In Vitro Self-Renewal Assays for Brain Tumor Stem Cells
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Early development of human organisms relies on stem cells, a population of non-specialized cells that can divide symmetrically to give rise to two identical daughter cells, or divide asymmetrically to produce one identical daughter cell and another more specialized cell. The capacity to undergo cellular divisions while maintaining an undifferentiated state is termed self-renewal and is responsible for the maintenance of stem cell populations during development. In addition, self-renewal plays a crucial role in the homeostasis of developed organism through replacement of defective cells.Similar to their non-malignant counterparts, it has been postulated that tumor cells follow a differentiation hierarchy, with the least differentiated cells termed cancer stem cells (CSCs) at the apex. These tumor stem cells possess the ability to self-renew, have a higher capacity to initiate tumor growth when xenografted into an animal model, and can recapitulate the cell heterogeneity of the tumor they originate from. Hence, further investigation of mechanisms governing the self-renewal in cancer can lead to development of novel therapies targeting CSCs.In this chapter, we described the soft agar assay and the limiting dilution assay (LDA) as two easy-to-implement and inexpensive assays to measure the stemness properties of brain tumor stem cells (BTSCs). These techniques constitute useful tools for the preclinical evaluation of therapeutic strategies targeting BTSCs clonogenicity.