Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renewal, for the regenerative process to last a lifetime. How stem cells renew is of critical biological and medical significance. Here we use the skeletal muscle stem cell (MuSC) to study this process. Using a combination of genetic, molecular, and biochemical approaches, we show that MPP7, AMOT, and TAZ/YAP form a complex that activates a common set of target genes. Among these targets, Carm1 can direct MuSC renewal. In the absence of MPP7, TAZ can support regenerative progenitors and activate Carm1 expression, but not to a level needed for self-renewal. Facilitated by the actin polymerization-responsive AMOT, TAZ recruits the L27 domain of MPP7 to up-regulate Carm1 to the level necessary to drive MuSC renewal. The promoter of Carm1, and those of other common downstream genes, also contain binding site(s) for YY1. We further demonstrate that the L27 domain of MPP7 enhances the interaction between TAZ and YY1 to activate Carm1. Our results define a renewal transcriptional program embedded within the progenitor program, by selectively up-regulating key gene(s) within the latter, through the combination of protein interactions and in a manner dependent on the promoter context.

The symbioses between leguminous plants and nitrogen-fixing bacteria known as rhizobia are well known for promoting plant growth and sustainably increasing soil nitrogen. Recent evidence indicates that hopanoids, a family of steroid-like lipids, promote Bradyrhizobium symbioses with tropical legumes. To characterize hopanoids in Bradyrhizobium symbiosis with soybean, the most economically significant Bradyrhizobium host, we validated a recently published cumate-inducible hopanoid mutant of Bradyrhizobium diazoefficiens USDA110, Pcu-shc::Δshc .GC-MS analysis showed that this strain does not produce hopanoids without cumate induction, and under this condition, is impaired in growth in rich medium and under osmotic, temperature, and pH stress. In planta, Pcu-shc Δshc is an inefficient soybean symbiont with significantly lower rates of nitrogen fixation and low survival within host tissue. RNA-seq revealed that hopanoid loss reduces the expression of flagellar motility and chemotaxis-related genes, further confirmed by swim plate assays, and enhances the expression of genes related to nitrogen metabolism and protein secretion. These results suggest that hopanoids provide a significant fitness advantage to B. diazoefficiens in legume hosts and provide a foundation for future mechanistic studies of hopanoid function in protein secretion and motility.

The European ammonia industry emits 36 million tons of carbon dioxide annually, primarily from steam methane reforming (SMR) hydrogen production. These emissions can be mitigated by producing hydrogen via water electrolysis using dedicated renewables with grid backup. This study investigates the impact of decarbonization targets for hydrogen synthesis on the economic viability and technical feasibility of retrofitting existing European ammonia plants for on-site, semi-islanded electrolytic hydrogen production. Results show that electrolytic hydrogen cuts emissions, on average, by 85% (36%-100% based on grid price and carbon intensity), even without enforcing emission limits. However, an optimal lifespan average well-to-gate emission cap of 1 kg carbon dioxide equivalent (CO2e)/kg H2 leads to a 95% reduction (92%-100%) while maintaining cost-competitiveness with SMR in renewable-rich regions (mean levelized cost of hydrogen (LCOH) of 4.1 euro/kg H2). Conversely, a 100% emissions reduction target dramatically increases costs (mean LCOH: 6.3 euro/kg H2) and land area for renewables installations, likely hindering the transition to electrolytic hydrogen in regions with poor renewables and limited land. Increasing plant flexibility effectively reduces costs, particularly in off-grid plants (mean reduction: 32%). This work guides policymakers in defining cost-effective decarbonization targets and identifying region-based strategies to support an electrolytic hydrogen-fed ammonia industry.

(Received 5 September 2023; accepted 20 March 2024; published 11 April 2024) Recent studies indicate that thermally produced dark matter will form highly concentrated, low -mass cusps in the early universe that often survive until the present. While these cusps contain a small fraction of the dark matter, their high density significantly increases the expected gamma-ray flux from dark matter annihilation, particularly in searches of large angular regions. We utilize 14 years of Fermi -LAT data to set strong constraints on dark matter annihilation through a detailed study of the isotropic gamma-ray background, excluding with 95% confidence dark matter annihilation to bb final states for dark matter masses below 120 GeV.

Crystal precipitation from aqueous solution occurs through multiple pathways. Besides the classical ion -byion addition, non-classical crystallization mechanisms, such as multi-ion polymer and nano-particle attachment, could be significant. These non-classical crystallization processes have been observed with advanced microscopy, yet detailed quantification of their contributions remains challenging. Building from paired Ca and Sr isotope observations, we develop a theoretical framework to quantify the contributions of classical and non-classical crystallization pathways on the precipitation of the calcium carbonate mineral calcite, a common precipitate in nature. We demonstrate that the classical crystallization pathway alone is insufficient to account for the observed isotope behaviors and, thus, the entire calcite precipitation process. We further present a surface kinetic model that incorporates non-classical crystallization pathways. This model enables the characterization of the roles of classical and non-classical crystallization mechanisms in calcite precipitation. The results suggest that the relative contribution of non-classical crystallization pathways increases with saturation state and can, under high supersaturation levels, be comparable to or greater than the classical pathway. The presented theoretical framework readily explains observed trace element partitioning and isotope fractionation behaviors during calcite precipitation and can be further expanded onto other mineral systems to gain insights into crystal growth mechanisms.

The eukaryotic algal CO2-concentrating mechanism (CCM) is based on a Rubisco-rich organelle called the pyrenoid, which is typically traversed by a network of thylakoid membranes. BST4 is a bestrophin-like transmembrane protein that has previously been identified in the model alga Chlamydomonas reinhardtii as a putative tether that could link the traversing thylakoid membrane network to the Rubisco matrix. In the present study, we show that BST4 forms a higher order complex assembly that localizes to the thylakoid network within the pyrenoid. However, investigation of a bst4 knock-out mutant in Chlamydomonas showed that the absence of BST4 did not result in a CCM-deficient phenotype and that BST4 is not necessary for the formation of the trans-pyrenoid thylakoids. Furthermore, heterologous expression of BST4 was not sufficient to facilitate the incorporation of thylakoids into a reconstituted Rubisco condensate in the land plant Arabidopsis. Subsequent analyses revealed that bst4 was under oxidative stress and showed enhanced non-photochemical quenching associated with CO2 limitation and over acidification of the thylakoid lumen. We conclude that the primary role of BST4 is not as a tethering protein, but rather as an ion channel involved in pH regulation in pyrenoid-based CCMs.

Many geoscience departments are taking steps to recruit and retain faculty from underrepresented groups. Here we interview 19 geoscientists who identify as an underrepresented race or gender who recently declined a tenure-track faculty job offer. A range of key factors influenced their decisions to accept or decline a position including commitment to diversity, equity, and inclusion (DEI) including personal identities, DEI initiatives, and mentorship; (in)civility during job interviews; values revealed in negotiation; and compatibility with personal life including family and geography. Many of the participants experienced hiring processes inconsistent with existing recommendations to increase faculty diversity. Therefore, we leverage our results to provide actionable recommendations for improving the equity and effectiveness of faculty recruitment efforts. We find that departments may doubly benefit from improving their culture: in addition to benefiting current members of the department, it may also help with recruitment.