Abstract
ABSTRACTRetinitis 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.
Highlights
Retinitis pigmentosa (RP; OMIM 268000) represents a heterogeneous group of hereditary eye disorders characterized by a progressive degeneration of the light-sensing photoreceptor cells in the retina
We establish the Drosophila model of human RP type 13 (RP13) caused by mutations in Prp8, the key component of the U4/U6.U5 trisnRNP and the catalytic core of the spliceosome
We demonstrate the versatility of the fly model to screen and compare the tissuespecific impact of different RP-Prp8 mutations and its suitability to untangle the genetic and molecular mechanisms underlying their larval prothoracic gland delayed the timing of the larval to pupal pathogenesis
Summary
Retinitis pigmentosa (RP; OMIM 268000) represents a heterogeneous group of hereditary eye disorders characterized by a progressive degeneration of the light-sensing photoreceptor cells in the retina. Nearly one-quarter of these genes encode core components of the spliceosome, a macromolecular RNA-protein complex that removes introns from nascent pre-mRNAs, generating mature transcripts. The subsequent recruitment of the pre-assembled U4/U6.U5 tri-snRNP triggers changes in conformation and composition of snRNAs and snRNPs converting the pre-spliceosome to a catalytically active complex that executes the splicing reaction (Matera and Wang, 2014; Will and Lührmann, 2011). All of the pre-mRNA splicingassociated genes mutated in adRP are components of the U4/U6.U5 tri-snRNP including PRPF3, PRPF4, PRPF6, PRPF8, PRPF31, retinitis pigmentosa 9 protein (PAP-1; known as RP9) and the U5 small nuclear ribonucleoprotein 200 kDa DEAD-box RNA helicase (SNRNP200 or Brr2) (Ružicková and Staněk, 2017). How malfunctions in core splicing factors manifest in tissue-specific pathogenesis rather than a systemic disease remains puzzling
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