Fig. 1. Different categories of gene expression corresponding to successive stages of early development. (A) Early Drosophila development showing representative embryos of the five successive stages of epithelium formation and remodelling selected for transcriptome analysis (T0-T4, DIC images, the dorsal side is towards the top and anterior towards the left). (B-D) Examples of genes exhibiting a developmental regulation of expression. Increased and decreased expression compared with the mean expression of the five time points (set to 0) for each gene are shown in red and green, respectively. The colour scale ranges from saturated green for log2 ratios -2.0 and below, to saturated red for log2 ratios +2.0 and above. Cluster of genes with a predominant maternal expression (T0, B). Clusters of genes displaying an increased expression in slow phase of cellularisation (T1, C) or throughout cellularisation (T1+T2, D). (E) Schematic representation of the different categories of gene expression profiles identified. The variations are only qualitative. The number of genes associated with each category is indicated. Some genes are absent from T0 to T4 (7232, bright green), or display a uniform expression from T0 to T4 (278, dark green).