miR-7 buffers differentiation in the developing Drosophila visual system

Elizabeth E. Caygill and Andrea H. Brand (2017) Cell Reports 20, 1255–1261.

DOI: 10.1016/j.celrep.2017.07.047

Author’s summary

Many microRNAs have been discovered in different tissues during development but their roles are often unclear. Here we show that the microRNA miR-7 has a specific role in buffering stem cell production in the Drosophila brain under conditions of environmental stress. In the optic lobe, the visual processing centre of the brain, the formation of neural stem cells (neuroblasts) and their progeny (neurons) needs to match that in the eye to coordinate the synaptic connections made between the two organs. We demonstrate that miR-7 enables the timely production of neural stem cells and buffers their generation against environmental stress. 

Summary from the paper

The 40,000 neurons of the medulla, the largest visual processing center of the Drosophila brain, derive from a sheet of neuroepithelial cells. During larval development a wave of differentiation sweeps across the neuroepithelium converting neuroepithelial cells into neuroblasts that sequentially express transcription factors specifying different neuronal cell fates. The switch from neuroepithelial cells to neuroblasts is controlled by a complex gene regulatory network and marked by the expression of the proneural gene l’sc. We discovered that microRNA miR-7 is expressed at the transition between neuroepithelial cells and neuroblasts. We showed that miR-7 promotes neuroepithelial cell to neuroblast transition by targeting downstream Notch effectors to limit Notch signaling. miR-7 acts as a buffer to ensure a precise and stereotypical pattern of transition is maintained even under conditions of environmental stress, echoing the role miR-7 plays in the eye imaginal disc. This common mechanism reflects the importance of robust visual system development.

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