Dynamic gene expression during EB differentiation in serum and serum-free media containing BMP4 [2 ng/ml]. Expression of stem cell, primitive streak and late mesoderm genes were analysed by quantitative RT-PCR in undifferentiated ES cells (0, grey bar) and in EBs collected for up to 16 days in serum (white bars) or defined media (black bars) from the same starting ES cell populations. Bars represent the means of three (serum) or two (serum-freeB4L) biological replicates. The Y-axis represents a log scale normalized relative to the housekeeping gene HPRT. Error bars indicate standard deviation.