Full genotype of offspring for each experiment.

MicroRNAs are essential regulators of gene expression. Their function is particularly important during neurogenesis, when the production of large numbers of neurons from a limited number of neural stem cells depends on the precise control of determination, proliferation and differentiation. However, microRNAs can target many mRNAs and vice-versa, raising the question of how specificity is achieved to elicit a precise regulatory response. Here we introduce in vivo AGO-APP, a novel approach to purify Argonaute-bound, and therefore active microRNAs from specific cell types. Using AGO-APP in the larval Drosophila central nervous system, we identify a module of microRNAs predicted to redundantly target all iconic genes known to control the transition from neuroblasts to neurons. While microRNA overexpression generally validated predictions, knockdown of individual microRNAs did not induce detectable phenotypes. In contrast, neuroblasts were induced to differentiate precociously when several microRNAs were knocked down simultaneously. Our data supports the concept that at physiological expression levels, the cooperative action of miRNAs allows efficient targeting of entire gene networks.

微小RNA（MicroRNAs）是基因表达的关键调控因子。其功能在神经发生过程中至关重要：有限数量的神经干细胞需通过精准调控细胞定型、增殖与分化，才能产生大量神经元。然而，微小RNA可靶向调控众多信使RNA（mRNA），反之亦然，这引发了一个核心科学问题：机体如何实现调控特异性，以触发精准的基因表达应答。
本研究介绍了一种活体AGO-APP（in vivo AGO-APP）全新实验策略，能够从特定细胞类群中纯化结合Argonaute蛋白（Argonaute）的活性微小RNA。我们在果蝇幼虫中枢神经系统中应用该方法，鉴定出一组微小RNA模块，经预测该模块可冗余靶向所有已知的、调控成神经细胞向神经元转化的经典基因。
尽管微小RNA过表达实验基本验证了上述预测，但单独敲低单个微小RNA并未引发可检测到的表型变化。与之相反，当同时敲低多个微小RNA时，成神经细胞被诱导发生提前分化。本研究数据支持以下结论：在生理表达水平下，微小RNA的协同作用可实现对完整基因调控网络的高效靶向调控。