Biology subjects

Mercier, L.

Publications and source records attributed to Mercier, L..

8 recordsLinked to original sources

bioRxiv2026

EMT associated transcription factors Slug and Snail demonstrate specific expression patterns in breast cancer subtypes, involving tumor or stroma components and correlating with proliferation status and complex clinical prognosis.

EMT associated transcription factors (EMTaTF) controls the epithelial-mesenchymal transition (EMT) process, but their detailed expression pattern in cancer is poorly documented at the cellular level. Here, we located two major EMTaTF: Snail and Slug by immunochemistry using validated antibodies in a cohort of 569 invasive breast carcinomas. We screened all tumor molecular types using TMA analysis in addition to full tumor sections, identifying cell types and structures involved in their expression, correlated to morphological, functional, and clinical characteristics. Briefly, Slug was expressed in Luminal A/B and HER2 breast cancer subtypes by almost all cells from the basal layer in normal-looking tubule structures and was very sporadically seen in transformed cells in the in situ or invasive components. In contrast, Slug was visibly expressed in 28% of our triple-negative (TN) tumor samples, significantly expressed by invasive tumor cells. Slug was also strongly expressed in a large subpopulation of stroma fibroblast-like cells in all breast carcinoma subtypes. Conversely, Snail was frequently expressed in transformed cells in all invasive breast carcinomas subtypes, up to 54 and 64% of tumor cells in TN and HER2 tumors respectively. Expression pattern was heterogeneous and included invasive areas and in situ component. Some stroma cells, particularly endothelial cells from the tumor microenvironment were also found to express Snail. Slug and Snail proteins were also detected in metastatic foci, sometimes with an increase in the expression level, particularly for Snail. Unexpectedly, we found a significant positive correlation between cell proliferation and Slug stroma cell expression in luminal A and B subtypes. This link bolstered the relative proximity we uncovered between CK- KI67- Slug+ stoma cells and CK8+ KI67+ Slug- tumor cells in LumB samples. However, survival long-term studies failed to demonstrate a link between slug tumor or stromal expression and long-term survival. On the other hand, Snail protein expression in tumor cells was surprisingly and significantly linked to a better survival fate overall. In contrast, Snail overexpression in stroma cells from primary tumors was significantly linked to a time-dependent tendency for relapses, metastasis and poorer survival, arising when post-surgery time lapse increased. In conclusion, these findings offer new and unsuspected understanding of the complex localization pattern and clinical involvement of Snail genes in breast cancer, beyond classic EMT pathways.

cancer biology↗

bioRxiv2023

Impact of a tilted coverslip on two-photon and STED microscopy

The advent of super-resolution microscopy has opened up new avenues to unveil brain structures with unprecedented spatial resolution in the living state. Yet, its application to live animals remains a genuine challenge. Getting optical access to the brain in vivo requires the use of a cranial window, whose mounting greatly influences image quality. Indeed, the coverslip used for the cranial window should lie as orthogonal as possible to the optical axis of the objective, or else significant optical aberrations occur. In this work, we assess the effect of the tilt angle of the coverslip on STED and two-photon microscopy, in particular image brightness and spatial resolution. We then propose an approach to measure and reduce the tilt using a simple device added to the microscope, which can ensure orthogonality with a precision of 0.07{degrees}.

neuroscience↗

bioRxiv2023

Imaging dendritic spines in the hippocampus of a living mouse by 3D-STED microscopy

STED microscopy has been used to address a wide range of neurobiological questions in optically well-accessible samples like cell culture or brain slices. However, the application of STED to deeply embedded structures in the brain of living animals remains technically challenging. In previous work, we established chronic STED imaging in the hippocampus in vivo but the gain in spatial resolution was restricted to the lateral plane. In this study, we report on extending the gain in STED resolution into the optical axis to visualize dendritic spines in the hippocampus in vivo. The approach is based on a spatial light modulator to shape the focal STED light intensity in all three dimensions and a conically shaped window that is compatible with an objective that has a long working distance and a high numerical aperture. Moreover, we corrected distortions of the laser wavefront to optimize the shape of the bottle beam of the STED laser, which is required for 3D-STED microscopy. In summary, we present a methodology to improve the axial resolution for STED microscopy in the deeply embedded hippocampus in vivo, facilitating longitudinal studies of neuroanatomical plasticity at the nanoscale in a wide range of (patho-)physiological contexts.

neuroscience↗

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↗

bioRxiv2021

Aberration correction in STED microscopy to increase imaging depth in living brain tissue

We demonstrate an approach based on adaptive optics to improve the spatial resolution of STED microscopy inside thick biological tissue by a priori correction of spherical aberrations as a function of imaging depth. We first measured the aberrations in a phantom sample of gold and fluorescent nanoparticles suspended in an agarose gel with a refractive index closely matching living brain tissue. Using a spatial light modulator to apply corrective phase shifts, we imaged neurons in living brain slices and show that the corrections can substantially increase image quality. Specifically, we could measure structures as small as 80 nm at a depth of 90 m inside the biological tissue, and obtain a 60% signal increase after correction.

neuroscience↗

bioRxiv2020

A prevalent and culturable microbiota links ecological balance to clinical stability of the human lung after transplantation

There is accumulating evidence that the lower airway microbiota impacts lung health. However, the link between microbial community composition and lung homeostasis remains elusive. We combined amplicon sequencing and culturomics to characterize the viable bacterial community in 234 longitudinal bronchoalveolar lavage samples from 64 lung transplant recipients and established links to viral loads, host gene expression, lung function, and transplant health. We find that the lung microbiota post-transplant can be categorized into four distinct compositional states, pneumotypes. The predominant balanced pneumotype was characterized by a diverse bacterial community with moderate viral loads, and host gene expression profiles suggesting immune tolerance. The other three pneumotypes were characterized by being either microbiota-depleted, or dominated by potential pathogens, and were linked to increased immune activity, lower respiratory function, and increased risks of infection and rejection. Collectively, our findings establish a link between the lung microbial ecosytem, human lung function, and clinical stability post-transplant. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=191 SRC="FIGDIR/small/106211v1_ufig1.gif" ALT="Figure 1"> View larger version (57K): org.highwire.dtl.DTLVardef@1df2be3org.highwire.dtl.DTLVardef@ba839dorg.highwire.dtl.DTLVardef@116f657org.highwire.dtl.DTLVardef@86d8ac_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2018

Studying the fate of tumor extracellular vesicles at high spatio-temporal resolution using the zebrafish embryo

Tumor extracellular vesicles (tumor EVs) mediate the communication between tumor and stromal cells mostly to the benefit of tumor progression. Notably, tumor EVs have been reported to travel in the blood circulation, reach specific distant organs and locally modify the microenvironment. However, visualizing these events in vivo still faces major hurdles. Here, we show a new method for tracking individual circulating tumor EVs in a living organism: we combine novel, bright and specific fluorescent membrane probes, MemBright, with the transparent zebrafish embryo as an animal model. We provide the first description of tumor EVs hemodynamic behavior and document their arrest before internalization. Using transgenic lines, we show that circulating tumor EVs are uptaken by endothelial cells and blood patrolling macrophages, but not by leukocytes, and subsequently stored in acidic degradative compartments. Finally, we prove that the MemBright can be used to follow naturally released tumor EVs in vivo. Overall, our study demonstrates the usefulness and prospects of zebrafish embryo to track tumor EVs in vivo.\n\nHighlightsO_LIMemBright, a new family of membrane probes, allows for bright and specific staining of EVs\nC_LIO_LIZebrafish melanoma EVs are very similar to human and mouse melanoma EVs in morphology and protein content\nC_LIO_LIThe zebrafish embryo is an adapted model to precisely track tumor EVs dynamics and fate in a living organism from light to electron microscopy\nC_LIO_LICirculating tumor EVs are rapidly uptaken by endothelial cells and patrolling macrophages\nC_LIO_LICorrelated light and electron microscopy can be used in zebrafish to identify cells and compartments uptaking tumor EVs\nC_LI\n\nBlurbDispersion of tumor extracellular vesicles (EVs) throughout the body promotes tumor progression. However the behavior of tumor EVs in body fluids remains mysterious due to their small size and the absence of adapted animal model. Here we show that the zebrafish embryo can be used to track circulating tumor EVs in vivo and provide the first high-resolution description of their dissemination and uptake.

cell biology↗

bioRxiv2017

Hemodynamic forces tune the arrest, adhesion and extravasation of circulating tumor cells

Metastatic seeding is driven by cell-intrinsic and environmental cues, yet the contribution of biomechanics is poorly known. We aim to elucidate the impact of blood flow on the arrest and the extravasation of circulating tumor cells (CTCs) in vivo. Using the zebrafish embryo, we show that arrest of CTCs occurs in vessels with favorable flow profiles where flow forces control the adhesion efficacy of CTCs to the endothelium. We biophysically identified the threshold values of flow and adhesion forces allowing successful arrest of CTCs. In addition, flow forces fine-tune tumor cell extravasation by impairing the remodeling properties of the endothelium. Importantly, we also observe endothelial remodeling at arrest sites of CTCs in mouse brain capillaries. Finally, we observed that human supratentorial brain metastases preferably develop in areas with low perfusion. Altogether, these results demonstrate that hemodynamic profiles at metastatic sites regulate key steps of extravasation preceding metastatic outgrowth.

cancer biology↗