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The biotech industry relies on cell factories for production of pharmaceutical proteins, of which several are among the top-selling medicines. There is, therefore, considerable interest in improving the efficiency of protein production by cell factories. Protein secretion involves numerous intracellular processes with many underlying mechanisms still remaining unclear. Here, we use RNA-seq to study the genome-wide transcriptional response to protein secretion in mutant yeast strains. We find that many cellular processes have to be attuned to support efficient protein secretion. In particular, altered energy metabolism resulting in reduced respiration and increased fermentation, as well as balancing of amino-acid biosynthesis and reduced thiamine biosynthesis seem to be particularly important. We confirm our findings by inverse engineering and physiological characterization and show that by tuning metabolism cells are able to efficiently secrete recombinant proteins. Our findings provide increased understanding of which cellular regulations and pathways are associated with efficient protein secretion. The contribution of metabolic pathways to protein secretion is largely unknown. Here, the authors find conserved metabolic patterns in yeast by examining genome-wide transcriptional responses in high protein secretion mutants and reveal critical factors that can be tuned for efficient protein secretion.

Microglia and central nervous system (CNS)-associated macrophages (CAMs), such as perivascular and meningeal macrophages, are implicated in virtually all diseases of the CNS. However, little is known about their cell-type-specific roles in the absence of suitable tools that would allow for functional discrimination between the ontogenetically closely related microglia and CAMs. To develop a new microglia gene targeting model, we first applied massively parallel single-cell analyses to compare microglia and CAM signatures during homeostasis and disease and identified hexosaminidase subunit beta ( Hexb) as a stably expressed microglia core gene, whereas other microglia core genes were substantially downregulated during pathologies. Next, we generated Hexb tdTomato mice to stably monitor microglia behavior in vivo. Finally, the Hexb locus was employed for tamoxifen-inducible Cre-mediated gene manipulation in microglia and for fate mapping of microglia but not CAMs. In sum, we provide valuable new genetic tools to specifically study microglia functions in the CNS. Microglia have key roles in central nervous system (CNS) disease and homeostasis but their study can be challenging. Prinz and colleagues identify hexosaminidase subunit beta ( Hexb ) to be specifically expressed by microglia and stable even under inflammatory conditions.

To investigate the impact of different 5ʹ untranslated regions (UTRs) on mRNA vaccine translation efficiency, five dual-reporter gene expression plasmids with different 5ʹUTRs were constructed. The corresponding mRNA transcripts were transcribed and capped in vitro. By comparing the expression levels of reporter genes with different 5ʹUTRs, we identified the 5ʹUTR associated with the highest expression level. Subsequently, HIVgp145 mRNA vaccines containing various 5ʹUTRs were constructed and verified. The results demonstrated that mRNA 3 (β-globin 5ʹUTR) displayed the greatest number of green fluorescence-positive cells and the highest luciferase fluorescence intensity in the reporter gene expression system. Further, among the HIVgp145 mRNA vaccines with different 5ʹUTRs, mRNA 7 (β-globin 5ʹUTR) exhibited the highest level of expression. These findings indicate that it is feasible to use the 5ʹUTR of β-globin in an mRNA vaccine, laying the foundation for animal immunogenicity testing.

Massively parallel reporter gene assays are key tools in regulatory genomics but cannot be used to identify cell-type-specific regulatory elements without performing assays serially across different cell types. To address this problem, we developed a single-cell massively parallel reporter assay (scMPRA) to measure the activity of libraries of cis -regulatory sequences (CRSs) across multiple cell types simultaneously. We assayed a library of core promoters in a mixture of HEK293 and K562 cells and showed that scMPRA is a reproducible, highly parallel, single-cell reporter gene assay that detects cell-type-specific cis -regulatory activity. We then measured a library of promoter variants across multiple cell types in live mouse retinas and showed that subtle genetic variants can produce cell-type-specific effects on cis -regulatory activity. We anticipate that scMPRA will be widely applicable for studying the role of CRSs across diverse cell types. A single-cell massively parallel reporter assay is used to compare cis -regulatory sequence activities in cell line models and mouse retinal tissue ex vivo, identifying cell state- and cell-type-specific effects of sequence variation.

High-throughput screening of chemicals with reporter gene assays in Tox21 has produced a large database on cytotoxicity and specific modes of action. However, the validity of some of the reported activities is questionable due to the \"cytotoxicity burst,\" which refers to the supposition that many stress responses are activated in a nonspecific way at concentrations close to cell death. We propose a pragmatic method to identify whether reporter gene activation is specific or cytotoxicity-triggered by comparing the measured effects with baseline toxicity. Baseline toxicity, also termed narcosis, is the minimal toxicity any chemical causes. Quantitative structure-activity relationships (QSARs) developed for baseline toxicity in mammalian reporter gene cell lines served as anchors to define the chemical-specific threshold for the cytotoxicity burst and to evaluate the degree of specificity of the reporter gene activation. Measured 10% effect concentrations were related to measured or QSAR-predicted 10% cytotoxicity concentrations yielding specificity ratios (SR). We applied this approach to our own experimental data and to chemicals that were tested in six of the high-throughput Tox21 reporter gene assays. Confirmed baseline toxicants activated reporter gene activity around cytotoxic concentrations triggered by the cytotoxicity burst. In six Tox21 assays, 37%-87% of the active hits were presumably caused by the cytotoxicity burst ( ) and only 2%-14% were specific with against experimental cytotoxicity but 75%-97% were specific against baseline toxicity. This difference was caused by a large fraction of chemicals showing excess cytotoxicity. The specificity analysis for measured effects identified whether a cytotoxicity burst had likely occurred. The SR-analysis not only prevented false positives, but it may also serve as measure for relative effect potency and can be used for quantitative extrapolation and risk assessment of chemicals. https://doi.org/10.1289/EHP6664.

Background Individual cells from isogenic populations often display large cell-to-cell differences in gene expression. This “noise” in expression derives from several sources, including the genomic and cellular environment in which a gene resides. Large-scale maps of genomic environments have revealed the effects of epigenetic modifications and transcription factor occupancy on mean expression levels, but leveraging such maps to explain expression noise will require new methods to assay how expression noise changes at locations across the genome. Results To address this gap, we present Single-cell Analysis of Reporter Gene Expression Noise and Transcriptome (SARGENT), a method that simultaneously measures the noisiness of reporter genes integrated throughout the genome and the global mRNA profiles of individual reporter-gene-containing cells. Using SARGENT, we perform the first comprehensive genome-wide survey of how genomic locations impact gene expression noise. We find that the mean and noise of expression correlate with different histone modifications. We quantify the intrinsic and extrinsic components of reporter gene noise and, using the associated mRNA profiles, assign the extrinsic component to differences between the CD24+ “stem-like” substate and the more “differentiated” substate. SARGENT also reveals the effects of transgene integrations on endogenous gene expression, which will help guide the search for “safe-harbor” loci. Conclusions Taken together, we show that SARGENT is a powerful tool to measure both the mean and noise of gene expression at locations across the genome and that the data generatd by SARGENT reveals important insights into the regulation of gene expression noise genome-wide.

Summary A critical step in generating gene‐edited plants is the removal of CRISPR‐related transgenes from T0 plants and their progenies, a process that is generally time‐consuming and labour‐intensive. We previously reported a Transgene Killer CRISPR (TKC) technology that enables self‐elimination of transgenes after the targeted gene has been edited. However, we observed that a small number of T1 plants generated by TKC still retained the transgenes. Herein, we first integrated Cas9 and guide RNA (gRNA) with the RUBY reporter gene (RUBY‐CRISPR) to monitor the Cas9/sgRNA expression and track the presence or absence of transgenes in the T0 generation and its progenies. We then combined the RUBY‐CRISPR unit with several TKC variants to develop four RUBY‐TKC (TKC2) systems including TKC2.1, TKC2.2, TKC2.3 and TKC2.4, to facilitate the elimination of escaped transgene plants. Compared to non‐TKC, TKC alone and RUBY‐CRISPR, our TKC2s were much more efficient in the generation of transgene‐free edited progenies by up to 100% in the T0 generation. TKC2s not only omit the need for screening of the plants with transgenes in the T0 generation, but also enable visualisation of the escape of plants with transgenes in the following progenies. The TKC2 systems developed here provide straightforward yet highly effective approaches for the generation of transgene‐free edited plants for either rice functional genomics or genetic improvement, with potential applications in gene editing of other crops.

• Virus-induced gene silencing (VIGS) can be harnessed to sequence-specifically degrade host transcripts and induce heritable epigenetic modifications referred to as virus-induced post-transcriptional gene silencing (ViPTGS) and virus-induced transcriptional gene silencing (ViTGS), respectively. Both ViPTGS and ViTGS enable manipulation of endogenous gene expression without the need for transgenesis. • Although VIGS has been widely used in many plant species, it is not always uniform or highly efficient. The efficiency of VIGS is affected by developmental, physiological and environmental factors. Here, we use recombinant Tobacco rattle viruses (TRV) to study the effect of temperature on ViPTGS and ViTGS using GFP as a reporter gene of silencing in N. benthamiana 16c plants. • We found that unlike ViPTGS, ViTGS was impaired at high temperature. Using a novel mismatch-small interfering RNA (siRNA) tool, which precisely distinguishes virus-derived (primary) from target-generated (secondary) siRNAs, we demonstrated that the lack of secondary siRNA production/amplification was responsible for inefficient ViTGS at 29°C. Moreover, inefficient ViTGS at 29°C inhibited the transmission of epigenetic gene silencing to the subsequent generations. • Our finding contributes to understanding the impact of environmental conditions on primary and secondary siRNA production and may pave the way to design/optimize ViTGS for transgene-free crop improvement.

Background Lipoxygenases (LOXs) play significant roles in abiotic stress responses, and identification of LOX gene promoter function can make an important contribution to elucidating resistance mechanisms. Here, we cloned the CmLOX08 promoter of melon ( Cucumis melo ) and identified the main promoter regions regulating transcription in response to signalling molecules and abiotic stresses. Results The 2054-bp promoter region of CmLOX08 from melon leaves was cloned, and bioinformatic analysis revealed that it harbours numerous cis -regulatory elements associated with signalling molecules and abiotic stress. Five 5′-deletion fragments obtained from the CmLOX08 promoter—2054 (LP1), 1639 (LP2), 1284 (LP3), 1047 (LP4), and 418 bp (LP5)—were fused with a GUS reporter gene and used for tobacco transient assays. Deletion analysis revealed that in response to abscisic acid, salicylic acid, and hydrogen peroxide, the GUS activity of LP1 was significantly higher than that of the mock-treated control and LP2, indicating that the − 2054- to − 1639-bp region positively regulates expression induced by these signalling molecules. However, no deletion fragment GUS activity was induced by methyl jasmonate. In response to salt, drought, and wounding treatments, LP1, LP2, and LP4 promoted significantly higher GUS expression compared with the control. Among all deletion fragments, LP4 showed the highest GUS expression, indicating that − 1047 to − 1 bp is the major region regulating promoter activity and that the − 1047 to − 418-bp region positively regulates expression induced by salt, drought, and wounding, whereas the − 1284 to − 1047-bp region is a negative regulatory segment. Interestingly, although the GUS activity of LP1 and LP2 was not affected by temperature changes, that of LP3 was significantly induced by heat, indicating that the − 1284- to − 1-bp region is a core sequence responding to heat and the − 2054- to − 1284-bp region negatively regulates expression induced by heat. Similarly, the − 1047- to − 1-bp region is the main sequence responding to cold, whereas the − 2054- to − 1047-bp region negatively regulates expression induced by cold. Conclusions We cloned the CmLOX08 promoter and demonstrated that it is a signalling molecule/stress-inducible promoter. Furthermore, we identified core and positive/negative regulatory regions responding to three signalling molecules and five abiotic stresses.

Efficient precision genome engineering requires high frequency and specificity of integration at the genomic target site. Here, we describe a set of resources to streamline reporter gene knock-ins in zebrafish and demonstrate the broader utility of the method in mammalian cells. Our approach uses short homology of 24–48 bp to drive targeted integration of DNA reporter cassettes by homology-mediated end joining (HMEJ) at high frequency at a double strand break in the targeted gene. Our vector series, pGTag (plasmids for Gene Tagging), contains reporters flanked by a universal CRISPR sgRNA sequence which enables in vivo liberation of the homology arms. We observed high rates of germline transmission (22–100%) for targeted knock-ins at eight zebrafish loci and efficient integration at safe harbor loci in porcine and human cells. Our system provides a straightforward and cost-effective approach for high efficiency gene targeting applications in CRISPR and TALEN compatible systems.