Progenitor Cell Types Research Articles

HDAC1 regulates the proliferation of radial glial cells in the developing Xenopus tectum.

In the developing central nervous system (CNS), progenitor cells differentiate into progeny to form functional neural circuits. Radial glial cells (RGs) are a transient progenitor cell type that is present during neurogenesis. It is thought that a combination of neural trophic factors, neurotransmitters and electrical activity regulates the proliferation and differentiation of RGs. However, it is less clear how epigenetic modulation changes RG proliferation. We sought to explore the effect of histone deacetylase (HDAC) activity on the proliferation of RGs in the visual optic tectum of Xenopus laevis. We found that the number of BrdU-labeled precursor cells along the ventricular layer of the tectum decrease developmentally from stage 46 to stage 49. The co-labeling of BrdU-positive cells with brain lipid-binding protein (BLBP), a radial glia marker, showed that the majority of BrdU-labeled cells along the tectal midline are RGs. BLBP-positive cells are also developmentally decreased with the maturation of the brain. Furthermore, HDAC1 expression is developmentally down-regulated in tectal cells, especially in the ventricular layer of the tectum. Pharmacological blockade of HDACs using Trichostatin A (TSA) or Valproic acid (VPA) decreased the number of BrdU-positive, BLBP-positive and co-labeling cells. Specific knockdown of HDAC1 by a morpholino (HDAC1-MO) decreased the number of BrdU- and BLBP-labeled cells and increased the acetylation level of histone H4 at lysine 12 (H4K12). The visual deprivation-induced increase in BrdU- and BLBP-positive cells was blocked by HDAC1 knockdown at stage 49 tadpoles. These data demonstrate that HDAC1 regulates radial glia cell proliferation in the developing optical tectum of Xenopus laevis.

Novel subventricular zone early progenitor cell-specific adenovirus for in vivo therapy of central nervous system disorders reinforces brain stem cell heterogeneity.

Neural stem/progenitor cells (NSPCs) have the potential to self-renew and to generate all neural lineages as well as to repopulate damaged areas in the brain. Our previous targeting strategies have indicated precursor cell heterogeneity between different brain regions that warrants the development of NSPC-specific delivery vehicles. Here, we demonstrate a target-specific adenoviral vector system for the in vivo manipulation of progenitor cells in the subventricular zone of the adult mouse brain. For this purpose, we identified a series of peptide ligands via phage display. The peptide with the highest affinity, SNQLPQQ, was expressed in conjunction with a bispecific adaptor molecule. To verify the targeting potential of the specific peptide, green fluorescent protein-expressing Ad vectors were coupled with the adaptor molecule and injected into the subventricular region of adult mice by stereotaxic surgery. An efficient and selective transduction of NSPCs in the SVZ was achieved, whereas hippocampal NSPCs were negative. Our results offer an expeditious and simple tool to produce retargeted viral vectors for a specific and direct in vivo manipulation of these progenitor cells. This powerful technique provides an opportunity to develop innovative strategies and express therapeutic genes in specific types of neural progenitor cells to allow success in treatment of brain disorders.

Expression of coxsackievirus and adenovirus receptor separates hematopoietic and cardiac progenitor cells in fetal liver kinase 1-expressing mesoderm.

In developing embryos or in vitro differentiation cultures using pluripotent stem cells (PSCs), such as embryonic stem cells and induced pluripotent stem cells, fetal liver kinase 1 (Flk1)-expressing mesodermal cells are thought to be a heterogeneous population that includes hematopoietic progenitors, endothelial progenitors, and cardiac progenitors. However, information on cell surface markers for separating these progenitors in Flk1⁺ cells is currently limited. In the present study, we show that distinct types of progenitor cells in Flk1⁺ cells could be separated according to the expression of coxsackievirus and adenovirus receptor (CAR, also known as CXADR), a tight junction component molecule. We found that mouse and human PSC- and mouse embryo-derived Flk1⁺ cells could be subdivided into Flk1⁺CAR⁺ cells and Flk1⁺CAR⁻ cells. The progenitor cells with cardiac potential were almost entirely restricted to Flk1⁺CAR⁺ cells, and Flk1⁺CAR⁻ cells efficiently differentiated into hematopoietic cells. Endothelial differentiation potential was observed in both populations. Furthermore, from the expression of CAR, Flk1, and platelet-derived growth factor receptor-α (PDGFRα), Flk1⁺ cells could be separated into three populations (Flk1⁺PDGFRα⁻ CAR⁻ cells, Flk1⁺PDGFRα⁻CAR⁺ cells, and Flk1⁺PDGFRα⁺CAR⁺ cells). Flk1⁺PDGFRα⁺ cells and Flk1⁺PDGFRα⁻ cells have been reported as cardiac and hematopoietic progenitor cells, respectively. We identified a novel population (Flk1⁺PDGFRα⁻ CAR⁺ cells) with the potential to differentiate into not only hematopoietic cells and endothelial cells but also cardiomyocytes. Our findings indicate that CAR would be a novel and prominent marker for separating PSC- and embryo-derived Flk1⁺ mesodermal cells with distinct differentiation potentials.

Generation of Distal Airway Epithelium from Multipotent Human Foregut Stem Cells.

Collectively, lung diseases are one of the largest causes of premature death worldwide and represent a major focus in the field of regenerative medicine. Despite significant progress, only few stem cell platforms are currently available for cell-based therapy, disease modeling, and drug screening in the context of pulmonary disorders. Human foregut stem cells (hFSCs) represent an advantageous progenitor cell type that can be used to amplify large quantities of cells for regenerative medicine applications and can be derived from any human pluripotent stem cell line. Here, we further demonstrate the application of hFSCs by generating a near homogeneous population of early pulmonary endoderm cells coexpressing NKX2.1 and FOXP2. These progenitors are then able to form cells that are representative of distal airway epithelium that express NKX2.1, GATA6, and cystic fibrosis transmembrane conductance regulator (CFTR) and secrete SFTPC. This culture system can be applied to hFSCs carrying the CFTR mutation Δf508, enabling the development of an in vitro model for cystic fibrosis. This platform is compatible with drug screening and functional validations of small molecules, which can reverse the phenotype associated with CFTR mutation. This is the first demonstration that multipotent endoderm stem cells can differentiate not only into both liver and pancreatic cells but also into lung endoderm. Furthermore, our study establishes a new approach for the generation of functional lung cells that can be used for disease modeling as well as for drug screening and the study of lung development.

Periostin conditions the matrix to generate a niche for islet regeneration.

Islet replacement via the Edmonton Protocol offers proof of concept that transient insulin independence can be achieved in patients with diabetes (1–4). However, the need for life-long immunosuppression, an extreme shortage of human islets, along with graft failure due to rejection and continued autoimmunity, limits the widespread application of this approach. Although recent progress has been made in the derivation of “ -like” cells from human pluripotent stem cell sources (embryonic stem cells or induced pluripotent stem cells) (5–10), inducing the replication of surviving -cells in situ (11, 12) and/or stimulating new islet formation from progenitor cells within the pancreas (islet neogenesis) (13–16) represents the most direct way to increase -cell mass. Studies in both rodents and humans suggest endogenous islet repair mechanisms may remain intact during diabetes and can be activated by cellor pharmacologically-mediated stimuli. Evidence of ongoing -cell regeneration has been observed in type 1 diabetes (T1D) patients at early onset (17) or many years after diagnosis (18). Indeed, recent analysis of T1D patients with disease duration of more than 50 years (medalists) has uncovered sustained c-peptide and proliferating -cells within the pancreas in the face of ongoing autoimmunity (19). Moreover, the increase in -cell mass in response to pregnancy suggests that the human endocrine pancreas has the capacity to regenerate if we can understand how to “tip the balance” in favor of islet regeneration vs destruction during diabetes. Interestingly, increased -cell replication was first suggested as the mechanism for increased -cell mass during pregnancy, but a recent autopsy study of human pancreases during pregnancy showed an increased proportion of small islets and increased number of insulin cells in the ducts but no change in -cell replication or apoptosis frequency (20). Nonetheless, novel strategies to optimize islet regeneration, either by stimulating -cell replication or by harnessing endogenous islet neogenic processes within the diabetic pancreas, remain under intense investigation for the treatment of diabetes. In initial publications documenting endogenous islet regeneration by stem cells, transplantation of bone marrow-derived c-kit cells reduced hyperglycemia in mice with streptozotocin (STZ)-induced -cell deletion (21). Importantly, transplanted stem cells did not acquire insulin expression as previously thought. In contrast, donor cells surrounded regenerating islets or engrafted in ductal regions and stimulated proliferation within recipient islets via undetermined paracrine activities (21). Subsequently, other preclinical and early clinical reports have shown that both human hematopoietic (22–26) or multipotent stromal cell (25–28), also known as mesenchymal stem cell (MSC) lineages, can enhance islet regeneration. Furthermore, islet regeneration and immune protection may be achieved by coinfusion of murine hematopoietic cells with MSC in autoimmune non-obese diabetic mice (29). Although this concept termed “stem cell-stimulated islet regeneration” has emerged as a central process for pancreas repair, either by stimulating -cell proliferation (11, 24– 26) or by initiating new islet formation from ductal or islet-derived precursors (14–16, 25, 26), the molecular signaling mechanisms by which distinct stem and progenitor cell types mediate islet recovery are not well understood. More importantly, recent controversy of the role of betatrophin in islet regeneration (30, 31) has underscored

Stem cell autotomy and niche interaction in different systems

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes (platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells (GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug. In both, moths and the milkweed bug, GSCs form finger-like projections toward the niche, the apical cells (homologs of the hub cells in Drosophila). Whereas in the milkweed bug the projection terminals remain at the surface of the niche cells, in the gipsy moth they protrude deeply into the singular niche cell. In both cases, the projections undergo serial retrograde fragmentation with progressing signs of autophagy. In the gipsy moth, the autotomized vesicles are phagocytized and digested by the niche cell. In the milkweed bug the autotomized vesicles accumulate at the niche surface and disintegrate. Autotomy and sprouting of new projections appears to occur continuously. The significance of the GSC-niche interactions, however, remains enigmatic. Our concept on the signaling relationship between stem cell-niche in general and GSC and niche (hub cells and cyst stem cells) in particular has been greatly shaped by Drosophila melanogaster. In comparing the interactions of GSCs with their niche in Drosophila with those in species exhibiting GSC autotomy it is obvious that additional or alternative modes of stem cell-niche communication exist. Thus, essential signaling pathways, including niche-stem cell adhesion (E-cadherin) and the direction of asymmetrical GSC division - as they were found in Drosophila - can hardly be translated into the systems where GSC autotomy was reported. It is shown here that the serial autotomy of GSC projections shows remarkable similarities with Wallerian axonal destruction, developmental axon pruning and dying-back degeneration in neurodegenerative diseases. Especially the hypothesis of an existing evolutionary conserved "autodestruction program" in axons that might also be active in GSC projections appears attractive. Investigations on the underlying signaling pathways have to be carried out. There are two other well known cases of programmed cell autotomy: the enucleation of erythroblasts in the process of erythrocyte maturation and the segregation of thousands of thrombocytes (platelets) from one megakaryocyte. Both progenitor cell types - erythroblasts and megakaryocytes - are associated with a niche in the bone marrow, erythroblasts with a macrophage, which they surround, and the megakaryocytes with the endothelial cells of sinusoids and their extracellular matrix. Although the regulatory mechanisms may be specific in each case, there is one aspect that connects all described processes of programmed cell autotomy and neuronal autodestruction: apoptotic pathways play always a prominent role. Studies on the role of male GSC autotomy in stem cell-niche interaction have just started but are expected to reveal hitherto unknown ways of signal exchange. Spermatogenesis in mammals advance our understanding of insect spermatogenesis. Mammal and insect spermatogenesis share some broad principles, but a comparison of the signaling pathways is difficult. We have intimate knowledge from Drosophila, but of almost no other insect, and we have only limited knowledge from mammals. The discovery of stem cell autotomy as part of the interaction with the niche promises new general insights into the complicated stem cell-niche interdependence.

Therapeutic potential of human mesenchymal stromal cells secreted components: a problem with standartization

Regenerative medicine approaches, such as replacement of damaged tissue by ex vivo manufactured constructions or stimulation of endogenous reparative and regenerative processes to treat different diseases, are actively developing. One of the major tools for regenerative medicine are stem and progenitor cells, including multipotent mesenchymal stem/stromal cells (MSC). Because the paracrine action of bioactive factors secreted by MSC is considered as a main mechanism underlying MSC regenerative effects, application of MSC extracellular secreted products could be a promising approach to stimulate tissue regeneration; it also has some advantages compared to the injection of the cells themselves. However, because of the complexity of composition and multiplicity of mechanisms of action distinguished the medicinal products based on bioactive factors secreted by human MSC from the most of pharmaceuticals, it is important to develop the approaches to their standardization and quality control. In the current study, based on the literature data and guidelines as well as on our own experimental results, we provided rationalization for nomenclature and methods of quality control for the complex of extracellular products secreted by human adipose-derived MSC on key indicators, such as "Identification", "Specific activity" and "Biological safety". Developed approaches were tested on the samples of conditioned media contained products secreted by MSC isolated from subcutaneous adipose tissue of 30 donors. This strategy for the standardization of innovative medicinal products and biomaterials based on the bioactive extracellular factors secreted by human MSC could be applicable for a wide range of bioactive complex products, produced using the different types of stem and progenitor cells.

Dynamic expression of ATF3 as a novel tool to study activation and migration of endogenous spinal stem cells and their role in neural repair.

One of the major problems of modern neurobiology is how to replace dead or damaged neurons in the human brain or spinal cord after injury or as a consequence of neurodegenerative diseases. In fact, because adult mammalian neurons are post-mitotic cells that cannot divide to replace dead cells, loss due to lesion or disease is permanent. Furthermore, surviving neurons have modest capacity to regenerate their damaged axons and re-establish functional connections. Thus, a gradual neurodegenerative scenario with certain similarities in stroke, brain or spinal cord injuries and neurological diseases like Alzheimer's disease is produced. These conditions represent the major disease burden of the modern world in terms of mortality, disability, productivity loss and health-care costs (World Health Organization, 2008). While much effort has been directed to understand the molecular and cellular mechanisms involved in the pathology of these diseases to set new effective treatments, many neuroprotective and regenerative approaches, although showing positive results in preclinical studies, have so far failed to provide strong benefit to patients.

Stem Cell Differentiation and Therapeutic Use.

Stem Cell Differentiation and Therapeutic Use.

Recent developments in cardiovascular stem cells.

Heart failure, a common consequence of ischemic heart disease, is a major cause of morbidity and mortality in the world.1–3 Pharmacological treatment with β-blockers and inhibitors of the renin–angiotensin–aldosterone system has improved the clinical outcomes in patients with heart failure.4–7 Likewise, mechanical unloading with left ventricular assist devices and resynchronization therapy have led to partial reversal of cardiac structural and molecular remodeling and symptomatic improvement.8–10 Despite these remarkable advances, however, mortality and morbidity of patients with heart failure, with or without reduced ejection fraction remains high.1,2 Moreover, heart transplantation, while an effective option, is available only for a selected number of patients and is not without considerable negative consequences.11 Furthermore, gene therapy still remains in early investigational stages and not yet ready for clinical applications.12 The high residual mortality and morbidity of patients with heart failure might be inherent to the shortcomings of the current therapeutic approaches, as none directly targets the underlying causal problem in heart failure, that is, loss of or intrinsically dysfunctional myocytes. Consequently, novel therapeutic approaches are necessary to further improve the clinical outcomes in patients with heart failure. The heart is considered, by and large, a terminally differentiated organ with a limited intrinsic regenerative capacity that alone is insufficient to compensate for the pathological loss of cardiac myocytes during the postnatal period.13–15 The discovery of cardiac progenitor cells (CPCs) in the heart more than a decade ago along with the recent data showing that the existing myocytes undergo a gradual turnover have raised the potentials for regenerative cardiac repair.16,17 Likewise, the discovery of mesenchymal stem cells (MSCs), which was thought to have the potential to differentiate to cardiac myocytes, but yet to proven, or enhance …

Abstract 19641: Novel Microprinted Elisa Platform for High Throughput Screening of Protein Secretion Reveals a Comprehensive Strategy to Prevent Ischemia Reperfusion Induced Apoptosis

Introduction: A major challenge in using stem cells to treat myocardial infarction (MI) is the massive cell death post transplant. Many progenitor cell types limit disrepair post MI without significant cardiac differentiation, possibly by anti-apoptotic signals in their secretions. The signature of these secretions is however not well known. Methods: We created a novel high throughput microELISA platform by combining microprinting and microfluidics to precisely estimate secretions of a small population of cells over time. Screening the secretions in many stem cell types used previously to treat MI, i.e. BMSCs (Bone marrow derived stem cells), CDCs (Cardiosphere derived cells), and iPSC-CMs (induced pluripotent stem cell derived cardiomyocytes), we found a common preserved secretory signature of growth factors. Results: Using a high throughput screen of pro-apoptotic factors that prevent CDCs from peroxide induced cell death, we surprisingly found that these factors were identical to the preserved secretory signature. Using the constituents of the anti-apoptotic secretory signature in combination with ischemic and mechanical preconditioning in myocardium mimicking rigidity, we created a comprehensive cytoprotective cocktail to prevent CDCs from ischemia induced cell death. We tested the cocktail in a rat model of ischemia reperfusion, and found a stark reduction in CDC retention post injection. Figures: (A) MicroELISA schematic. Secretions from cells in left are detected by rows of microprinted capture antibodies; photograph in (C-D). Bioluminescence imaging of CDCs treated with comprehensive cocktail show significantly high cell retention vs untreated CDCs.

Boolean modelling reveals new regulatory connections between transcription factors orchestrating the development of the ventral spinal cord.

We have assembled a network of cell-fate determining transcription factors that play a key role in the specification of the ventral neuronal subtypes of the spinal cord on the basis of published transcriptional interactions. Asynchronous Boolean modelling of the network was used to compare simulation results with reported experimental observations. Such comparison highlighted the need to include additional regulatory connections in order to obtain the fixed point attractors of the model associated with the five known progenitor cell types located in the ventral spinal cord. The revised gene regulatory network reproduced previously observed cell state switches between progenitor cells observed in knock-out animal models or in experiments where the transcription factors were overexpressed. Furthermore the network predicted the inhibition of Irx3 by Nkx2.2 and this prediction was tested experimentally. Our results provide evidence for the existence of an as yet undescribed inhibitory connection which could potentially have significance beyond the ventral spinal cord. The work presented in this paper demonstrates the strength of Boolean modelling for identifying gene regulatory networks.

C ux2 activity defines a subpopulation of perinatal neurogenic progenitors in the hippocampus

The hippocampus arises from the medial region of the subventricular (SVZ) within the telencephalon. It is one of two regions in the postnatal brain that harbors neural progenitors (NPs) capable of giving rise to new neurons. Neurogenesis in the hippocampus is restricted to the subgranular zone (SGZ) of the dentate gyrus (DG) where it contributes to the generation of granule cell layer (gcl) neurons. It is thought that SGZ progenitors are heterogeneous, differing in their morphology, expression profiles, and developmental potential, however it is currently unknown whether they display differences in their developmental origins and cell fate-restriction in the DG. Here we demonstrate that Cux2 is a marker for SGZ progenitors and nascent granule cell neurons in the perinatal brain. Cux2 was expressed in the presumptive hippocampal forming region of the embryonic forebrain from E14.5 onwards. At fetal stages, Cux2 was expressed in early-forming Prox1+ granule cell neurons as well as the SVZ of the DG germinal matrix. In the postnatal brain, Cux2 was expressed in several types of progenitors in the SGZ of the DG, including Nestin/Sox2 double-positive radial glia, Sox2+ cells that lacked a radial glial process, DCX+ neuroblasts, and Calretinin-expressing nascent neurons. Another domain characterized by a low level of Cux2 expression emerged in Calbindin+ neurons of the developing DG blades. We used Cux2-Cre mice in genetic fate-mapping studies and showed almost exclusive labeling of Calbindin-positive gcl neurons, but not in any progenitor cell types or astroglia. This suggests that Cux2+ progenitors directly differentiate into gcl neurons and do not self-renew. Interestingly, developmental profiling of cell fate revealed an outside-in formation of gcl neurons in the DG, likely reflecting the activity of Cux2 in the germinative matrices during DG formation and maturation. However, DG morphogenesis proceeded largely normally in hypomorphic Cux2 mutants lacking Cux2 expression. Taken together we conclude that Cux2 expression reflects hippocampal neurogenesis and identifies non-self-renewing NPs in the SGZ.

Redox signaling in cardiac renewal.

Utilizing oxygen (O2) through mitochondrial oxidative phosphorylation enables organisms to generate adenosine triphosphate (ATP) with a higher efficiency than glycolysis, but it results in increased reactive oxygen species production from mitochondria, which can result in stem cell dysfunction and senescence. In the postnatal organism, the hematopoietic system represents a classic example of the role of stem cells in cellular turnover and regeneration. However, in other organs such as the heart, both the degree and source of cellular turnover have been heavily contested. Although recent evidence suggests that the major source of the limited cardiomyocyte turnover in the adult heart is cardiomyocyte proliferation, the identity and potential role of undifferentiated cardiac progenitor cells remain controversial. Several types of cardiac progenitor cells have been identified, and several studies have identified an important role of redox and metabolic regulation in survival and differentiation of cardiac progenitor cells. Perhaps a simple way to approach these controversies is to focus on the multipotentiality characteristics of a certain progenitor population, and not necessarily its ability to give rise to all cell types within the heart. In addition, it is important to note that cycling cells in the heart may express markers of differentiation or may be truly undifferentiated, and for the purpose of this review, we will refer to these cycling cells as progenitors. We propose that hypoxia, redox signaling, and metabolic phenotypes are major regulators of cardiac renewal, and may prove to be important therapeutic targets for heart regeneration.

β-catenin activation in a novel liver progenitor cell type is sufficient to cause hepatocellular carcinoma and hepatoblastoma.

Hepatocellular carcinoma (HCC) was thought historically to arise from hepatocytes, but gene expression studies have suggested that it can also arise from fetal progenitor cells or their adult progenitor progeny. Here, we report the identification of a unique population of fetal liver progenitor cells in mice that can serve as a cell of origin in HCC development. In the transgenic model used, mice carry the Cited1-CreER(TM)-GFP BAC transgene in which a tamoxifen-inducible Cre (CreER(TM)) and GFP are controlled by a 190-kb 5' genomic region of Cited1, a transcriptional coactivator protein for CBP/p300. Wnt signaling is critical for regulating self-renewal of progenitor/stem cells and has been implicated in the etiology of cancers of rapidly self-renewing tissues, so we hypothesized that Wnt pathway activation in CreER(TM)-GFP(+) progenitors would result in HCC. In livers from the mouse model, transgene-expressing cells represented 4% of liver cells at E11.5 when other markers were expressed, characteristic of the hepatic stem/progenitor cells that give rise to adult hepatocytes, cholangiocytes, and SOX9(+) periductal cells. By 26 weeks of age, more than 90% of Cited1-CreER(TM)-GFP;Ctnnb1(ex3(fl)) mice with Wnt pathway activation developed HCC and, in some cases, hepatoblastomas and lung metastases. HCC and hepatoblastomas resembled their human counterparts histologically, showing activation of Wnt, Ras/Raf/MAPK, and PI3K/AKT/mTOR pathways and expressing relevant stem/progenitor cell markers. Our results show that Wnt pathway activation is sufficient for malignant transformation of these unique liver progenitor cells, offering functional support for a fetal/adult progenitor origin of some human HCC. We believe this model may offer a valuable new tool to improve understanding of the cellular etiology and biology of HCC and hepatoblastomas and the development of improved therapeutics for these diseases.

Cell therapies for tendons: old cell choice for modern innovation.

Although tissue engineering and cell therapies are becoming realistic approaches for medical therapeutics, it is likely that musculoskeletal applications will be among the first to benefit on a large scale. Cell sources for tissue engineering and cell therapies for tendon pathologies are reviewed with an emphasis on small defect tendon injuries as seen in the hand which could adapt well to injectable cell administration. Specifically, cell sources including tenocytes, tendon sheath fibroblasts, bone marrow or adipose-derived stem cells, amniotic cells, placenta cells and platelet-derivatives have been proposed to enhance tendon regeneration. The associated advantages and disadvantages for these different strategies will be discussed and evolving regulatory requirements for cellular therapies will also be addressed. Human progenitor tenocytes, along with their clinical cell banking potential, will be presented as an alternative cell source solution. Similar cell banking techniques have already been described with other progenitor cell types in the 1950's for vaccine production, and these "old" cell types incite potentially interesting therapeutic options that could be improved with modern innovation for tendon regeneration and repair.

Overexpression of epigen during embryonic development induces reversible, epidermal growth factor receptor-dependent sebaceous gland hyperplasia.

The epidermal growth factor receptor (EGFR) system is a key regulator of epithelial development and homeostasis. Its functions in the sebaceous gland (SG), however, remain poorly characterized. In this study, using a transgenic mouse line with tissue-specific and inducible expression of the EGFR ligand epigen, we showed that increased activation of the EGFR in skin keratinocytes results in enlarged SGs and increased sebum production. The phenotype can be reverted by interrupting transgene expression and is EGFR dependent, as gland size and sebum levels return to normal values after crossing to the EGFR-impaired mouse line Wa5. Intriguingly, however, the SG enlargement appears only if EGFR activation occurs before birth. Importantly, the enlarged sebaceous glands are associated with an increased expression of the transcription factor MYC and of the transmembrane proteins LRIG1, an established negative-feedback regulator of the EGFR/ERBB tyrosine kinase receptors and a stem cell marker. Our findings identify EGFR signaling as a major pathway determining SG activity and suggest a functional relationship between the EGFR/ERBB system and MYC/LRIG1 in the commitment of stem cells toward specific progenitor cell types, with implications for our understanding of their role in tissue development, homeostasis, and disease.

Different forms of tenascin-C with tenascin-R regulate neural differentiation in bone marrow-derived human mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are currently thought to transdifferentiate into neural lineages under specific microenvironments. Studies have reported that the tenascin family members, tenascin-C (TnC) and tenascin-R (TnR), regulate differentiation and migration, in addition to neurite outgrowth and survival in numerous types of neurons and mesenchymal progenitor cells. However, the mechanisms by which TnC and TnR affect neuronal differentiation are not well understood. In this study, we hypothesized that different forms of tenascin might regulate the neural transdifferentiation of human bone marrow-derived mesenchymal stem cells. Human MSCs were cultured in media incorporated with soluble tenascins, or on precoated tenascins. In a qualitative polymerase chain reaction analysis, adding a soluble TnC and TnR mixture to the medium significantly enhanced the expression of neuronal and glial markers, whereas no synaptic markers were expressed. Conversely, in groups of cells treated with coated TnC, hMSCs showed neurite outgrowth and synaptic marker expression. After being treated with coated TnR, hMSCs exhibited neuronal differentiation; however, it inhibited neurite outgrowth and synaptic marker expression. A combination of TnC and TnR significantly promoted hMSC differentiation in neurons or oligodendrocytes, induced neurite formation, and inhibited differentiation into astrocytes. Furthermore, the effect of the tenascin mixture showed dose-dependent effects, and a mixture ratio of 1:1 to 1:2 (TnC:TnR) provided the most obvious differentiation of neurons and oligodendrocytes. In a functional blocking study, integrin α7 and α9β1-blocking antibodies inhibited, respectively, 80% and 20% of mRNA expression by hMSCs in the coated tenascin mixture. In summary, the coated combination of TnC and TnR appeared to regulate neural differentiation signaling through integrin α7 and α9β1 in bone marrow-derived hMSCs. Our findings demonstrate novel mechanisms by which tenascin regulates neural differentiation, and enable the use of cell therapy to treat neurodegenerative diseases.

Src kinase function controls progenitor cell pools during regeneration and tumor onset in the Drosophila intestine.

Src non-receptor kinases have been implicated in events late in tumor progression. Here, we study the role of Src kinases in the Drosophila intestinal stem cell (ISC) lineage, during tissue homeostasis and tumor onset. The adult Drosophila intestine contains only two progenitor cell types, division-capable ISCs and their daughters, postmitotic enteroblasts (EBs). We found that Drosophila Src42a and Src64b were required for optimal regenerative ISC division. Conversely, activation of Src42a, Src64b or another non-receptor kinase, Ack, promoted division of quiescent ISCs by coordinately stimulating G1/S and G2/M cell cycle phase progression. Prolonged Src kinase activation caused tissue overgrowth owing to cytokine receptor-independent Stat92E activation. This was not due to increased symmetric division of ISCs, but involved accumulation of weakly specified Notch(+) but division-capable EB-like cells. Src activation triggered expression of a mitogenic module consisting of String/Cdc25 and Cyclin E that was sufficient to elicit division not only of ISCs but also of EBs. A small pool of similarly division-capable transit-amplifying Notch(+) EBs was also identified in the wild type. Expansion of intermediate cell types that do not robustly manifest their transit-amplifying potential in the wild type may also contribute to regenerative growth and tumor development in other tissues in other organisms.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature