Renewal Capability Research Articles

Size-sieved subpopulations of mesenchymal stem cells from intervascular and perivascular equine umbilical cord matrix

Umbilical cord matrix (UCM) has been recently proposed as an alternative source of mesenchymal stem cells (MSCs). The aim of this study was to isolate and characterize presumptive stem cells from intervascular and perivascular equine UCM and to obtain homogeneous subpopulations from both sites. Umbilical cords were processed for retrieval of MSCs. Unsieved cells from intervascular and perivascular portions were evaluated for cell cycle analysis and for immunophenotyping by flow cytometry. Cells from each site were separated into larger and smaller sieved populations using multi-dishes with 8-μm pore transwell inserts. Each cell population was characterized in terms of renewal capability, specific marker expression and differentiation potential. Cryopreservation was performed on sieved cells only. Cells from both areas expressed MSC and pluripotential specific markers and were able to differentiate into mesodermic and ectodermic lineages. The sieving procedure yielded two relatively homogeneous subpopulations with comparable characteristics. Surprisingly, after sieving, large intervascular and small perivascular cells were the most rapidly replicating cells [20.53 and 19.49 cell population doublings (PD) after 31 days respectively] and also showed higher fibroblast colony forming unit frequency. Unsieved cell populations were used as controls, and showed PD of 9.42(intervascular cells) and 8.54 (perivascular cells) after 31 days. Here, cells from UCM represented an intermediate stage between pluripotent embryonic and adult stem cells. Size-sieving can be used to isolate more rapidly proliferating cell populations.

Measuring organizational renewal capability: case training service business

PurposeThe purpose of this paper is to provide a quantitative measure for organizational renewal capability which would enable inter‐firm comparison and external communication. To make the tool more concrete for the reader, a case organization with the measurement results and conclusions is described.Design/methodology/approachA method of how renewal capability can be shown on an organizational level and measurement is demonstrated. The approach is based on systems thinking, but it also has boundary surfaces with the knowledge‐based theory of the firm, dynamic capability approach, and intellectual capital (IC) research. A tool for analyzing and measuring organizational renewal, called KM‐factor®, and the theoretical model behind it, is presented.FindingsThe preliminary analysis indicates that the indexes of KM‐factor® correlate strongly with the future financial success of the company. Thus, the results refer to the fact that companies with (system based and strategy connected) renewal capability have more competitive advantage than others. It is crucial for the organization to understand the required change direction in renewal capability to achieve sustainable competitive advantage.Originality/valueThe topic of renewal has been increasingly dealt with by the research traditions of IC, knowledge management and strategic management. However, even if several relatively consolidated theories about the composition of IC or competitiveness have been presented – renewal being one of the components – the operational and measurement perspectives of continuous renewal have mainly been neglected. This paper demonstrates a quantitative and practical implementation of organizational renewal capability measurement.

Cancer Stem Cells in Hematological Disorders: Current and Possible New Therapeutic Approaches

An increasing body of evidence has shown that hematologic malignancies, alike normal hematopoiesis, has a hierarchical structure including a stem cell compartment with self renewal capability, endowed in a neoplastic niche bearing resemblance to its normal hematopoietic counterpart. According to experimental data on NOD-SCID mice, leukemic stem cells are characterized by a CD34+/CD38- surface profile and account for 1 in 10(3) to 1 in 10(6) of the total amount of leukemic cells. The available knowledge about leukemic stem cells (LSC) has arisen the question as to whether some targeting of LSC is achieved by current treatments; the answer is dubitative at best, with the possible exception of arsenic trioxide in promyelocytic leukemia. On the other side, the unsatisfactory results in the treatment of many hematological neoplasms has prompted many research groups to find out whether direct targeting of LSC, possibly in its niche, would result in an improvement in cure rates. This approach implies the identification of LSC specific markers, clearly distinct from their normal counterpart in order to spare normal hematopoietic stem cells. Adhesion/surface antigens, metabolic pathways involved in LSC survival and renewal, telomerase, commonly mutated genes and epigenetic phenomena have been investigated as candidate targets for newer therapeutic strategies. So far, most of the possibly effective agents have been studied in experimental models only. FLT-3 inhibitors account for a notable exception since they have resulted effective in vivo in AML with mutated, but not over expressed, FLT-3. A main task for the future is to find out whether some common LSC specific markers would be identifiable in a substantial proportion of AML cases, or whether each AML case shows a unique fingerprint of markers. In the latter event, targeting of LSC could result in an arduous task.

Reversing Breast Cancer Stem Cell into Breast Somatic Stem Cell

Stem cells have an important role in cell biology, allowing tissues to be renewed by freshly created cells throughout their lifetime. The specific micro-environment of stem cells is called stem cell niche; this environment influences the development of stem cells from quiescence through stages of differentiation. Recent advance researches have improved the understanding of the cellular and molecular components of the micro-environment--or niche--that regulates stem cells. We point out an important trend to the study of niche activity in breast cancers. Breast cancer has long been known to conserve a heterogeneous population of cells. While the majority of cells that make up tumors are destined to differentiate and eventually stop dividing, only minority populations of cells, termed cancer stem cell, possess extensive self renewal capability. These cancer stem cells possess characteristics of both stem cells and cancer cells. Breast cancer stem cells reversal to breast somatic stem cells offer a new therapy, that not only can stop the spread of breast cancer cells, but also can differentiate breast cancer stem cells into normal breast somatic stem cells. These can replace damaged breast tissue. Nevertheless, the complexity of realizing this therapy approach needs further research.

Accurate Quantification of More Than 4000 Mouse Tissue Proteins Reveals Minimal Proteome Changes During Aging

The biological process of aging is believed to be the result of an accumulation of cellular damage to biomolecules. Although there are numerous studies addressing mutation frequencies, morphological or transcriptional changes in aging mammalian tissues, few have measured global changes at the protein level. Here, we present an in depth proteomic analysis of three brain regions as well as heart and kidney in mice aged 5 or 26 months, using stable isotope labeling of whole animals (SILAC mouse) and high resolution mass spectrometry. In the frontal cortex and hippocampal regions of the brain, more than 4200 proteins were quantitatively compared between age groups. Proteome differences between individual mice were observable within and between age groups. However, mean protein abundance changes of more than twofold between young and old mice were detected in less than 1% of all proteins and very few of these were statistically significant. Similar outcomes were obtained when comparing cerebellum, heart, and kidney between age groups. Thus, unexpectedly, our results indicate that aging-related effects on the tissue proteome composition at the bulk level are only minor and that protein homeostasis remains functional up to a relatively high age.

Organizational Learning

Organizational learning is key to an organization’s capability for continuous change and renewal. As a result, scholarly interest in identifying the antecedents of organizational learning has greatly increased over the past couple of decades. This study focuses on (1) identifying and measuring the distinct subprocesses that make up the organizational learning construct to obtain a more detailed understanding of the construct and (2) exploring the effect that organizational culture and, more particularly, four dimensions of culture—participative decision making, openness, learning orientation, and transformational leadership—have on each of the organizational learning subprocesses. The authors use two samples of subject matter experts and the responses of 631 managers to test their propositions. Their results yielded five independent but interrelated subprocesses—information acquisition, information distribution, information interpretation, knowledge integration, and organizational memory. Furthermore, their results indicate that the four different cultural antecedents studied have different kinds of significant relationships with each of the organizational learning subprocesses. This study contributes to the literature on organizational learning by identifying and validating the organizational learning subprocesses, and by offering a detailed picture of the relationship between key organizational antecedents to learning and the individual subprocesses of learning. In addition, since they use systematic and thorough methodological techniques to develop an instrument to test, measure, and validate those subprocesses of learning that constitute a common body of knowledge in this area, the authors’ instrument could prove to be a valuable tool for future research.

An empirical study on paths to develop dynamic capabilities: From the perspectives of entrepreneurial orientation and organizational learning

Dynamic capabilities are regarded as a strategic premise to creating, maintaining and upgrading sustainable competitiveness. Considering organizational learning as a mediator variable, this study tests the relationship between entrepreneurial orientation and dynamic capabilities, and identifies paths to develop dynamic capabilities and the components of these capabilities. More specifically, the factor analysis method was employed to verify that dynamic capabilities are comprised of four dimensions, i.e. environmental sensing capabilities, change and renewal capabilities, technological and organizational flexibility capabilities. It was found that dimensions of entrepreneurial orientation have a significantly positive effect on dynamic capabilities to different extents, while organizational learning, which has significantly positive effect on dynamic capabilities, plays a partial mediating role between the two. These findings indicate that companies can build dynamic capabilities through different levels of organizational learning in the context of innovative and proactive atmosphere.

Renewable Energies

At prevailing economic practice the alarming “two degrees-limit” of global warming will be reached long before the known fossil fuel reserves are gone. A future alternative energy economy relying on renewable energies will be more diverse yet more expensive than traditional combustion the new figure of merit is the cost of CO2 avoidance. This communication surveys the relevant alternatives – solar energy in its various manifestations, geothermal and tidal energy - and assesses their current contribution to the over-all energy supply, revealing a deplorable lag between renewable capability and the needs of climate conservation. Nuclear energy is seen as low-CO2 bridging technology between the fossil period and the age of renewables; being restrained in Germany in favor of subsidizing alternative energies, the German experience with renewables is drawn upon in this survey. Thermodynamics teaches: Energy can be transferred from one system to another, as from sun to earth. It can be transformed from one form into another, as from light to electricity. Energy can not be produced nor destroyed nor renewed. The term “Renewable Energy” is applied to energy derived from our surrounding for human use. Renewable energies will have to replace fossil fuels - coal, oil and gas - for two reasons: If we continue to burn them, reserves will be exhausted before long; emission of carbon dioxide is about to change our climate by the so-called green house effect.

Mesenchymal stem cells improve small intestinal integrity through regulation of endogenous epithelial cell homeostasis

Patients who undergo pelvic or abdominal radiotherapy may develop acute and/or chronic side effects resulting from gastrointestinal tract (GIT) alterations. In this study, we address the question of the regenerative capability of mesenchymal stem cells (MSC) after radiation-induced GIT injury. We also propose cellular targets of MSC therapy. We report that the infusion of human bone marrow-derived MSC (hMSC) provides a therapeutic benefit to NOD/SCID mice undergoing radiation-induced GIT failure. We observed that hMSC treatment brings about fast recovery of the small intestine (structure and function) in mice with reversible alterations and extends the life of mice with irreversible GIT disorders. The effects of hMSC are a consequence of their ability to improve the renewal capability of small intestinal epithelium. hMSC treatment favors the re-establishment of cellular homeostasis by both increasing endogenous proliferation processes (Ki67 immunostaining) and inhibiting apoptosis (TUNEL staining) of radiation-induced small intestinal epithelial cells. Our results suggest that MSC infusion may be used as a therapeutic treatment to limit radiation-induced GIT damage.

Interruption of β-Catenin Signaling Reduces Neurogenesis in Alzheimer's Disease

The neuronal loss associated with Alzheimer's disease (AD) affects areas of the brain that are vital to cognition. Although recent studies have shown that new neurons can be generated from progenitor cells in the neocortices of healthy adults, the neurogenic potential of the stem/progenitor cells of AD patients is not known. To answer this question, we compared the properties of glial progenitor cells (GPCs) from the cortices of healthy control (HC) and AD subjects. The GPCs from AD brain samples displayed reduced renewal capability and reduced neurogenesis compared with GPCs from HC brains. To investigate the mechanisms underlying this difference, we compared beta-catenin signaling proteins in GPCs from AD versus HC subjects and studied the effect of amyloid beta peptide (Abeta, a hallmark of AD pathology) on GPCs. Interestingly, GPCs from AD patients exhibited elevated levels of glycogen synthase kinase 3beta (GSK-3beta, an enzyme known to phosphorylate beta-catenin), accompanied by an increase in phosphorylated beta-catenin and a decrease in nonphosphorylated beta-catenin compared with HC counterparts. Furthermore. we found that Abeta treatment impaired the ability of GPCs from HC subjects to generate new neurons and caused changes in beta-catenin signaling proteins similar to those observed in GPCs from AD patients. Similar results were observed in GPCs isolated from AD transgenic mice. These results suggest that Abeta-induced interruption of beta-catenin signaling may contribute to the impairment of neurogenesis in AD progenitor cells.

Current knowledge in the renewal capability of germ cells in the adult ovary

It is a central dogma in reproductive biology that oogenesis is completed before or just after birth and that the postnatal ovary is endowed by a fixed and non-renewing number of oocytes in mammals. However, this widely accepted doctrine was recently challenged by studies showing regeneration of oocytes from putative germ cells in bone marrow and peripheral blood. These results not only triggered an enormous amount of interest among reproductive biologists but also a great deal of debate. In this review we will provide an update on the molecular aspects of the formation of primordial germ cells (PGC), the precursors of adult gametocytes, beginning from their specification to their migration to prospective gonads and formation of the ovary and follicular structures. We will also discuss more recent studies that showed in vivo regeneration of germ cells in the postnatal ovary in situ, along with other pioneering works that demonstrated generation of germ cells in vitro from embryonic and somatic stem cells.

Neural stem cells at the crossroads: MMPs may tell the way

Matrix metalloproteinases (MMP) constitute a family of more than 25 enzymes which process a large number of pericellular substrates. Even though initially reported to have an ability to degrade almost all of the extracellular components, MMP are now known to play roles which are not limited to the breakdown of extracellular barriers. In fact, MMPs regulate many biological processes, being involved not only in physiological events, but also in pathological processes. Strikingly, MMPs have been found to be involved in the physiology of the Central Nervous System (CNS), taking part and playing important roles in several processes such as repair and ontogeny, as well as in pathological conditions of the CNS. Initially considered to be a static structure, lacking regenerative capability, the CNS has been considered for a long time to be a system without renewal capabilities. Recently, the discovery of constant neural replacement has changed our way of considering the adult brain, and the finding of the existence of neural stem cells has opened the way to exciting and fascinating perspectives of the CNS. So, could MMPs, originally found during metamorphosis in tadpoles, and now amazingly identified in the CNS, have something to do in neuronal function? In this review we take into consideration the possible roles of two metalloproteinases, MMP-2 and MMP-9, also called gelatinases, in controlling several aspects of CNS organization, including the modulation of neural stem cell properties and the differentiation of their progeny, both under normal and pathophysiological conditions.

Evolution of sub-clinical metastases in breast cancer

12024 Some early stage breast cancer patients bear sub-clinical nodal and/or distant metastases. After primary extirpation, the proportion of failure is lower than would be expected in non-dissected axilla patients and in bone marrow biopsy positive patients. This meant that only some sub-clinical metastases progressed. Since tumor cells continually immigrate into distant or regional sites, but this stops after surgery, progression vs. extinction depends on the unlimited self renewal capability of the resident cells. In turn, this suggested a role for stem cells, specifically their number and character. The number of stem cells in a sub-clinical metastatic focus (regional or distant) can vary considerably from as few as single digits to a hundred thousand. The variation depended on both the size of the tumor at the time of metastatic transformation vs. time of surgery and on the self renewal probability of resident stem cells (Psr). The extinction probability of a single stem cell (E) depends on its Psr. ...

Mature adipocytes may be a source of stem cells for tissue engineering

Adipose tissue contains a large portion of stem cells. These cells appear morphologically like fibroblasts and are primarily derived from the stromal cell fraction. Mature (lipid-filled) adipocytes possess the ability to become proliferative cells and have been shown to produce progeny cells that possess the same morphological (fibroblast-like) appearance as the stem cells from the stromal fraction. A closer examination of mature adipocyte-derived progeny cells may prove to be an emerging area of growth/metabolic physiology that may modify present thinking about adipose tissue renewal capabilities. Knowledge of these cells may also prove beneficial in cell-based therapies for tissue repair, regeneration, or engineering.

Evagination and Infectivity of Taenia crassiceps Cysticerci in Experimental Animals

Cysticerci of Taenia crassiceps reproduce asexually by exogenous budding in the rodent intermediate host, and can experimentally develop to the adult stage within the small intestine of golden hamsters. In the present study, we report the loss of cysticercus infectivity for hamsters after maintaining the strain for 4 yr by consecutive peritoneal passage in mice. Larval infectivity was restored after a cysticercus from the WFU strain developed into a gravid tapeworm after being passaged through a dog. The eggs of this tapeworm were infective for mice, which subsequently developed cysticerci with renewed capability for infecting experimental hamsters. An in vitro evagination assay was also conducted using eleventh-generation WFU strain cysticerci, as well as second- and fourth-generation dog-derived cysticerci. Significantly higher (P < 0.0001) evagination was observed for 5-mo-old dog-derived and WFU infrapopulations when compared with respective evagination values for 9- and 12-mo-old infrapopulations. The extent of evagination was linked to the capacity of cysticerci to infect hamsters, so that greater evagination resulted in a higher infectivity for hamsters and vice versa.

Assessing organisational renewal capability

Even though mastering continuous change has become a significant issue for an increasing number of organisations, the Intellectual Capital (IC) literature has so far remained quite isolated from the themes of innovation, learning and organisational development. Most of IC research adopts the viewpoint of IC as a static stock, and ignores that especially in dynamic environments, it is important to be able to renew the intangible assets continuously. This paper adopts the concept of renewal capability to examine how an organisation is able to use its knowledge resources for learning and innovation. Renewal capability is based on a combination of organisational characteristics that enable the firm to learn and innovate, which in turn produce sustainability in the face of changing market conditions. This paper contributes to the literature on IC by providing a theoretical concept and a survey instrument for understanding and assessing organisational renewal capability.

Development and validation of a survey instrument for measuring organisational renewal capability

Mastering continuous change has become an important issue for an increasing number of organisations. However, the management of innovative performance is hindered by the lack of measures that could enable the reliable assessment and effective development of organisational capabilities for continuous renewal, learning and innovation. The objective of this paper is to describe the development of a survey instrument, the Organisational Renewal Capability Inventory, for measuring organisational renewal capability, and to assess its validity and reliability. This paper contributes to the literature on innovation by providing a systematic technique for collecting, analysing and interpreting data about organisational capability for continuous renewal.

Survivin Regulates Aberrant Proliferation of Hematopoietic Progenitor Cells with Self Renewal Capability and Development of Acute Leukemia Induced by Internal-Tandem-Duplication of Flt3.

Internal Tandem Duplication mutations in the Flt3 tyrosine kinase gene (ITD-Flt3) and over-expression of the inhibitor of apoptosis protein Survivin are frequently found in patients with acute myeloid leukemia (AML) and are associated with poor prognosis. We have shown that ITD-Flt3 increases expression of Survivin in Ba/F3 cells and that antagonizing Survivin inhibits growth factor independent proliferation of primary mouse hematopoietic stem and progenitor cells (HSPC) expressing ITD-Flt3 (Fukuda et al. ASH, 2005). This suggests that Survivin may regulate proliferation of AML cells expressing ITD-Flt3. Herein we investigated the functional role of Survivin in self-renewal and proliferation of transformed HSPC and development of acute leukemia induced by ITD-Flt3 in mice. Treatment of ITD-Flt3 positive human AML MV4-11 cells with the ITD-Flt3 kinase inhibitor AG1296 reduced their proliferation by 33±4% coincident with 50% reduction in Survivin protein, suggesting a functional link between ITD-Flt3 and Survivin in AML cell proliferation. Conditional Survivin deletion significantly reduced growth factor independent proliferation of primary mouse marrow c-kit+, Sca-1+, lin− cells that express ITD-Flt3 by 46±7%, which was further accentuated by AG1296 (76±8% reduction). The effect of Survivin deletion was associated with increased apoptosis measured by Annexin V, sub G1 content and G0/G1 arrest (101±38, 169±44 and14±5% increase, respectively). Overexpressing ITD-Flt3 reduced the proportion of lin+ cells derived from lin− marrow cells cultured with GM-CSF plus Stem Cell Factor compared to wild-type Flt3, while Survivin deletion in ITD-Flt3 expressing cells partially abrogated the effect (53±6% increase in lin+ cells, P<0.05). Furthermore, Survivin deletion dramatically diminished secondary CFU formation induced by ITD-Flt3 in the absence of hematopoietic growth factors (74±5% reduction, P<0.005). These results suggest that ITD-Flt3 promotes self renewal and inhibits differentiation of primary HSPC that is mediated through Survivin. However, over-expressing Survivin alone failed to transform these cells, suggesting that Survivin is required but not sufficient for ITD-Flt3 signaling in primary HSPC. BALB/c mice transplanted with Ba/F3 cells overexpressing ITD-Flt3 (Ba/F3-ITD) died of acute leukemia within 5 weeks (32±1 days), whereas significantly delayed leukemia progression and prolonged survival was observed in mice transplanted with Ba/F3-ITD cells expressing T34A dominant-negative Survivin (70±13 days, P<0.05, N=10), suggesting that Survivin is involved in the acute leukemia induced by ITD-Flt3. These results suggest that Survivin regulates expansion of HSPC with self-renewal capability transformed by ITD-Flt3 and development of ITD-Flt3 positive acute leukemia and that antagonizing Survivin may provide therapeutic benefit for acute leukemias expressing ITD-Flt3. However, since we previously showed that Survivin regulates normal hematopoiesis (Fukuda et al. ASH 2006), development of strategies that disrupt Survivin specifically in malignant hematopoietic cells expressing ITD-Flt3 without affecting normal HSC are warranted.

Donor age intensifies the early immune response after transplantation

Increasing donor age is associated with reduced graft function. We wondered if donor age may not only affect intrinsic function but also alter the immune response of the recipient. Kidneys from young and old F-344 rats (3 vs 18 months) were transplanted into bilaterally nephrectomized young Lewis recipients and compared with age-matched controls (follow-up: 6 months). Renal function and structural changes were assessed serially in both native kidneys and allografts. Host alloreactivity, graft-infiltrating cells, and their inflammatory products were determined at intervals to examine the correlation of immune response and donor age. Functional and structural deterioration had advanced significantly in older allografts compared with age-matched native controls, whereas differences between young allografts and native controls of similar age were only minor. Changes in grafts from elderly rats were associated with a more intense host immune response early post-transplant (up to 1 month) reflected by significantly higher numbers of peripheral T and B cells, increased T-cell alloreactivity and modified cytokine patterns associated with elevated frequencies of intragraft dendritic cells, B cells, and CD31+ cells. By 6 months, recipients of young donor grafts produced comparable or more intense alloantigen-specific immune responses. Older donor grafts elicit a stronger immune response in the early period after transplantation.

Leukemia Stem Cells in Murine MLL−AF9 AML Are Downstream Myeloid Lineage Cells That Have Acquired Stem−Like Biological and Genetic Properties.

An essential prerequisite for the development of more effective targeted therapies in AML is a characterization of the frequency and biological properties of leukemia stem cells (LSCs), which sustain the disease and mediate relapse. Previous studies have shown that hematopoietic stem cells, as well as progenitors, may be targeted by MLL oncoproteins to give rise to AML, however it was unclear whether these lineage negative cells also functioned as LSCs to sustain disease. To address this issue, we have identified and characterized LSCs in a somatic, genetic mouse model of leukemia that faithfully recapitulates many of the pathologic and clinical attributes of human leukemia initiated by the MLL−AF9 oncogene. In this model, CFCs in the bone marrow and spleen of leukemic mice were demonstrated to be LSCs, based on the observation that secondary transplantation of the progeny of individually isolated AML CFCs cultured in vitro for seven days or longer invariably resulted in transfer of short latency disease. These self−renewing cells were remarkably frequent, accounting for 25–30% of myeloid lineage cells at late−stage disease. Unexpectedly, they expressed mature myeloid lineage antigens (91.3 ± 3.8% Mac1+ Gr1+ immunophenotype, versus fewer than 0.2% lineage negative), placing them downstream of the known hematopoietic progenitor compartment. Furthermore, LSCs in this model generated a phenotypic, morphologic and functional leukemia cell hierarchy loosely defined by expression of c−kit. When compared with immortalized progenitors, LSCs exhibited a markedly enhanced ability to engraft secondary recipients, which was not due to differences in bone marrow homing, which was equivalently poor in the compared populations. Rather, LSCs exhibited an acquired ability to proliferate in response to stromal cell derived cytokines, an enhanced SDF1 induced chemotaxis, and increased proliferation in contact with OP9 stromal cells demonstrating that LSCs exhibit altered microenvironmental interactions by comparison with the oncogene immortalized CFCs that initiated the disease. Thus, the LSCs responsible for sustaining, expanding and regenerating MLL−AF9 AML are downstream myeloid lineage cells, outside of the normal stem and progenitor compartment. They have acquired an aberrant Hox−associated self−renewal program as well as other biologic features of hematopoietic stem cells. Our findings support a revision of the prevailing hypothesis that AML LSCs are always rare and solely located within the most immature bone marrow progenitor compartment. Furthermore, LSCs exhibit markedly different microenvironmental interactions, by comparison with cells simply immortalized by MLL−AF9, indicating that acquisition of sensitivity to stromal derived survival and proliferative signals is a critical feature of LSCs, in addition to their extensive self−renewal capabilities.