Biology subjects

Croteau, D.

Publications and source records attributed to Croteau, D..

7 recordsLinked to original sources

bioRxiv2025

A photoprotection dial maps holistic light-stress response in diatoms

Cellular responses to light stress operate on two timescales: short-term responses, driven by dynamic photosynthetic mechanisms such as non-photochemical quenching (NPQ), and long-term responses, characterized by various physiological and metabolic shifts driven by changes in gene expression. Understanding the coordination within and between these layers represents a major challenge in photosynthesis research. We achieved this in the diatom Phaeodactylum tricornutum using an adjustable "photoprotection dial" across 10 mutant strains expressing different constitutive levels of the Lhcx1 protein, which determine their latent NPQ capacity. Crucially, a near-identical initial state is preserved among strains, which allows a precise mapping of the causal chain of events initiated by NPQ induction under high light. This unlocks exceptional leverage to examine holistic interactions between functional photosynthesis and gene expression within their natural regulatory architecture. We observe that increasing NPQ maintains the PSII primary acceptor QA in a more oxidized state with little effect on linear electron flow. This oxidation limits PSII photodamage and promotes cyclic electron flow around PSI, which in turn is consistent with enhanced ATP production supporting PSII repair. Moreover, transcriptomic analysis across high-light exposure time suggests that the expression of nearly half of the genome is modulated via NPQ-driven effects. Gene expression profile clustering reveals distinct and coherent transcriptomic regulatory networks. The short-term response is characterized by a strong downregulation of light-harvesting-related genes -- independently of NPQ -- and an upregulation of oxidative stress response genes that scales inversely with NPQ magnitude. In the long term, most of the transcriptome is deeply impacted by high-light stress in a widely NPQ-dependent manner, highlighting the critical role of this process in shaping photophysiology, which in turn influences gene expression. By engineering a native functional feedback loop into an experimental dial, our approach establishes a generalizable framework for studying the complex interplay between physiology and system-wide biological regulation.

plant biology↗

bioRxiv2024

Circadian regulation of key physiological processes by the RITMO1 clock protein in the marine diatom Phaeodactylum tricornutum

O_LIPhasing biological and physiological processes to periodic light-dark cycles is crucial for the life of most organisms. Marine diatoms, as many phytoplanktonic species, exhibit biological rhythms, yet their molecular timekeepers remain largely uncharacterized. Recently, the bHLH-PAS protein RITMO1 has been proposed to act as a regulator of circadian rhythms. C_LIO_LIIn this study, we first determined the physiological conditions to monitor circadian clock activity and its perturbation in the diatom model species Phaeodactylum tricornutum by using cell fluorescence as a circadian output. Employing ectopic overexpression, targeted gene mutagenesis, and functional complementation, we then investigated the role of RITMO1 in various circadian processes. C_LIO_LIOur findings reveal that RITMO1 significantly influences the P. tricornutum circadian rhythms not only of cellular fluorescence, but also of photosynthesis and of the expression of clock-controlled genes, including transcription factors and putative clock input/output components. RITMO1 effects on rhythmicity are unambiguously detectable under free running conditions. C_LIO_LIBy uncovering the complex regulation of biological rhythms in P. tricornutum, these results provide a key step in understanding the endogenous regulators of phytoplankton physiological responses to environmental changes. Furthermore, these studies position diatoms as instrumental and novel model systems for elucidating key mechanistic principles of oscillator functions in marine ecosystems. C_LI

molecular biology↗

bioRxiv2024

Urolithin A improves Alzheimers disease cognition and restores mitophagy and lysosomal functions

BackgroundCompromised autophagy, including impaired mitophagy and lysosomal function, is thought to play a pivotal role in Alzheimers disease (AD). Urolithin A (UA) is a gut microbial metabolite of ellagic acid that stimulates mitophagy. The effects of early and/or long-term treatment, as well as more detailed mechanisms of action, are not known. MethodsWe addressed these questions in three mouse models of AD, and behavioral, electrophysiological and biochemistry assays were performed. ResultsLong-term UA treatment significantly improved learning, memory and olfactory function in different AD transgenic mice. UA also reduced A{beta} and Tau pathologies, and improved long-term potentiation. We found that UA activated autophagy/mitophagy via increasing lysosomal functions. At the cellular level, UA improved lysosomal function and normalized lysosomal cathepsins, especially targeting cathepsin Z, to restore lysosomal function in AD, indicating the important role of cathepsins in UA-induced therapeutic effects of AD. ConclusionsCollectively, our study highlights the importance of lysosomal dysfunction in AD etiology, and points to the high translational potential of UA.

neuroscience↗

bioRxiv2024

Environmentally-informed functional characterization of a plastid diatom metabolic bridge of mitochondrial origin

Withdrawal statementThe authors have withdrawn this manuscript due to a duplicate posting of manuscript number BIORXIV/2022/507166. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author. The correct preprint can be found at doi: 10.1101/2022.09.08.507166

evolutionary biology↗

bioRxiv2022

A Plastidial Glycolytic-Gluconeogenic Switch of Mitochondrial Origin Enables Diatom Adaptations to High Latitudes

Organic carbon fixed in chloroplasts through the Calvin Cycle can be diverted towards different metabolic fates, including cytoplasmic and mitochondrial respiration; gluconeogenesis; and synthesis of diverse plastid metabolites via the pyruvate hub. In plants, pyruvate is principally produced via cytoplasmic glycolysis, although a plastid-targeted lower glycolytic pathway is known in non-photosynthetic tissue. Here, we characterize a lower plastid glycolytic-gluconeogenesis pathway in diatoms, ecologically important marine algae distantly related to plants. We show that two reversible enzymes required to complete diatom plastid glycolysis-gluconeogenesis, Enolase and PGAM (bis- phospho-glycerate mutase), originated through duplications of mitochondria-targeted respiratory isoforms. Through CRISPR-Cas9 mutagenesis, integrative omic analyses, and measured kinetics of expressed enzymes in the diatom Phaeodactylum tricornutum, we present evidence that this pathway diverts plastid glyceraldehyde-3-phosphate into the pyruvate hub, and may also function in the gluconeogenic direction. Considering experimental data, we show that this pathway has different roles dependent in particular on day length and environmental temperature, and show that it is expressed at elevated levels in high latitude oceans where diatoms are abundant. Our data provide evolutionary, meta-genomic and functional insights into a poorly understood yet evolutionarily recurrent plastid metabolic pathway.

plant biology↗

bioRxiv2022

Long-term NAD+ supplementation prevents the progression of age-related hearing loss in mice

Age-related hearing loss (ARHL) is the most common sensory disability associated with human aging. Yet, there are no approved measures for preventing or treating this debilitating condition. With its slow progression, continuous and safe approaches are critical for ARHL treatment. Nicotinamide Riboside (NR), a NAD+ precursor, is well tolerated even for long-term use and is already shown effective in various disease models including Alzheimers and Parkinsons Disease. It has also been beneficial against noise induced hearing loss and in hearing loss associated with premature aging. However, its beneficial impact on ARHL is not known. Using two different wild-type mouse strains, we show that long-term NR administration prevents the progression of ARHL. Through transcriptomic and biochemical analysis, we find that NR administration restores age-associated reduction in cochlear NAD+ levels, upregulates biological pathways associated with synaptic transmission and PPAR signaling, and reduces the number of orphan ribbon synapses between afferent auditory neurons and inner hair cells. We also find that NR targets a novel pathway of lipid droplets in the cochlea by inducing the expression of CIDEC and PLIN1 proteins that are downstream of PPAR signaling and are key for lipid droplet growth. Taken together, our results demonstrate the therapeutic potential of NR treatment for ARHL and provide novel insights into its mechanism of action.

animal behavior and cognition↗

bioRxiv2020

Cockayne syndrome proteins CSA and CSB maintain mitochondrial homeostasis through NAD+ signaling

BackgroundCockayne syndrome (CS) is a rare premature aging disease, most commonly caused by mutations of the genes encoding the CSA or CSB proteins. CS patients display cachectic dwarfism and severe neurological manifestations and have an average life expectancy of 12 years. The CS proteins are involved in transcription and DNA repair, with the latter including transcription-coupled nucleotide excision repair (TC-NER). However, there is also evidence for mitochondrial dysfunction in CS, which likely contributes to the severe premature aging phenotype of this disease. While damaged mitochondria and impaired mitophagy were characterized in mice with CSB deficiency, such changes in the CS nematodes and CS patients are not fully known. ResultsOur cross-species transcriptomic analysis in CS postmortem brain tissue, CS mouse and nematode models show that mitochondrial dysfunction is indeed a common feature in CS. Restoration of mitochondrial dysfunction through NAD+ supplementation significantly improved lifespan and healthspan in the CS nematodes, highlighting mitochondrial dysfunction as a major driver of the aging features of CS. In cerebellar samples from CS patients, we found molecular signatures of dysfunctional mitochondrial dynamics and impaired mitophagy/autophagy. In primary cells depleted for CSA or CSB, this dysfunction can be corrected with NAD+ supplementation. ConclusionsOur study provides support for the interconnection between major causative aging theories, DNA damage accumulation, mitochondrial dysfunction, and compromised mitophagy/autophagy. Together these three agents contribute to an accelerated aging program that can be averted by NAD+ supplementation.

cell biology↗