BCL-XL Mediates the Strong Selective Advantage of a 20q11.21 Amplification Commonly Found in Human Embryonic Stem Cell Cultures

摘要

class="head no_bottom_margin" id="sec1title">IntroductionHuman embryonic stem cells (hESCs) have an indefinite capacity to self-renew, a key attribute that is necessary for the scale-up production required to translate their potential into direct clinical and industrial applications. However, during progressive culture, cells are susceptible to acquiring genetic and chromosomal abnormalities, which can provide a competitive growth advantage and become fixed in the population. Chromosomal aberrations in hESCs are nonrandom and commonly involve gains of chromosomes (or fragments of) 1, 12, 17, and X (), which are also commonly observed in human embryonal carcinoma cells (hECCs), the stem cells of teratocarcinomas (). Although this selection clearly reflects culture adaptation to an in vitro environment due to increases in the cell growth rate, survival, or suppression of differentiation, the region selected may also comprise or form part of stem cell neoplastic progression. Identifying possible driver mutations for this process is a major challenge, due in part to the relatively large genomic size of the chromosomal amplifications and the number of genes encompassed. The pluripotency gene NANOG, which maps to chromosome 12 (p13.31), is a potential candidate for driving the establishment of chromosome 12 duplication; however, it is not uniformly present in the minimal amplicons identified in hECCs. Recently, molecular karyotyping by SNP array and array comparative genomic hybridization (aCGH) analysis has revealed another amplification that is common among hESC lines, representing chromosome 20q11.21 (). This copy number variant (CNV) was present in >20% of 125 screened hESC lines, with a minimal amplicon of 0.55 MB (), and in 18% of 34 screened human induced pluripotent cells (hiPSCs) (). The amplification is not of donor origin, but arises during culture. In this study, we aimed to determine whether this amplification confers a competitive advantage to the cells, define the mechanism behind the advantage, and identify the driving mutation.