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PubMed2003

Molecular complexities of stem cells.

Stem cells continue to attract considerable attention and provide hope for the development of new cell-based therapies for degenerative diseases. Unlocking the full therapeutic potential of stem cells requires an understanding of the mechanisms by which they are generated, self-renew, and differentiate. The application of post-genomic technologies is beginning to provide insight into the nature of the molecular ground state of different stem cell compartments. One emerging theme is the considerable molecular complexity in which many possible differentiation pathways are primed, providing one possible strategy for enabling the diverse responsiveness of stem cells. This new information should ultimately reveal any common molecular attributes of "stemness" and aid in rational approaches to the manipulation of stem cells for therapeutic benefit.

Animals↗
PubMed1998

The C8/144B monoclonal antibody recognizes cytokeratin 15 and defines the location of human hair follicle stem cells.

Stem cells are vital for the homeostasis of self-renewing tissues such as the hair follicle. Epithelial stem cells have been implicated in tumorigenesis and wound healing, and their manipulation may have wide ranging applications including gene therapy and tissue transplantation. Rodent hair follicle stem cells have been localized to an area of the follicle called the bulge, however, the identification and characterization of human hair follicle stem cells has been hampered by a lack of cellular markers for this area. We have determined that the C8/144B monoclonal antibody, originally generated against a short intracytoplasmic peptide of CD8, preferentially immunostains hair follicle bulge keratinocytes without staining the remaining hair follicle. Using expression cloning, we identified cytokeratin 15 as the keratinocyte protein recognized by the C8/144B monoclonal antibody. By delineating the bulge using this antibody, we demonstrated that bulge cells possess a stem cell phenotype characterized by their slowly-cycling nature, preferential proliferation at the onset of new hair follicle growth, high level of beta1 integrin expression, and expression of cytokeratin 19.

Adult↗
PubMed2002

[Embryonic and adult stem cells].

Stem cells possess an unlimited potential to regenerate and can acquire the identity of various differentiated cells. In the case of embryonic stem cells all the different cells of an organism can be generated. Recently the hitherto underestimated differentiation potential of adult stem cells has also taken center stage. These findings have opened up new perspectives in transplantation medicine and cell therapy for degenerative diseases. Before these possibilities can be realized, however, a number of ethical and scientific-technical obstacles have to be overcome. The latter are caused for example by the low abundance of the cell material as well as by possible immunological rejection reactions.

Adult↗
PubMed2004

Molecular signatures of proliferation and quiescence in hematopoietic stem cells.

Stem cells resident in adult tissues are principally quiescent, yet harbor enormous capacity for proliferation to achieve self renewal and to replenish their tissue constituents. Although a single hematopoietic stem cell (HSC) can generate sufficient primitive progeny to repopulate many recipients, little is known about the molecular mechanisms that maintain their potency or regulate their self renewal. Here we have examined the gene expression changes that occur over a time course when HSCs are induced to proliferate and return to quiescence in vivo. These data were compared to data representing differences between naturally proliferating fetal HSCs and their quiescent adult counterparts. Bioinformatic strategies were used to group time-ordered gene expression profiles generated from microarrays into signatures of quiescent and dividing stem cells. A novel method for calculating statistically significant enrichments in Gene Ontology groupings for our gene lists revealed elemental subgroups within the signatures that underlie HSC behavior, and allowed us to build a molecular model of the HSC activation cycle. Initially, quiescent HSCs evince a state of readiness. The proliferative signal induces a preparative state, which is followed by active proliferation divisible into early and late phases. Re-induction of quiescence involves changes in migratory molecule expression, prior to reestablishment of homeostasis. We also identified two genes that increase in both gene and protein expression during activation, and potentially represent new markers for proliferating stem cells. These data will be of use in attempts to recapitulate the HSC self renewal process for therapeutic expansion of stem cells, and our model may correlate with acquisition of self renewal characteristics by cancer stem cells.

Analysis of Variance↗
PubMed2003

Dpp signaling silences bam transcription directly to establish asymmetric divisions of germline stem cells.

Stem cells execute self-renewing and asymmetric cell divisions in close association with stromal cells that form a niche. The mechanisms that link stromal cell signaling to self-renewal and asymmetry are only beginning to be identified, but Drosophila oogenic germline stem cells (GSCs) have emerged as an important model for studying stem cell niches. A member of the Bone Morphogenetic Protein (BMP) ligand family, Decapentaplegic (Dpp), sustains ovarian GSCs by suppressing differentiation in the stem cell niche (Figure 1A). Dpp overexpression expands the niche, blocks germ cell differentiation, and causes GSC hyperplasty. Here, we show that the bag-of-marbles (bam) differentiation factor is the principal target of Dpp signaling in GSCs; ectopic bam expression restores differentiation even when Dpp is overexpressed. We show that the transcriptional silencer element in the bam gene integrates Dpp control of bam expression. Finally and most significantly, we demonstrate for the first time that Dpp signaling regulates bam expression directly since the bam silencer element is a strong binding site for the Drosophila Smads, Mad and Medea. These studies provide a simple mechanistic explanation for how stromal cell signals regulate both the self-renewal and asymmetric fates of the products of stem cell division.

Animals↗
PubMed2003

Biology and clinical applications of mesenchymal stem cells.

Stem cell populations are found in most adult tissues and, in general, their differentiation potential may reflect the local cell population. Hematopoietic, epidermal, mesenchymal, neural and hepatic stem cells have been described. It may be that, in the adult, these cells are the reservoirs of reparative cells that are mobilized following injury and migrate to the wound site where, in cooperation with local cells, they participate in the repair response. Mesenchymal stem cells, isolated from the bone marrow, have the capacity to differentiate into cells of connective tissues. Some striking examples of the therapeutic use of MSCs have been reported recently in applications such as coronary artery disease, spinal cord injury, Parkinson's Disease, and liver regeneration. In orthopaedic medicine, MSC therapy has been applied in bone and cartilage repair and in the treatment of osteoarthritis. The question of the host response to implanted MSCs is critical as these cells are being evaluated in clinical applications. There are several aspects to the implanted cell-host interaction that need to be addressed as we attempt to understand the mechanisms underlying stem cell therapies. These are (1) the host immune response to implanted cells, (2) the homing mechanisms that guide delivered cells to a site of injury, and (3) differentiation of implanted cells under the influence of local signals.

Animals↗
PubMed2006

Isolation of rat bone marrow stem cells.

Stem cell research has become an important field of study for molecular, cellular, and clinical biology as well as pharmaco-toxicology. Indeed, stem cells have a strong proliferative and unlimited self-renewal potential and are multipotent. In vivo as well as in vitro studies have confirmed the differentiation of adult bone marrow stem cells into muscle cells, adipocytes, cardiomyocytes, neuroectodermal cells, osteoblasts, chondroblasts, and so on. Recently, it has been shown that, under appropriate culture conditions, adult bone marrow stem cells may also differentiate into hepatocyte-like cells. Because of their extensive proliferative capacity and pluripotency, adult bone marrow stem cells could serve in the future as an unlimited source of hepatocytes for pharmaco-toxicological research and testing. We describe a protocol for isolation of mononuclear cells from adult rat bone marrow.

Animals↗
PubMed2004

CD133, a novel marker for human prostatic epithelial stem cells.

Stem cells are clonogenic cells with self-renewal and differentiation properties, which may represent a major target for genetic damage leading to prostate cancer and benign prostatic hyperplasia. Stem cells remain poorly characterised because of the absence of specific molecular markers that permit us to distinguish them from their progeny, the transit amplifying cells, which have a more restricted proliferative potential. Human CD133 antigen, also known as AC133, was recently identified as a haematopoietic stem cell marker. Here we show that a small population (approximately 1%) of human prostate basal cells express the cell surface marker CD133 and are restricted to the alpha(2)beta(1)(hi) population, previously shown to be a marker of stem cells in prostate epithelia. alpha(2)beta(1)(hi)/CD133(+) cells exhibit two important attributes of epithelial stem cells: they possess a high in vitro proliferative potential and can reconstitute prostatic-like acini in immunocompromised male nude mice.

AC133 Antigen↗
PubMed2004

Mechanisms controlling pathogenesis and survival of leukemic stem cells.

Stem cells are an integral component of normal mammalian physiology and have been intensively studied in many systems. Intriguingly, substantial evidence indicates that stem cells also play an important role in the initiation and pathogenesis of at least some cancers. In particular, myeloid leukemias have been extensively characterized with regard to stem and progenitor cell involvement. Thus, as a focal point for both scientific and therapeutic endeavors, leukemic stem cells (LSC) represent a critical area of investigation. LSC appear to retain many characteristics of normal hematopoietic stem cells (HSC) as evidenced by a hierarchical developmental pattern, a mostly quiescent cell cycle profile, and an immunophenotype very similar to HSC. Consequently, defining unique properties of LSC remains a high priority in order to elucidate the molecular mechanisms driving stem cell transformation, and for developing therapeutic strategies that specifically target the LSC population. In this review, we discuss emerging concepts in the field and describe how various molecular and cellular characteristics of leukemia cells might be exploited as a means to preferentially ablate malignant stem cells.

Acute Disease↗
PubMed2003

Expression of a novel recombinant dual human stem cell factor in insect cells.

Stem cell factor (SCF) is a hematopoietic cytokine that promotes the survival, proliferation, and differentiation of hematopoietic cells. A dual human stem cell factor (dhSCF) cDNA was constructed, which consisted of a full-length human stem cell factor cDNA plus a truncated hSCF cDNA (1-145aa), linked by a peptide (GGGGSGGGGSGG) coding region. The dhSCF gene was cloned into baculovirus transfer vector pAcSecG2T under the control of polyhedrin promoter. The Sf9 cells infected with the recombinant virus expressed rdhSCF up to 6000 U/10(6) cell in flask and 8300 U/10(6) cell in spinner flask. The rdhSCF was purified by two-step chromatography. The molecular mass of rdhSCF was examined by western blotting and HPLC analysis. The specific activity of rdhSCF was up to 3.1x10(6) U/mg, about 8.7 times as high as that of monomer rhSCF from Escherichia coli.

Animals↗
PubMed2006

Target for cancer therapy: proliferating cells or stem cells.

Tumor stem cells are quiescent and, therefore, resistant to therapy, yet harbor the capacity to replenish a tumor after therapy. Therefore, it is tempting to explain all therapeutic failures by the persistence of tumor stem cells. Yet, this explanation is relevant only to initial stages of stem-cell-dependent tumors (such as chronic myeloid leukemia) that, actually, are well controlled by therapy. In advanced cancers that poorly respond to therapy, quiescent tumor stem cells play a negligible role. Instead, proliferating cells determine disease progression, prognosis, therapeutic failures, and resistance to therapy. And therapy fails not because it eliminates only proliferating tumor cells, but because it does not eliminate them. With noticeable exceptions, it is the proliferating cell that should be targeted, whereas resting cancer cells including stem and dormant cells need to be targeted only when they 'wake up'. Finally, I discuss a strategy of selectively killing dominant proliferating clones, including proliferating stem-like and drug-resistant cancer cells, while sparing normal cells.

Cell Division↗
PubMed2004

[Research advances of adult stem cells and dental stem cells].

Human stem cells have a major effect in the development of human bodies. Acting as an in vitro model, human stem cells have a great value in the study of the mechanism of individual development and in the cell-replacement treatments and gene therapy of tissue deficiency diseases. The study of stem cells has been given rise to a keen interests in the bio-medical area at present. This paper reviews the present status and progress of adult stem cells and dental stem cells.

Adult Stem Cells↗
PubMed2000

Why stem cells?

Stem cells are viewed from the perspectives of their function, evolution, development, and cause. Counterintuitively, most stem cells may arise late in development, to act principally in tissue renewal, thus ensuring an organism's long-term survival. Surprisingly, recent reports suggest that tissue-specific adult stem cells have the potential to contribute to replenishment of multiple adult tissues.

Animals↗