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Spontaneous Differentiation (spontaneous + differentiation)

Distribution by Scientific Domains

Life Sciences	83%

Selected Abstracts

Vascular gene expression and phenotypic correlation during differentiation of human embryonic stem cells

DEVELOPMENTAL DYNAMICS, Issue 2 2005
Sharon Gerecht-Nir
Abstract The study of the cascade of events of induction and sequential gene activation that takes place during human embryonic development is hindered by the unavailability of postimplantation embryos at different stages of development. Spontaneous differentiation of human embryonic stem cells (hESCs) can occur by means of the formation of embryoid bodies (EBs), which resemble certain aspects of early embryos to some extent. Embryonic vascular formation, vasculogenesis, is a sequential process that involves complex regulatory cascades. In this study, changes of gene expression along the development of human EBs for 4 weeks were studied by large-scale gene screening. Two main clusters were identified,one of down-regulated genes such as POU5, NANOG, TDGF1/Cripto (TDGF, teratocarcinoma-derived growth factor-1), LIN28, CD24, TERF1 (telomeric repeat binding factor-1), LEFTB (left,right determination, factor B), and a second of up-regulated genes such as TWIST, WNT5A, WT1, AFP, ALB, NCAM1. Focusing on the vascular system development, genes known to be involved in vasculogenesis and angiogenesis were explored. Up-regulated genes include vasculogenic growth factors such as VEGFA, VEGFC, FIGF (VEGFD), ANG1, ANG2, TGF,3, and PDGFB, as well as the related receptors FLT1, FLT4, PDGFRB, TGF,R2, and TGF,R3, other markers such as CD34, VCAM1, PECAM1, VE-CAD, and transcription factors TAL1, GATA2, and GATA3. The reproducibility of the array data was verified independently and illustrated that many genes known to be involved in vascular development are activated during the differentiation of hESCs in culture. Hence, the analysis of the vascular system can be extended to other differentiation pathways, allocating human EBs as an in vitro model to study early human development. Developmental Dynamics 232:487,497, 2005. © 2004 Wiley-Liss, Inc. [source]

Cytochemical and ultrastructural characterization of growing colonies of human embryonic stem cells

JOURNAL OF ANATOMY, Issue 4 2004
Kohei Johkura
Abstract The morphology of human embryonic stem (ES) cells changes with their colonial growth. For a better understanding of the growth of ES cell colonies in culture, we determined their cytochemical and ultrastructural characteristics focusing on images of living cells under a phase contrast microscope. During the initial growth stages, the colonies exhibited a mosaic appearance with discernible cell,cell borders. PAS staining coupled with amylase digestion demonstrated that the bright granules and dark deposits in the cytoplasm contained glycogen. Ultrastructurally they were glycogen accumulations, and clustered open spaces associated with various amounts of glycogen. Although intercellularly heterogeneous, these structures were detectable throughout colony growth. As the colonies grew, compaction towards the centre emerged and increased, accompanied by heterogeneous increases in coarse particles with or without a halo. TUNEL showed these particles to consist at least in part of apoptotic cells/bodies. Transmission electron microscopy indicated that most apoptotic cells had been phagocytosed by intact ES cells. Spontaneous differentiation was detected occasionally in the periphery of the colonies. The presence of PAS-positive fibrous structures not susceptible to amylase digestion and laminin-immunoreactivity indicated the accumulation of extracellular matrix in the peripheral differentiated areas. These findings made it possible to determine the growth stage of human ES cell colonies. [source]

Noggin maintains pluripotency of human embryonic stem cells grown on Matrigel

CELL PROLIFERATION, Issue 4 2009
G. Chaturvedi
Objective:, Spontaneous differentiation of human embryonic stem cell (hESC) cultures is a major concern in stem cell research. Physical removal of differentiated areas in a stem cell colony is the current approach used to keep the cultures in a pluripotent state for a prolonged period of time. All hESCs available for research require unidentified soluble factors secreted from feeder layers to maintain the undifferentiated state and pluripotency. Under experimental conditions, stem cells are grown on various matrices, the most commonly used being Matrigel. Materials and Methods:, We propose an alternative method to prevent spontaneous differentiation of hESCs grown on Matrigel that uses low amounts of recombinant noggin. We make use of the porosity of Matrigel to serve as a matrix that traps noggin and gradually releases it into the culture to antagonize bone morphogenetic proteins (BMP). BMPs are known to initiate differentiation of hESCs and are either present in the conditioned medium or are secreted by hESCs themselves. Results:, hESCs grown on Matrigel supplemented with noggin in conditioned medium from feeder layers (irradiated mouse embryonic fibroblasts) retained both normal karyotype and markers of hESC pluripotency for 14 days. In addition, these cultures were found to have increased cell proliferation of stem cells as compared to hESCs grown on Matrigel alone. Conclusion:, Noggin can be utilized for short term prevention of spontaneous differentiation of stem cells grown on Matrigel. [source]

Strategies for Directing the Differentiation of Stem Cells Into the Osteogenic Lineage In Vitro,

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2004
Boon Chin Heng
Abstract A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro. [source]

Temporal Changes in Expression of FoxA1 and Wnt7A in Isolated Adult Human Alveolar Epithelial Cells Enhanced by Heparin

THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 6 2010
K.B.C. Apparao
Abstract Pre- and postnatal developmental studies of the lung have provided compelling evidence demonstrating multiple factors that orchestrate alveolar epithelial cell differentiation. The extent to which reactivation of certain developmental pathways in the adult might influence the course of differentiation of alveolar type 2 cells (AT2) into AT1 cells is not known. In this study, we examined selected members of the forkhead (Fox) family of transcription factors and the Wnt (wingless) family of signaling proteins for expression during human alveolar cell differentiation in vitro and determined their potential responses to sulfated components of extracellular matrix (ECM), like those shed from cell surfaces or found in basement membrane and modeled by heparin. Isolated adult human AT2 cells cultured over a 9-day period were used to define the temporal profile of expression of targeted factors during spontaneous differentiation to AT1-like cells. FoxA1 protein was upregulated at early to intermediate time points, where it was strongly elevated by heparin. Gene expression of wnt7A increased dramatically beginning on day 3 and was enhanced even further on days 7 and 9 by heparin, whereas protein expression appeared at days 7 and 9. These temporal changes of expression suggest that sulfated ECMs may act to enhance the increase in FoxA1 at the critical juncture when AT2 cells commence the differentiation process to AT1 cells, in addition to enhancing the increase in wnt7A when the AT1 cell phenotype stabilizes. Collectively, these factors may act to modulate differentiation in the adult human pulmonary alveolus. Anat Rec, 293:938,946, 2010. © 2010 Wiley-Liss, Inc. [source]