Pathophysiological lessons from rare associations of immunological disorders

Rare associations of immunological disorders can often tell more than mice and rats about the pathogenesis of immunologically mediated human kidney disease. Cases of glomerular disease with thyroiditis and Graves’ disease and of minimal change disease with lymphoepithelioma-like thymic carcinoma and lymphomatoid papulosis were recently reported in Pediatric Nephrology. These rare associations can contribute to the unraveling of the pathogenesis of membranous nephropathy (MN) and minimal change disease (MCD) and lead to the testing of novel research hypotheses. In MN, the target antigen may be thyroglobulin or another thyroid-released antigen that becomes planted in the glomerulus, but other scenarios can be envisaged, including epitope spreading, polyreactivity of pathogenic antibodies, and dysregulation of T regulatory cells, leading to the production of a variety of auto-antibodies with different specificities [immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX syndrome)]. The occurrence of MCD with hemopathies supports the role of T cells in the pathogenesis of proteinuria, although the characteristics of those T cells remain to be established and the glomerular permeability factor(s) identified

The topographic evolution of the Tibetan Region as revealed by palaeontology

The Tibetan Plateau was built through a succession of Gondwanan terranes colliding with Asia during the Mesozoic. These accretions produced a complex Paleogene topography of several predominantly east–west trending mountain ranges separated by deep valleys. Despite this piecemeal assembly and resultant complex relief, Tibet has traditionally been thought of as a coherent entity rising as one unit. This has led to the widely used phrase ‘the uplift of the Tibetan Plateau’, which is a false concept borne of simplistic modelling and confounds understanding the complex interactions between topography climate and biodiversity. Here, using the rich palaeontological record of the Tibetan region, we review what is known about the past topography of the Tibetan region using a combination of quantitative isotope and fossil palaeoaltimetric proxies, and present a new synthesis of the orography of Tibet throughout the Paleogene. We show why ‘the uplift of the Tibetan Plateau’ never occurred, and quantify a new pattern of topographic and landscape evolution that contributed to the development of today’s extraordinary Asian biodiversity

MULTIPLE PALAEOECOLOGICAL PROXIES CONSTRAIN THE INTERPLAY BETWEEN TIBETAN PLATEAU GROWTH, THE PROTO-MONSOONS AND FLORAL DISPERSAL DURING THE EARLY INDIA-ASIA COLLISION

International audienceThe interplay between tectonics, monsoonal climate regimes, andbiodiversity of the Tibetan Plateau has been the recent focus ofmuch investigation. However, the linkages between orogeny andclimate, as well as their impacts on floral diversity, are still unclear.The Nangqian Basin of east-central Tibet holds a key Paleocene–Eocene record of deformation and environmental change duringthe early stage of the India-Asia collision, the development of theTibetan Plateau, and the proto-monsoons. Here, we examine newpalynoassemblages recovered from this basin and apply FourierTransform Infrared (FTIR) microspectroscopy to quantify ultravioletirradiance based on pollen chemistry, in combination with plantleaf wax biomarkers. Although the studied section was previouslyassigned a mid-Cretaceous age based on ostracods, this new palynologicalevidence combined with magnetostratigraphy rather indicatesa Paleogene age. Volcanic intrusives and extrusives crosscutthe lacustrine to alluvial Cenozoic Nangqian strata, providing aminimum age constraint at ca. 37 Ma. In the context of a proto-TibetanPlateau established early in the Cenozoic, the abundance ofhigh-altitude bisaccates from the Nangqian section is of particularinterest. It largely predates the spread of high-altitude elements tothe North in Central Asia from 36 Ma, and their diversification afterthe 34 Ma Eocene–Oligocene transition cooling. These observationsare in line with a growing body of evidence that parts of the TibetanPlateau had attained high elevations similar to modern conditionssoon after the India-Asia collision. The outward growth from this elevatedcentral part of the Tibetan Plateau, with associated effects onthe monsoons, is envisioned to have had major effects on dispersaland speciation of the Pinophyta across Asia during the Paleogene

Cooling, vegetation shift and decline in monsoonal rainfall in NE Tibet through the greenhouse to icehouse transition

International audienceUnderstanding how and why global climate tipped from greenhouse to icehouse conditions remains a major challenge.This critical shift is well documented in the marine realm characterized by a steady decline in global temperatureuntil a large and rapid cooling step at the Eocene-Oligocene Transition (EOT). However, the chronology andmechanisms of cooling on land remain unclear. To reconstruct Paleogene climate conditions for the Tibetan Plateauand the Asian continental interior, clumped isotope thermometry and palynology in accurately-dated continentalrecords from northeastern Tibet, are here combined with climate and vegetation simulations. Our results show twosuccessive dramatic (>9 C) drops in soil carbonate temperature, at 37 Ma and at 33.5 Ma associated respectivelywith the appearance and dominance of high altitude conifer forests. Such large temperature decreases associatedwith ecological reorganisations cannot result from regional cooling alone. They require shifting of the rainy seasonto cooler months, which we interpret to reflect a decline of monsoonal intensity. Our results suggest that theresponse of Asian temperatures, monsoonal rainfall and vegetation to the decline of atmospheric CO2 and globaltemperature through the late Eocene occurred in two steps separated by a period of climatic instability. Our resultssupport the onset of the Antarctic Circumpolar Current coeval to the Oligocene isotope event 1 (Oi-1) glaciationat 33.5 Ma, reshaping the distribution of surface heat worldwide; however, the origin of the 37 Ma cooling eventremains to be determined

Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia

International audienceSedimentary basins in eastern Africa preserve a record of continental rifting and contain important fossil assemblages for interpreting hominin evolution. However, the record of hominin evolution between 3 and 2.5 million years ago (Ma) is poorly documented in surface outcrops, particularly in Afar, Ethiopia. Here we present the discovery of 2.84-2.58 Ma fossil and hominin-bearing sediments in the Ledi-Geraru research area that have produced the earliest record of the genus Homo. Vertebrate fossils record a faunal turnover indicative of more open and probable arid habitats than those reconstructed earlier in this region, in broad agreement with hypotheses addressing the role of environmental forcing in hominin evolution at this time. Geological analyses constrain depositional and structural models of the Afar and date the LD 350-1 Homo mandible to 2.80-2.75 Ma

Lateral translation of the Burma Platelet since the late Cretaceous: An Asian analogue for the Baja-BC hypothesis?

International audienceThe Burma Platelet is a 1200 km long sliver plate stretching along the Burmese subduction margin. It is commonly seen as being dragged by the northwards convergence of the Indian plate since the late Miocene, as a result of the hyper-oblique convergence of India relative to Indochina and the opening of the Andaman Sea. This talk proposes an overview of the history of the Burma Platelet since the Late Cretaceous based on new data from the Myanmar Paleoclimate and Geodynamics Research Group (MyaPGR), including sedimentological, geochronological, and paleomagnetic data from central Myanmar.We show that the Burma Platelet has been forming an individual sliver plate since at least the middle Eocene –and possibly much earlier-- and that the duration and distance of its coastwise translation have been significantly underestimated. Preliminary paleomagnetic data suggest up to 2500 km of northward translation of the Burma Platelet at a relatively moderate pace since the Late Cretaceous, which seems supported by sedimentary provenance data from central Myanmar.The amplitude and duration of the lateral translation of the Burma Platelet provides a potential analogue to the controversial coastwise translations of terranes along the western margin of North America (the famous ‘Baja-BC Hypothesis’). Its mechanisms and triggers remain to be documented

Late Eocene sea retreat from the Tarim Basin (west China) and concomitant Asian paleoenvironmental change

International audienceThe Paleogene sediments of the southwest Tarim Basin along the West Kunlun Shan in western China include the remnants of the easternmost extent of a large epicontinental sea. This shallow sea once extended across the Eurasian continent before it retreated westward and eventually separated as the Paratethys Sea. Climate modeling results suggest that this sea retreat is an equally important forcing mechanism as the Tibetan plateau uplift in the aridification of the Asian continental interior and the intensification of the Asian monsoon system. The age and paleogeography of the retreat are poorly constrained, hindering the understanding of its cause and paleoenvironmental impacts. This study reports litho- and biostratigraphic results from two sections recording the last major regression out of the Tarim Basin that is expressed by a regional transition from marine clastics and limestones to continental red-beds. Rich micro- and macrofossil assemblages, including benthic foraminifera, ostracods, bivalves, calcareous nannofossils and organic walled dinoflagellate cysts (dinocysts), indicate a shallow, proximal and marine environment. Strong similarity to assemblages known from Central Asia and Europe confirms that surface­ocean connections extended across Eurasia from the Tarim Basin to the western Tethys during the latest Eocene. Moreover, the recovered fossil associations date the last marine sediments as earliest Priabonian in age (~37 Ma; overlap between dinoflagellate Mps Interval Zone and calcareous nannofossil Zone CP 14). The retreat of the sea from the Tarim Basin is timeequivalent with the sea level lowstand at the Bartonian­Priabonian boundary but pre-dates both the Oligocene­Miocene regional uplift of the Pamir mountains and Kunlun Shan and the major eustatic sea-level falls of the Eocene­Oligocene Transition (~34 Ma) and mid-Oligocene (~30 Ma), which are usually held responsible for the sea retreat. Furthermore, a concomitant and significant aridification step occurs at ~36.6 Ma (top of chron C17n.1n) as recorded by regional sedimentary records of the Xining Basin along the northeastern Tibetan Plateau, suggesting that the Tarim Sea served as a significant moisture contributor for the Asian interior

Caractérisation de la crise climatique à la transition Greenhouse-Icehouse enregistrée dans le rift de la Limagne, Puy de Dôme

National audienceLa transition Éocène-Oligocène se caractérise par un refroidissement climatique global rapide, marquant le passage d'un état « Greenhouse » à un état « Icehouse ». Cet événement est lié à la baisse de la pCO2 atmosphérique et la formation de la calotte glaciaire de l'Antarctique, entraînant une baisse du niveau marin. Les enregistrements sédimentaires marins ont attesté de l'existence de ce changement majeur. Toutefois, cette transition demeure mal définie dans le domaine continental bien que ce dernier permette d'appréhender plus directement comment une transition climatique peut engendrer des crises environnementales et biotiques majeures. Plusieurs bassins sédimentaires à travers la France ont enregistré le passage Eocène-Oligocène en domaine continental et une crise biotique majeure, la Grande Coupure. Les changements climatiques et environnementaux associés à la transition Eocène-Oligocène sont notamment consignés dans les archives sédimentaires des bassins extensifs à haut taux de subsidence, idéaux pour établir une chronologie haute-résolution des événements environnementaux et biotiques associés à la transition. Une étude de datation est réalisée sur une carotte de sédiments lacustres provenant du Rift de la Limagne, dans le Massif Central, d'une longueur de 1089 mètres, couvre une période de 10 Ma. Sur 110 échantillons paléomagnétiques pilotes, des aimantations primaires de polarités normales et inverses ont été identifiées préférentiellement sur les lithologies argileuses indiquant l'applicabilité de la magnétostratigraphie. Cette approche est associée à une analyse cyclostratigraphique des données de diagraphie suggère que les cycles d'excentricité (400 ka et 100 ka), d'obliquité (40 ka) et de précession (20 ka), sont respectivement enregistrés sur des périodes moyennes de 45 m, 11 m, 3.8 m et 2.3 m. Ces observations permettent de déduire un taux de sédimentation moyen estimé entre 100 et 120 m/Ma. Cette étude montre que la série sédimentaire de la carotte de Limagne s'est déposée suffisamment rapidement pour documenter les changements climatiques et biotiques de la transition Eocène-Oligocène en France avec une résolution pluri-centennale.

Evidence for northeastern Tibetan Plateau uplift between 25 and 20 Ma in the sedimentary archive of the Xining Basin, Northwestern China

International audienceThe growth history of the Tibetan Plateau provides a valuable natural laboratory to understand tectonic processes of the India-Asia collision and their impact on and interactions with Asian and global climate change. However, both Tibetan Plateau growth and Asian paleoenvironments are generally poorly documented in pre-Pliocene times and reflect limited temporal coverage for different parts of the plateau. Here we present magnetostratigraphic results from the Xining Basin, at the NE margin of the Tibetan Plateau, precisely dating the record between the earliest Oligocene (~33 Ma) to the middle Miocene (~16 Ma). The pattern of observed paleomagnetic polarity zones is unequivocally correlated to the geomagnetic polarity time scale (GPTS) indicating relatively constant and low sediment accumulation rates (32 m/Myr) except for a peculiar period of unstable accumulation between 25.3 and 19.7Ma. At the beginning of this interval, a marked permanent increase in magnetite content of the sediments is observed and likely relates to a change in provenance. We directly relate this unstable period of sediment accumulation and provenance change to the coeval exhumation recently reported by low-temperature thermochronology from the Laji Shan range, which subsequently formed the southernmargin of the Xining Basin. Evidence for NE Tibet tectonismat 25-20 Ma can be associated with widespread deformation over the entire Himalayan-Tibetan orogen at this time, which may be linked to the coeval appearance of monsoon climate in Eastern Asia and the onset of central Asian desertification