EXTL3 and cancer: Together with the fact that the regulatory sequences flanking the Drosophila rpr coding region show significantly less sequence divergence than expected and a high occurrence of conserved transcription factor binding motifs (Figure 6B, 6C), these findings lead us to propose that coupling of differentiation and cell death repression via a single transcription factor represents a general cancer prevention mechanism (Figure 7), which could be employed by a large number of developmental regulators in diverse organisms.