Figure 1. Experimental setup and an overview of the expression changes.

(a) Sampling setup. At 20°C, eggs hatch 10–12 hours after they were laid, leading to L1 stage worms. First, 2nd, 3rd and 4th molts occur 26, 34, 44 and 56 hours after egg laying resp., leading to L2, L3, L4 and adult worms. Microscopic observations of the developmental stage of the vulva at several time points are summarized in the blue graph. The red lines in the diagram below the graph represent the time points at which samples for the microarrays (MA) were drawn. The yellow lines show sampling points that were used later to confirm that the MA data could be used to predict the age of a sample (see Supplementary methods for more information). (b) A Principal component analysis of the relative gene expression shows that 66.3% of the variation sorts the time-points in a chronological order. Notably, the 50 h time-point is very distant from the others, indicating the sudden switch in expression. (c) The relative expression in log2 ratio of the mean, shown in 100 kb bins. There is a pronounced shift in the expression activity of the chromosomal regions, centring around 50 hrs.