Mechanisms Of Stem Cell Biology Research Articles

Purification and transcriptomic characterization of proliferative cells of Mesocestoides corti selectively affected by irradiation

Flatworms depend on stem cells for continued tissue growth and renewal during their life cycles, making these cells valuable drug targets. While neoblasts are extensively characterized in the free-living planarian Schmidtea mediterranea, and similar stem cells have been characterized in the trematode Schistosoma mansoni, their identification and characterization in cestodes is just emerging. Since stem cells are generally affected by irradiation, in this work we used this experimental approach to study the stem cells of the model cestode Mesocestoides corti. We found that gamma irradiation produces a dose-dependent decrease in proliferative cells, requiring higher doses than in other flatworms to completely abolish proliferation. The treatment results in the downregulation of candidate marker genes. Transcriptomic studies reveal that several genes downregulated after irradiation are conserved with other flatworms, and are related to cell cycle, DNA replication and repair functions. Furthermore, proliferative cells were isolated by cell sorting and also characterized transcriptomically. We found that the set of genes characteristic of proliferative cells agrees well with those downregulated during irradiation, and have a significant overlap with those expressed in planarian neoblasts or S. mansoni stem cells. Our study highlights that conserved mechanisms of stem cell biology may be functional in flatworms, suggesting that these could be relevant targets to evaluate in the control of parasitic species.

Multimodality Molecular Imaging of Stem Cells Therapy of Myocardial Infarction

Stem cell therapy in patients with acute myocardial infarction promises a new exciting option. However, the long term fate of stem cells transplanted into myocardial is not clear. Molecular imaging play a vital role in tracking stem cells after intramyocardial delivery as well as in helping us understand the mechanisms of stem cell biology in vivo. In this review, we summarize the principles underlying four kinds of stem cells applied into myocardial infarction and the major tracking methods. Finally, we discuss that molecular imaging will be useful to the successful clinical implementation of this novel therapy.

A Novel Taxon of Monosegmented Double-Stranded RNA Viruses Endemic to Triclad Flatworms.

Freshwater planarians, flatworms from order Tricladida, are experimental models of stem cell biology and tissue regeneration. An aspect of their biology that remains less well studied is their relationship with viruses that may infect them. In this study, we identified a taxon of monosegmented double-stranded RNA (dsRNA) viruses in five planarian species, including the well-characterized model Schmidtea mediterranea Sequences for the S. mediterranea virus (abbreviated SmedTV for S. mediterranea tricladivirus) were found in public transcriptome data from multiple institutions, indicating that SmedTV is prevalent in S. mediterranea lab colonies, though without causing evident disease. The presence of SmedTV in discrete cells was shown through in situ hybridization methods for detecting the viral RNA. SmedTV-staining cells were found to be concentrated in neural structures (eyes and brain) but were also scattered in other worm tissues as well. In contrast, few SmedTV-staining cells were seen in stem cell compartments (also consistent with RNA sequencing data) or early blastema tissue. RNA interference (RNAi) targeted to the SmedTV sequence led to apparent cure of infection, though effects on worm health or behavior were not observed. Efforts to transmit SmedTV horizontally through microinjection were unsuccessful. Based on these findings, we conclude that SmedTV infects S. mediterranea in a persistent manner and undergoes vertical transmission to progeny worms during serial passage in lab colonies. The utility of S. mediterranea as a regeneration model, coupled with the apparent capacity of SmedTV to evade normal host immune/RNAi defenses under standard conditions, argues that further studies are warranted to explore this newly recognized virus-host system.IMPORTANCE Planarians are freshwater flatworms, related more distantly to tapeworms and flukes, and have been developed as models to study the molecular mechanisms of stem cell biology and tissue regeneration. These worms live in aquatic environments, where they are likely to encounter a variety of viruses, bacteria, and eukaryotic organisms with pathogenic potential. How the planarian immune system has evolved to cope with these potential pathogens is not well understood, and only two types of planarian viruses have been described to date. Here, we report discovery and inaugural studies of a novel taxon of dsRNA viruses in five different planarian species. The virus in the best-characterized model species, Schmidtea mediterranea, appears to persist long term in that host while avoiding endogenous antiviral or RNAi mechanisms. The S. mediterranea virus-host system thus seems to offer opportunity for gaining new insights into host defenses and their evolution in an important lab model.

From Neural Crest Development to Cancer and Vice Versa: How p75NTR and (Pro)neurotrophins Could Act on Cell Migration and Invasion?

The p75 neurotrophin receptor (p75NTR), also known as low-affinity nerve growth factor, belongs to the tumor necrosis factor family of receptors. p75NTR is widely expressed in the nervous system during the development, as well as, in the neural crest population, since p75NTR has been described as ubiquitously expressed and considered as a neural crest marker. Neural crest cells (NCCs) constitute an transient population accurately migrating and invading, with precision, defined sites of the embryo. During migration, NCCs are guided along distinct migratory pathways by specialized molecules present in the extracellular matrix or on the surfaces of those cells. Two main processes direct NCC migration during the development: (1) an epithelial-to-mesenchymal transition and (2) a process known as contact inhibition of locomotion. In adults, p75NTR remains expressed by NCCs and has been identified in an increasing number of cancer cells. Nonetheless, the regulation of the expression of p75NTR and the underlying mechanisms in stem cell biology or cancer cells have not yet been sufficiently addressed. The main objective of this review is therefore to analyze elements of our actual knowledge regarding p75NTR roles during the development (mainly focusing on neural crest development) and see how we can transpose that information from development to cancer (and vice versa) to better understand the link between p75NTR and cell migration and invasion. In this review, we successively analyzed the molecular mechanisms of p75NTR when it interacts with several coreceptors and/or effectors. We then analyzed which signaling pathways are the most activated or linked to NCC migration during the development. Regarding cancer, we analyzed the described molecular pathways underlying cancer cell migration when p75NTR was correlated to cancer cell migration and invasion. From those diverse sources of information, we finally summarized potential molecular mechanisms underlying p75NTR activation in cell migration and invasion that could lead to new research areas to develop new therapeutic protocols.

Derivation of Neural Precursor Cells from Human Embryonic Stem Cells for DNA Methylomic Analysis.

Embryonic stem cells are self-renewing pluripotent cells with competency to differentiate into all three-germ lineages. Many studies have demonstrated the importance of genetic and epigenetic molecular mechanisms in the maintenance of self-renewal and pluripotency. Stem cells are under unique molecular and cellular regulations different from somatic cells. Proper regulation should be ensured to maintain their unique self-renewal and undifferentiated characteristics. Understanding key mechanisms in stem cell biology will be important for the successful application of stem cells for regenerative therapeutic medicine. More importantly practical use of stem cells will require our knowledge on how to properly direct and differentiate stem cells into the necessary type of cells. Embryonic stem cells and adult stem cells have been used as study models to unveil molecular and cellular mechanisms in various signaling pathways. They are especially beneficial to developmental studies where in vivo molecular/cellular study models are not available. We have derived neural stem cells from human embryonic stem cells as a model to study the effect of teratogen in neural development. We have tested commercial neural differentiation system and successfully derived neural precursor cells exhibiting key molecular features of neural stem cells, which will be useful for experimental application.

Chemical approaches to studying stem cell biology

Stem cells, including both pluripotent stem cells and multipotent somatic stem cells, hold great potential for interrogating the mechanisms of tissue development, homeostasis and pathology, and for treating numerous devastating diseases. Establishment of in vitro platforms to faithfully maintain and precisely manipulate stem cell fates is essential to understand the basic mechanisms of stem cell biology, and to translate stem cells into regenerative medicine. Chemical approaches have recently provided a number of small molecules that can be used to control cell self-renewal, lineage differentiation, reprogramming and regeneration. These chemical modulators have been proven to be versatile tools for probing stem cell biology and manipulating cell fates toward desired outcomes. Ultimately, this strategy is promising to be a new frontier for drug development aimed at endogenous stem cell modulation.

Therapeutic Polycomb Targeting in Human Cancer

The ability of cancer cells to divide indefinitely whilst supporting tumor growth, metastasis and invasiveness resembles the behavior of stem cells. Here, we overview the role of Polycomb (PcG)-dependent epigenetic silencing mechanisms in stem cell biology and cancer, focusing on two major PcG components, Ezh2 and Bmi1. In a recent patent, stem cell PcG targets were shown to be more prone to cancer-specific promoter DNA methylation than non-targets, indicating that reversible PcG-mediated gene repression becomes replaced by permanent silencing. This epigenetic switching keeps the cell in a sustained state of self-renewal, predisposing it to tumorigenic transformation. These findings might provide the means of identifying the stem-cell epigenetic signatures associated with the origin of specific types of cancer. Based on the reversibility of epigenetic histone modifications, PcG proteins have become established targets in clinical practice for the treatment of a variety of cancers, notably treatments with histone deacetylase and methyltransferase inhibitors. A number of reports and patents highlight the potential of alternative approaches to targeting PcG for cancer therapy, including micro-RNA expression and the use of Hedgehog signaling pathway antagonists. The major shortcoming of current approaches is their lack of specificity. The identification of tumorigenic epigenetic alterations together with the development of inhibitors to target them promises to open the way toward personalized cancer treatment.

Concise Review: A Chemical Approach to Control Cell Fate and Function

Stem cells are essential for maintaining tissue homeostasis and mediating physiological and pathological regeneration. Recent breakthroughs in stem cell biology have generated tremendous enthusiasm and hope for the therapeutic potential of stem cells in regenerative medicine. However, this research is still in an early development stage. An improved understanding of stem cell biology is required to precisely manipulate stem cell fate and to harness these cells for regenerative medicine. Small molecules, targeting specific signaling pathways and mechanisms, are powerful tools for manipulating stem cells for desired outcomes. Those small molecules are increasingly important in probing the fundamental mechanisms of stem cell biology and facilitating the development of therapeutic approaches for regenerative medicine. These could involve cell replacement therapies with homogenous functional cells produced under chemically defined conditions in vitro and the development of small-molecule drugs that modulate patient's endogenous cells for therapeutic benefit.

Growth Characteristics of the Nonhuman Primate Embryonic Stem Cell Line Cjes001 Depending on Feeder Cell Treatment

Embryonic stem cells (ESC) hold tremendous potential for therapeutic applications, including regenerative medicine, as well as for understanding basic mechanisms in stem cell biology. Since numerous experiments cannot be conducted in human ESC because of ethical or practical limitations, nonhuman primate ESC serve as invaluable clinically relevant models. The novel marmoset (Callithrix jacchus) ESC line cjes001 was characterized using different stem cell markers. The cells were stained positively with Oct4, SSEA-3, SSEA-4, Tra-1-60, Tra-1-81, and Sox-2 underscoring their status as undifferentiated ESC. ESC are typically grown on mouse embryonic fibroblasts (MEF) as feeder cells whose proliferation is arrested either by treatment with Mitomycin C or by gamma-irradiation. To assess the impact of these treatments on the ability of MEF to support the growth of undifferentiated ESC, we used an MTT assay to evaluate the cellular metabolic activity of growth arrested feeder cells. There was a significant (p < 0.02) difference in gamma-irradiated cells displaying a higher metabolic activity compared to Mitomycin C inactivation. Also we quantified 69 soluble factors in the supernatant of both Mitomycin-treated and gamma-irradiated MEF by bead-based multiplex analysis, and thus established a profile of MEF-secreted factors. The time course of secretion was analyzed by monitoring the supernatant at 0, 6, 12, and 24 h after changing the medium. Comparing gamma-irradiated and Mitomycin-treated MEF suggested higher amounts of some cytokines including FGF or SCF by the former. We also assessed whether the method of inactivation had an effect on growth kinetics and differentiation of primate ESC. There appeared to be a trend to a lower number of differentiated ESC colonies on the gamma-irradiated feeder cells, suggesting that this may be the preferable method of growth arrest.