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94 results on '"Hégaret, Helene"'

28. Morphological and functional characterization of the oyster Crassostrea gasar circulating hemocytes: Cell types and phagocytosis activity

Author

Silva Freire, Jesarela Merabe, Dantas Farias, Natanael, Hégaret, Helene, Da Silva, Patricia Mirella, Silva Freire, Jesarela Merabe, Dantas Farias, Natanael, Hégaret, Helene, and Da Silva, Patricia Mirella

Abstract

Hemocytes are the circulating cells of the hemolymph of oysters and are responsible for numerous physiological functions, including immune defense. The oyster Crassostrea gasar is a native species inhabiting mangrove habitat and is of great commercial interest, cultured throughout the Brazilian coast, mainly in the north and northeast. Despite its commercial importance, little is known about its immunological aspects and defense cells, the hemocytes. This work aimed to morphologically characterize hemocytes of the oyster C. gasar and to study one of the main cellular defense response, phagocytosis, using light microscopy and flow cytometry. The results showed the presence of six hemocyte populations in C. gasar hemolymph. These comprise of large and small granulocytes, large and small hyalinocytes, blast-like cells and a rare type classified as vesicular or serous hemocytes. Hyalinocytes were highly abundant and the most heterogeneous cell population, while small granulocytes, along with vesicular hemocytes were the less abundant population. Hemocytes of C. gasar oysters demonstrated capabilities to phagocytose three different types of particles tested: zymosan A, latex particles and Escherichia coli, indicating a broad defense capacity. The zymosan A were the most engulfed particles, followed by beads, mainly phagocytized by granulocytes, the most phagocytic cells, and finally E. coli, which were the least phagocytized. This study is the first characterization of C. gasar oyster hemocytes and will support future studies that aim to understand the participation of different hemocyte types in defense responses against pathogens and/or environmental changes.

Published
2023
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29. Mortality and histopathology in sheepshead minnow (Cyprinodon variegatus) larvae exposed to pectenotoxin-2 and Dinophysis acuminata

Author

Gaillard, Sylvain, Réveillon, Damien, Mason, P.l., Ayache, Nour, Sanderson, M., Smith, J.l., Giddings, S., Mccarron, P., Séchet, Veronique, Hégaret, Helene, Hess, Philipp, Vogelbein, W.k., Gaillard, Sylvain, Réveillon, Damien, Mason, P.l., Ayache, Nour, Sanderson, M., Smith, J.l., Giddings, S., Mccarron, P., Séchet, Veronique, Hégaret, Helene, Hess, Philipp, and Vogelbein, W.k.

Abstract

Toxic species of the dinoflagellate genus Dinophysis can produce diarrheic toxins including okadaic acid (OA) and dinophysistoxins (DTXs), and the non-diarrheic pectenotoxins (PTXs). Okadaic acid and DTXs cause diarrheic shellfish poisoning (DSP) in human consumers, and also cause cytotoxic, immunotoxic and genotoxic effects in a variety of mollusks and fishes at different life stages in vitro. The possible effects of co-produced PTXs or live cells of Dinophysis to aquatic organisms, however, are less understood. Effects on an early life stage of sheepshead minnow (Cyprinodon variegatus), a common finfish in eastern USA estuaries, were evaluated using a 96-h toxicity bioassay. Three-week old larvae were exposed to PTX2 concentrations from 50 to 4000 nM, live Dinophysis acuminata culture (strain DAVA01), live cells resuspended in clean medium or culture filtrate. This D. acuminata strain produced mainly intracellular PTX2 (≈ 21 pg cell−1), with much lower levels of OA and dinophysistoxin-1. No mortality or gill damages were observed in larvae exposed to D. acuminata (from 5 to 5500 cells mL−1), resuspended cells and culture filtrate. However, exposure to purified PTX2 at intermediate to high concentrations (from 250 to 4000 nM) resulted in 8 to 100% mortality after 96 h (24-h LC50 of 1231 nM). Histopathology and transmission electron microscopy of fish exposed to intermediate to high PTX2 concentrations revealed important gill damage, including intercellular edema, necrosis and sloughing of gill respiratory epithelia, and damage to the osmoregulatory epithelium, including hypertrophy, proliferation, redistribution and necrosis of chloride cells. Tissue damage in gills is likely caused by the interaction of PTX2 with the actin cytoskeleton of the affected gill epithelia. Overall, the severe gill pathology observed following the PTX2 exposure suggested death was due to loss of respiratory and osmoregulatory functions in C. variegatus larvae.

Published
2023
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43. Genetic association of toxin production in the dinoflagellate Alexandrium minutum

Author

Mary, Lou, Quere, Julien, Latimier, Marie, Rovillon, Georges-augustin, Hégaret, Helene, Réveillon, Damien, Le Gac, Mickael, Mary, Lou, Quere, Julien, Latimier, Marie, Rovillon, Georges-augustin, Hégaret, Helene, Réveillon, Damien, and Le Gac, Mickael

Abstract

Dinoflagellates of the genus Alexandrium are responsible for harmful algal blooms and produce paralytic shellfish toxins (PSTs). Their very large and complex genomes make it challenging to identify the genes responsible for toxin synthesis. A family-based genomic association study was developed to determine the inheritance of toxin production in Alexandrium minutum and identify genomic regions linked to this production. We show that the ability to produce toxins is inheritable in a Mendelian way, while the heritability of the toxin profile is more complex. We developed the first dinoflagellate genetic linkage map. Using this map, several major results were obtained: 1. A genomic region related to the ability to produce toxins was identified. 2. This region does not contain any polymorphic sxt genes, known to be involved in toxin production in cyanobacteria. 3. The sxt genes, known to be present in a single cluster in cyanobacteria, are scattered on different linkage groups in A. minutum. 4. The expression of two sxt genes not assigned to any linkage group, sxtI and sxtG, may be regulated by the genomic region related to the ability to produce toxins. Our results provide new insights into the organization of toxicity-related genes in A. minutum, suggesting a dissociated genetic mechanism for the production of the different analogues and the ability to produce toxins. However, most of the newly identified genes remain unannotated. This study therefore proposes new candidate genes to be further explored to understand how dinoflagellates synthesize their toxins.

Published
2022
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