Éditeur(s) : HAL CCSD Oldendorf/Luhe
Résumé : International audience
Non-calcifying photosynthetic anthozoans have emerged as a group that may thrive under high carbon dioxide partial pressure (pCO(2)) conditions via increased productivity. However, the physiological mechanisms underlying this potential success are unclear. Here we investigated the impact of high pCO(2) on the dissolved inorganic carbon (DIC) use in the temperate sea anemone Anemonia viridis. We assessed the impacts of long-term exposure to high pCO(2), i.e. sampling in situ natural CO2 vents (Vulcano, Italy), and short-term exposure, i.e. during a 3 wk controlled laboratory experiment. We focused on photo-physiological parameters (net photosynthesis rates, chlorophyll a content and Symbiodinium density) and on carbonic anhydrase (CA) activity, an enzyme involved in the energy-demanding process of DIC absorption. Long-term exposure to high pCO(2) had no impact on Symbiodinium density and chlorophyll a content. In contrst, short-term exposure to high pCO(2) induced a significant reduction in Symbiodinium density, which together with unchanged net photosynthesis resulted in the increase of Symbiodinium productivity per cell. Finally, in both in situ long-term and laboratory short-term exposure to high pCO(2), we observed a significant decrease in the CA activity of sea anemones, suggesting a change in DIC use (i.e. from an HCO3- to a CO2 user). This change could enable a shift in the energy budget that may increase the ability of non-calcifying photosynthetic anthozoans to cope with ocean acidification.
ISSN: 0171-8630

hal-01546163
https://hal.archives-ouvertes.fr/hal-01546163
DOI : 10.3354/meps11916

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
High-mobility group box-1 (HMGB1) is remarkably mobile in living cells, which reflects its ability to interact only transiently with both DNA and protein. This property is likely essential for HMGB1 nuclear activities. Nonetheless the weak interaction of HMGB1 with DNA and/or protein partners has also been a major limitation for investigating HMGB1 subnuclear localisation and for the identification of HMGB1 containing complexes by conventional biochemical approaches. In the present study, FRAP experiments demonstrated that DsRed-mediated oligomerization strongly reduces HMGB1 mobility due to an increased affinity for cellular chromatin. Moreover, oligomerized DsRed HMGB1 exhibited a higher affinity for supercoiled DNA in vitro compared to its monomeric counterpart. These results indicate that DsRed-meditated oligomerization is prone to stabilize labile interactions involving HMGB1 both in vivo and in vitro.
ISSN: 0300-9084

hal-01546170
https://hal.archives-ouvertes.fr/hal-01546170
DOI : 10.1016/j.biochi.2012.11.001

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The actin cytoskeleton is a dynamic structure that provides an interactive platform for organelles and cellular components. It also serves as track for membranes and vesicles that move via myosin. The actin cytoskeleton of Symbiodinium is a well-organized reticular structure suggestive of multiple membrane interactions, very likely including those of the chloroplast. The Symbiodinium chloroplast membrane network is, in turn, a highly organized structure, suggestive of being under the control of an organizing network. We visualized the chloroplast membranes of cultured Symbiodinium sp. under various light conditions and observed changes dependent on illumination intensity. Since we suspected interaction between these two organelles, and we knew that the Symbiodinium actin cytoskeleton collapses upon treatment with either latrunculin B, an actin microfilament-disrupting agent, or butanedione monoxime, a myosin function inhibitor, we tested the Symbiodinium sp. oxygen evolution in their presence. Upon latrunculin B addition, the oxygen production decreased compared to non-treated cells; however, this was not observed after a 24 h latrunculin treatment. On the contrary, butanedione monoxime treatment caused a non-recoverable dysfunction of the chloroplast causing a severe loss in oxygen production even after long-term exposure. Using electron microscopy, we observed an alteration of the Symbiodinium sp. chloroplast distribution after latrunculin B treatment, with respect to untreated cells. Furthermore, a thorough disorganization of the chloroplast grana was observed after butanedione monoxime treatment. These data suggest that an actomyosin system would be important for chloroplast organization and distribution, and critical for normal photosynthetic function of Symbiodinium sp.
ISSN: 0166-8595

hal-01546164
https://hal.archives-ouvertes.fr/hal-01546164
DOI : 10.1007/s11120-015-0142-9

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
o abstract
ISSN: 0920-9069

hal-01546171
https://hal.archives-ouvertes.fr/hal-01546171

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The temperate symbiotic sea anemone Anemonia viridis, a member of the Cnidaria phylum, is a relevant experimental model to investigate the molecular and cellular events involved in the preservation or in the rupture of the symbiosis between the animal cells and their symbiotic microalgae, commonly named zooxanthellae. In order to increase research tools for this model, we developed a primary culture from A. viridis animal cells. By adapting enzymatic dissociation protocols, we isolated animal host cells from a whole tentacle in regeneration state. Each plating resulted in a heterogeneous primary culture consisted of free zooxanthellae and many regular, small rounded and adherent cells (of 3-5 mu m diameter). Molecular analyses conducted on primary cultures, maintained for 2 weeks, confirmed a specific signature of A. viridis cells. Further serial dilutions and micromanipulation allowed us to obtain homogenous primary cultures of the small rounded cells, corresponding to A. viridis ``epithelial-like cells''. The maintenance and the propagation over a 4 weeks period of primary cells provide, for in vitro cnidarian studies, a preliminary step for further investigations on cnidarian cellular pathways notably in regard to symbiosis interactions.
ISSN: 0920-9069

hal-01546173
https://hal.archives-ouvertes.fr/hal-01546173
DOI : 10.1007/s10616-013-9566-2