Differentiation capacity of hESC lines carrying a 20q11.21 amplification

Being present in over 20% of human embryonic stem cell (hESC) lines worldwide, a gain of 20q11.21 is one of the most recurrent chromosomal abnormalities in hESC. The smallest region of amplification comprises 3 genes: BCL2L1, ID1 and HM13. Bcl-xL, the predominantly expressed isoform of BCL2L1, has an anti-apoptotic function and is responsible for the selective advantage during culture of hESC carrying the 20q11.21 amplification. ID1 plays an important role in maintaining pluripotency while HM13 has no known implication in this phenomenon. Two independent studies have thoroughly described the mechanism behind the selective advantage of the mutation, but important information on whether it influences differentiation is nevertheless still lacking. We aimed to compare the behavior of genetically normal hESC lines to that of lines carrying a gain of 20q11.21, after spontaneous and lineage directed differentiation. We studied 3 pairs of in-house derived hESC lines for their differentiation capacity towards the mesodermal lineage (osteoprogenitor-like cells) and endodermal lineage (definitive endoderm), as well as after embryoid body formation. We used gene expression data (mRNA and protein levels) to assess the overall onset of differentiation and the probability of the mutant lines retaining higher numbers of undifferentiated cells after differentiation. We observed comparable differentiation efficiency among all pairs of lines with small inter-line variability, which is a frequently observed phenomenon. Moreover, the mutant lines consistently expressed low levels of pluripotency markers (POU5F1 and NANOG) after differentiation excluding an influence of the extra copy(ies) of ID1. However, immunohistochemistry suggested an improved cell survival of the mutant cells during differentiation. Moreover, mutant cells appear to survive in the differentiation media better than their normal counterparts, regardless of whether the cells differentiated to the intended cell type or not. Further quantification of apoptosis to confirm this hypothesis is ongoing. Overall our study suggests that aberrant cells display similar differentiation ability (whether in a spontaneous or lineage-specific way), but maintain a character that is less prone to apoptosis throughout the process of differentiation.