The Loss of Phenotypic Traits by Differentiated Cells in Vitro, I. Dedifferentiation of Cartilage Cells

Abstract

The experiments to be described were designed to approach the following type of question: Will the differentiated state of a tissue cell survive multiple divisions in vitro? Do the cultured progeny of differentiated cells inherit the cellular mechanisms determining the unique somatic traits of their parental cells in a manner analogous to the way in which (1) Paramecia transmit Kappa particles to their daughter cells (Sonneborn,33 34 Beale,2 Preer3), (2) bacteria inherit genes for constitutive or inducible enzymes in the absence of substrate (Novick and Weiner,28 Spiegel-man35) or (3) temperate phage particles give rise to lysogenic progeny (Jacob and Wollman20)? Information of this kind is essential if the roles of the nucleus (i.e., genes) and the cytoplasm in cell differentiation are to be defined. An unambiguous approach to these problems requires that the following five conditions be fulfilled: (1) The initial population of differentiated cells must be homogeneous. (2) The cells must divide many times during the experiment. (3) The cells must not back-differentiate to the parental type immediately after each division. (4) The initial population must consist of differentiated cells and not dividing precursor cells whose progeny differentiate and thereafter cease dividing (e.g., presumptive muscle cells, presumptive blood cells, presumptive pigment cells, etc.). (5) The somatic traits used as markers must be specific to the parent cell and readily characterized. Given this list of conditions, it is clear that many kinds of somatic cells are excluded as test material. For example, both nerve cells and keratinizing skin cells do not divide. Liver and kidney cells offer difficulties of another kind; since it is difficult to secure a homogeneous population of either type of epithelial cell, it is possible that in long-term cultures the epithelial cells are selected against and the surviving population is derived from one of the "contaminating" cell types. Cartilage cells from vertebrae of 10-day chick embryos, on the other hand, satisfy the five conditions outlined. Pieces of cartilage may be obtained which consist * This investigation was supported, in part, by Research Grants B-493 and B-1629 from the

Differences in the secretome of cartilage explants and cultured chondrocytes unveiled by SILAC technology

“…During the expansion phase, the cells dedifferentiate and gradually shift to a more fibroblastic phenotype, featured by a change in the synthesis of matrix constituents. 1,2 Generally, the dedifferentiation process is characterized by a downregulation of cartilage-specific proteoglycans and other cartilage structural proteins, such as collagen type II, cartilage oligomeric matrix protein, and collagen type IX. Concomitantly, the synthesis of matrix proteins characteristic of more fibrous tissues, such as collagen type I, are induced.…”

Assessment of the gene expression profile of differentiated and dedifferentiated human fetal chondrocytes by microarray analysis

“…Studies that have examined the plasticity of the chondrocyte phenotype from many different species have consistently shown that culture of these cells in monolayers on plastic substrata for prolonged periods or upon repeated passages leads to the loss of their spherical shape and to the acquisition of an elongated fibroblast-like morphology (7,(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). These morphologic alterations are accompanied by profound biochemical changes, including loss of the cartilage-specific phenotype, as evidenced by an arrest of the synthesis of the cartilage-specific collagens (types II, IX, and XI) and proteoglycans (aggrecan), initiation of synthesis of the interstitial collagens (types I, III, and V), and increase in the synthesis of fibroblasttype proteoglycans (versican) at the expense of aggrecan (7,17,(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29).…”

Influence of culture conditions on expansion and re-differentiation of chondrocytes from horses of different ages

“…The long accepted postulation has been that low seeding densities allow for higher proliferation rates but lead to more pronounced de-differentiation (Holtzer et al 1960, Watt 1988. Several mechanisms have been suggested to explain this phenomenon, including more population doublings before confluence is reached and changes in cytoskeletal microfilament organization (Lim et al 2000, Mandl et al 2004.…”