Figure 7.

Model of MB neurogenesis regulated by the ecdysone-induced miRNA let-7. Temporal cues such as systemic steroid signalling via the differentially expressed let-7 miRNA regulate a spatially distributed target Abrupt to adjust cell adhesion. During prepupal stages, a cell fate intrinsic determinant Ab is present in the nuclei of early-born α′/β′ neurons. At the pupal stage, the chronologically regulated pulse of ecdysteroids induces let-7 expression. let-7 targets the transcription factor Ab and modulates levels of the cell adhesion molecule Fas II. Since cell adhesion is a critical characteristic of neuronal identity, regulation of cell adhesion levels allows for MB neuron differentiation. Therefore, cell adhesiveness regulated by the ecdysone-let-7 pathway is important for an establishment of neuronal temporal identity.