Functional unknomics: Systematic screening of conserved genes of unknown function.

The human genome encodes approximately 20,000 proteins, many still uncharacterised. It has become clear that scientific research tends to focus on well-studied proteins, leading to a concern that poorly understood genes are unjustifiably neglected. To address this, we have developed a publicly available and customisable "Unknome database" that ranks proteins based on how little is known about them. We applied RNA interference (RNAi) in Drosophila to 260 unknown genes that are conserved between flies and humans. Knockdown of some genes resulted in loss of viability, and functional screening of the rest revealed hits for fertility, development, locomotion, protein quality control, and resilience to stress. CRISPR/Cas9 gene disruption validated a component of Notch signalling and 2 genes contributing to male fertility. Our work illustrates the importance of poorly understood genes, provides a resource to accelerate future research, and highlights a need to support database curation to ensure that misannotation does not erode our awareness of our own ignorance.

A phagocytic route for uptake of double-stranded RNA in RNAi.

RNA interference (RNAi) has a range of physiological functions including as a defence mechanism against viruses. To protect uninfected cells in a multicellular organism, not only a cell-autonomous RNAi response is required but also a systemic one. However, the route of RNA spread in systemic RNAi remains unclear. Here we show that phagocytosis can be a route for double-stranded RNA uptake. Double-stranded RNA expressed in Escherichia coli induces robust RNAi in Drosophila S2 cells, with effectiveness comparable to that of naked dsRNA. We could separate this phagocytic uptake route from that for RNAi induced by naked dsRNA. Therefore, phagocytic uptake of dsRNA offers a potential route for systemic spread of RNAi.

Bicaudal-D binds clathrin heavy chain to promote its transport and augments synaptic vesicle recycling.

Cargo transport by microtubule-based motors is essential for cell organisation and function. The Bicaudal-D (BicD) protein participates in the transport of a subset of cargoes by the minus-end-directed motor dynein, although the full extent of its functions is unclear. In this study, we report that in Drosophila zygotic BicD function is only obligatory in the nervous system. Clathrin heavy chain (Chc), a major constituent of coated pits and vesicles, is the most abundant protein co-precipitated with BicD from head extracts. BicD binds Chc directly and interacts genetically with components of the pathway for clathrin-mediated membrane trafficking. Directed transport and subcellular localisation of Chc is strongly perturbed in BicD mutant presynaptic boutons. Functional assays show that BicD and dynein are essential for the maintenance of normal levels of neurotransmission specifically during high-frequency electrical stimulation and that this is associated with a reduced rate of recycling of internalised synaptic membrane. Our results implicate BicD as a new player in clathrin-associated trafficking processes and show a novel requirement for microtubule-based motor transport in the synaptic vesicle cycle.