Biology subjects

Osinalde, N.

Publications and source records attributed to Osinalde, N..

3 recordsLinked to original sources

bioRxiv2024

Fbxo42 promotes the degradation of Ataxin-2 granules to trigger terminal Xbp1 signaling

The Unfolded Protein Response (UPR) is composed by homeostatic signaling pathways that are activated by the accumulation of misfolded proteins in the Endoplasmic Reticulum (ER), a condition known as ER stress. Prolonged ER stress and activation of the UPR causes cell death, by mechanisms that remain poorly understood. Here, we report that regulation of Ataxin-2 by Fbxo42 is a crucial step during UPR-induced cell death. From a genetic screen in Drosophila, we identified loss of function mutations in Fbxo42 that suppress cell death and retinal degeneration induced by the overexpression of Xbp1spliced, an important mediator of the UPR. We identified the RNA binding protein Ataxin-2 as a substrate of Fbxo42, which, as part of a Skp-A/Cullin-1 complex, promotes the ubiquitylation and degradation of Ataxin-2. Upon ER-stress, the mRNA of Xbp1 is not immediately translated but instead it is sequestered and stabilized in Ataxin-2 granules, until the Fbxo42 recruitment to these granules promotes the degradation of Ataxin-2, allowing the translation of Xbp1 mRNA at later stages of UPR activation. Our results identify Fbxo42-mediated degradation of Ataxin-2 as a key mechanism regulating the levels of Xbp1 mRNA and protein, to trigger cell death during the terminal stages of UPR activation.

cell biology↗

bioRxiv2020

The ubiquitin ligase Ariadne-1 regulates NSF for neurotransmitter release

Ariadne-1 (Ari-1) is an essential E3 ubiquitin-ligase whose neuronal substrates are yet to be identified. We have used an in vivo ubiquitin biotinylation strategy coupled to quantitative proteomics to identify putative Ari-1 substrates in Drosophila heads. Sixteen candidates met the established criteria. Amongst those, we identified Comatose (Comt), the homologue of the N-ethylmaleimide sensitive factor (NSF). Using an in vivo GFP pulldown approach, we validate Comt/NSF to be an ubiquitination substrate of Ari-1 in fly neurons. The interaction results in the monoubiquitination of Comt/NSF. We also report that Ari-1 loss of function mutants display a lower rate of spontaneous neurotransmitter release due to failures at the pre-synaptic side. By contrast, evoked release in Ari-1 mutants is enhanced in a Ca2+ dependent manner without modifications in the number of active zones, indicating that the probability of release per synapse is increased in these mutants. The distinct Ari-1 mutant phenotypes in spontaneous versus evoked release indicate that NSF activity discriminates the two corresponding protein ensembles that mediate each mode of release. Our results, thus, provide a mechanism to regulate NSF activity in the synapse through Ari-1-dependent ubiquitination.

neuroscience↗

bioRxiv2017

Fundamental Constraints In Synchronous Muscle Limit Superfast Motor Control In Vertebrates

Superfast muscles (SFM) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. To allow such speed, the archetypal SFM, found in the toadfish swimbladder, has hallmark structural and kinetic adaptations at each step of the conserved excitation-contraction coupling (ECC) pathway. More recently SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFM share ECC adaptations for speed, and if SFM arose once, or from independent evolutionary events. Here we use genomic analysis to identify the myosin heavy chain genes expressed in bat and songbird SFM to achieve rapid actomyosin crossbridge kinetics and demonstrate that these are evolutionarily and ontologically distinct. Furthermore, by quantifying cellular morphometry and calcium signal transduction combined with force measurements we show that all known SFM share multiple functional adaptations that minimize ECC transduction times. Our results suggest that SFM evolved independently in sound producing organs in ray-finned fish, birds, and mammals, and that SFM phenotypes operate at a maximum operational speed set by fundamental constraints in synchronous muscle. Consequentially, these constraints set a fundamental limit to the maximum speed of fine motor control.

physiology↗