC-endogenous mechanism. Our study identifies a duple role for PROS1 in stem-cell quiescence and as a pro-neurogenic factor, and highlights a unique segregation of increased stem cell proliferation from enhanced neuronal differentiation, providing important insight into the regulation and control of NSC quiescence and differentiation. Stem Cells 2017;35:679-693.

Asymmetric cell division in plants: mechanisms of symmetry breaking and cell fate determination.

Asymmetric cell division is a fundamental mechanism that generates cell diversity while maintaining self-renewing stem cell populations in multicellular organisms. Both intrinsic and extrinsic mechanisms underpin symmetry breaking and differential daughter cell fate determination in animals and plants. The emerging picture suggests that plants deal with the problem of symmetry breaking using unique cell polarity proteins, mobile transcription factors, and cell wall components to influence asymmetric divisions and cell fate. There is a clear role for altered auxin distribution and signaling in distinguishing two daughter cells and an emerging role for epigenetic modifications through chromatin remodelers and DNA methylation in plant cell differentiation. The importance of asymmetric cell division in determining final plant form provides the impetus for its study in the areas of both basic and applied science.

In Utero Electroporation(IUE) and mouse genetic model approach to assess PITP‐dependent inositol lipid signaling in NSC pool maintenance in embryonic brain

Inositol (Ins) and phosphoinositide (PIP) signaling pathways are major intracellular regulatory systems of eukaryotic cells. Phosphatidylinositol transfer proteins (PITPs) execute novel modes of inositol lipid signal control by tightly channeling PIP production to specific biological outcomes. PITPα and PITPβ are highly expressed in mouse embryonic neocortex. We exploit an in utero electroporation approach to investigate the role of PITP‐dependent inositol lipid signaling in the embryonic neural stem cell (NSC) pool. We found that the combination of a PITPα null mouse line and PITPβ silencing evokes a dramatic depletion of NSC pools in embryonic brain. And, we finally have generated PITPαflox/flox and PITPβflox/flox single mutants, and PITPαflox/flox, PITPβflox/flox double mutant mouse line. In an experiment using Emx1‐Cre driver, which is forebrain specific driver, eviction of both PITPα and PITPβ in forebrain leads to a mouse that is born but has an amazing microcephaly that is due to virtual loss of the forebrain. Neither PITPα nor PITPβ eviction alone has any such effect. This experiment result is consistent with In utero electroporation data. Thus, we demonstrate that PITPα and PITPβ redundantly control NSC homeostasis in mouse brain development. Based on these data, we will observe carefully daughter cell fate during NSC division to investigate whether PITPs deficiency defeats NSC division program, asymmetric self‐renewing/differentiating cell divisions. Moreover, we will exploit our unique library of mutant PITPs with defined biochemical defects, to assess whether PtdCho‐ and PtdIns‐binding are required for PITP function in embryonic NSCs. Our research will generate completely new information regarding how lipid signaling contributes to NSC homeostasis in the developing mammalian brain.Support or Funding InformationNIH 1R01GM112591‐01A1

The Arabidopsis Receptor Kinase ZAR1 Is Required for Zygote Asymmetric Division and Its Daughter Cell Fate.

Asymmetric division of zygote is critical for pattern formation during early embryogenesis in plants and animals. It requires integration of the intrinsic and extrinsic cues prior to and/or after fertilization. How these cues are translated into developmental signals is poorly understood. Here through genetic screen for mutations affecting early embryogenesis, we identified an Arabidopsis mutant, zygotic arrest 1 (zar1), in which zygote asymmetric division and the cell fate of its daughter cells were impaired. ZAR1 encodes a member of the RLK/Pelle kinase family. We demonstrated that ZAR1 physically interacts with Calmodulin and the heterotrimeric G protein Gβ, and ZAR1 kinase is activated by their binding as well. ZAR1 is specifically expressed micropylarly in the embryo sac at eight-nucleate stage and then in central cell, egg cell and synergids in the mature embryo sac. After fertilization, ZAR1 is accumulated in zygote and endosperm. The disruption of ZAR1 and AGB1 results in short basal cell and an apical cell with basal cell fate. These data suggest that ZAR1 functions as a membrane integrator for extrinsic cues, Ca2+ signal and G protein signaling to regulate the division of zygote and the cell fate of its daughter cells in Arabidopsis.

Concentration Sensing by the Moving Nucleus in Cell Fate Determination: A Computational Analysis.

During development of the vertebrate neuroepithelium, the nucleus in neural progenitor cells (NPCs) moves from the apex toward the base and returns to the apex (called interkinetic nuclear migration) at which point the cell divides. The fate of the resulting daughter cells is thought to depend on the sampling by the moving nucleus of a spatial concentration profile of the cytoplasmic Notch intracellular domain (NICD). However, the nucleus executes complex stochastic motions including random waiting and back and forth motions, which can expose the nucleus to randomly varying levels of cytoplasmic NICD. How nuclear position can determine daughter cell fate despite the stochastic nature of nuclear migration is not clear. Here we derived a mathematical model for reaction, diffusion, and nuclear accumulation of NICD in NPCs during interkinetic nuclear migration (INM). Using experimentally measured trajectory-dependent probabilities of nuclear turning, nuclear waiting times and average nuclear speeds in NPCs in the developing zebrafish retina, we performed stochastic simulations to compute the nuclear trajectory-dependent probabilities of NPC differentiation. Comparison with experimentally measured nuclear NICD concentrations and trajectory-dependent probabilities of differentiation allowed estimation of the NICD cytoplasmic gradient. Spatially polarized production of NICD, rapid NICD cytoplasmic consumption and the time-averaging effect of nuclear import/export kinetics are sufficient to explain the experimentally observed differentiation probabilities. Our computational studies lend quantitative support to the feasibility of the nuclear concentration-sensing mechanism for NPC fate determination in zebrafish retina.

Cell Fate Decision Making through Oriented Cell Division.

The ability to dictate cell fate decisions is critical during animal development. Moreover, faithful execution of this process ensures proper tissue homeostasis throughout adulthood, whereas defects in the molecular machinery involved may contribute to disease. Evolutionarily conserved protein complexes control cell fate decisions across diverse tissues. Maintaining proper daughter cell inheritance patterns of these determinants during mitosis is therefore a fundamental step of the cell fate decision-making process. In this review, we will discuss two key aspects of this fate determinant segregation activity, cortical cell polarity and mitotic spindle orientation, and how they operate together to produce oriented cell divisions that ultimately influence daughter cell fate. Our focus will be directed at the principal underlying molecular mechanisms and the specific cell fate decisions they have been shown to control.

Vegfc Regulates Bipotential Precursor Division and Prox1 Expression to Promote Lymphatic Identity in Zebrafish.

Lymphatic vessels arise chiefly from preexisting embryonic veins. Genetic regulators of lymphatic fate are known, but how dynamic cellular changes contribute during the acquisition of lymphatic identity is not understood. We report the visualization of zebrafish lymphatic precursor cell dynamics during fate restriction. In the cardinal vein, cellular commitment is linked with the division of bipotential Prox1-positive precursor cells, which occurs immediately prior to sprouting angiogenesis. Following precursor division, identities are established asymmetrically in daughter cells; one daughter cell becomes lymphatic and progressively upregulates Prox1, and the other downregulates Prox1 and remains in the vein. Vegfc drives cell division and Prox1 expression in lymphatic daughter cells, coupling signaling dynamics with daughter cell fate restriction and precursor division.

Concise Review: Asymmetric Cell Divisions in Stem Cell Biology

Somatic stem cells are rare cells with unique properties residing in many organs and tissues. They are undifferentiated cells responsible for tissue regeneration and homeostasis, and contain both the capacity to self-renew in order to maintain their stem cell potential and to differentiate towards tissue-specific, specialized cells. However, the knowledge about the mechanisms controlling somatic stem cell fate decisions remains sparse. One mechanism which has been described to control daughter cell fates in selected somatic stem cell systems is the process of asymmetric cell division (ACD). ACD is a tightly regulated and evolutionary conserved process allowing a single stem or progenitor cell to produce two differently specified daughter cells. In this concise review, we will summarize and discuss current concepts about the process of ACD as well as different ACD modes. Finally, we will recapitulate the current knowledge and our recent findings about ACD in human hematopoiesis.

Transcriptional control of tissue formation throughout root development.

Tissue patterns are dynamically maintained. Continuous formation of plant tissues during postembryonic growth requires asymmetric divisions and the specification of cell lineages. We show that the BIRDs and SCARECROW regulate lineage identity, positional signals, patterning, and formative divisions throughout Arabidopsis root growth. These transcription factors are postembryonic determinants of the ground tissue stem cells and their lineage. Upon further activation by the positional signal SHORT-ROOT (a mobile transcription factor), they direct asymmetric cell divisions and patterning of cell types. The BIRDs and SCARECROW with SHORT-ROOT organize tissue patterns at all formative steps during growth, ensuring developmental plasticity.

Microenvironmental control of stem cell fate in intestinal homeostasis and disease.

The conventional model of intestinal epithelial architecture describes a unidirectional tissue organizational hierarchy with stem cells situated at the crypt base and daughter cells proliferating and terminally differentiating as they progress along the vertical (crypt–luminal) axis. In this model, the fate of a cell that has left the niche is determined and its lifespan limited. Evidence is accumulating to suggest that stem cell control and daughter cell fate determination is not solely an intrinsic, cell autonomous property but is heavily influenced by the microenvironment including paracrine, mesenchymal, and endogenous epithelial morphogen gradients. Recent research suggests that in intestinal homeostasis, stem cells transit reversibly between states of variable competence in the niche. Furthermore, selective pressures that disrupt the homeostatic balance, such as intestinal inflammation or morphogen dysregulation, can cause committed progenitor cells and even some differentiated cells to regain stem cell properties. Importantly, it has been recently shown that this disruption of cell fate determination can lead to somatic mutation and neoplastic transformation of cells situated outside the crypt base stem cell niche. This paper reviews the exciting developments in the study of stem cell dynamics in homeostasis, intestinal regeneration, and carcinogenesis, and explores the implications for human disease and cancer therapies. © 2015 Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

The art of fin regeneration in zebrafish.

The zebrafish fin provides a valuable model to study the epimorphic type of regeneration, whereby the amputated part of the appendage is nearly perfectly replaced. To accomplish fin regeneration, two reciprocally interacting domains need to be established at the injury site, namely a wound epithelium and a blastema. The wound epithelium provides a supporting niche for the blastema, which contains mesenchyme‐derived progenitor cells for the regenerate. The fate of blastemal daughter cells depends on their relative position with respect to the fin margin. The apical compartment of the outgrowth maintains its undifferentiated character, whereas the proximal descendants of the blastema progressively switch from the proliferation program to the morphogenesis program. A delicate balance between self‐renewal and differentiation has to be continuously adjusted during the course of regeneration. This review summarizes the current knowledge about the cellular and molecular mechanisms of blastema formation, and discusses several studies related to the regulation of growth and morphogenesis during fin regeneration. A wide range of canonical signaling pathways has been implicated during the establishment and maintenance of the blastema. Epigenetic mechanisms play a crucial role in the regulation of cellular plasticity during the transition between differentiation states. Ion fluxes, gap‐junctional communication and protein phosphatase activity have been shown to coordinate proliferation and tissue patterning in the caudal fin. The identification of the downstream targets of the fin regeneration signals and the discovery of mechanisms integrating the variety of input pathways represent exciting future aims in this fascinating field of research.

A pseudokinase couples signaling pathways to enable asymmetric cell division in a bacterium.

Bacteria face complex decisions when initiating developmental events such as sporulation, nodulation, virulence, and asymmetric cell division. These developmental decisions require global changes in genomic readout, and bacteria typically employ intricate (yet poorly understood) signaling networks that enable changes in cell function. The bacterium Caulobacter crescentus divides asymmetrically to yield two functionally distinct cells: a motile, chemotactic swarmer cell, and a sessile stalked cell with replication and division capabilities. Work from several Caulobacter labs has revealed that differentiation requires concerted regulation by several two-component system (TCS) signaling pathways that are differentially positioned at the poles of the predivisional cell (Figure 1). The strict unidirectional flow from histidine kinase (HK) to the response regulator (RR), observed in most studied TCS, is difficult to reconcile with the notion that information can be transmitted between two or more TCS signaling pathways. In this study, we uncovered a mechanism by which daughter cell fate, which is specified by the DivJ-DivK-PleC system and effectively encoded in the phosphorylation state of the single-domain RR DivK, is communicated to the CckA-ChpT-CtrA signaling pathway that regulates more than 100 genes for polar differentiation, replication initiation and cell division. Using structural biology and biochemical findings we proposed a mechanistic basis for TCS pathway coupling in which the DivL pseudokinase is repurposed as a sensor rather than participant in phosphotransduction.

An Interview with Professor Gian Garriga on Asymmetric Cell Divisions: Distinct Fates of Daughter Cells

An Interview with Professor Gian Garriga on Asymmetric Cell Divisions: Distinct Fates of Daughter Cells

Fine-tuning of cortical progenitor proliferation by thalamic afferents.

During cerebral cortical cortex neurogenesis two major types of progenitors generate a variety of morphologically and functionally diverse projection neurons destined for the different cortical layers in non-gyrified mice. Radial glia cells (RGCs) undergo mitosis in the cortical ventricular zone and exhibit an apical-basal cell polarity, whereas non-polar intermediate progenitor cells (IPCs) divide basally in the subventricular zone (Franco and Muller, 2013; Taverna et al., 2014). The contribution of these cortical progenitor subtypes to particular cortical layers remains debated. Several lines of evidence suggest that IPCs give rise to the majority of cortical neurons, while only 10–20 % are directly generated by apical progenitors (Franco and Muller, 2013). The generation of excitatory cortical neurons follows a temporal order with deep layer neurons born first and upper layers are generated successively during later stages of neurogenesis. Furthermore, the symmetry of mitotic division is instructive for the prospective fate of daughter cells and thus for their laminar destination (Taverna et al., 2014). Various intrinsic and extrinsic cues have been identified that regulate the division mode and cell fate of cortical precursors. In addition to intra-cortical control of cortical neurogenesis such as paracrine interactions between progenitor cells (North et al., 2009) and feedback signaling from post-mitotic neurons of the cortical plate (Seuntjens et al., 2009), extra-cortical signals exerting control over cortical proliferation are increasingly attracting attention. These include factors from the cortico-spinal fluid (Lehtinen and Walsh, 2011) or invading glutamatergic neurons (Teissier et al., 2012). However, the impact of invading thalamo-cortical axons on cortical neurogenesis and layer formation remains largely unknown. Previous in vitro studies suggested that thalamic fibres regulate cell cycle properties and division mode by releasing soluble factors (Dehay et al., 2001). In turn, our data show a contact-mediated extra-cortical regulation of cortical neurogenesis by invading thalamic afferents (Figure 1) (Gerstmann et al., 2015).

Asymmetric inheritance of the apical domain and self-renewal of retinal ganglion cell progenitors depend on Anillin function.

Divisions that generate one neuronal lineage-committed and one self-renewing cell maintain the balance of proliferation and differentiation for the generation of neuronal diversity. The asymmetric inheritance of apical domains and components of the cell division machinery has been implicated in this process, and might involve interactions with cell fate determinants in regulatory feedback loops of an as yet unknown nature. Here, we report the dynamics of Anillin - an essential F-actin regulator and furrow component - and its contribution to progenitor cell divisions in the developing zebrafish retina. We find that asymmetrically dividing retinal ganglion cell progenitors position the Anillin-rich midbody at the apical domain of the differentiating daughter. anillin hypomorphic conditions disrupt asymmetric apical domain inheritance and affect daughter cell fate. Consequently, the retinal cell type composition is profoundly affected, such that the ganglion cell layer is dramatically expanded. This study provides the first in vivo evidence for the requirement of Anillin during asymmetric neurogenic divisions. It also provides insights into a reciprocal regulation between Anillin and the ganglion cell fate determinant Ath5, suggesting a mechanism whereby the balance of proliferation and differentiation is accomplished during progenitor cell divisions in vivo.

EGFR signaling promotes self-renewal through the establishment of cell polarity in Drosophila follicle stem cells.

Epithelial stem cells divide asymmetrically, such that one daughter replenishes the stem cell pool and the other differentiates. We found that, in the epithelial follicle stem cell (FSC) lineage of the Drosophila ovary, epidermal growth factor receptor (EGFR) signaling functions specifically in the FSCs to promote the unique partially polarized state of the FSC, establish apical-basal polarity throughout the lineage, and promote FSC maintenance in the niche. In addition, we identified a novel connection between EGFR signaling and the cell-polarity regulator liver kinase B1 (LKB1), which indicates that EGFR signals through both the Ras-Raf-MEK-Erk pathway and through the LKB1-AMPK pathway to suppress apical identity. The development of apical-basal polarity is the earliest visible difference between FSCs and their daughters, and our findings demonstrate that the EGFR-mediated regulation of apical-basal polarity is essential for the segregation of stem cell and daughter cell fates.

Pom1 regulates the assembly of Cdr2–Mid1 cortical nodes for robust spatial control of cytokinesis

Proper division plane positioning is essential to achieve faithful DNA segregation and to control daughter cell size, positioning, or fate within tissues. In Schizosaccharomyces pombe, division plane positioning is controlled positively by export of the division plane positioning factor Mid1/anillin from the nucleus and negatively by the Pom1/DYRK (dual-specificity tyrosine-regulated kinase) gradients emanating from cell tips. Pom1 restricts to the cell middle cortical cytokinetic ring precursor nodes organized by the SAD-like kinase Cdr2 and Mid1/anillin through an unknown mechanism. In this study, we show that Pom1 modulates Cdr2 association with membranes by phosphorylation of a basic region cooperating with the lipid-binding KA-1 domain. Pom1 also inhibits Cdr2 interaction with Mid1, reducing its clustering ability, possibly by down-regulation of Cdr2 kinase activity. We propose that the dual regulation exerted by Pom1 on Cdr2 prevents Cdr2 assembly into stable nodes in the cell tip region where Pom1 concentration is high, which ensures proper positioning of cytokinetic ring precursors at the cell geometrical center and robust and accurate division plane positioning.