Influence of environmental variability and Emiliania huxleyi ecotypes on alkenone-derived temperature reconstructions in the subantarctic Southern Ocean.

Long-chain unsaturated alkenones produced by haptophyte algae are widely used as paleotemperature indicators. The unsaturation relationship to temperature is linear at mid-latitudes, however, non-linear responses detected in subpolar regions of both hemispheres have suggested complicating factors in these environments. To assess the influence of biotic and abiotic factors in alkenone production and preservation in the Subantarctic Zone, alkenone fluxes were quantified in three vertically-moored sediment traps deployed at the SOTS observatory (140°E, 47°S) during a year. Alkenone fluxes were compared with coccolithophore assemblages, satellite measurements and surface-water properties obtained by sensors at SOTS. Alkenone-based temperature reconstructions generally mirrored the seasonal variations of SSTs, except for late winter when significant deviations were observed (3-10 °C). Annual flux-weighted averages in the 3800 m trap returned alkenone-derived temperatures ~1.5 °C warmer than those derived from the 1000 m trap, a distortion attributed to surface production and signal preservation during its transit through the water column. Notably, changes in the relative abundance of E. huxleyi var. huxleyi were positively correlated with temperature deviations between the alkenone-derived temperatures and in situ SSTs (r = 0.6 and 0.7 at 1000 and 2000 m, respectively), while E. huxleyi var. aurorae, displayed an opposite trend. Our results suggest that E. huxleyi var. aurorae produces a higher proportion of C37:3 relative to C37:2 compared to its counterparts. Therefore, the dominance of var. aurorae south of the Subtropical Front could be at least partially responsible for the less accurate alkenone-based SST reconstructions in the Southern Ocean using global calibrations. However, the observed correlations were largely influenced by the samples collected during winter, a period characterized by low particle fluxes and slow sinking rates. Thus, it is likely that other factors such as selective degradation of the most unsaturated alkenones could also account for the deviations of the alkenone paleothermometer.

Gut-derived acetate promotes B10 cells with antiinflammatory effects.

Autoimmune diseases are characterized by a breakdown of immune tolerance partly due to environmental factors. The short-chain fatty acid acetate, derived mostly from gut microbial fermentation of dietary fiber, promotes antiinflammatory Tregs and protects mice from type 1 diabetes, colitis, and allergies. Here, we show that the effects of acetate extend to another important immune subset involved in tolerance, the IL-10-producing regulatory B cells (B10 cells). Acetate directly promoted B10 cell differentiation from mouse B1a cells both in vivo and in vitro. These effects were linked to metabolic changes through the increased production of acetyl-coenzyme A, which fueled the TCA cycle and promoted posttranslational lysine acetylation. Acetate also promoted B10 cells from human blood cells through similar mechanisms. Finally, we identified that dietary fiber supplementation in healthy individuals was associated with increased blood-derived B10 cells. Direct delivery of acetate or indirect delivery via diets or bacteria that produce acetate might be a promising approach to restore B10 cells in noncommunicable diseases.

Full annual monitoring of Subantarctic Emiliania huxleyi populations reveals highly calcified morphotypes in high-CO2 winter conditions.

Ocean acidification is expected to have detrimental consequences for the most abundant calcifying phytoplankton species Emiliania huxleyi. However, this assumption is mainly based on laboratory manipulations that are unable to reproduce the complexity of natural ecosystems. Here, E. huxleyi coccolith assemblages collected over a year by an autonomous water sampler and sediment traps in the Subantarctic Zone were analysed. The combination of taxonomic and morphometric analyses together with in situ measurements of surface-water properties allowed us to monitor, with unprecedented detail, the seasonal cycle of E. huxleyi at two Subantarctic stations. E. huxleyi subantarctic assemblages were composed of a mixture of, at least, four different morphotypes. Heavier morphotypes exhibited their maximum relative abundances during winter, coinciding with peak annual TCO2 and nutrient concentrations, while lighter morphotypes dominated during summer, coinciding with lowest TCO2 and nutrients levels. The similar seasonality observed in both time-series suggests that it may be a circumpolar feature of the Subantarctic zone. Our results challenge the view that ocean acidification will necessarily lead to a replacement of heavily-calcified coccolithophores by lightly-calcified ones in subpolar ecosystems, and emphasize the need to consider the cumulative effect of multiple stressors on the probable succession of morphotypes.

Data on lithofacies, sedimentology and palaeontology of South Rifian Corridor sections (Morocco).

We provide lithological, sedimentological and micropalaeontological descriptions of 39 sections and boreholes crossing the upper Miocene deposits of the Rifian Corridor. These deposits represent the sedimentary remnants of the marine gateway that connected the Atlantic to the Mediterranean in the late Miocene. Results from these 39 sites were adopted to reconstruct the palaeogeographic evolution of the gateway presented in the associated research article (Capella et al., 2018) [1]. For each outcrop we present a synthesis of field observations, lithofacies, key sedimentological features, planktic and benthic assemblages.

Suicidal emperipolesis: a process leading to cell-in-cell structures, T cell clearance and immune homeostasis.

"Suicidal emperipolesis" is one of the most recently reported processes leading to cell-in-cell structures that promote cell death. This process was discovered in studies investigating the fate of autoreactive CD8 T cells activated within the liver. Recently, we reported that activated T cells invaded hepatocytes, formed transient cell-in-cell structures, and were rapidly degraded within endosomal/lysosomal compartments by a non-apoptotic pathway. Importantly, pharmacological inhibition of this process caused intrahepatic accumulation of tissue-reactive T cells and breach of immune tolerance. The characterization of the molecular mechanisms of suicidal emperipolesis is still in its infancy, but initial studies suggest this phenomenon is distinct from other reported cell-in-cell structures. As opposed to the formation of other cell-in-cell structures, suicidal emperipolesis takes place in a non-malignant environment, and without obvious pathology. It is therefore the first cell-in-cell structure described to have a role in maintaining homeostasis in normal physiology in higher organisms. T cell emperipolesis within hepatocytes has also been observed by pathologists in a range of chronic human liver pathologies. As T cell-in-hepatocyte structures resulting from suicidal emperipolesis are very transiently observed in normal physiology, their accumulation during liver disease would suggest that severe tissue injury is promoted by, or associated with, defective T cell clearance. In this review, we compare "suicidal emperipolesis" to other processes leading to cell-in-cell structures, and consider its potential biological roles in maintaining immune homeostasis and tolerance in the context of the hepatic environment.

Effect of mature lymphocytes and lymphotoxin on the development of the follicle-associated epithelium and M cells in mouse Peyer's patches.

BACKGROUND AND AIMS: Mechanisms regulating M-cell formation are still poorly understood. In vitro studies showed that lymphocytes trigger the conversion of enterocyte cell lines into M cell-like cells on coculture, whereas in vivo their role in M cell differentiation is still elusive. Our aim was first to examine Rag-1-/- mice, lacking B and T lymphocytes, for the presence of intestinal M cells. Second, we investigated the role of lymphotoxin alphabeta signaling on M-cell formation, given its pivotal role in the development of mouse Peyer's patches. METHODS: Small intestines of Rag-1-/- mice, injected or not with soluble lymphotoxin beta receptor-immunoglobulin fusion protein, were analyzed morphologically using whole mount cytochemical staining, immunohistochemistry, and electron microscopy. RESULTS: Small Peyer's patch-like aggregates were found in Rag-1-/- mice in normal number and location. The overlying epithelium of such aggregates was reduced in size but still harbored M cells. In vivo neutralization of lymphotoxin beta-receptor signaling partially reduced the percentage of M cells. CONCLUSIONS: The absence of mature lymphocytes does not prevent the formation of M cells, indicating that the signaling molecules that support M-cell differentiation, such as lymphotoxin alphabeta, may also be supplied by non-B and non-T cells. Mature B lymphocytes, however, are required for the formation of a full-sized follicle-associated epithelium.

Development of Peyer's patches, follicle-associated epithelium and M cell: lessons from immunodeficient and knockout mice.

Studies with immunodeficient and knockout mice have revealed that the development of mucosa-associated lymphoid tissues (MALT) and peripheral lymphoid nodes share common mechanisms, but also require distinct signals. Gene disruption of lymphotoxins or their cognate receptors affects both Peyer's patch and lymph node organogenesis. Disruption of the osteoprotegerin TNF-family member gene does not impair Peyer's patch development, but prevents formation of peripheral lymph nodes. Peyer's patch do not form in mice with a deleted gene encoding a B lymphocyte-specific chemokine receptor, while most peripheral lymph nodes, except inguinal, are normal in numbers and architecture. In B or T lymphocyte-deficient mice, Peyer's patches, with their overlying follicle-associated epithelium (FAE), are present although reduced in number and size. No Peyer's patches develop in RAG deficient mice. Formation of FAE with typical M cells has not been analyzed in these mice. M cell formation requires the close association of immune cells with differentiated enterocytes and their conversion appears to be transcriptionally regulated. The development of MALT, FAE and probably M cells is a multistep process that requires signalling pathways common to all secondary lymphoid tissues, but also MALT-specific factors.

Transient expression of M-cell phenotype by enterocyte-like cells of the follicle-associated epithelium of mouse Peyer's patches.

BACKGROUND & AIMS: The follicle-associated epithelium (FAE) over mucosa-associated lymphoid tissues consists of distinct enterocytes and M cells concentrated at its periphery. The basement membrane composition was analyzed to test whether differences account for the distinct differentiation programs along the crypt-villus and crypt-FAE axes. To determine whether the decreased number of M cells in the FAE apex is caused by premature extrusion, we mapped the site where they undergo apoptosis. METHODS: The FAE basal lamina of Peyer's patches from BALB/c mice was analyzed by immunochemistry. M cells were identified using the Ulex europaeus agglutinin lectin. The cell proliferation and apoptotic compartments were characterized using bromodeoxyuridine incorporation and the TUNEL assay. RESULTS: The perlecan and laminin 2 stainings were different in FAE and villi. Myofibroblasts were absent beneath the FAE. The migration kinetics of cells along the FAE was similar to that along the villi. Apoptotic cells were detected exclusively at the apex of the FAE. CONCLUSIONS: FAE and M-cell differentiation is associated with a distinct basal lamina composition. FAE enterocytes express transient M-cell features as they move from the crypts toward the apoptotic compartment. M cells have a highly plastic phenotype that raises interesting questions about the control of intestinal epithelial cell differentiation.

Flagellin stimulation of intestinal epithelial cells triggers CCL20-mediated migration of dendritic cells.

Enteropathogenic bacteria elicit mucosal innate and adaptive immune responses. We investigated whether gut epithelial cells played a role in triggering an adaptive immune response by recruiting dendritic cells (DCs). Immature DCs are selectively attracted by the CCL20 chemokine. The expression of the CCL20 gene in human intestinal epithelial cell lines was up-regulated by pathogenic bacteria, including Salmonella species, but not by indigenous bacteria of the intestinal flora. The Salmonella machinery for epithelial cell invasion was not required for CCL20 gene activation. Flagellin but not the lipopolysaccharide was found to be the Salmonella factor responsible for stimulation of epithelial CCL20 production. CCL20 in turn triggered a specific migration of immature DCs. Our data show that crosstalk between bacterial flagellin and epithelial cells is essential for the recruitment of DCs, a mechanism that could be instrumental to initiate adaptive immune responses in the gut.

Geological record and reconstruction of the late Pliocene impact of the Eltanin asteroid in the Southern Ocean.

In 1995, an expedition on board the research vessel FS Polarstern explored the impact site of the Eltanin asteroid in the Southern Ocean, the only known asteroid impact into a deep ocean basin. Analyses of the geological record of the impact region place the event in the late Pliocene (approximately 2.15 Myr) and constrain the size of the asteroid to be >1 km. The explosive force inferred for this event places it at the threshold of impacts believed to have global consequences, and its study should therefore provide a baseline for the reconstruction and modelling of similar events, which are common on geological timescales.