MicroRNAs are abundant in animal genomes, yet little is known about their functions in vivo. Here, we report the production of 80 new Drosophila miRNA mutants by targeted homologous recombination. These mutants remove 104 miRNAs. Together with 15 previously reported mutants, this collection includes 95 mutants deleting 130 miRNAs. Collectively, these genes produce over 99% of all Drosophila miRNAs, measured by miRNA sequence reads. We present a survey of developmental and adult miRNA phenotypes. Over 80% of the mutants showed at least one phenotype using a p < 0.01 significance threshold. We observed a significant correlation between miRNA abundance and phenotypes related to survival and lifespan, but not to most other phenotypes. miRNA cluster mutants were no more likely than single miRNA mutants to produce significant phenotypes. This mutant collection will provide a resource for future analysis of the biological roles of Drosophila miRNAs.

Asymmetric cell division is a widespread mechanism in developing tissues that leads to the generation of cell diversity. In the embryonic central nervous system of Drosophila melanogaster, secondary precursor cells-ganglion mother cells (GMCs)-divide and produce postmitotic neurons that take on different cell fates. In this study, we show that binary fate decision of two pairs of sibling neurons is accomplished through the interplay of Notch (N) signaling and the intrinsic fate determinant Numb. We show that GMCs have apical-basal polarity and Numb localization and the orientation of division are coordinated to segregate Numb to only one sibling cell. The correct positioning of Numb and the proper orientation of division require Inscuteable (Insc). Loss of insc results in the generation of equivalent sibling cells. Our results provide evidence that sibling neuron fate decision is nonstochastic and normally depends on the presence of Numb in one of the two siblings. Moreover, our data suggest that the fate of some sibling neurons may be regulated by signals that do not require lateral interaction between the sibling cells.

We sequenced Drosophila head RNA to identify a small set of miRNAs that undergo robust circadian cycling. We concentrated on a cluster of six miRNAs, mir-959-964, all of which peak at about ZT12 or lights-off. The cluster pri-miRNA is transcribed under bona fide circadian transcriptional control, and all 6 mature miRNAs have short half-lives, a requirement for cycling. A viable Gal4 knock-in strain localizes prominent cluster miRNA expression to the adult head fat body. Analysis of cluster knock-out and over-expression strains indicates that innate immunity, metabolism, and feeding behavior are under cluster miRNA regulation. Manipulation of food intake also affects the levels and timing of cluster miRNA transcription with no more than minor effects on the core circadian oscillator. These observations indicate a feedback circuit between feeding time and cluster miRNA expression-function as well as a surprising role of post-transcriptional regulation in the circadian control of these phenotypes.

The data we present here indicate that mid and H15 are important components in pattern formation in the ventral epidermis. In odd-numbered abdominal segments, Mid/H15 activity plays an important role in restricting the expression of Wg to a single domain.