How to make stripes: revising the pair-rules

A key step in Drosophila segmentation is the transition from non-periodic to periodic gene expression patterns, a process that is controlled by transcriptional regulation of the pair-rule genes. Primary pair-rule genes generate their striped expression patterns through stripe-specific cis-regulatory elements that are controlled by the preceding maternal and gap gene expression patterns, whereas secondary pair-rule genes establish their stripe patterns in response to positional cues already provided by the primary pair-rule genes. On p. 3067, Ulrike Gaul and colleagues use computational and experimental approaches to systematically reappraise the complex regulatory architecture that underlies pair-rule stripe formation and, based on their analyses, reclassify fushi tarazu and odd skipped as primary rather than secondary pair-rule genes The researchers also present results that point to a much closer integration of maternal/gap-mediated and pair-rule-mediated regulation than previously recognised and provide new insights into the function of stripe-specific cis-regulatory elements. Together, these results deepen our understanding of periodic pattern generation in the Drosophila embryo.