Figure 3:

The Hox code and positional memory. A) The Hox genes are encoded as two separate gene clusters in the fly and share a high degree of conservation with the four clusters, arising through the process of genome duplication, in most vertebrates. The gene clusters are expressed in a spatial co-linear manner resulting in the coordinated and progressive segmentation of the developing embryo. B) The spatial and temporal co-linear expression pattern of the Hox genes during development is regulated, in part, through activating (H3K4me3) and repressive (H3K27me3) chromatin marks. C) Fibroblast populations derived from the adult lung and foot show distinct, location specific differences in transcriptional machinery (RNA polymerase II) and repressive epigenetic marks (H3K27me3) associated with the Hox genes (image modified with permission from (Lan et al., 2007)).