Whe embryonic stem cells are in vitro expanded threir telomereres lengthen, in the absence of genetic manipulations, concomitant with the loss of heterochromatic marks. In order to analyze whether there would be changes in gene expression during in vitro expansion we performed RNA-seq and found no substantial differences in gene expression at passage 6 or 16. Overall design: Embryonic stem (ES) cells were derived from blastocysts expressing GFP in the Rosa26 locus. Four independent lines of ES were in vitro expanded to passage 16. Total RNA was extracted from each independent clones, RNA was extracted and prepared for RNA-seq.