In insects, the sequential expression of gap genes during segmentation patterns the anterior–posterior axis to regulate segmentation and segment identity. Similarly, the sequential expression of neuroblast timer genes controls embryonic neural patterning by regulating neuroblast differentiation into different cell types. These similar temporal mechanisms may share a common regulatory network. Two neuroblast timer genes (hunchback and Krüppel) are also canonical gap genes, but whether other neuroblast timer genes are involved in segmentation has been unclear. Now, Olivia Tidswell and colleagues investigate the expression of neuroblast timer genes, nubbin and castor, during Tribolium segmentation. The authors first show that nubbin and castor are sequentially expressed during the patterning of parasegments 4–12 and 7–12, respectively. Using parental and embryonic knockdowns, they reveal that nubbin, but not castor, subtly affects segment identity specification. To explore this further, the researchers simultaneously knockdown nubbin, giant and knirps, which causes loss of abdominal segment identity and ectopic leg formation. Finally, they show that these three genes act redundantly to regulate segment identity by repressing Krüppel and thereby de-repressing Hox genes. Together, these data indicate that neuroblast timer genes may have been co-opted during evolution to regulate insect segmental patterning.
