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Origin of cultured cells
The origin of cultured cells Most people work with limited or continuous cell lines under standard conditions. Therefore, it is very important to consider the cell composition in the culture. For example, the cells exhibit differentiation characteristics under induced conditions, or it means that the cultured cells It is mature, it is enough to maintain its ability to continuously synthesize special proteins; or it means that the cultured cells are composed of precursor cells or stem cells, these cells have the ability to proliferate, and the artist maintains an undifferentiated state, when proper induction conditions are available, which Some or all of the cells will mature and differentiate. The guiding consideration is that the culture is considered to be a balanced state composed of pluripotent stem cells, undifferentiated directional precursor cells and mature cells, and this balance can Changes in environmental conditions. In the case of low cell density, continuous passage can promote cell proliferation and limit cell differentiation, while high cell density, low serum and appropriate hormone conditions can promote cell differentiation and resist cell proliferation. The source can determine the cell composition of the culture formed later. Therefore, the cell line obtained from the embryo is smaller than that derived from mature tissue The line contains a relatively large number of stem cells and precursor cells and has a stronger self-renewal capacity. In addition, cell cultures obtained from tissues that are constantly renewed in the body (such as epidermis, intestinal epithelium, and hematopoietic cells) may still contain stem cells. Under appropriate conditions, they will have a longer life span. However, those cultures derived from tissues that are only renewed under stress conditions, such as fibroblasts, muscles, and glials, may only contain some clear life spans. Precursor cells that can be directed to differentiate. Therefore, the identification of cultured cells can not only be limited to the cell lineage in the body (hematopoietic cells, hepatocytes, glial cells, etc.), but also must consider the growth stage of the lineage (stem cells , Oriented precursor cells or mature differentiated cells). Although, along the path of differentiation is considered irreversible, the concept of commitment is currently being questioned [Kondo and Raff, 2004; Le Douarin et al. , 2004]. Some precursor cells can be transformed back into stem cell state and redifferentiated along the same or different lineage. During the cultivation process, cells obtained from tumors do not follow the above rules, for example, large Mouse hepatoma cells proliferate in vitro and still exhibit some differentiation characteristics. The closer they are to the phenotype of normal cells, the stronger the inhibition of cell proliferation. Although the position of cells in cell lines may not be closely related to proliferation, But it is not unrelated (for example, at high density and low proliferation rate, B1, melanoma cells produce more melanin). Up to now, people have not been sure whether there can be a transition between cell lineages.