Biology subjects

Marechal, E.

Publications and source records attributed to Marechal, E..

11 recordsLinked to original sources

bioRxiv2025

Decoupling of plastid and endomembrane homeoviscous response to low temperature and darkness in Phaeodactylum tricornutum

Understanding how marine diatoms adapt to fluctuating environmental conditions is critical for deciphering their ecological success. Here, we investigated the lipidomic responses of the model diatom Phaeodactylum tricornutum to low temperatures (10 {degrees}C), darkness, and combined stress. Using a detailed lipidomics approach, we revealed significant remodeling of plastidial and extraplastidial lipid species. Plastidial lipids showed increased unsaturation levels, particularly the 16:3-to-16:4 fatty acid switch, only under light conditions. This light-dependent adaptation suggests a tightly regulated mechanism that aligns lipid remodeling with photosynthetic activity. Phospholipids in the endomembrane system exhibited less dependency on light, with notable changes even under extended dark periods. These findings highlight distinct strategies employed by diatoms to maintain membrane fluidity and protect cellular processes during stress. Unlike plants, P. tricornutum lacks polygalactosyldiacylglycerols, underscoring a divergent adaptation pathway. Our results demonstrate that P. tricornutum adapts to cold and dark environments through lipid composition changes, supporting survival in variable marine habitats. This study provides critical insights into diatom resilience, paving the way for understanding their role in global biogeochemical cycles. HighlightLow temperature and darkness trigger distinct lipidomic remodeling in Phaeodactylum tricornutum, revealing species-specific adaptive mechanisms that maintain membrane integrity and enhance resilience under extreme environmental conditions.

physiology↗

bioRxiv2024

Functional study of Phaeodactylum tricornutum Seipin homolog highlights unique features of lipid droplets biogenesis in diatoms.

Diatoms are a major phylum of microalgae, playing crucial ecological roles. They derive from secondary endosymbiosis of a red alga by an unknown heterotrophic eukaryote, leading to a complex intracellular organization. In response to unfavorable conditions (stress), diatoms store oil in lipid droplets (LD), raising interest for applications, in particular biofuels. In spite of numerous investigations aiming to increase their oil content, LD biogenesis mechanisms in these organisms remain poorly understood. In this study, we functionally characterized the homolog of Seipin, a major actor of LD biogenesis, in the diatom Phaeodactylum tricornutum. PtSeipin shares conserved structural features with other Seipins, yet presents unique characteristics, that appear common to diatoms and more broadly Stramenopiles. We provide evidence that Stramenopiles Seipins were inherited from the host during secondary endosymbiosis. The localization of PtSeipin highlights that LD biogenesis can arise simultaneously from the endoplasmic reticulum (ER) and the plastids most external membrane. Finally, the knock-out of PtSeipin leads to a strong increase of TAG accumulation, a feature that is not observed in other organisms and is greatly enhanced following high light exposure. Our results suggest a redirection of lipid fluxes towards TAG synthesis, reduced TAG recycling or a combination of both.

plant biology↗

bioRxiv2024

Subcellular ToF-SIMS imaging of the snow algae Sanguina nivaloides by combining high mass and high lateral resolution acquisitions

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging has demonstrated great potential for metabolic imaging, yet achieving sufficiently high lateral and mass resolution to reach the organelle scale remains challenging. We have developed an approach by combining ToF-SIMS imaging acquisitions at high lateral resolution (> 150 nm) and high mass resolution (9,000). The data were then merged and processed using multivariate analysis (MVA), allowing for the precise identification and annotation of 85% of the main contributors to the multivariate analysis components at high lateral resolution. Insights into the electron microscopy sample preparation are provided, especially as we reveal that at least three different osmium-containing complexes can be found depending on the specific chemical environment of organelles. In cells of the snow alga Sanguina nivaloides, living in a natural environment limited in nutrients such as phosphorus (P), we were able to map elements and molecules within their subcellular context, allowing for the molecular fingerprinting of organelles at a resolution of 100 nm, as confirmed by correlative electron microscopy. It was thus possible to highlight that S. nivaloides likely absorbed selectively some inorganic P forms provided by P-rich dust deposited on the snow surface. S. nivaloides cells could maintain phosphorylations in the stroma of the chloroplast, consistently with the preservation of photosynthetic activity. The presented method can thus overcome the current limitations of ToF-SIMS for subcellular imaging and contribute to the understanding of key questions such as P homeostasis and other cell physiological processes.

plant biology↗

bioRxiv2024

Deconvoluted methylation profiles discriminate between closely related melanocytic nevi

Congenital melanocytic nevi (CMN) and common acquired melanocytic nevi (AMN) are melanoma-predisposing skin conditions presenting excessive numbers of melanocytes but arising at different times in life. Appropriately weighted whole-genome methylation analysis can be used as a basis for further research in dermatopathology and as applied here provides new insights into nevus biology.

cancer biology↗

bioRxiv2024

Braf-mutant Schwann cells divert to a repair phenotype to induce congenital demyelinating neuropathy

RASopathies, rare congenital syndromes affecting multiple organ systems, often include peripheral neuropathy of unknown origin. While RASopathy-associated gene variants are proto-oncogenic, the impact of timing and mosaicism on pathogenicity remains poorly understood. Here, we investigate the links between Braf, a key mitogen-activated protein kinase (MAPK) effector, and peripheral neuropathy. By targeting Braf p.V600E, an oncogenic variant found in mosaic RASopathies, to embryonic Mpz-expressing cells in mice, we induced a congenital Charcot-Marie-Tooth-like degenerative neuropathy. This phenotype was characterized by hyperplastic nerves, hindlimb weakness, and unexpectedly reduced body size. Constitutively active Braf expanded a Jun+ Schwann cell repair state, impairing myelination and nerve homeostasis. To examine relevance to RASopathies, we differentiated patient-derived stem cells bearing the cardio-facio-cutaneous syndrome-associated BRAF p.Q257R variant into Schwann cells. Compared to wild-type controls, CFC-derived cells failed to acquire mature phenotypes, instead exhibiting progenitor or repair-type transcriptional profiles. Our findings implicate somatic mosaicism in the unresolved genetic heterogeneity of neuropathies and expand the candidate gene list for peripheral nerve disorders. Moreover, they reveal a MAPK-dependent mechanism linking neural crest-derived Schwann cell dysfunction to both body growth and nerve homeostasis, providing new insights into the mechanisms in RASopathy-associated neuropathy and potential therapeutic targets.

developmental biology↗

bioRxiv2024

Delta-5 elongase knockout reduces DHA and TAG synthesis coupled with an increase of heat sensitivity in a marine diatom

Recent global marine lipidomic analysis reveals a strong relationship in the ocean between temperature and phytoplanktonic abundance of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are essential for human nutrition and primarily from phytoplankton in marine food webs. In phytoplanktonic organisms, EPA may play a major role in regulating the phase transition temperature of membranes, while the function of DHA remains to be explored. In the oleaginous diatom Phaeodactylum tricornutum, DHA is distributed mainly on extraplastidial phospholipids, which is very different from the EPA enriched in thylakoid lipids. Here, CRISPR/Cas9-mediated knockout of ptELO5a, which encodes a delta-5 elongase catalyzing the elongation of EPA to synthesize DHA, led to a substantial interruption of DHA synthesis in P. tricornutum. The ptELO5a mutants show significant alterations in transcriptome and glycerolipidomes including membrane lipids and triacylglycerols under normal temperature (22{degrees}C), and are more sensitive to elevated temperature (28{degrees}C) than wild type. We conclude that the PtELO5a-mediated synthesis of small amounts of DHA has indispensable functions in regulating the membrane lipid, and indirectly contributing storage lipid accumulation and maintaining thermomorphogenesis in P. tricornutum. This study also highlights the significance of DHA synthesis and lipid composition for environmental adaptation of P. tricornutum.

plant biology↗

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↗

bioRxiv2023

Deciphering lipid mutant phenotypes with a new genome-scale metabolic model of Microchloropsis gaditana encompassing detailed lipid metabolism

The oleaginous microalga Microchloropsis gaditana (formerly Nannochloropsis gaditana) has gained large interest due to its potential to produce lipids for a wide range of biotechnological applications. To optimize M. gaditana growth conditions and develop new strains to enhance lipid synthesis and accumulation, a broad understanding of the organism metabolism is essential. Computational models such as genome-scale metabolic models constitute powerful tools for unravelling microorganism metabolism. In this work we present iMgadit23, a new genome-scale metabolic model for M. gaditana. Model covers 2330 reactions involving 1977 metabolites and associated with 889 genes. Pathways involved in membrane and storage glycerolipid biosynthesis and degradation have undergone thorough manual curation and have been comprehensively described based on current knowledge of M. gaditana lipid metabolism. Additionally, we developed a detailed 2D-pathway map of model content to provide a systems-level visualization of M. gaditana metabolism. We demonstrated the predictive capabilities of iMgadit23, validating its ability to qualitatively and quantitatively capture in vivo growth phenotypes under diverse environmental and genetic conditions. Model was also able to capture the role of the Bubblegum acyl-CoA synthetase in remodeling M. gaditana lipid metabolism. iMgadit23 and its 2D map constitute valuable tools to increase understanding of M. gaditana metabolism and deciphering mutant phenotypes, specifically in the context of lipid metabolism. The model holds significant promise in predicting M. gaditana metabolic capabilities, facilitating strain engineering, and optimizing cultivation processes for a broad range of industrial applications.

plant 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

Multiple congenital malformations arise from somatic mosaicism for constitutively active Pik3ca signalling

Recurrent missense mutations of the PIK3CA oncogene are among the most frequent drivers of human cancers. These often lead to constitutive activation of its product p110, a phosphatidylinositol 3-kinase (PI3K) catalytic subunit. In addition to causing a broad range of cancers, the H1047R mutation is also found in affected tissues of a distinct set of congenital tumors and malformations. Collectively termed PIK3CA-related disorders (PRDs), these lead to overgrowth of brain, adipose, connective and musculoskeletal tissues and/or blood and lymphatic vessel components. Vascular malformations are frequently observed in PRD, due to cell-autonomous activation of PI3K signaling within endothelial cells. These, like most muscle, connective tissue and bone, are derived from the embryonic mesoderm. However, important organ systems affected in PRDs are neuroectodermal derivatives. To further examine their development, we drove the most common post-zygotic activating mutation of Pik3ca in neural crest and related embryonic lineages. Outcomes included macrocephaly, cleft secondary palate and more subtle skull anomalies. Surprisingly, Pik3ca-mutant subpopulations of neural crest origin were also associated with widespread cephalic vascular anomalies. Mesectodermal neural crest is a major source of non-endothelial connective tissue in the head, but not the body. To examine the response of vascular connective tissues of the body to constitutive Pik3ca activity during development, we expressed the mutation by way of an Egr2 (Krox20) Cre driver. Lineage tracing led us to observe new lineages that had normally once expressed Krox20 and that may be co-opted in pathogenesis, including vascular pericytes and perimysial fibroblasts. Finally, Schwann cell precursors having transcribed either Krox20 or Sox10 and induced to express constitutively active PI3K were associated with vascular and other tumors. These murine phenotypes may aid discovery of new candidate human PRDs affecting craniofacial and vascular smooth muscle development as well as the reciprocal paracrine signaling mechanisms leading to tissue overgrowth.

developmental biology↗

bioRxiv2021

RNA labelling in live plants reveals single cell transcriptional dynamics: application to phosphate signaling

Plants are sessile organisms constantly adapting to ambient fluctuations through spatial and temporal transcriptional responses. Here, we implemented the latest generation RNA imaging system and combined it with microfluidics to visualize transcriptional regulation in living Arabidopsis plants. This enabled quantitative measurements of the transcriptional activity of single loci in single cells, real time and changing environmental conditions. Using phosphate responsive genes as model, we found that active genes displayed high transcription initiation rates ([~]3s) and frequently clustered together in endoreplicated cells. We observed gene bursting and large allelic differences in single cells, revealing that at steady-state, intrinsic noise dominated extrinsic variations. Moreover, we established that transcriptional repression triggered in roots by phosphate, a crucial macronutrient limiting plant development, occurred with unexpected fast kinetics ([~]minutes) and striking heterogeneity between neighboring cells. Access to single cell RNA polymerase II dynamics within live plants will benefit future studies of signaling processes.

plant biology↗