Downstream Fate Research Articles

Impounded sediment and dam removal: Erosion rates and proximal downstream fate

AbstractSediment management is an important aspect of dam removal projects, often driving costs and influencing community acceptance. For dams storing uncontaminated sediments, downstream release is often the cheapest and most practical approach and can be ecologically beneficial to downstream areas deprived of sediment for years. To employ this option, project proponents must estimate the sediment quantity to be released and, if substantial, estimate how long it will take to erode, where it will go and how long it will stay there. We investigated these issues when the Bloede Dam was removed from the Patapsco River in Maryland, USA, in 2018. The dam was about 10 m high, and its impoundment was nearly filled with an estimated 186 600 m3 of sediment composed of 70% sand and 30% mud. After removal, using elevation surveys generated by traditional methods as well as structure‐from‐motion (SfM) photogrammetry at high temporal resolution, we documented rapid erosion of stored sediments in the first 6 months (~60%) followed by greatly reduced erosion rates for the next two and a half years. A stable channel developed in the impoundment during the rapid erosion phase. These results were predicted by a two‐phased erosion response model developed from observations at sand‐filled impoundments, thus expanding its applicability to include impoundments with a sand‐over‐mud stratigraphy. A similar two‐phase erosion response has been reported for sediment releases at other dam removals in the United States, France and Japan across a range of dam and watershed scales, indicating what practitioners and communities should expect in similar settings. Downstream, repeat surveys combined with discharge and sediment gaging showed rapid transport of eroded sediments through a 5‐km reach, especially during the first year when discharges were above normal, and little overbank storage.

Detection and transport of environmental DNA from two federally endangered mussels.

Environmental DNA (eDNA) offers a novel approach to supplement traditional surveys and provide increased spatial and temporal information on species detection, and it can be especially beneficial for detecting at risk or threatened species with minimal impact on the target species. The transport of eDNA in lotic environments is an important component in providing more informed descriptions of where and when a species is present, but eDNA transport phenomena are not well understood. In this study, we used species-specific assays to detect eDNA from two federally endangered mussels in two geographically distinct rivers. Using the eDNA concentrations measured from field samples, we developed a one-dimensional (1D) hydrodynamic transport model to predict the downstream fate and transport of eDNA. We detected eDNA from both federally endangered mussels across several seasons and flow rates and up to 3.5 km downstream from the source populations, but the detection rates and eDNA concentrations were highly variable across and within rivers and study reaches. Our 1D transport models successfully integrated the variability of the eDNA field samples into the model predictions and overall model results were generally within ±1 standard error of the eDNA field concentration values. Overall, the results of this study demonstrate the importance of optimizing the spatial locations from where eDNA is collected downstream from a source population, and it highlights the need to improve understanding on the shedding mechanisms and magnitude of eDNA from source populations and biogeomorphic processes that influence eDNA transport.

Abstract P1004: Cellular Heterogeneity In The Nkx2.5 + Anterior Lateral Plate Mesoderm Underlies Lineage Diversity Of The Cardiovascular System

The cardiovascular system comprises diverse cellular lineages that emerge from progenitor cells in the anterior lateral plate mesoderm (ALPM). In zebrafish, nkx2.5 expression initiates in the bilateral field of ALPM progenitors during early somitogenesis before their spatial segregation into two main subpopulations. The cardiac fraction, including first (FHF) and second heart field (SHF) progenitors, migrates to the midline and gives rise to ventricular myocardium. The pharyngeal fraction remains lateral and sequesters in the cores of the pharyngeal arches (PAs). Progenitors in PA2 give rise to craniofacial muscles and three lineages in the outflow tract, while those in PA3-6 differentiate into pharyngeal arch artery (PAA) endothelium. The mechanisms underlying nkx2.5 + progenitor cell segregation into the various downstream fates remain unclear. Here, we demonstrate that nkx2.5 + progenitors in the ALPM are heterogenous with predetermined lineage outcomes. Specifically, single-cell RNA sequencing of nkx2.5:ZsYellow + progenitors revealed six transcriptionally unique populations, including a cardiomyocyte cluster (FHF-derived) and a large lateral plate mesoderm (LPM) population that further subclustered into three distinct groups. LPM-1 differentially expressed aplnra , hey1 , and the retinoic acid (RA)-eliminating enzyme cyp26c1 , LPM-2 expressed bmp4, bmp6 , and cdh11 , and LPM-3 expressed the transcriptional repressor prdm1a and the RA-producing enzymes rhd10a and aldh1a2 . In situ hybridization uncovered regionalization in the nkx2.5 + ALPM with LPM-1 cells occupying the anterior-medial and central region of the field and LPM-3 the posterior domain. Targeted photoconversion of nkx2.5:Kaede revealed that LPM-1 are PA2 progenitors while LPM-3 are progenitors for PA3-6. We are currently performing spatial transcriptomics to generate a comprehensive expression map of the ALPM, localizing and tracing LPM-2 progenitors, and performing functional studies that suggest a tbx1 -RA-prdm1a signaling pathway is required for LPM-3 specification. In conclusion, our data highlight progenitor heterogeneity in the ALPM as a source of the lineage diversification required to build the cardiovascular system.

The N-terminal region of yeast mitoribosomal Mrp7/bL27m protein serves to optimize translation of nascent chains competent for OXPHOS complex assembly.

The extreme N-terminal residues of the mitochondrial ribosomal bL27m proteins reside within the ribosomal peptidyl transferase center (PTC) and are conserved from their bacterial ancestors. Mutation or truncation of the N-terminal region of the yeast Mrp7/bL27m protein did not inhibit protein synthesis but significantly impacted the efficacy of the mitochondrial translational process with respect to yielding proteins competent to assemble into functional oxidative phosphorylation enzymes. The requirement for the N-terminal residues of Mrp7/bL27m to support normal mitotranslation wasmore apparent under respiratory growth. We demonstrate that the N-terminal region of Mrp7/bL27m impacts the environment of the PTC and speculate the bL27m proteins serve to fine-tune and optimize mitoribosomal activity with respect to the downstream fate of the nascent chain.

Trees in the Stream: Determining Patterns of Terrestrial Dissolved Organic Matter Contributions to the Northeast Pacific Coastal Temperate Rainforest

AbstractDissolved organic matter (DOM) composition in small watersheds depends on complex antecedent conditions that ultimately influence DOM generation, processing, and stability downstream. Here, we used ultrahigh resolution Fourier‐transform ion cyclotron resonance mass spectrometry and total dissolved nitrogen and dissolved organic carbon concentrations to investigate how DOM is produced in distinct sub‐catchment types (poor fen, forested wetland, and upland forest) and transported through a watershed in the northeast Pacific coastal temperate rainforest (NPCTR). We traced a suite of previously identified source‐specific marker formulae from vegetation and soil downstream and used them to test models of terrestrial DOM inputs. Marker formulae escaped microbial degradation and were exported from the watershed, demonstrating strong land‐to‐ocean connectivity through the transfer of unmodified tree DOM from specific tree species into the marine environment. Simple hydrologic and temperature variables were better able to predict inputs of soil‐sourced DOM into the stream network than tree‐sourced DOM, highlighting the role of antecedent conditions (e.g., plant growth stage) in DOM source availability and hydrologic flow connectivity, particularly for plant‐derived material. Forested wetland pore waters featured thousands of nitrogen‐containing molecular formulae that potentially provide a path of direct organic nitrogen uptake to organisms. The modified aromaticity index peaked in midsummer (up to 0.55 for fen headwaters) suggesting DOM inputs from freshly produced vegetation provide a strong summertime terrestrial signal. As the climate changes, new watershed‐scale conditions may further complicate predictions of DOM source availability, flow connectivity, and downstream fate in NPCTR watersheds.

Recurrent debris flows and their downstream fate: Geomorphic drivers of an anomalous sediment load, Suiattle River, Washington State, USA

AbstractAlpine mass wasting events have impacts that extend past their headwater origins, sometimes reaching populated lowlands. Understanding the processes driving these sediment pulses, and how they contribute to basin‐scale sediment fluxes, is important for hazard assessment and aquatic habitat management. The Suiattle River, which drains Glacier Peak stratovolcano in Washington State, is a dominant contributor of suspended sediment in the region. Normalized for drainage area, it supplies more suspended sediment than nearly any other river in the area and more than twice as much as the White Chuck River, which drains the opposite flank of the volcano. Despite its importance to the regional sediment budget, geomorphic processes in the basin have received relatively little attention in the literature. In this study, we build on previous work to explore the magnitude, timing and triggering mechanisms of sediment loading events in the basin. We find that outburst flood‐triggered debris flows from Chocolate Glacier are of widely varying magnitude and coincide with high temperatures in the late summer. Major debris flow activity initiated in the late 1930s, with at least eight valley‐filling debris flows since then. Smaller, more recent debris flows, likely also driven by outburst floods, occur in five of seven years of complete data. In total, the small debris flows and the subsequent autumn flushing events explain ~21% of the ‘anomalous’ sediment load in the basin, while reworking and abrasion of the historic events may explain another ~26%. We speculate that some of the remaining unexplained ‘anomalous’ load could be the result of a feedback between channel lateral instability (originally triggered by the valley‐spanning debris flows) and bluff erosion.

The dendritic cell receptor Clec9A: receptor regulation and immune modulation

Dendritic cells (DC) use a variety of cell surface receptors to monitor the environment for potential dangers, including cells that have died of non-homeostatic causes (eg. infected cells), to induce appropriate immune responses. Clec9A is a DC-specific Damage-Associated Molecular Pattern receptor, that is expressed by mouse and human cross-presenting DC subsets. Clec9A recognises actin filaments exposed on dead cells, and facilitates the processing of dead cell-derived antigen (Ag) for the induction of effective immune responses. A major focus of our research is identification of the molecular mechanisms that underpin Clec9A function and the control of immune responses to dead cell-associated Ag, and on the development of Clec9A-targeting approaches for enhancing immune responses. We recently identified a novel intracellular Clec9A-binding partner, the E3 ubiquitin ligase, RNF41. We discovered RNF41 ubiquitinates Clec9A to regulate its downstream fate. Intriguingly, RNF41 ubiquitinates the extracellular domains of Clec9A, revealing a novel mechanism of receptor regulation. Furthermore, RNF41 regulates DC cross-presentation of Ag acquired from dead cells. Our research is now focussed on elucidating this novel pathway of Clec9A regulation, and the role of this pathway in regulating MHCI processing and presentation of dead cell Ag.

A plant tethering system for the functional study of protein-RNA interactions in vivo

The sorting of RNA transcripts dictates their ultimate post-transcriptional fates, such as translation, decay or degradation by RNA interference (RNAi). This sorting of RNAs into distinct fates is mediated by their interaction with RNA-binding proteins. While hundreds of RNA binding proteins have been identified, which act to sort RNAs into different pathways is largely unknown. Particularly in plants, this is due to the lack of reliable protein-RNA artificial tethering tools necessary to determine the mechanism of protein action on an RNA in vivo. Here we generated a protein-RNA tethering system which functions on an endogenous Arabidopsis RNA that is tracked by the quantitative flowering time phenotype. Unlike other protein-RNA tethering systems that have been attempted in plants, our system circumvents the inadvertent triggering of RNAi. We successfully in vivo tethered a protein epitope, deadenylase protein and translation factor to the target RNA, which function to tag, decay and boost protein production, respectively. We demonstrated that our tethering system (1) is sufficient to engineer the downstream fate of an RNA, (2) enables the determination of any protein’s function upon recruitment to an RNA, and (3) can be used to discover new interactions with RNA-binding proteins.

The surfactant Dioctyl Sodium Sulfosuccinate (DOSS) exposure causes adverse effects in embryos and adults of zebrafish (Danio rerio)

Dioctyl Sodium Sulfosuccinate (DOSS, CAS 577-11-7) is a chemical emulsifying surfactant that is widely used in the food and the cosmetic industry, and it is also the major component of the crude oil chemical dispersant Corexit™. Despite of its wide use, the studies related to its negative effect have been evaluated mainly in marine environments showing that DOSS is highly bioactive, extremely low volatile, and potential to persist in the environment longer than other dispersant components. Up to date, there is no available information of DOSS concentration in freshwater environments, little is known about its downstream fate after excretion and its effect on freshwater organisms. The objective of this study was to evaluate the effect of DOSS at different concentrations in embryos and adults of zebrafish Danio rerio in an acute-static bioassays of 96 h. The median lethal concentration in embryos was 33.3 mg/L. Malformations started to be observed at 10 mg/L. In adults, the gene expression analysis in gill tissues showed a deregulation in genes associated with the antioxidant system and the nucleotide excision repair mechanism. Additionally, Micronuclei (DNA damage) in erythrocytes, and fat degeneration in liver, hypertrophy and hyperplasia in gills, and hyaline drops in kidney tissues were also observed. In conclusion, the concentrations of DOSS evaluated here would be of health relevance to fish based on morphological alterations in embryos and changes in the gene expression profile, DNA damage and tissue impairment in adults.

Aged soils contribute little to contemporary carbon cycling downstream of thawing permafrost peatlands.

Vast stores of millennial-aged soil carbon (MSC) in permafrost peatlands risk leaching into the contemporary carbon cycle after thaw caused by climate warming or increased wildfire activity. Here we tracked the export and downstream fate of MSC from two peatland-dominated catchments in subarctic Canada, one of which was recently affected by wildfire. We tested whether thermokarst bog expansion and deepening of seasonally thawed soils due to wildfire increased the contributions of MSC to downstream waters. Despite being available for lateral transport, MSC accounted for ≤6% of dissolved organic carbon (DOC) pools at catchment outlets. Assimilation of MSC into the aquatic food web could not explain its absence at the outlets. Using δ13 C-Δ14 C-δ15 N-δ2 H measurements, we estimated only 7% of consumer biomass came from MSC by direct assimilation and algal recycling of heterotrophic respiration. Recent wildfire that caused seasonally thawed soils to reach twice as deep in one catchment did not change these results. In contrast to many other Arctic ecosystems undergoing climate warming, we suggest waterlogged peatlands will protect against downstream delivery and transformation of MSC after climate- and wildfire-induced permafrost thaw.

FSH mediated cAMP signalling upregulates the expression of Gα subunits in pubertal rat Sertoli cells

Follicle Stimulating Hormone (FSH) acts via FSH-Receptor (FSH-R) by employing cAMP as the dominant secondary messenger in testicular Sertoli cells (Sc) to support spermatogenesis. Binding of FSH to FSH-R, results the recruitment of the intracellular GTP binding proteins, either stimulatory Gαs or inhibitory Gαi that in turn regulate cAMP production in Sc. The cytosolic concentration of cAMP being generated by FSH-R thereafter critically determines the downstream fate of the FSH signalling. The pleiotropic action of FSH due to differential cAMP output during functional maturation of Sc has been well studied. However, the developmental and cellular regulation of the Gα proteins associated with FSH-R is poorly understood in Sc. In the present study, we report the differential transcriptional modulation of the Gα subunit genes by FSH mediated cAMP signalling in neonatal and pubertal rat Sc. Our data suggested that unlike in neonatal Sc, both the basal and FSH/forskolin induced expression of Gαs, Gαi-1, Gαi-2 and Gαi-3 transcripts was significantly (p < 0.05) up-regulated in pubertal Sc. Further investigations involving treatment of Sc with selective Gαi inhibitor pertussis toxin, confirmed the elevated expression of Gi subunits in pubertal Sc. Collectively our results indicated that the high level of Gαi subunits serves as a negative regulator to optimize cAMP production in pubertal Sc.

Role of hepcidin in oxidative stress and cell death of cultured mouse renal collecting duct cells: protection against iron and sensitization to cadmium

The liver hormone hepcidin regulates systemic iron homeostasis. Hepcidin is also expressed by the kidney, but exclusively in distal nephron segments. Several studies suggest hepcidin protects against kidney damage involving Fe2+ overload. The nephrotoxic non-essential metal ion Cd2+ can displace Fe2+ from cellular biomolecules, causing oxidative stress and cell death. The role of hepcidin in Fe2+ and Cd2+ toxicity was assessed in mouse renal cortical [mCCD(cl.1)] and inner medullary [mIMCD3] collecting duct cell lines. Cells were exposed to equipotent Cd2+ (0.5–5 μmol/l) and/or Fe2+ (50–100 μmol/l) for 4–24 h. Hepcidin (Hamp1) was transiently silenced by RNAi or overexpressed by plasmid transfection. Hepcidin or catalase expression were evaluated by RT-PCR, qPCR, immunoblotting or immunofluorescence microscopy, and cell fate by MTT, apoptosis and necrosis assays. Reactive oxygen species (ROS) were detected using CellROX™ Green and catalase activity by fluorometry. Hepcidin upregulation protected against Fe2+-induced mIMCD3 cell death by increasing catalase activity and reducing ROS, but exacerbated Cd2+-induced catalase dysfunction, increasing ROS and cell death. Opposite effects were observed with Hamp1 siRNA. Similar to Hamp1 silencing, increased intracellular Fe2+ prevented Cd2+ damage, ROS formation and catalase disruption whereas chelation of intracellular Fe2+ with desferrioxamine augmented Cd2+ damage, corresponding to hepcidin upregulation. Comparable effects were observed in mCCD(cl.1) cells, indicating equivalent functions of renal hepcidin in different collecting duct segments. In conclusion, hepcidin likely binds Fe2+, but not Cd2+. Because Fe2+ and Cd2+ compete for functional binding sites in proteins, hepcidin affects their free metal ion pools and differentially impacts downstream processes and cell fate.

Origin and Fate of the Chukchi Slope Current Using a Numerical Model and In‐Situ Data

AbstractA regional coupled sea ice‐ocean model and mooring/shipboard measurements are used to investigate the origins, seasonality, and downstream fate of the Chukchi Slope Current (CSC). Three years (2013–2015) of model integration indicates that, in the mean, the model slope current transports ∼0.45 Sv of Pacific water northwestward along the Chukchi continental slope. Only 62% of this water emanates from Barrow Canyon, while the rest (38%) is fed by a westward jet extending from the southern Beaufort Sea. The jet merges with the outflow from the canyon, forming the CSC. Due to these two distinct origins, the slope current in the model has a double velocity core at times. This is consistent with the double‐core structure of the slope current seen in ship‐based observations. Seasonal changes in the volume, heat, and freshwater transports by the slope current appear to be related to the changes in the upstream flows. A tracer diagnostic in the model suggests that the part of the slope current over the upper continental slope continues westward toward the East Siberian Sea, while the portion of the current overlying deeper isobaths flows northward into the Chukchi Borderland, where it ultimately gets entrained into the Beaufort Gyre. Our study provides a detailed and complete picture of the slope current.

RNF41 regulates the damage recognition receptor Clec9A and antigen cross-presentation in mouse dendritic cells.

The dendritic cell receptor Clec9A facilitates processing of dead cell-derived antigens for cross-presentation and the induction of effective CD8+ T cell immune responses. Here, we show that this process is regulated by E3 ubiquitin ligase RNF41 and define a new ubiquitin-mediated mechanism for regulation of Clec9A, reflecting the unique properties of Clec9A as a receptor specialized for delivery of antigens for cross-presentation. We reveal RNF41 is a negative regulator of Clec9A and the cross-presentation of dead cell-derived antigens by mouse dendritic cells. Intriguingly, RNF41 regulates the downstream fate of Clec9A by directly binding and ubiquitinating the extracellular domains of Clec9A. At steady-state, RNF41 ubiquitination of Clec9A facilitates interactions with ER-associated proteins and degradation machinery to control Clec9A levels. However, Clec9A interactions are altered following dead cell uptake to favor antigen presentation. These findings provide important insights into antigen cross-presentation and have implications for development of approaches to modulate immune responses.

Consistent apparent Young\u2019s modulus of human embryonic stem cells and derived cell types stabilized by substrate stiffness regulation promotes lineage specificity maintenance

BackgroundApparent Young’s modulus (AYM), which reflects the fundamental mechanical property of live cells measured by atomic force microscopy and is determined by substrate stiffness regulated cytoskeletal organization, has been investigated as potential indicators of cell fate in specific cell types. However, applying biophysical cues, such as modulating the substrate stiffness, to regulate AYM and thereby reflect and/or control stem cell lineage specificity for downstream applications, remains a primary challenge during in vitro stem cell expansion. Moreover, substrate stiffness could modulate cell heterogeneity in the single-cell stage and contribute to cell fate regulation, yet the indicative link between AYM and cell fate determination during in vitro dynamic cell expansion (from single-cell stage to multi-cell stage) has not been established.ResultsHere, we show that the AYM of cells changed dynamically during passaging and proliferation on substrates with different stiffness. Moreover, the same change in substrate stiffness caused different patterns of AYM change in epithelial and mesenchymal cell types. Embryonic stem cells and their derived progenitor cells exhibited distinguishing AYM changes in response to different substrate stiffness that had significant effects on their maintenance of pluripotency and/or lineage-specific characteristics. On substrates that were too rigid or too soft, fluctuations in AYM occurred during cell passaging and proliferation that led to a loss in lineage specificity. On a substrate with ‘optimal’ stiffness (i.e., 3.5 kPa), the AYM was maintained at a constant level that was consistent with the parental cells during passaging and proliferation and led to preservation of lineage specificity. The effects of substrate stiffness on AYM and downstream cell fate were correlated with intracellular cytoskeletal organization and nuclear/cytoplasmic localization of YAP.ConclusionsIn summary, this study suggests that optimal substrate stiffness regulated consistent AYM during passaging and proliferation reflects and contributes to hESCs and their derived progenitor cells lineage specificity maintenance, through the underlying mechanistic pathways of stiffness-induced cytoskeletal organization and the downstream YAP signaling. These findings highlighted the potential of AYM as an indicator to select suitable substrate stiffness for stem cell specificity maintenance during in vitro expansion for regenerative applications.

Sources, fate, and flux of riverine solutes in the Southwest Yellowstone Plateau Volcanic Field, USA

Since the 1970s, temporal variations of hydrothermal discharge and thermal output from the numerous hydrothermal features in the Yellowstone Plateau Volcanic Field (YPVF) have been studied by measuring the chloride flux in the major rivers. In this study, the sources, fate, and flux of solutes in the Fall River and its major tributaries, in southwest Yellowstone National Park, were determined. The considerable precipitation in southwest YPVF and high groundwater flow through Quaternary rhyolites results in river solute fluxes that originate from shallow non-thermal groundwater and deep-thermal water. Specific conductance serves as a surrogate measure for thirteen riverine solute concentrations. Combining continuous 15-minute specific conductance and discharge data, the annual chloride, arsenic, fluoride, and silica fluxes from the Fall River were determined to be 11%, 5%, 25%, and 19% of the total flux exiting YPVF. Approximately 11% of the Fall River chloride flux is from non-thermal waters, which is larger than the previous estimate of 4 to 6%. Furthermore, a large proportion of fluoride and silica in the Fall River are derived from water-rock interaction in the shallow non-thermal groundwater system and the non-thermal weathering rate (30 ± 2 t/yr·km2) is higher than other rivers draining the Yellowstone caldera. Consequently, 73 ± 3% of the annual total dissolved solid flux in the Fall River is from thermal sources. Synoptic sampling of river water and discharge measurements was performed during low-flow conditions that allowed for the determination of solute sources and their downstream fate. It was determined that chloride, sodium, arsenic, rubidium, lithium, and boron are primarily (>89%) associated with thermal waters and the Bechler River is the primary source of most hydrothermal solutes in the Fall River, but the major source of arsenic is Boundary Creek. Using the chloride inventory method, the thermal water discharge from several thermal areas was also determined.

Metabolic Regulation of Stem Cell Fate and Function

The overarching goal of this project is to understand how diet‐derived nutrients regulate stem cell metabolism and downstream fate decisions in the setting of normal development and disease. Quiescent adult stem cells typically favor glycolytic metabolism over the oxidative metabolism utilized by differentiating cells. Importantly, manipulating stem cell metabolism is sufficient to alter cell fate decisions. While the serum concentrations of endogenous metabolites such as glucose and lactate are under homeostatic constraints, diet can cause vast fluctuations in circulating levels of certain metabolites that serve as co‐factors for chromatin and DNA modifying enzymes. As such, exogenous nutrients can control the epigenome and gene expression programs, thus altering differentiation and cell fate. However, little is known about how changing nutrient levels will affect the metabolism and chromatin status in the adult stem cell populations. To address this question, we have adapted a recently described mouse liver organoid system. The liver coordinates whole‐body metabolism and detoxification, and therefore is acutely tuned to respond to dietary changes. Liver organoids generate 3D assemblies that mirror the native physiology of the tissue and self‐renew in vitro due to the activity of Wnt‐responsive stem cells that reside in the hepatic ductal compartment. We have found that treatment with physiologically attainable concentrations of ascorbic acid inhibits hepatic organoid expansion in a dose‐dependent manner. Ascorbic acid, commonly known as Vitamin C, is a water‐soluble antioxidant that is obtained exclusively through the diet in humans. Ascorbic acid is an essential co‐factor for the Fe‐ and α‐ketoglutarate dependent dioxygenase (α‐KGDDs) class of enzymes, which includes collagen hydroxylases, prolyl hydroxylases, and epigenetic erasers such as DNA and histone demethylases. To determine if activation of α‐KGDDs enzymes suppresses organoid expansion, we treated hepatic organoids with a cell permeable form of α‐KG and observed growth inhibition identical to that observed with ascorbic acid treatment. α‐KG/succinate ratios and expression of the ascorbate transporters increases in differentiated hepatic organoids compared to cultures maintained in expansion media, suggesting that ascorbic acid may preferentially accumulate and function during terminal differentiation. Taken together, we propose that ascorbic acid acts as a cofactor for α‐KGDD enzymes in order to restrain stem cell activity and may play a role in promoting differentiation to the hepatic lineage.Support or Funding InformationS.N.S is supported by a postdoctoral grant from the Eli and Edythe Broad Stem Cell Research Center at UCLA. H.R.C is supported by a CTSI seed grant from the David Geffen School of Medicine at UCLA.

Sources, fate, and flux of geothermal solutes in the Yellowstone and Gardner Rivers, Yellowstone National Park, WY

The total discharge and thermal output from the numerous hydrothermal features in Yellowstone National Park (YNP) can be estimated from the chloride (Cl) flux in the Madison, Yellowstone, Falls, and Snake Rivers. Monitoring the Cl flux in these four major rivers provides a holistic view of the hydrothermal output from YNP and changes in the Cl flux may indicate changes in geothermal or magmatic activity. In this study, the source, fate, and flux of geothermal solutes in the Yellowstone River and Gardner Rivers were determined. Beginning in 2012, the fluxes of geothermal solutes, including Cl, were determined at monitoring sites in the Yellowstone and Gardner Rivers downstream of geothermal inputs within YNP. A method was developed using specific conductance as a surrogate measure for solute concentrations at these monitoring sites. Combining continuous (15-min) specific conductance and discharge data, Cl and other geothermal solute fluxes were determined and approximately 32% of the Cl flux exiting YNP is from the Yellowstone River watershed. Synoptic sampling of river water and discharge measurements were performed during low-flow conditions of September 2014 allowed for the determinations of geothermal solute sources and their downstream fate. Thus, the contribution of geothermal solutes from the various geothermal areas at the downstream monitoring sites was quantified. The thermal features draining into Yellowstone Lake account for 34% of the Cl flux at the Yellowstone River monitoring site which is located approximately 5 km north of YNP. The Gardner River, which captures geothermal water from Mammoth Hot Springs, is responsible for 22% of the Cl at the Yellowstone River monitoring site. Because the Yellowstone River watershed is large and contains numerous thermal areas, knowing the source and fate of geothermal solutes is import baseline information that can be used to identify future changes in thermal activity.

A conserved regulatory program initiates lateral plate mesoderm emergence across chordates

Cardiovascular lineages develop together with kidney, smooth muscle, and limb connective tissue progenitors from the lateral plate mesoderm (LPM). How the LPM initially emerges and how its downstream fates are molecularly interconnected remain unknown. Here, we isolate a pan-LPM enhancer in the zebrafish-specific draculin (drl) gene that provides specific LPM reporter activity from early gastrulation. In toto live imaging and lineage tracing of drl-based reporters captures the dynamic LPM emergence as lineage-restricted mesendoderm field. The drl pan-LPM enhancer responds to the transcription factors EomesoderminA, FoxH1, and MixL1 that combined with Smad activity drive LPM emergence. We uncover specific activity of zebrafish-derived drl reporters in LPM-corresponding territories of several chordates including chicken, axolotl, lamprey, Ciona, and amphioxus, revealing a universal upstream LPM program. Altogether, our work provides a mechanistic framework for LPM emergence as defined progenitor field, possibly representing an ancient mesodermal cell state that predates the primordial vertebrate embryo.

The ELAV family of RNA-binding proteins in synaptic plasticity and long-term memory.

The mechanisms of de novo gene expression and translation of specific gene transcripts have long been known to support long-lasting changes in synaptic plasticity and behavioral long-term memory. In recent years, it has become increasingly apparent that gene expression is heavily regulated not only on the level of transcription, but also through post-transcriptional gene regulation, which governs the subcellular localization, stability, and likelihood of translation of mRNAs. Specific families of RNA-binding proteins (RBPs) bind transcripts which contain AU-rich elements (AREs) within their 3' UTR and thereby govern their downstream fate. These post-transcriptional gene regulatory mechanisms are coordinated through the same cell signaling pathways that play critical roles in long-term memory formation. In this review, we discuss recent results that demonstrate the roles that these ARE-binding proteins play in LTM formation.