Human embryonic stem cells do not change their X-inactivation status during differentiation [RNA-Seq]

Female human ESC-lines can carry active X-chromosomes (Xa) or an XIST-RNA-coated inactive X-chromosome (XiXIST+). Additionally, many ESC lines have abnormal X-chromosomeinactivation (XCI)-states where the Xi no longer expresses XIST-RNA and has transcriptionally active regions (eroded Xi=Xe). The fate of each XCI-state upon differentiation is unclear because individual lines often contain a mixture of XCI-states. Here, we established homogeneous XiXa, XeXa, and XaXa ESC-lines. Employing RNA-FISH, RNA-sequencing and DNA methylation analyses, we found that these lines were unable to initiate XIST-expression and X-chromosome-wide silencing upon differentiation indicating that the ESC XCI-state is maintained in differentiated cells. Consequently, differentiated XeXa and XaXa cells displayed higher levels of X-linked gene-expression than XiXa cells. Although global transcriptional compensation between X-chromosomes and autosomes is not required for female ESC-differentiation, the degree of X-chromosome-silencing influences differentiation efficiencies. Our data suggest that the XiXIST+Xa state is inherent to human ESCs and that all other XCI-states, including XaXa, are abnormal and arise during ESC-derivation or maintenance. RNA-seq was used to measure the expression state of X-linked and autosomal genes in undifferentiated human embryonic stem cells with different X-chromosome states and their differentiated cells.