The mechanosensor Filamin A/Cheerio promotes tumourigenesis via specific interactions with components of the cell cortex.

Cancer development has been linked to aberrant sensing and interpretation of mechanical cues and force-generating properties. Here, we show that upregulation of the actin crosslinking protein Cheerio (Cher), the fly ortholog of Filamin A (FLNA), and the conformation of its mechanosensitive region (MSR) are instrumental to the malignancy of polarity-deficient, Ras-driven tumours in Drosophila epithelia. We demonstrate that impaired growth and cytoskeletal contractility of tumours devoid of cher can be rescued by stimulating myosin activity. Profiling the Cher interactome in tumour-bearing imaginal discs identified several components of the cell cortex, including the ß-heavy Spectrin Karst (Kst), the scaffolding protein Big bang (Bbg), and 14-3-3ε. We show that Cher binds Bbg through the MSR while the interaction with 14-3-3ε and Kst is MSR-independent. Importantly, our genetic studies define Bbg, Kst, and 14-3-3ε as tumour suppressors. The tumour-promoting function of Cher thus relies on its capacity to control the contractile state of the cytoskeleton through interactions with myosin and specific components of the cell cortex.

Ecd promotes U5 snRNP maturation and Prp8 stability.

Pre-mRNA splicing catalyzed by the spliceosome represents a critical step in the regulation of gene expression contributing to transcriptome and proteome diversity. The spliceosome consists of five small nuclear ribonucleoprotein particles (snRNPs), the biogenesis of which remains only partially understood. Here we define the evolutionarily conserved protein Ecdysoneless (Ecd) as a critical regulator of U5 snRNP assembly and Prp8 stability. Combining Drosophila genetics with proteomic approaches, we demonstrate the Ecd requirement for the maintenance of adult healthspan and lifespan and identify the Sm ring protein SmD3 as a novel interaction partner of Ecd. We show that the predominant task of Ecd is to deliver Prp8 to the emerging U5 snRNPs in the cytoplasm. Ecd deficiency, on the other hand, leads to reduced Prp8 protein levels and compromised U5 snRNP biogenesis, causing loss of splicing fidelity and transcriptome integrity. Based on our findings, we propose that Ecd chaperones Prp8 to the forming U5 snRNP allowing completion of the cytoplasmic part of the U5 snRNP biogenesis pathway necessary to meet the cellular demand for functional spliceosomes.

A Drosophila model to study retinitis pigmentosa pathology associated with mutations in the core splicing factor Prp8.

Retinitis pigmentosa (RP) represents genetically heterogeneous and clinically variable disease characterized by progressive degeneration of photoreceptors resulting in a gradual loss of vision. The autosomal dominant RP type 13 (RP13) has been linked to the malfunction of PRPF8, an essential component of the spliceosome. Over 20 different RP-associated PRPF8 mutations have been identified in human patients. However, the cellular and molecular consequences of their expression in vivo in specific tissue contexts remain largely unknown. Here, we establish a Drosophila melanogaster model for RP13 by introducing the nine distinct RP mutations into the fly PRPF8 ortholog prp8 and express the mutant proteins in precise spatiotemporal patterns using the Gal4/UAS system. We show that all nine RP-Prp8 mutant proteins negatively impact developmental timing, albeit to a different extent, when expressed in the endocrine cells producing the primary insect moulting hormone. In the developing eye primordium, uncommitted epithelial precursors rather than differentiated photoreceptors appeared sensitive to Prp8 malfunction. Expression of the two most pathogenic variants, Prp8S>F and Prp8H>R, induced apoptosis causing alterations to the adult eye morphology. The affected tissue mounted stress and cytoprotective responses, while genetic programs underlying neuronal function were attenuated. Importantly, the penetrance and expressivity increased under prp8 heterozygosity. In contrast, blocking apoptosis alleviated cell loss but not the redox imbalance. Remarkably, the pathogenicity of the RP-Prp8 mutations in Drosophila correlates with the severity of clinical phenotypes in patients carrying the equivalent mutations, highlighting the suitability of the Drosophila model for in-depth functional studies of the mechanisms underlying RP13 etiology.This article has an associated First Person interview with the first author of the paper.