Global S&T Development Trend Analysis Platform of Resources and Environment
Most magmatism occurring on Earth is conventionally attributed to passive mantle upwelling at mid-ocean ridges, to slab devolatilization at subduction zones, or to mantle plumes. However, the widespread Cenozoic intraplate volcanism in northeast China(1-3) and the young petit-spot volcanoes(4-7) offshore of the Japan Trench cannot readily be associated with any of these mechanisms. In addition, the mantle beneath these types of volcanism is characterized by zones of anomalously low seismic velocity above and below the transition zone(8-12) (a mantle level located at depths between 410 and 660 kilometres). A comprehensive interpretation of these phenomena is lacking. Here we show that most (or possibly all) of the intraplate and petit-spot volcanism and low-velocity zones around the Japanese subduction zone can be explained by the Cenozoic interaction of the subducting Pacific slab with a hydrous mantle transition zone. Numerical modelling indicates that 0.2 to 0.3 weight per cent of water dissolved in mantle minerals that are driven out from the transition zone in response to subduction and retreat of a tectonic plate is sufficient to reproduce the observations. This suggests that a critical amount of water may have accumulated in the transition zone around this subduction zone, as well as in others of the Tethyan tectonic belt(13) that are characterized by intraplate or petit-spot volcanism and low-velocity zones in the underlying mantle.
The widespread intraplate volcanism in northeast China and the unusual '
The biology of haematopoietic stem cells (HSCs) has predominantly been studied under transplantation conditions(1,2). It has been particularly challenging to study dynamic HSC behaviour, given that the visualization of HSCs in the native niche in live animals has not, to our knowledge, been achieved. Here we describe a dual genetic strategy in mice that restricts reporter labelling to a subset of the most quiescent long-term HSCs (LT-HSCs) and that is compatible with current intravital imaging approaches in the calvarial bone marrow(3-5). We show that this subset of LT-HSCs resides close to both sinusoidal blood vessels and the endosteal surface. By contrast, multipotent progenitor cells (MPPs) show greater variation in distance from the endosteum and are more likely to be associated with transition zone vessels. LT-HSCs are not found in bone marrow niches with the deepest hypoxia and instead are found in hypoxic environments similar to those of MPPs. In vivo time-lapse imaging revealed that LT-HSCs at steady-state show limited motility. Activated LT-HSCs show heterogeneous responses, with some cells becoming highly motile and a fraction of HSCs expanding clonally within spatially restricted domains. These domains have defined characteristics, as HSC expansion is found almost exclusively in a subset of bone marrow cavities with bone-remodelling activity. By contrast, cavities with low bone-resorbing activity do not harbour expanding HSCs. These findings point to previously unknown heterogeneity within the bone marrow microenvironment, imposed by the stages of bone turnover. Our approach enables the direct visualization of HSC behaviours and dissection of heterogeneity in HSC niches.
A dual genetic strategy enables the labelling and in vivo imaging of native long-term haematopoietic stem cells in the mouse calvarial bone marrow.
