Biology subjects

Pilon, M.

Publications and source records attributed to Pilon, M..

6 recordsLinked to original sources

bioRxiv2026

A pcyt-1 Allelic Series Reveals In Vivo Consequences of Reduced Phosphatidylcholine Synthesis in C. elegans

Phosphatidylcholine (PC) is the most abundant phospholipid in eukaryotic membranes and is synthesized in part via the rate-limiting enzyme PCYT1A. In humans, hypomorphic PCYT1A variants cause diverse disorders, including retinal dystrophy, lipodystrophy with fatty liver, and spondylometaphyseal dysplasia. To define how graded reductions in PC synthesis affect organismal physiology, we generated and characterized a series of mutant alleles in the Caenorhabditis elegans homolog pcyt-1, including variants corresponding to disease-causing human mutations, as well as an auxin-inducible degradation (AID) allele. We identify a clear allelic hierarchy. The V146M variant is embryonic lethal, whereas A97T is largely benign. P154A is temperature-sensitive, and C211Y causes growth delay, reduced brood size, sterility, and lengthened lifespan at standard temperature. Phenotypes of C211Y are rescued by choline, CDP-choline, or phosphatidylcholine supplementation, supporting reduced enzymatic function. Lipidomic profiling reveals that decreased PC synthesis consistently increases long-chain polyunsaturated fatty acids (LCPUFAs) in both PCs and PEs at the expense of shorter saturated species, without markedly altering the PC/PE ratio at 20{degrees}C. At elevated temperature, the P154A variant exhibits protein instability and a decreased PC/PE ratio. Despite significant lipid remodeling, canonical ER, mitochondrial, and metabolic stress GFP-based reporters are not activated; only the oxidative stress response is elevated, consistent with increased peroxidation-prone LCPUFAs in the pcyt-1 mutant. Acute auxin-induced degradation of PCYT-1 in larvae causes developmental arrest, while acute PCYT-1 degradation in adults disrupts oogenesis, demonstrating a continuous requirement for PC synthesis. Together, these findings establish a functional pcyt-1 allelic series and show that limiting PC synthesis drives compensatory remodeling toward LCPUFA-enriched membranes while rendering the germline particularly vulnerable.

cell biology↗

bioRxiv2025

Forward Genetics Identifies ptr-18 and Other Genes as Developmental Regulators of the Four-Cell Tail Tip in C. elegans

In C. elegans, the epidermis and its overlying extracellular matrix form a primary protective barrier, functioning as the first line of defense against environmental factors. To properly develop those cellular boundaries, a tightly controlled interaction of many molecules and pathways is needed. Mutant alleles of paqr-2 and iglr-2 (lipid homeostasis), dpy-21 (membrane trafficking), and sma-1 (actin-binding spectrin) result in hermaphrodite tail tip defects suggesting that this simple four-cell structure can serve as a sensitive model for the identification of pathways responsible for the establishment of cellular boundaries. With this in mind, we performed a small forward genetics screen of [~]800 ethyl methanesulfonate-mutagenized haploid genomes and identified 21 mutants with a tail end defective (Ted) phenotype. Whole genome sequencing of these mutants identified mutations in genes encoding either structural constituents of the cuticle itself (mostly collagen genes) or protein with regulatory functions. By using CRISPR/Cas9 we confirmed six novel alleles of ptr-18, paqr-2, nab-1, ncam-1, vab-9 and efn-4. We further characterized the loss of function allele ptr-18(et70), which encodes a patch domain-containing (PTCHD) protein homologous to human PTCHD1. ptr-18(et70) has a significant effect on growth and development of the worms, while also increasing membrane permeability. Lipidomics analysis revealed no major alterations in membrane lipid composition, implicating cuticle defects as the primary cause of the observed permeability phenotype. Article summaryWe performed a forward genetics screen to identify hermaphrodite C. elegans mutants with a tail end defect with the goal to discover membrane and morphogenesis regulators. The screen of 800 haploid genomes revealed 21 tail end defective mutants, including 8 novel alleles of interesting regulator protein. We conclude that the tail tip phenotype can be useful in discovery of new pathways and interactions during development.

cell biology↗

bioRxiv2025

Oncogene Silencing via ecDNA Micronucleation

Extrachromosomal DNA (ecDNA) contributes to cancer genome instability by enabling high-copy oncogene amplification, intratumoural heterogeneity and rapid genetic change. Micronuclei (MN) are frequently observed in chromosomally unstable cancers, yet their origins and relevance in ecDNA-driven tumours remain incompletely understood. Here, we investigate the relationship between ecDNA segregation errors and MN formation. We find that ecDNA frequently localizes to MN and represents a prominent source of MN content in ecDNA-positive cancer cells. Mitotic clustering of oncogene-bearing ecDNAs is associated with asymmetric inheritance and mis-segregation into MN. Transfer of oncogenes from ecDNA into MN is accompanied by reduced transcriptional output. Single-MN sequencing shows that individual MN are enriched for ecDNA to a degree that exceeds expectations from stochastic mis-segregation and that in MN oncogenes originating from multiple distinct ecDNAs coalesce. Using live-cell imaging, we observe that cells inheriting ecDNA-positive MN show limited proliferative capacity and an increased likelihood of cell death. In neuroblastoma patients with MYCN-amplified ecDNA, higher frequencies of ecDNA-positive MN at diagnosis are associated with improved event-free and overall survival. Together, these findings link ecDNA mis-segregation to MN formation and reduced cellular fitness, suggesting that ecDNA-positive MN may reflect a state of impaired oncogenic ecDNA function with potential relevance for clinical outcome.

cancer biology↗

bioRxiv2024

A fat-2(wa17) suppressor screen in C. elegans reveals genetic adaptations to polyunsaturated fatty acid deficiency

Polyunsaturated fatty acids (PUFAs) are essential for mammalian health and function as membrane fluidizers and precursors for signaling lipids though the primary essential function of PUFAs within organisms has not been established. Unlike mammals who cannot endogenously synthesize PUFAs, C. elegans can de novo synthesize PUFAs starting with the {Delta}12 desaturase FAT-2 which introduces a second double bond to monounsaturated fatty acids to generate the PUFA linoleic acid. FAT-2 desaturation is essential for C. elegans survival since fat-2 null mutants are non-viable; the near-null fat-2(wa17) allele synthesizes only small amounts of PUFAs and produces extremely sick worms. Using fluorescence recovery after photobleaching (FRAP), we found that the fat-2(wa17) mutant has rigid membranes and can be efficiently rescued by dietarily providing various PUFAs, but not by fluidizing treatments or mutations. With the aim of identifying mechanisms that compensate for PUFA-deficiency, we performed a forward genetics screen to isolate novel fat-2(wa17) suppressors and identified four internal mutations within fat-2, and six mutations within the HIF-1 pathway. The suppressors increase PUFA levels in fat-2(wa17) mutant worms and additionally suppress the activation of the daf-16, UPRer and UPRmt stress response pathways that are active in fat-2(wa17) worms. We hypothesize that the six HIF-1 pathway mutations, found in egl-9, ftn-2, and hif-1 all converge on raising Fe2+ levels and in this way boost desaturase activity, including that of the fat-2(wa17) allele. We conclude that PUFAs cannot be genetically replaced and that the only genetic mechanism that can alleviate PUFA-deficiency do so by increasing PUFA levels.

cell biology↗

bioRxiv2021

Sphingosine 1-Phosphate Mediates Adiponectin Receptor Signaling Essential For Lipid Homeostasis And Embryogenesis

Cells and organisms require proper membrane composition to function and develop. Phospholipids are the major component of membranes and are primarily acquired through the diet. Given great variability in diet composition, cells must be able to deploy mechanisms that correct deviations from optimal membrane composition and properties. Here, using lipidomics and unbiased proteomics, we found that the embryonic lethality in mice lacking the fluidity regulators Adiponectin Receptors 1 and 2 (AdipoR1/2) is associated with aberrant high saturation of the membrane phospholipids. Using mouse embryonic fibroblasts (MEFs) derived from AdipoR1/2-KO embryos, human cell lines and the model organism C. elegans we found that, mechanistically, AdipoR1/2-derived sphingosine 1-phosphate (S1P) signals in parallel through S1PR3-SREBP1 and PPAR{gamma} to sustain the expression of the fatty acid desaturase SCD and maintain membrane properties. Thus, our work identifies an evolutionary conserved pathway by which cells and organism achieve membrane homeostasis and adapt to a variable environment.

cell biology↗

bioRxiv2020

AdipoR2 is Essential for Membrane Lipid Homeostasis in Response to Dietary Saturated Fats

Membrane lipid composition influences vital processes in all types of cells. The mechanisms by which cells maintain membrane lipid homeostasis while obtaining most of their constituent fatty acids from a varied diet remain largely unknown. In an attempt to discover such mechanisms, we performed an unbiased forward genetic screen in Caenorhabditis elegans and conclude that the adiponectin receptor 2 (AdipoR2) pathway is essential to prevent saturated fat-mediated cellular toxicity. Transcriptomics, lipidomics and membrane property analyses in human HEK293 cells and primary human endothelial cells further support our conclusion that the essential function of AdipoR2 is to respond to membrane rigidification by promoting fatty acid desaturation. Our results demonstrate that AdipoR2-dependent regulation of membrane homeostasis is a fundamental mechanism conserved from nematodes to mammals that prevents saturated fat-mediated lipotoxicity. ONE SENTENCE SUMMARYThe AdipoR2 protein insures membrane homeostasis in response to dietary saturated fatty acids that promote membrane rigidification.

cell biology↗