Progenitor cell proliferation in the retina is dependent on Notch-independent Sonic hedgehog/Hes1 activity

Sonic hedgehog (Shh) is an indispensable, extrinsic cue that regulates progenitor and stem cell behavior in the developing and adult mammalian central nervous system. Here, we investigate the link between the Shh signaling pathway and Hes1, a classical Notch target. We show that Shh-driven stabilization of Hes1 is independent of Notch signaling and requires the Shh effector Gli2. We identify Gli2 as a primary mediator of this response by showing that Gli2 is required for Hh (Hedgehog)-dependent up-regulation of Hes1. We also show using chromatin immunoprecipitation that Gli2 binds to the Hes1 promoter, which suggests that Hes1 is a Hh-dependent direct target of Gli2 signaling. Finally, we show that Shh stimulation of progenitor proliferation and cell diversification requires Gli2 and Hes1 activity. This paper is the first demonstration of the mechanistic and functional link between Shh, Gli, and Hes1 in the regulation of progenitor cell behavior

Strong margin influence on the Arctic Ocean Barium Cycle revealed by pan‐Arctic synthesis

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Whitmore, L., Shiller, A., Horner, T., Xiang, Y., Auro, M., Bauch, D., Dehairs, F., Lam, P., Li, J., Maldonado, M., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., & Thomas, H. Strong margin influence on the Arctic Ocean Barium Cycle revealed by pan‐Arctic synthesis. Journal of Geophysical Research: Oceans, 127(4), (2022): e2021JC017417, https://doi.org/10.1029/2021jc017417.Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one-of-a-kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean-derived waters and Baffin Bay-derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.This research was supported by the National Science Foundation [OCE-1434312 (AMS), OCE-1436666 (RN), OCE-1535854 (PL), OCE-1736949, OCE-2023456 (TJH), and OCE-1829563 (R. Anderson for open access support)], Natural Sciences and Engineering Research Council of Canada (NSERC)-Climate Change and Atmospheric Research (CCAR) Program (MTM), and LEFE-CYBER EXPATE (HP). HT acknowledges support by the Canadian GEOTRACES via NSERC-CCAR and the German Academic Exchange Service (DAAD): MOPGA-GRI (Make Our Planet Great Again—Research Initiative) sponsored by BMBF (Federal German Ministry of Education and Research; Grant No. 57429828)

Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis

Laura M. Whitmore et al, 2022, Strong margin influence on the Arctic Ocean barium cycle revealed by Pan‐Arctic synthesis, Journal of Geophysical Research: Oceans, Citation number, 10.1029/2021JC017417. To view the published open abstract, go to https://doi.org/10.1029/2021JC017417

10Be erosion rates and riverine alkalinity concentration globally

The erosional influence on terrestrial alkalinity generation globally has been discussed over the last decades. In regional studies, long-term catchment-average denudation rates, determined from the concentration of the cosmogenic nuclide 10Be, have proven to be a powerful tool to quantify how physical erosion rates impact chemical weathering rates. Despite this, little research has been done relating 10Be-derived physical erosion rates with riverine alkalinity concentrations at a global scale. Our dataset aims to fill this gap by matching 10Be erosion rates with alkalinity measurements from 233 locations on six continents, covering latitudes from 44 °S to 51 °N. The locations of published 10Be erosion rates were extracted from the OCTOPUS database (doi:10.5194/essd-10-2123-2018) and either assigned alkalinity concentrations from published manuscripts, the GLORICH database (doi:10.1594/PANGAEA.902360), governmental agencies, or sampled ourselves. Our dataset comprises erosion rates spanning 4 orders of magnitude (2-9829 mm ka-1) and single and time-series measurements of alkalinity (1-3940 measurements per location) covering a large concentration range (4-4626 μmol L-1). We complemented the point sampling measurements of erosion rate and alkalinity concentration with the spatial description of runoff, lithology, temperature, precipitation, permanent snow and ice cover, forest cover, soil thickness and area affected by dams, of the respective catchment upstream from the erosion rate measurement location

Inorganic Carbon, Ra, Ba and, δ18O tracer distribution in the Canadian Arctic Archipelago from the 2015 Canadian GEOTRACES expedition

This dataset comprises Radium (Ra), Barium (Ba) and δ18O tracers in addition to chemical constituents (Dissolved Inorganic Carbon (DIC) and Total Alkalinity (AT)) collected during 2015 Canadian GEOTRACES expedition (GN02/GN03) throughout the Canadian Arctic Archipelago aboard the CCGS Amundsen. Included within the dataset are the latitude and longitudes of sampling stations, as well as the sampled depths and the associated basic hydrographic data (T and SP). For every data point, in addition to date and time of collection, the accompanying event, cast and bottle number are recorded as well as GEOTRACES Event ID number. The compilation of this dataset was supported by the Canadian GEOTRACES program as part of the NSERC-CCAR, the U.S. GEOTRACES via NSF Chemical Oceanography (grant no. OCE-1458305), and the DAAD, MOPGA-GRI (grant no.57429828)

Alkalinity responses to climate warming destabilise the Earth's thermostat

<p>Alkalinity generation from rock weathering modulates Earth's climate at geological time scales. Although lithology is thought to dominantly control alkalinity generation globally, the role of other first-order controls appears elusive. Particularly challenging remains the discrimination of climatic and erosional influences. Based on global observations, here we uncover the role of erosion rate in governing riverine alkalinity, accompanied by areal proportion of carbonate, mean annual temperature, catchment area, and soil regolith thickness. We show that the weathering flux to the ocean will be significantly altered by climate warming as early as 2100, by up to 68% depending on the environmental conditions, constituting a sudden feedback of ocean CO2 sequestration to climate. Interestingly, warming under a low-emissions scenario will reduce terrestrial alkalinity flux from mid-latitudes (–1.6 t(bicarbonate) a−1 km−2) until the end of the century, resulting in a reduction in CO2 sequestration, but an increase (+0.5 t(bicarbonate) a−1 km−2) from mid-latitudes is likely under a high-emissions scenario, yielding an additional CO2 sink.</p&gt

Using <sup>226</sup>Ra and <sup>228</sup>Ra isotopes to distinguish water mass distribution in the Canadian Arctic Archipelago

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