Stem cells system

Chiba S.(2006) Notch signaling in stem cell systems. Stem Cell 24 2437-2447. 

Schematic representation of the hematopoietic cascade in mice and human (hum). All the cells of the hematopoietic system are positive for antigen CD45. Based on this, the dynamics of surface antigen expression along development of different mature cells derived from the hematopoietic stem cell system can be observed. Rounded arrows indicate self-renewal potential. Smooth thinner arrows indicate directions of cellular differentiation. The identification of CDs (clusters definition) and other antigen cell markers are listed in the glossary. (LT-HSC - long term hematopoietic stem cell ST-HSC - short term hematopoietic stem cell MPP - multipotent progenitor CLP - common lymphoid precursor CMP - common myeloid precursor GMP - granulocyte-monocyte precursor MEP - megacaryocyte-erythrocyte precursor T - T lymphocyte B - B lymphocyte NK - natural killer cell DC - dendritic cell).

Klebe, R. J., and Ruddle. F. H. (1969). Neuroblastoma Cell culture analysis of a differentiating stem cell system. J. Cell Biol. 43, 69A. 

It would be impossible to review the fundamental characteristics of every stem ceU/organ system in the body in this chapter. Thus, I wiU focus on only one stem cell system, the mesenchymal stem cells (MSCs), that has already proven to be a versatile source of reparative cells for Tissue Engineering applications. 

Significant differences are also apparent for the effect of pH on the fermentation rate. The narrow pH optimum characteristic of a free cell system is replaced by an extremely broad range upon immobilisation. This effect stems from the gradient pH that exists within the bead. 

To circumvent this problem, vectors that are based on lentiviruses have been developed. In contrast to prototypic retroviruses, lentiviruses do not require cell division for integration. Gene-therapy vectors have been developed from a broad spectrum of lentiviruses including human immunodeficiency vims (HIV), simian and feline immunodeficiency vims as well as visna/maedi vims. The most widely used lentiviral vector system is based on HIV-1. These vectors can efficiently transduce a broad spectrum of dividing and nondividing cells including neurons, hepatocytes, muscle cells, and hematopoietic stem cells [1,2]. 

For patients with leukemia, the transfer of siRNA-based strategies into clinical applicability will certainly be both frustrating and time-consuming and many hurdles still have to be overcome in order to realize the therapeutic potential of siRNAs. Efficient delivery of siRNA into the leukemic stem cell and their unknown influence of the patient s immune system are the most challenging issues that need to be addressed. 

A further interesting phenotype identified in SDF-1/CXCR4 knockout mice is a deficiency in blood vessel development, initially observed in the gastrointestinal system (Tachibana et al. 1998). Consistent with such observations, CXCR4 receptors have been shown to be expressed by hemangioblasts, the earliest common precursor to hematopoietic and endothelial stem cells, found in yolk sac... 

A large number of cells are involved in the immune response and all are derived fiom the multipotential stem cells of the bone marrow. The predominant cell is the lymphocyte but monocytes-macrophages, endothelial cells, eosinophils and mast cells are also involved with certain immune responses. The two types of immunity (humoral and cell-mediated) are dependent on two distinct populations of lymphocytes, the B cells and the T cells respectively. Both the humoral and the cell-mediated systems interact to achieve an effective immune response. 

Beyond roles of chemokine receptors in hematopoiesis and innate immunity, roles for chemokines in adaptive immunity emerged. Moreover, other nonleukocyte migration properties of chemokine receptors have been identified. These include roles in the biology of endothelial cells (Chapter 15), cancer (Chapter 16), smooth muscle (Chapter 11), fibroblasts (Chapter 14), stem cells (Chapter 8), and all cell types associated with nervous system tissues (Chapter 17). In many instances, broad functional overlap is evident as chemokines can direct the migration of these cells just as they do with leukocytes. In certain instances, the ability of chemokines to retain cell populations within a specific microenvironment is as important as their migration-promoting properties. However, it is also clear that migration and retention are not the sole end points. 

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