Biology subjects

Pirritano, M.

Publications and source records attributed to Pirritano, M..

4 recordsLinked to original sources

bioRxiv2026

Mitochondrial protein import stress causes progressive neurodegeneration opposed by PERK - eIF2α signalling

Mitochondrial dysfunction and impairments of the mitochondrial protein import system are often linked to neurodegenerative disease, but whether import stress per se causes neurodegeneration has not been tested. Here, we adapted the yeast clogger system to Drosophila motoneurons to block TOM-TIM23-mediated import with temporal control. Sustained import stress converts somatic mitochondria into donut-shaped structures, depletes functional mitochondria from synaptic terminals, and causes progressive neurodegeneration with impaired neurotransmitter release and locomotor dysfunction. This neurodegeneration is mechanistically distinct from mitochondrial absence, as miro mutant neurons that completely lack presynaptic mitochondria do not degenerate. Import-stressed motoneurons activate multiple protective programmes, including chaperone remodelling, metabolic repression, and translational control through the eIF2 kinase PERK. Both pharmacological PERK inhibition and reversal of translational attenuation via ISRIB accelerate neurodegeneration, whereas PERK overexpression alone is sufficient to cause it, defining a protective range of eIF2-dependent translational control. The observation that PERK inhibition is protective in protein misfolding models but detrimental during import stress shows that the nature of mitochondrial dysfunction determines the molecular consequence of translational control in neurodegeneration.

neuroscience↗

bioRxiv2025

Exogenous dsRNA made accessible to Dicer by two eukaryotic RNA-dependent RNA polymer-ases

Discrimination of self from non-self RNA is a critical requirement for any cell to respond to infections and to maintain cellular integrity. We report novel functions for two RNA-dependent RNA polymerases (RDRs) in Paramecium in the detection of exogenous RNA. In the RNA interference (RNAi) mechanism, RDRs are normally involved in the production of large amounts of secondary siRNAs in response to an initial primary siRNA. To characterize the function of RDRs in context of exogenous RNA recognition, we developed a novel dsRNA delivery system using dextran nanoparticles to deliver heteroduplex dsRNA to cells as food particles, mimicking the natural phagosomal entry pathway. Subsequent small RNA sequencing allows us to dissect siRNAs produced from exogenous RNA or RDR transcripts. Contrary to expectations of how dsRNA-induced silencing is triggered, our data show that Dicer is unable to directly cleave exogenous dsRNA while two RDRs are required for the initial steps of dsRNA-induced RNAi. Paradoxically, these two RDRs must replicate dsRNA to make it available for Dicer cleavage and primary siRNA accumulation. Our data also show that this system works efficiently also with exogenous ssRNA, although RDR2 is dispensable for ssRNA conversion. The function of RDRs in this protist is in contrast to that in animals, plants and fungi and extends the functional diversity of these polymerases. RDR-associated complexes appear to control the entry of food and symbiont-derived RNA into the RNAi machinery, enabling complex RNA interactions with the environment.

genetics↗

bioRxiv2024

Metabolic and transcriptomic analyses of nectaries reveal differences in the mechanism of nectar production between monocots (Ananas comosus) and dicots (Nicotiana tabacum)

BackgroundNectar is offered by numerous flowering plants to attract pollinators. To date, the production and secretion of nectar have been analyzed mainly in eudicots, particularly rosids such as Arabidopsis. However, due to the enormous diversity of flowering plants, further research on other plant species, especially monocots, is needed. Ananas comosus (monocot) is an economically important species and ideal for such analyses because it produce easily accessible nectar in sufficient quantities. In addition, the analyses were also carried out with Nicotiana tabacum (dicot, asterids) for comparison. ResultsWe performed transcriptome sequencing (RNA-Seq) analyses of the nectaries of Ananas comosus and Nicotiana tabacum, to test whether mechanisms described for nectar production and secretion in Arabidopsis are also present in these plant species. The focus of these analyses is on carbohydrate metabolism and transport (e.g., sucrose-phosphate synthases, invertases, sucrose synthases, SWEETs and further sugar transporters). In addition, the metabolites were analyzed in the nectar, nectaries and leaves of both plant species to address the question whether concentration gradients for different metabolites exist between the nectaries and nectar. The nectar of N. tabacum contains large amounts of glucose, fructose and sucrose, and the sucrose concentration in the nectar appears to be similar to the sucrose concentration in the nectaries. Nectar production and secretion in this species closely resembles corresponding processes in some other dicots, including sucrose synthesis in nectaries and sucrose secretion by SWEET9. The nectar of A. comosus also contains large amounts of glucose, fructose and sucrose and in this species the sucrose concentration in the nectar appears to be higher than the sucrose concentration in the nectaries. Furthermore, orthologs of SWEET9 appear to be generally absent in A. comosus and other monocots. Therefore, sucrose export by SWEETs from the nectaries into the nectar can be excluded, rather, other mechanisms, such as active sugar export or exocytosis, are more likely. ConclusionThe mechanisms of nectar production and secretion in N. tabacum appear to be largely similar to those in other dicots, whereas in the monocotyledonous species A. comosus, different synthesis and transport processes are involved.

plant biology↗

bioRxiv2020

Two Piwis with Ago-like functions silence somatic genes at the chromatin level

Most sRNA biogenesis mechanisms involve either RNAseIII cleavage or ping-pong amplification by different Piwi proteins harboring slicer activity. Here, we follow the question why the mechanism of transgene-induced silencing in the ciliate Paramecium needs both Dicer activity and two Ptiwi proteins. This pathway involves primary siRNAs produced from non-translatable transgenes and secondary siRNAs from endogenous remote loci. Our data does not indicate any signatures from ping-pong amplification but Dicer cleavage of long dsRNA. We show that Ptiwi13 and 14 have different preferences for primary and secondary siRNAs but do not load them mutually exclusive. Both Piwis enrich for antisense RNAs and Ptiwi14 loaded siRNAs show a 5'-U signature. Both Ptiwis show in addition a general preference for Uridine-rich sRNAs along the entire sRNA length. Our data indicates both Ptiwis and 2-O-methylation to contribute to strand selection of Dicer cleaved siRNAs. This unexpected function of two distinct vegetative Piwis extends the increasing knowledge of the diversity of Piwi functions in diverse silencing pathways. As both Ptiwis show differential subcellular localisation, Ptiwi13 in the cytoplasm and Ptiwi14 in the vegetative macronucleus, we conclude that cytosolic and nuclear silencing factors are necessary for efficient chromatin silencing.

genetics↗