Biology subjects

Girard, J.

Publications and source records attributed to Girard, J..

6 recordsLinked to original sources

bioRxiv2026

Bacteria hyperpolarize in response to oxygen drop

Aerobic microbes use oxygen as a terminal electron acceptor to establish an electrochemical gradient across their cell membranes. While this membrane potential ({triangleup}{Psi}) is essential for multiple cellular processes, it is unknown if and how it is maintained in bacteria during shifts in oxygen availability. We find that bacteria hyperpolarize in response to drops in oxygen. Focusing on Bacillus subtilis and guided by modeling, we report that hyperpolarization magnitude scales with the degree of electron acceptor deprivation. We find that potassium efflux contributes to the response. Surveying mutants, we uncover genes involved in potassium homeostasis and oxygen stress that contribute to hyperpolarization. We show that hyperpolarization scales with faster growth rates resulting from nutrient type and colony spatial heterogeneity. Finally, we demonstrate that oxygen shift increases susceptibility to antibiotics. Our results demonstrate a conserved link between {triangleup}{Psi} and oxygen stress, suggesting a common mechanism for responding to shifting oxygen availability.

microbiology↗

bioRxiv2023

In situ characterization of late Chikungunya virus replication organelle

Chikungunya virus (CHIKV) is a mosquito-borne pathogen responsible for an acute musculo-skeletal disease in humans. The viral RNA genome replication occurs in membrane spherules named replication organelles (ROs). In this work, we investigate the native structural organization of CHIKV ROs in their cellular context using in situ cryogenic-electron microscopy approaches at late replication stage. We observed previously unreported diameter heterogeneity of ROs at the plasma membrane of infected human cells. CHIKV ROs were only marginally detected in cytopathic vacuoles where they are homogeneous in size, suggesting a finely regulated internalization process. Our data show that ROs maintained at the plasma membrane beyond the first viral cycle are dynamically active both in viral RNA replication, in its export to the cell cytosol, but also in the production of viral proteins. We suggest that late CHIKV ROs have an amplifying role or represent an alternative pathway in the production of infectious viral particles. All these observations bring new insight into the CHIKV life cycle in human cells.

molecular biology↗

bioRxiv2022

Shadow imaging for panoptical visualisation of living brain tissue

Progress in neuroscience research hinges on technical advances in visualizing living brain tissue with high fidelity and facility. Current neuroanatomical imaging approaches either require tissue fixation, do not have cellular resolution or only give a fragmented view. Here, we show how regular light microscopy together with fluorescence labeling of the interstitial fluid in the extracellular space provide comprehensive optical access in real-time to the anatomical complexity and dynamics of living brain tissue.

neuroscience↗

bioRxiv2020

DNA repair-based classification of melanoma cell lines reveals an effect of mutations in BRAF and NRAS driver genes on DNA repair capacity

Melanoma, the most serious form of skin cancer, frequently involves the dysregulation of key signaling pathways. Treatment strategies presently target the MAPK/ERK pathway, which is overactive in melanomas due in part to BRAF and NRAS mutations, and involve inhibitors against mutated BRAF (vemurafenib or dabrafenib) or MEK kinases (cobimetinib or trametinib), or a combination of the two. Using an established biochip technology, we assessed base excision repair (BER) and nucleotide excision repair (NER) activities in a collection of BRAF mutated (A-375, Colo 829, HT-144, Malme-3M, SK-mel5, SK-mel24 and SK-mel28) and NRAS mutated (M18, MZ2 and SK-mel2) melanoma cell lines, as well as wild-type controls (A7, CHL-1). We evaluated both basal activities (i.e., without treatment) and repair capacities after treatment with vemurafenib or cobimetinib alone, or in combination. Our results indicate that globally the DNA repair capacity of the cell lines was determined by the mutation status of the BRAF and NRAS genes, indicating that the MAPK pathway participates in the regulation of both BER and NER. Treatment of BRAF mutated melanoma cells with vemurafenib alone or the vemurafenib/cobimetinib combination, but not cobimetinib alone, led to reduced DNA repair capacity in about 60% of the BRAF mutated samples, indicating that signaling pathway inhibition can alter DNA repair activity. Upregulation of some DNA repair activities was also observed in several of the treated samples, suggesting activation of compensatory signaling pathways upon treatment. The data collectively indicate that mutations in the BRAF and NRAS genes exert distinct regulatory effects on the excision/synthesis steps of the BER and NER pathways and that targeted pharmacological inactivation of the signaling mechanism can translate into specific consequences in DNA repair capacity. The heterogeneity of the responses reported herein could help define subtypes of melanoma that are associated with resistance to targeted therapies.

cancer biology↗

bioRxiv2019

A scalable culturing system for the marine annelid Platynereis dumerilii.

Platynereis dumerilii is a marine segmented worm (annelid) with externally fertilized embryos and it can be cultured for the full life cycle in the laboratory. The accessibility of embryos and larvae combined with the breadth of the established molecular and functional techniques has made P. dumerilii an attractive model for studying development, cell lineages, cell type evolution, reproduction, regeneration, the nervous system, and behavior. Traditionally, these worms have been kept in rooms dedicated for their culture. This allows for the regulation of temperature and light cycles, which is critical to synchronizing sexual maturation. However, regulating the conditions of a whole room present limitations, especially if experiments require being able to change culturing conditions. Here we present scalable and flexible culture methods that provide ability to control the environmental conditions, and have a multi-purpose culture space. We provide a closed setup shelving design with proper light conditions necessary for P. dumerilii to mature. We also implemented a standardized method of feeding P. dumerilii cultures with powdered spirulina which relieves the ambiguity associated with using frozen spinach, and helps standardize nutrition conditions across experiments and across different labs. By using these methods, we were able to raise mature P. dumerilii, capable of spawning and producing viable embryos for experimentation and replenishing culture populations. These methods will allow for the further accessibility of P. dumerilii as a model system, and they can be adapted for other aquatic organisms.

developmental biology↗

bioRxiv2018

Inferring biochemical reactions and metabolite structures to cope with metabolic pathway drift

Inferring genome-scale metabolic networks in emerging model organisms is challenging because of incomplete biochemical knowledge and incomplete conservation of biochemical pathways during evolution. This limits the possibility to automatically transfer knowledge from well-established model organisms. Therefore, specific bioinformatic tools are necessary to infer new biochemical reactions and new metabolic structures that can be checked experimentally. Using an integrative approach combining both genomic and metabolomic data in the red algal model Chondrus crispus, we show that, even metabolic pathways considered as conserved, like sterol or mycosporine-like amino acids (MAA) synthesis pathways, undergo substantial turnover. This phenomenon, which we formally define as \"metabolic pathway drift\", is consistent with findings from other areas of evolutionary biology, indicating that a given phenotype can be conserved even if the underlying molecular mechanisms are changing. We present a proof of concept with a new methodological approach to formalize the logical reasoning necessary to infer new reactions and new molecular structures, based on previous biochemical knowledge. We use this approach to infer previously unknown reactions in the sterol and MAA pathways.\n\nAuthor summaryGenome-scale metabolic models describe our current understanding of all metabolic pathways occuring in a given organism. For emerging model species, where few biochemical data are available about really occurring enzymatic activities, such metabolic models are mainly based on transferring knowledge from other more studied species, based on the assumption that the same genes have the same function in the compared species. However, integration of metabolomic data into genome-scale metabolic models leads to situations where gaps in pathways cannot be filled by known enzymatic reactions from existing databases. This is due to structural variation in metabolic pathways accross evolutionary time. In such cases, it is necessary to use complementary approaches to infer new reactions and new metabolic intermediates using logical reasoning, based on available partial biochemical knowledge. Here we present a proof of concept that this is feasible and leads to hypotheses that are precise enough to be a starting point for new experimental work.

systems biology↗