Normal expression of DNA methyltransferase (DNMT)1, DNMT3A, DNMT3B and DNA methyltransferase 3-like (DNMT3L) in XY and XX embryonic stem (ES) cells. (a) All three DNMTs and DNMT3L were expressed at similar levels regardless of passage history or sex chromosome substitution. (b) Comparison of a panel of eight XX and three XY ES cell lines showed similar expression of DNMT3A and DNMT3B. (c) Quantification of DNMT3A and DNMT3B expression. Signal intensities were measured by an imaging system as described in the text, and normalized against tubulin. The data showed that that XY and XX ES cells had very similar levels of DNMT3A and DNMT3B. Error bars indicate one standard deviation.