3D printed PCLA scaffold with nano‐hydroxyapatite coating doped green tea EGCG promotes bone growth and inhibits multidrug‐resistant bacteria colonization

Objectives3D‐printing scaffold with specifically customized and biomimetic structures gained significant recent attention in tissue engineering for the regeneration of damaged bone tissues. However, constructed scaffolds that simultaneously promote bone regeneration and in situ inhibit bacterial proliferation remains a great challenge. This study aimed to design a bone repair scaffold with in situ antibacterial functions.Materials and MethodsHerein, a general strategy is developed by using epigallocatechin‐3‐gallate (EGCG), a major green tea polyphenol, firmly anchored in the nano‐hydroxyapatite (HA) and coating the 3D printed polymerization of caprolactone and lactide (PCLA) scaffold. Then, we evaluated the stability, mechanical properties, water absorption, biocompatibility, and in vitro antibacterial and osteocyte inductive ability of the scaffolds.ResultsThe coated scaffold exhibit excellent activity in simultaneously stimulating osteogenic differentiation and in situ resisting methicillin‐resistant Staphylococcus aureus colonization in a bone repair environment without antibiotics. Meanwhile, the prepared 3D scaffold has certain mechanical properties (39.3 ± 3.2 MPa), and the applied coating provides the scaffold with remarkable cell adhesion and osteogenic conductivity.ConclusionThis study demonstrates that EGCG self‐assembled HA coating on PCLA surface could effectively enhance the scaffold''s water absorption, osteogenic induction, and antibacterial properties in situ. It provides a new strategy to construct superior performance 3D printed scaffold to promote bone tissue regeneration and combat postoperative infection in situ.

Schematic diagram of the 3D polymerization of caprolactone and lactide (PCLA) coated scaffold containing epigallocatechin‐3‐gallate (EGCG)‐modified nano‐HA as an artificial bone matrix with biphasic function to efficiently promote the growth of osteoblasts and inhibit methicillin‐resistant Staphylococcus aureus colonization in the bone repair microenvironment. PCLA/KH‐HA‐EGCG exhibited satisfactory antibacterial properties and leads to significant osteoinduction and osteogenic differentiation in osteoblasts cells, achieving a high‐efficient bone repair effect.     

Study on the development and integration of 3D‐printed optics in small‐scale productions of single‐use cultivation vessels

Integrating optical sensors and 3D‐printed optics into single‐use (SU) cultivation vessels for customized, tailor‐made equipment could be a next big step in the bioreactor and screening platform development enabling online bioprocess monitoring. Many different parameters such as pH, oxygen, carbon dioxide and optical density (OD) can be monitored more easily using online measuring instruments compared to offline sampling. Space‐saving integrated sensors in combination with adapted optics such as prisms open up vastly new possibilities to precisely guide light through SU vessels. This study examines how optical prisms can be 3D‐printed with a 3D‐inkjet printer, modified and then evaluated in a custom made optical bench. The prisms are coated or bonded with thin cover glasses. For the examination of reflectance performance and conformity prisms are compared on the basis of measured characteristics of a conventional glass prism. In addition, the most efficient and reproducible prism geometry and modification technique is applied to a customized 3D‐printed cultivation vessel. The vessel is evaluated on a commercial sensor‐platform, a shake flask reader (SFR) vario, to investigate its sensing‐characteristics while monitoring scattered light with the turbidity standard formazine and a cell suspension of Saccharomyces cerevisiae as model organism. It is demonstrated that 3D‐printed prisms can be used in combination with commercial scattered light sensor‐platforms to determine OD of a microbial culture and that a 3D‐printed unibody design with integrated optics in a cultivation vessel is feasible. In the range of OD₆₀₀ 0–1.16 rel.AU a linear correlation between sensor amplitude and offline determined OD can be achieved. Thus, enabling for the first time a measurement of low cell densities with the SFR vario platform. Moreover, sensitivity is also at least three times higher compared to the commonly used method.     

3D‐printed autoclavable plant holders to facilitate large‐scale protein production in plants

The Australian tobacco plant Nicotiana benthamiana is becoming increasingly popular as a platform for protein production and metabolic engineering. In this system, gene expression is achieved transiently by infiltrating N. benthamiana plants with suspensions of Agrobacterium tumefaciens carrying vectors with the target genes. To infiltrate larger numbers of plants, vacuum infiltration is the most efficient approach known, which is already used on industrial scale. Current laboratory‐scale solutions for vacuum infiltration, however, either require expensive custom‐tailored equipment or produce large amounts of biologically contaminated waste. To overcome these problems and lower the burden to establish vacuum infiltration in new laboratories, we present here 3D‐printed plant holders for vacuum infiltration. We demonstrate that our plant holders are simple to use and enable a throughput of around 40 plants per hour. In addition, our 3D‐printed plant holders are made from autoclavable material, which tolerate at least 12 autoclave cycles, helping to limit the production of contaminated waste and thus contributing to increased sustainability in research. In conclusion, our plant holders provide a simple, robust, safe and transparent platform for laboratory‐scale vacuum infiltration that can be readily adopted by new laboratories interested in protein and metabolite production in Nicotiana benthamiana. Practical application Transient expression in Nicotiana benthamiana provides a popular and rapid system for producing proteins in a plant host. To infiltrate larger numbers of plants (typically >20), vacuum infiltration is the method of choice. However, no system has been described so far which is robust to use and can be used without expensive and complex equipment. Our autoclavable 3D‐printed plant holders presented here will greatly reduce the efforts required to adopt the vacuum infiltration technique in new laboratories. They are easy to use and can be autoclaved at least 12 times, which contributes to waste reduction and sustainability in research laboratories. We anticipate that the 3D printing design provided here will drastically lower the bar for new groups to employ vacuum infiltration for producing proteins and metabolites in Nicotiana benthamiana.     

3D printing in biotechnology—An insight into miniaturized and microfluidic systems for applications from cell culture to bioanalytics

Since its invention in the 1980s, 3D printing has evolved into a versatile technique for the additive manufacturing of diverse objects and tools, using various materials. The relative flexibility, straightforwardness, and ability to enable rapid prototyping are tremendous advantages offered by this technique compared to conventional methods for miniaturized and microfluidic systems fabrication (such as soft lithography). The development of 3D printers exhibiting high printer resolution has enabled the fabrication of accurate miniaturized and microfluidic systems—which have, in turn, substantially reduced both device sizes and required sample volumes. Moreover, the continuing development of translucent, heat resistant, and biocompatible materials will make 3D printing more and more useful for applications in biotechnology in the coming years. Today, a wide variety of 3D‐printed objects in biotechnology—ranging from miniaturized cultivation chambers to microfluidic lab‐on‐a‐chip devices for diagnostics—are already being deployed in labs across the world. This review explains the 3D printing technologies that are currently used to fabricate such miniaturized microfluidic devices, and also seeks to offer some insight into recent developments demonstrating the use of these tools for biotechnological applications such as cell culture, separation techniques, and biosensors.     

PARD3 gene variation as candidate cause of nonsyndromic cleft palate only

Nonsyndromic cleft palate only (NSCP) is a common congenital malformation worldwide. In this study, we report a three‐generation pedigree with NSCP following the autosomal‐dominant pattern. Whole‐exome sequencing and Sanger sequencing revealed that only the frameshift variant c.1012dupG [p. E338Gfs*26] in PARD3 cosegregated with the disease. In zebrafish embryos, ethmoid plate patterning defects were observed with PARD3 ortholog disruption or expression of patient‐derived N‐terminal truncating PARD3 (c.1012dupG), which implicated PARD3 in ethmoid plate morphogenesis. PARD3 plays vital roles in determining cellular polarity. Compared with the apical distribution of wild‐type PARD3, PARD3‐p. E338Gfs*26 mainly localized to the basal membrane in 3D‐cultured MCF‐10A epithelial cells. The interaction between PARD3‐p. E338Gfs*26 and endogenous PARD3 was identified by LC–MS/MS and validated by co‐IP. Immunofluorescence analysis showed that PARD3‐p. E338Gfs*26 substantially altered the localization of endogenous PARD3 to the basement membrane in 3D‐cultured MCF‐10A cells. Furthermore, seven variants, including one nonsense variant and six missense variants, were identified in the coding region of PARD3 in sporadic cases with NSCP. Subsequent analysis showed that PARD3‐p. R133*, like the insertion variant of c.1012dupG, also changed the localization of endogenous full‐length PARD3 and that its expression induced abnormal ethmoid plate morphogenesis in zebrafish. Based on these data, we reveal PARD3 gene variation as a novel candidate cause of nonsyndromic cleft palate only.     

Deficiency of Ninjurin1 attenuates LPS/D‐galactosamine‐induced acute liver failure by reducing TNF‐α‐induced apoptosis in hepatocytes

Nerve injury‐induced protein 1 (Ninjurin1, Ninj1) is a membrane protein that mediates cell adhesion. The role of Ninj1 during inflammatory response has been widely investigated in macrophages and endothelial cells. Ninj1 is expressed in various tissues, and the liver also expresses high levels of Ninj1. Although the hepatic upregulation of Ninj1 has been reported in human hepatocellular carcinoma and septic mice, little is known of its function during the pathogenesis of liver diseases. In the present study, the role of Ninj1 in liver inflammation was explored using lipopolysaccharide (LPS)/D‐galactosamine (D‐gal)‐induced acute liver failure (ALF) model. When treated with LPS/D‐gal, conventional Ninj1 knock‐out (KO) mice exhibited a mild inflammatory phenotype as compared with wild‐type (WT) mice. Unexpectedly, myeloid‐specific Ninj1 KO mice showed no attenuation of LPS/D‐gal‐induced liver injury. Whereas, Ninj1 KO primary hepatocytes were relatively insensitive to TNF‐α‐induced caspase activation as compared with WT primary hepatocytes. Also, Ninj1 knock‐down in L929 and AML12 cells and Ninj1 KO in HepG2 cells ameliorated TNF‐α‐mediated apoptosis. Consistent with in vitro results, hepatocyte‐specific ablation of Ninj1 in mice alleviated LPS/D‐gal‐induced ALF. Summarizing, our in vivo and in vitro studies show that lack of Ninj1 in hepatocytes diminishes LPS/D‐gal‐induced ALF by alleviating TNF‐α/TNFR1‐induced cell death.     

Physiological and metabolic characteristics of novel double‐mutant female mice with targeted disruption of both growth hormone‐releasing hormone and growth hormone receptor

Mice with disruptions of growth hormone‐releasing hormone (GHRH) or growth hormone receptor (GHR) exhibit similar phenotypes of prolonged lifespan and delayed age‐related diseases. However, these two models respond differently to calorie restriction indicating that they might carry different and/or independent mechanisms for improved longevity and healthspan. In order to elucidate these mechanisms, we generated GHRH and GHR double‐knockout mice (D‐KO). In the present study, we focused specifically on the characteristics of female D‐KO mice. The D‐KO mice have reduced body weight and enhanced insulin sensitivity compared to wild‐type (WT) controls. Growth retardation in D‐KO mice is accompanied by decreased GH expression in pituitary, decreased circulating IGF‐1, increased high‐molecular‐weight (HMW) adiponectin, and leptin hormones compared to WT controls. Generalized linear model‐based regression analysis, which controls for body weight differences between D‐KO and WT groups, shows that D‐KO mice have decreased lean mass, bone mineral density, and bone mineral content, but increased adiposity. Indirect calorimetry markers including oxygen consumption, carbon dioxide production, and energy expenditure were significantly lower in D‐KO mice relative to the controls. In comparison with WT mice, the D‐KO mice displayed reduced respiratory exchange ratio (RER) values only during the light cycle, suggesting a circadian‐related metabolic shift toward fat utilization. Interestingly, to date survival data suggest extended lifespan in D‐KO female mice.     

High‐altitude adaptation in vertebrates as revealed by mitochondrial genome analyses

The high‐altitude environment may drive vertebrate evolution in a certain way, and vertebrates living in different altitude environments might have different energy requirements. We hypothesized that the high‐altitude environment might impose different influences on vertebrate mitochondrial genomes (mtDNA). We used selection pressure analyses and PIC (phylogenetic independent contrasts) analysis to detect the evolutionary rate of vertebrate mtDNA protein‐coding genes (PCGs) from different altitudes. The results showed that the ratio of nonsynonymous/synonymous substitutions (dN/dS) in the mtDNA PCGs was significantly higher in high‐altitude vertebrates than in low‐altitude vertebrates. The seven rapidly evolving genes were shared by the high‐altitude vertebrates, and only one positive selection gene (ND5 gene) was detected in the high‐altitude vertebrates. Our results suggest the mtDNA evolutionary rate in high‐altitude vertebrates was higher than in low‐altitude vertebrates as their evolution requires more energy in a high‐altitude environment. Our study demonstrates the high‐altitude environment (low atmospheric O₂ levels) drives vertebrate evolution in mtDNA PCGs.     

An integrated approach reveals how lipo‐chitooligosaccharides interact with the lysin motif receptor‐like kinase MtLYR3

N‐acetylglucosamine containing compounds acting as pathogenic or symbiotic signals are perceived by plant‐specific Lysin Motif Receptor‐Like Kinases (LysM‐RLKs). The molecular mechanisms of this perception are not fully understood, notably those of lipo‐chitooligosaccharides (LCOs) produced during root endosymbioses with nitrogen‐fixing bacteria or arbuscular mycorrhizal fungi. In Medicago truncatula, we previously identified the LysM‐RLK LYR3 (MtLYR3) as a specific LCO‐binding protein. We also showed that the absence of LCO binding to LYR3 of the non‐mycorrhizal Lupinus angustifolius, (LanLYR3), was related to LysM3, which differs from that of MtLYR3 by several amino acids and, particularly, by a critical tyrosine residue absent in LanLYR3. Here, we aimed to define the LCO binding site of MtLYR3 by using molecular modelling and simulation approaches, combined with site‐directed mutagenesis and LCO binding experiments. 3D models of MtLYR3 and LanLYR3 ectodomains were built, and homology modelling and molecular dynamics (MD) simulations were performed. Molecular docking and MD simulation on the LysM3 identified potential key residues for LCO binding. We highlighted by steered MD simulations that in addition to the critical tyrosine, two other residues were important for LCO binding in MtLYR3. Substitution of these residues in LanLYR3‐LysM3 by those of MtLYR3‐LysM3 allowed the recovery of high‐affinity LCO binding in experimental radioligand‐binding assays. An analysis of selective constraints revealed that the critical tyrosine has experienced positive selection pressure and is absent in some LYR3 proteins. These findings now pave the way to uncover the functional significance of this specific evolutionary pattern.     

Fat‐1 expression alleviates atherosclerosis in transgenic rabbits

Atherosclerosis is the main cause of cardiovascular diseases. The Fat‐1 gene can express the n‐3 fatty acid desaturase, which converts n‐6 polyunsaturated fatty acids (PUFA) to n‐3 PUFAs. The role of n‐3 PUFAs in atherosclerosis is widely debated. This study explored the effect of n‐3 PUFAs on atherosclerosis in rabbits. In this study, atherosclerosis was induced in Fat‐1 transgenic rabbits and their littermate (WT) rabbits by feeding a high‐cholesterol diet containing 0.3% cholesterol and 3% soybean oil for 16 weeks. Plasma lipid, fatty acid and pathological analyses of atherosclerotic lesions were conducted. Fatty acid composition in the liver and muscle showed that n‐3 PUFAs increased and n‐6 PUFAs decreased in the Fat‐1 group. Plasma high‐density lipoprotein cholesterol (HDL‐C) levels were significantly increased in the Fat‐1 group, and the atherosclerotic lesion area of the aortic arch in Fat‐1 transgenic rabbits was significantly reduced. Histological analysis showed that smooth muscle cells (SMCs) in atherosclerotic lesions decreased significantly. In conclusion, n‐3 PUFAs improve atherosclerosis in Fat‐1 transgenic rabbits, and this process may depend on the increase in plasma HDL‐C and the decrease in the amount of SMCs in atherosclerotic plaques.     

Ancestral ecological regime shapes reaction to food limitation in the Least Killifish,Heterandria formosa

Populations with different densities often show genetically based differences in life histories. The divergent life histories could be driven by several agents of selection, one of which is variation in per‐capita food levels. Its relationship with population density is complex, as it depends on overall food availability, individual metabolic demand, and food‐independent factors potentially affecting density, such as predation intensity. Here, we present a case study of two populations of a small live‐bearing freshwater fish, one characterized by high density, low predation risk, low overall food availability, and presumably low per‐capita food levels, and the other by low density, high predation risk, high overall food availability, and presumably high per‐capita food levels. Using a laboratory experiment, we examined whether fish from these populations respond differently to food limitation, and whether size at birth, a key trait with respect to density variation in this species, is associated with any such differential responses. While at the lower food level growth was slower, body size smaller, maturation delayed, and survival reduced in both populations, these fitness costs were smaller in fish from the high‐density population. At low food, only 15% of high‐density fish died, compared to 75% of low‐density fish. This difference was much smaller at high food (0% vs. 15% mortality). The increased survival of high‐density fish may, at least partly, be due to their larger size at birth. Moreover, being larger at birth enabled fish to mature relatively early even at the lower food level. We demonstrate that sensitivities to food limitation differ between study populations, consistent with selection for a greater ability to tolerate low per‐capita food availability in the high‐density population. While we cannot preclude other agents of selection from operating in these populations simultaneously, our results suggest that variation in per‐capita food levels is one of those agents.     

Dopamine and glutamate in individuals at high risk for psychosis: a meta‐analysis of in vivo imaging findings and their variability compared to controls

Dopaminergic and glutamatergic dysfunction is believed to play a central role in the pathophysiology of schizophrenia. However, it is unclear if abnormalities predate the onset of schizophrenia in individuals at high clinical or genetic risk for the disorder. We systematically reviewed and meta‐analyzed studies that have used neuroimaging to investigate dopamine and glutamate function in individuals at increased clinical or genetic risk for psychosis. EMBASE, PsycINFO and Medline were searched form January 1, 1960 to November 26, 2020. Inclusion criteria were molecular imaging measures of striatal presynaptic dopaminergic function, striatal dopamine receptor availability, or glutamate function. Separate meta‐analyses were conducted for genetic high‐risk and clinical high‐risk individuals. We calculated standardized mean differences between high‐risk individuals and controls, and investigated whether the variability of these measures differed between the two groups. Forty‐eight eligible studies were identified, including 1,288 high‐risk individuals and 1,187 controls. Genetic high‐risk individuals showed evidence of increased thalamic glutamate + glutamine (Glx) concentrations (Hedges’ g=0.36, 95% CI: 0.12‐0.61, p=0.003). There were no significant differences between high‐risk individuals and controls in striatal presynaptic dopaminergic function, striatal D2/D3 receptor availability, prefrontal cortex glutamate or Glx, hippocampal glutamate or Glx, or basal ganglia Glx. In the meta‐analysis of variability, genetic high‐risk individuals showed reduced variability of striatal D2/D3 receptor availability compared to controls (log coefficient of variation ratio, CVR=–0.24, 95% CI: –0.46 to –0.02, p=0.03). Meta‐regressions of publication year against effect size demonstrated that the magnitude of differences between clinical high‐risk individuals and controls in presynaptic dopaminergic function has decreased over time (estimate=–0.06, 95% CI: –0.11 to –0.007, p=0.025). Thus, other than thalamic glutamate concentrations, no neurochemical measures were significantly different between individuals at risk for psychosis and controls. There was also no evidence of increased variability of dopamine or glutamate measures in high‐risk individuals compared to controls. Significant heterogeneity, however, exists between studies, which does not allow to rule out the existence of clinically meaningful differences.     

Multi‐level metabolic engineering of Escherichia coli for high‐titer biosynthesis of 2′‐fucosyllactose and 3‐fucosyllactose

Fucosyllactoses (FL), including 2′‐fucosyllactose (2′‐FL) and 3‐fucosyllactose (3‐FL), have garnered considerable interest for their value in newborn formula and pharmaceuticals. In this study, an engineered Escherichia coli was developed for high‐titer FL biosynthesis by introducing multi‐level metabolic engineering strategies, including (1) individual construction of the 2′/3‐FL‐producing strains through gene combination optimization of the GDP‐L‐fucose module; (2) screening of rate‐limiting enzymes (α‐1,2‐fucosyltransferase and α‐1,3‐fucosyltransferase); (3) analysis of critical intermediates and inactivation of competing pathways to redirect carbon fluxes to FL biosynthesis; (4) enhancement of the catalytic performance of rate‐limiting enzymes by the RBS screening, fusion peptides and multi‐copy gene cloning. The final strains EC49 and EM47 produced 9.36 g/L for 2′‐FL and 6.28 g/L for 3‐FL in shake flasks with a modified‐M9CA medium. Fed‐batch cultivations of the two strains generated 64.62 g/L of 2′‐FL and 40.68 g/L of 3‐FL in the 3‐L bioreactors, with yields of 0.65 mol 2′‐FL/mol lactose and 0.67 mol 3‐FL/mol lactose, respectively. This research provides a viable platform for other high‐value‐added compounds production in microbial cell factories.

An engineered Escherichia coli was developed for high‐titer FL biosynthesis by introducing multi‐level metabolic engineering strategies. Combined with the optimization of metabolic pathways and the performance improvement of rate‐limiting enzymes, 64.62 g/L of 2 ''‐FL and 40.68 g/L of 3‐FL were finally obtained in the 3‐L bioreactors.     

U‐CIE [/juː ‘siː/]: Color encoding of high‐dimensional data

Data visualization is essential to discover patterns and anomalies in large high‐dimensional datasets. New dimensionality reduction techniques have thus been developed for visualizing omics data, in particular from single‐cell studies. However, jointly showing several types of data, for example, single‐cell expression and gene networks, remains a challenge. Here, we present ‘U‐CIE, a visualization method that encodes arbitrary high‐dimensional data as colors using a combination of dimensionality reduction and the CIELAB color space to retain the original structure to the extent possible. U‐CIE first uses UMAP to reduce high‐dimensional data to three dimensions, partially preserving distances between entities. Next, it embeds the resulting three‐dimensional representation within the CIELAB color space. This color model was designed to be perceptually uniform, meaning that the Euclidean distance between any two points should correspond to their relative perceptual difference. Therefore, the combination of UMAP and CIELAB thus results in a color encoding that captures much of the structure of the original high‐dimensional data. We illustrate its broad applicability by visualizing single‐cell data on a protein network and metagenomic data on a world map and on scatter plots.     

Characterization of an aminotransferase from Acanthamoeba polyphaga Mimivirus

Acanthamoeba polyphaga Mimivirus, a complex virus that infects amoeba, was first reported in 2003. It is now known that its DNA genome encodes for nearly 1,000 proteins including enzymes that are required for the biosynthesis of the unusual sugar 4‐amino‐4,6‐dideoxy‐d‐glucose, also known as d‐viosamine. As observed in some bacteria, the pathway for the production of this sugar initiates with a nucleotide‐linked sugar, which in the Mimivirus is thought to be UDP‐d‐glucose. The enzyme required for the installment of the amino group at the C‐4′ position of the pyranosyl moiety is encoded in the Mimivirus by the L136 gene. Here, we describe a structural and functional analysis of this pyridoxal 5′‐phosphate‐dependent enzyme, referred to as L136. For this analysis, three high‐resolution X‐ray structures were determined: the wildtype enzyme/pyridoxamine 5′‐phosphate/dTDP complex and the site‐directed mutant variant K185A in the presence of either UDP‐4‐amino‐4,6‐dideoxy‐d‐glucose or dTDP‐4‐amino‐4,6‐dideoxy‐d‐glucose. Additionally, the kinetic parameters of the enzyme utilizing either UDP‐d‐glucose or dTDP‐d‐glucose were measured and demonstrated that L136 is efficient with both substrates. This is in sharp contrast to the structurally related DesI from Streptomyces venezuelae, whose three‐dimensional architecture was previously reported by this laboratory. As determined in this investigation,DesI shows a profound preference in its catalytic efficiency for the dTDP‐linked sugar substrate. This difference can be explained in part by a hydrophobic patch in DesI that is missing in L136. Notably, the structure of L136 reported here represents the first three‐dimensional model for a virally encoded PLP‐dependent enzyme and thus provides new information on sugar aminotransferases in general.     

To minimize foraging time,use high‐efficiency,energy‐expensive search and capture methods when food is abundant but low‐efficiency,low‐cost methods during food shortages

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit‐and‐capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low‐efficiency, low‐cost foraging methods give shorter daily foraging times than high‐efficiency, energy‐expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high‐efficiency high‐cost foraging methods give shorter daily foraging times than low‐efficiency low‐cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high‐efficiency energy‐expansive foraging methods and to exploit patches and sites that require energy‐demanding locomotion modes. Survival selection takes place at food shortages, while low‐efficiency low‐cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high‐efficiency energy‐expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species‐poor communities of year‐round resident generalists. But a stable year‐round food supply favors specialization, niche narrowing, and dense species packing.     

Tnfaip2/exoc3‐driven lipid metabolism is essential for stem cell differentiation and organ homeostasis

Lipid metabolism influences stem cell maintenance and differentiation but genetic factors that control these processes remain to be delineated. Here, we identify Tnfaip2 as an inhibitor of reprogramming of mouse fibroblasts into induced pluripotent stem cells. Tnfaip2 knockout impairs differentiation of embryonic stem cells (ESCs), and knockdown of the planarian para‐ortholog, Smed‐exoc3, abrogates in vivo tissue homeostasis and regeneration—processes that are driven by somatic stem cells. When stimulated to differentiate, Tnfaip2‐deficient ESCs fail to induce synthesis of cellular triacylglycerol (TAG) and lipid droplets (LD) coinciding with reduced expression of vimentin (Vim)—a known inducer of LD formation. Smed‐exoc3 depletion also causes a strong reduction of TAGs in planarians. The study shows that Tnfaip2 acts epistatically with and upstream of Vim in impairing cellular reprogramming. Supplementing palmitic acid (PA) and palmitoyl‐L‐carnitine (the mobilized form of PA) restores the differentiation capacity of Tnfaip2‐deficient ESCs and organ maintenance in Smed‐exoc3‐depleted planarians. Together, these results identify a novel role of Tnfaip2 and exoc3 in controlling lipid metabolism, which is essential for ESC differentiation and planarian organ maintenance.     

Purification and characterization of the receptor‐binding domain of SARS‐CoV‐2 spike protein from Escherichia coli

SARS‐CoV‐2 is responsible for a disruptive worldwide viral pandemic, and renders a severe respiratory disease known as COVID‐19. Spike protein of SARS‐CoV‐2 mediates viral entry into host cells by binding ACE2 through the receptor‐binding domain (RBD). RBD is an important target for development of virus inhibitors, neutralizing antibodies, and vaccines. RBD expressed in mammalian cells suffers from low expression yield and high cost. E. coli is a popular host for protein expression, which has the advantage of easy scalability with low cost. However, RBD expressed by E. coli (RBD‐1) lacks the glycosylation, and its antigenic epitopes may not be sufficiently exposed. In the present study, RBD‐1 was expressed by E. coli and purified by a Ni Sepharose Fast Flow column. RBD‐1 was structurally characterized and compared with RBD expressed by the HEK293 cells (RBD‐2). The secondary structure and tertiary structure of RBD‐1 were largely maintained without glycosylation. In particular, the major β‐sheet content of RBD‐1 was almost unaltered. RBD‐1 could strongly bind ACE2 with a dissociation constant (K_D) of 2.98 × 10^–8 M. Thus, RBD‐1 was expected to apply in the vaccine development, screening drugs and virus test kit.