The timing of Hoxb gene expression in mouse embryonic stem cells following induction of differentiation. Mouse embryonic stem (ES) cells (CCE/R) were induced to differentiate by removal of the growth factor leukaemia inhibitory factor (LIF) and replating at day 0, followed by addition of retinoic acid (RA, 1 μM) at day 2. RNA and cDNA were prepared from cell pellets at day 0 and daily thereafter and transcript levels from individual Hoxb genes (Hoxb 1 to 9) were determined by real time-quantitative (RT-q)PCR. At each timepoint, expression was calculated as a percentage of the highest value in the untreated sample. Error bars represent the standard error of the mean of independent experiments (n = 3).