MicroRNA-276 promotes egg-hatching synchrony by up-regulating brm in locusts

Developmental synchrony, the basis of uniform swarming, migration, and sexual maturation, is an important strategy for social animals to adapt to variable environments. However, the molecular mechanisms underlying developmental synchrony are largely unexplored. The migratory locust exhibits polyphenism between gregarious and solitarious individuals, with the former displaying more synchronous sexual maturation and migration than the latter. Here, we found that the egg-hatching time of gregarious locusts was more uniform compared with solitarious locusts and that microRNA-276 (miR-276) was expressed significantly higher in both ovaries and eggs of gregarious locusts than in solitarious locusts. Interestingly, inhibiting miR-276 in gregarious females and over-expressing it in solitarious females, respectively, caused more heterochronic and synchronous hatching of progeny eggs. Moreover, miR-276 directly targeted a transcription coactivator gene, brahma (brm), resulting in its up-regulation. Knockdown of brm not only resulted in asynchronous egg hatching in gregarious locusts but also impaired the miR-276-induced synchronous egg hatching in solitarious locusts. Mechanistically, miR-276 mediated brm activation in a manner that depended on the secondary structure of brm, namely, a stem-loop around the binding site of miR-276. Collectively, our results unravel a mechanism by which miR-276 enhances brm expression to promote developmental synchrony and provide insight into regulation of developmental homeostasis and population sustaining that are closely related to biological synchrony.