Description: Although stress can suppress growth and proliferation, cells can induce adaptive responses that allow them to maintain these functions under stress. While numerous studies have focused on the inhibitory effects of stress on cell growth, less is known on how growth-promoting pathways influence stress responses. We have approached this question by analyzing the effect of mammalian target of rapamycin (mTOR), a central growth controller, on the osmotic stress response. Our results showed that mammalian cells exposed to moderate hypertonicity maintained active mTOR, which was required to sustain their cell size and proliferative capacity. Moreover, mTOR regulated the induction of diverse osmostress response genes, including targets of the tonicity-responsive transcription factor NFAT5 as well as NFAT5-independent genes. Genes sensitive to mTOR-included regulators of stress responses, growth and proliferation. Among them, we identified REDD1 and REDD2, which had been previously characterized as mTOR inhibitors in other stress contexts. We observed that mTOR facilitated transcription-permissive conditions for several osmoresponsive genes by enhancing histone H4 acetylation and the recruitment of RNA polymerase II. Altogether, these results reveal a previously unappreciated role of mTOR in regulating transcriptional mechanisms that control gene expression during cellular stress responses.

Description: Information on soil surface state is valuable for many applications such as climate studies and monitoring of permafrost regions. C-band scatterometer data indicate good potential to deliver information on surface freeze/thaw. Variation in state or amount of water contained in the soil causes significant alteration of dielectric properties of the soil which is markedly observable in scatterometer backscattered signal. A threshold-analysis method is developed to derive a set of parameters to be used in evaluating the normalized backscatter measurements through decision trees and anomaly detection modules for determination of freeze/thaw conditions. The model parameters are extracted from two years (2007-2008) backscatter data from ASCAT scatterometer onboard Metop satellite collocated with ECMWF ReAnalysis (ERA-Interim) soil temperature. Backscatter measurements are flagged as indicator of frozen/unfrozen surface, and snowmelt or existing water on the surface. The output product, so-called surface state flag (SSF), compares well with two modeled soil temperature data sets as well as the air temperature measurements from synoptic meteorological stations across the northern hemisphere. The SSF time series are also validated with soil temperature data available at four in situ observation sites in Siberian and Alaska regions showing the overall accuracy of about 80% to 90%.

Description: The task of the ESA Data User Element (DUE) Permafrost project is to build up an Earth Observation service for permafrost applications with extensive involvement of the permafrost research community. The DUE Permafrost remote sensing products are ‘Land Surface Temperature’ (LST), ‘Surface Soil Moisture’ (SSM), ‘Frozen/ Thawed Surface Status’ (Freeze/Thaw), ‘Terrain’, ‘Land Cover’ (LC), and ‘Surface Waters’. A major component is the evaluation of the DUE Permafrost products to test their scientific validity for high-latitude permafrost landscapes. There are no standard evaluation methods for this range of remote sensing products, specifically not for these latitudes. Evaluation experiments and inter-comparison is done on a case-by-case basis, adding value and experience in validating products for these regions. A significant challenge in the evaluation of remote sensing products for high-latitude permafrost landscapes are the very sparse ground data. We rely on ground data provided by the Users and by international programmes. The primary international programme is the Global Terrestrial Network for Permafrost (GTN-P) initiated by the International Permafrost Association (IPA). Leading projects are the networks of the ‘Circumpolar Active Layer Monitoring’ (CALM) and the ‘Thermal State of Permafrost’ (TSP). Prime sites for testing methods and scaling are the long-term Russian-German Samoylov Station in the Lena River Delta (Arctic Siberia), and the tundra and taiga-tundra transition regions in Western Siberia (RU). The results of the first evaluations of LST, SSM and Freeze/ Thaw using GTN-P and User’s data show the usability of the DUE Perma-frost products for high-latitude permafrost landscapes. The DUE Permafrost remote sensing products will be adapted as drivers, validation data and as newly available external input data for permafrost and climate models.

Description: Several global satellite-derived soil moisture datasets exist to date. They are based on analyses of passive or active microwave data. Resolution is coarse at 25 km, but temporal sampling is very high. A monitoring service for applications at high latitudes is implemented within the European Space Agency (ESA) data User Element (DUE) initiative ‘Permafrost.’ Measurements are based on Metop ASCAT, a European active microwave instrument (scatterometer, C-band). This study discusses comparisons between these data and in situ measurements from Alaska. Weekly averaged values have been compared to soil moisture records at several USDA stations. Results show that in situ soil moisture measurements at shallow depths reflect variations of satellite-derived relative near-surface soil moisture although the used sensor provides data at only 25 km resolution. There are indications that this relationship is impacted by micro-topography and temporal offsets related to snowmelt and active layer dynamics.

Description: The ESA Data User Element (DUE) Permafrost project provides a mid-to-long-term Earth observation service for permafrost remote sensing derived applications for Northern high-latitudinal permafrost areas. The DUE Permafrost remote sensing products are land surface temperature, surface soil moisture, frozen/thawed surface status, elevation, land cover and surface waters. A major component is the evaluation of the DUE Permafrost products to test their scientific validity for high-latitude permafrost landscapes. These case studies evaluate two DUE Permafrost products (MODIS Land Surface Temperature and ASCAT Surface State Flag) by comparing the results with field-based data obtained by the Global Terrestrial Network of Permafrost (GTN-P). First results showed good correlation which suggests that the DUE Permafrost approach is a promising one for long-term monitoring of permafrost surface conditions. Furthermore it demonstrates the great benefit of freely available ground truth databases for the evaluation of remote sensing derived products.