IRES-dependent second gene expression is significantly lower than cap-dependent first gene expression in a bicistronic vector

Polyplexes System to Enhance the LL-37 Antimicrobial Peptide Expression in Human Skin Cells

Inefficient autologous tissue recovery in diverse skin injuries increases the susceptibility of patients to infections caused by multiresistant microorganisms, resulting in a high mortality rate. Nonviral transfection is an attractive alternative for these patients, where genetically modified cells incorporated into skin substitutes could release additional antimicrobial agents into the native skin. In this work, we have modulated the conditions of using a nonviral system for transfection of primary human keratinocytes and fibroblasts, consisting of a polymer/plasmid DNA (pDNA) complex called polyplex and its effects on the expression of LL-37 antimicrobial peptide. Linear and branched polyethylenimine (PEI) polymers in different weight concentrations were varied for evaluating the formation and colloidal characteristics of the polyplexes. The PEI/pDNA polyplexes with 19 nitrogen/phosphate ratio are nanometric particles (400 and 250 nm with linear and branched PEI, respectively) exhibiting positive surface (+30 ± 2 mV). Both kinds of polyplexes allowed the expression of a reporter gene and increased the human cathelicidin antimicrobial peptide gene expression in transfected keratinocytes and fibroblasts; however, greater cytotoxicity was observed when polyplexes formed with branched PEI were used. Moreover, cell culture supernatants from transfected cells with linear PEI/pDNA polyplexes showed enhanced antimicrobial activity (decrease of bacterial growth in 95.8%) against a Staphylococcus aureus strain in vitro. The study of the PEI/pDNA polyplexes formation allowed us to develop an improved transfection strategy of skin cells, promoting the production of LL-37 antimicrobial peptide. In the future, this strategy could be used for the construction of skin substitutes to prevent, reduce, or eliminate bacterial infections. Impact statement The results of this study contribute to the understanding of the polyplexes system in the genetic modification of skin cells and its effects on the expression of the LL-37 antimicrobial peptide. In the future, three-dimensional skin substitutes built with these cells could be an efficient way to decrease bacterial growth and prevent the infections in skin wounds.

Generation of a ChATCre mouse line without the early onset hearing loss typical of the C57BL/6J strain

The development of knockin mice with Cre recombinase expressed under the control of the promoter for choline acetyltransferase (ChAT) has allowed experimental manipulation of cholinergic circuits. However, currently available ChAT^Cre mouse lines are on the C57BL/6J strain background, which shows early onset age-related hearing loss attributed to the Cdh23^753A mutation (a.k.a., the ahl mutation). To develop ChAT^Cre mice without accelerated hearing loss, we backcrossed ChAT^IRES-Cre mice with CBA/CaJ mice that have normal hearing. We used genotyping to obtain mice homozygous for ChAT^IRES-Cre and the wild-type allele at the Cdh23 locus (ChAT^Cre,Cdh23WT). In the new line, auditory brainstem response thresholds were ∼20 dB lower than those in 9 month old ChAT^IRES-Cre mice at all frequencies tested (4-31.5 kHz). These thresholds were stable throughout the period of testing (3-12 months of age). We then bred ChAT^Cre,Cdh23WT animals with Ai14 reporter mice to confirm the expression pattern of ChAT^Cre. In these mice, tdTomato-labeled cells were observed in all brainstem regions known to contain cholinergic cells. We then stained the tissue with a neuron-specific marker, NeuN, to determine whether Cre expression was limited to neurons. Across several brainstem nuclei (pontomesencephalic tegmentum, motor trigeminal and facial nuclei), 100% of the tdTomato-labeled cells were double-labeled with anti-NeuN (n = 1896 cells), indicating Cre-recombinase was limited to neurons. Almost all of these cells (1867/1896 = 98.5%) also stained with antibodies against ChAT, indicating that reporter label was expressed almost exclusively in cholinergic neurons. Finally, an average 88.7% of the ChAT+ cells in these nuclei were labeled with tdTomato, indicating that the Cre is expressed in a large proportion of the cholinergic cells in these nuclei. We conclude that the backcrossed ChAT^Cre,Cdh23WT mouse line has normal hearing and expresses Cre recombinase almost exclusively in cholinergic neurons. This ChAT^Cre,Cdh23WT mouse line may provide an opportunity to manipulate cholinergic circuits without the confound of accelerated hearing loss associated with the C57BL/6J background. Furthermore, comparison with lines that do show early hearing loss may provide insight into possible cholinergic roles in age-related hearing loss.

Three CNGC Family Members, CNGC5, CNGC6, and CNGC9, Are Required for Constitutive Growth of Arabidopsis Root Hairs as Ca2+-Permeable Channels

The genetic identities of Ca²⁺ channels in root hair (RH) tips essential for constitutive RH growth have remained elusive for decades. Here, we report the identification and characterization of three cyclic nucleotide-gated channel (CNGC) family members, CNGC5, CNGC6, and CNGC9, as Ca²⁺ channels essential for constitutive RH growth in Arabidopsis. We found that the cngc5-1cngc6-2cngc9-1 triple mutant (designated shrh1) showed significantly shorter and branching RH phenotypes as compared with the wild type. The defective RH growth phenotype of shrh1 could be rescued by either the expression of CNGC5, CNGC6, or CNGC9 single gene or by the supply of high external Ca²⁺, but could not be rescued by external K⁺ supply. Cytosolic Ca²⁺ imaging and patch-clamp data in HEK293T cells showed that these three CNGCs all function as Ca²⁺-permeable channels. Cytosolic Ca²⁺ imaging in growing RHs further showed that the Ca²⁺ gradients and their oscillation in RH tips were dramatically attenuated in shrh1 compared with those in the wild type. Phenotypic analysis revealed that these three CNGCs are Ca²⁺ channels essential for constitutive RH growth, with different roles in RHs from the conditional player CNGC14. Moreover, we found that these three CNGCs are involved in auxin signaling in RHs. Taken together, our study identified CNGC5, CNGC6, and CNGC9 as three key Ca²⁺ channels essential for constitutive RH growth and auxin signaling in Arabidopsis.

Multiplex Neural Circuit Tracing With G-Deleted Rabies Viral Vectors

Neural circuits interconnect to organize large-scale networks that generate perception, cognition, memory, and behavior. Information in the nervous system is processed both through parallel, independent circuits and through intermixing circuits. Analyzing the interaction between circuits is particularly indispensable for elucidating how the brain functions. Monosynaptic circuit tracing with glycoprotein (G) gene-deleted rabies viral vectors (RVΔG) comprises a powerful approach for studying the structure and function of neural circuits. Pseudotyping of RVΔG with the foreign envelope EnvA permits expression of transgenes such as fluorescent proteins, genetically-encoded sensors, or optogenetic tools in cells expressing TVA, a cognate receptor for EnvA. Trans-complementation with rabies virus glycoproteins (RV-G) enables trans-synaptic labeling of input neurons directly connected to the starter neurons expressing both TVA and RV-G. However, it remains challenging to simultaneously map neuronal connections from multiple cell populations and their interactions between intermixing circuits solely with the EnvA/TVA-mediated RV tracing system in a single animal. To overcome this limitation, here, we multiplexed RVΔG circuit tracing by optimizing distinct viral envelopes (oEnvX) and their corresponding receptors (oTVX). Based on the EnvB/TVB and EnvE/DR46-TVB systems derived from the avian sarcoma leukosis virus (ASLV), we developed optimized TVB receptors with lower or higher affinity (oTVB-L or oTVB-H) and the chimeric envelope oEnvB, as well as an optimized TVE receptor with higher affinity (oTVE-H) and its chimeric envelope oEnvE. We demonstrated independence of RVΔG infection between the oEnvA/oTVA, oEnvB/oTVB, and oEnvE/oTVE systems and in vivo proof-of-concept for multiplex circuit tracing from two distinct classes of layer 5 neurons targeting either other cortical or subcortical areas. We also successfully labeled common input of the lateral geniculate nucleus to both cortico-cortical layer 5 neurons and inhibitory neurons of the mouse V1 with multiplex RVΔG tracing. These oEnvA/oTVA, oEnvB/oTVB, and oEnvE/oTVE systems allow for differential labeling of distinct circuits to uncover the mechanisms underlying parallel processing through independent circuits and integrated processing through interaction between circuits in the brain.

Intravitreal application of AAV-BDNF or mutant AAV-CRMP2 protects retinal ganglion cells and stabilizes axons and myelin after partial optic nerve injury

Secondary degeneration following an initial injury to the central nervous system (CNS) results in increased tissue loss and is associated with increasing functional impairment. Unilateral partial dorsal transection of the adult rat optic nerve (ON) has proved to be a useful experimental model in which to study factors that contribute to secondary degenerative events. Using this injury model, we here quantified the protective effects of intravitreally administered bi-cistronic adeno-associated viral (AAV2) vectors encoding either brain derived neurotrophic factor (BDNF) or a mutant, phospho-resistant, version of collapsin response mediator protein 2 (CRMP2T555A) on retinal ganglion cells (RGCs), their axons, and associated myelin. To test for potential synergistic interactions, some animals received combined injections of both vectors. Three months post-injury, all treatments maintained RGC numbers in central retina, but only AAV2-BDNF significantly protected ventrally located RGCs exclusively vulnerable to secondary degeneration. Behaviourally, treatments that involved AAV2-BDNF significantly restored the number of smooth-pursuit phases of optokinetic nystagmus. While all therapeutic regimens preserved axonal density and proportions of typical complexes, including heminodes and single nodes, BDNF treatments were generally more effective in maintaining the length of the node of Ranvier in myelin surrounding ventral ON axons after injury. Both AAV2-BDNF and AAV2-CRMP2T555A prevented injury-induced changes in G-ratio and overall myelin thickness, but only AAV2-BDNF administration protected against large-scale myelin decompaction in ventral ON. In summary, in a model of secondary CNS degeneration, both BDNF and CRMP2T555A vectors were neuroprotective, however different efficacies were observed for these overexpressed proteins in the retina and ON, suggesting disparate cellular and molecular targets driving responses for neural repair. The potential use of these vectors to treat other CNS injuries and pathologies is discussed.

Gene delivery of a modified antibody to Aβ reduces progression of murine Alzheimer's disease

Antibody therapies for Alzheimer’s Disease (AD) hold promise but have been limited by the inability of these proteins to migrate efficiently across the blood brain barrier (BBB). Central nervous system (CNS) gene transfer by vectors like adeno-associated virus (AAV) overcome this barrier by allowing the bodies’ own cells to produce the therapeutic protein, but previous studies using this method to target amyloid-β have shown success only with truncated single chain antibodies (Abs) lacking an Fc domain. The Fc region mediates effector function and enhances antigen clearance from the brain by neonatal Fc receptor (FcRn)-mediated reverse transcytosis and is therefore desirable to include for such treatments. Here, we show that single chain Abs fused to an Fc domain retaining FcRn binding, but lacking Fc gamma receptor (FcγR) binding, termed a silent scFv-IgG, can be expressed and released into the CNS following gene transfer with AAV. While expression of canonical IgG in the brain led to signs of neurotoxicity, this modified Ab was efficiently secreted from neuronal cells and retained target specificity. Steady state levels in the brain exceeded peak levels obtained by intravenous injection of IgG. AAV-mediated expression of this scFv-IgG reduced cortical and hippocampal plaque load in a transgenic mouse model of progressive β-amyloid plaque accumulation. These findings suggest that CNS gene delivery of a silent anti-Aβ scFv-IgG was well-tolerated, durably expressed and functional in a relevant disease model, demonstrating the potential of this modality for the treatment of Alzheimer’s disease.

Achieving tight control of a photoactivatable Cre recombinase gene switch: new design strategies and functional characterization in mammalian cells and rodent

A common mechanism for inducibly controlling protein function relies on reconstitution of split protein fragments using chemical or light-induced dimerization domains. A protein is split into fragments that are inactive on their own, but can be reconstituted after dimerization. As many split proteins retain affinity for their complementary half, maintaining low activity in the absence of an inducer remains a challenge. Here, we systematically explore methods to achieve tight regulation of inducible proteins that are effective despite variation in protein expression level. We characterize a previously developed split Cre recombinase (PA-Cre2.0) that is reconstituted upon light-induced CRY2-CIB1 dimerization, in cultured cells and in vivo in rodent brain. In culture, PA-Cre2.0 shows low background and high induced activity over a wide range of expression levels, while in vivo the system also shows low background and sensitive response to brief light inputs. The consistent activity stems from fragment compartmentalization that shifts localization toward the cytosol. Extending this work, we exploit nuclear compartmentalization to generate light-and-chemical regulated versions of Cre recombinase. This work demonstrates in vivo functionality of PA-Cre2.0, describes new approaches to achieve tight inducible control of Cre DNA recombinase, and provides general guidelines for further engineering and application of split protein fragments.

Engineering strategies to overcome the current roadblocks in CAR T cell therapy

T cells genetically engineered to express chimeric antigen receptors (CARs) have proven — and impressive — therapeutic activity in patients with certain subtypes of B cell leukaemia or lymphoma, with promising efficacy also demonstrated in patients with multiple myeloma. Nevertheless, various barriers restrict the efficacy and/or prevent the widespread use of CAR T cell therapies in these patients as well as in those with other cancers, particularly solid tumours. Key challenges relating to CAR T cells include severe toxicities, restricted trafficking to, infiltration into and activation within tumours, suboptimal persistence in vivo, antigen escape and heterogeneity, and manufacturing issues. The evolution of CAR designs beyond the conventional structures will be necessary to address these limitations and to expand the use of CAR T cells to a wider range of malignancies. Investigators are addressing the current obstacles with a wide range of engineering strategies in order to improve the safety, efficacy and applicability of this therapeutic modality. In this Review, we discuss the innovative designs of novel CAR T cell products that are being developed to increase and expand the clinical benefits of these treatments in patients with diverse cancers.

Chimeric antigen receptor (CAR) T cell therapy, the first approved therapeutic approach with a genetic engineering component, holds substantial promise in the treatment of a range of cancers but is nevertheless limited by various challenges, including toxicities, intrinsic and acquired resistance mechanisms, and manufacturing issues. In this Review, the authors describe the innovative approaches to the engineering of CAR T cell products that are providing solutions to these challenges and therefore have the potential to considerably improve the safety and effectiveness of treatment.

Chimeric antigen receptor (CAR) T cells have induced remarkable responses in patients with certain haematological malignancies, yet various barriers restrict the efficacy and/or prevent the widespread use of this treatment.

Investigators are addressing these challenges with engineering strategies designed to improve the safety, efficacy and applicability of CAR T cell therapy.

CARs have modular components, and therefore the optimal molecular design of the CAR can be achieved through many variations of the constituent protein domains.

Toxicities currently associated with CAR T cell therapy can be mitigated using engineering strategies to make CAR T cells safer and that potentially broaden the range of tumour-associated antigens that can be targeted by overcoming on-target, off-tumour toxicities.

CAR T cell efficacy can be enhanced by using engineering strategies to address the various challenges relating to the unique biology of diverse haematological and solid malignancies.

Strategies to address the manufacturing challenges can lead to an improved CAR T cell product for all patients.

Production and Application of Multicistronic Constructs for Various Human Disease Therapies

The development of multicistronic vectors has opened up new opportunities to address the fundamental issues of molecular and cellular biology related to the need for the simultaneous delivery and joint expression of several genes. To date, the examples of the successful use of multicistronic vectors have been described for the development of new methods of treatment of various human diseases, including cardiovascular, oncological, metabolic, autoimmune, and neurodegenerative disorders. The safety and effectiveness of the joint delivery of therapeutic genes in multicistronic vectors based on the internal ribosome entry site (IRES) and self-cleaving 2A peptides have been shown in both in vitro and in vivo experiments as well as in clinical trials. Co-expression of several genes in one vector has also been used to create animal models of various inherited diseases which are caused by mutations in several genes. Multicistronic vectors provide expression of all mutant genes, which allows the most complete mimicking disease pathogenesis. This review comprehensively discusses multicistronic vectors based on IRES nucleotide sequence and self-cleaving 2A peptides, including its features and possible application for the treatment and modeling of various human diseases.

Internal Ribosome Entry Site Dramatically Reduces Transgene Expression in Hematopoietic Cells in a Position-Dependent Manner

Bicistronic transgene expression mediated by internal ribosome entry site (IRES) elements has been widely used. It co-expresses heterologous transgene products from a message RNA driven by a single promoter. Hematologic gene delivery is a promising treatment for both inherited and acquired diseases. A combined strategy was recently documented for potential genome editing in hematopoietic cells. A transduction efficiency exceeding ~90% can be achieved by capsid-optimized recombinant adeno-associated virus serotype 6 (rAAV6) vectors. In this study, to deliver an encephalomyocarditis virus (EMCV) IRES-containing rAAV6 genome into hematopoietic cells, we observed that EMCV IRES almost completely shut down the transgene expression during the process of mRNA–protein transition. In addition, position-dependent behavior was observed, in which only the EMCV IRES element located between a promoter and the transgenes had an inhibitory effect. Although further studies are warranted to evaluate the involvement of cellular translation machinery, our results propose the use of specific IRES elements or an alternative strategy, such as the 2A system, to achieve bicistronic transgene expression in hematopoietic cells.

TRPC channels regulate Ca2+-signaling and short-term plasticity of fast glutamatergic synapses

Transient receptor potential (TRP) proteins form Ca²⁺-permeable, nonselective cation channels, but their role in neuronal Ca²⁺ homeostasis is elusive. In the present paper, we show that TRPC channels potently regulate synaptic plasticity by changing the presynaptic Ca²⁺-homeostasis of hippocampal neurons. Specifically, loss of TRPC1/C4/C5 channels decreases basal-evoked secretion, reduces the pool size of readily releasable vesicles, and accelerates synaptic depression during high-frequency stimulation (HFS). In contrast, primary TRPC5 channel-expressing neurons, identified by a novel TRPC5–τ-green fluorescent protein (τGFP) knockin mouse line, show strong short-term enhancement (STE) of synaptic signaling during HFS, indicating a key role of TRPC5 in short-term plasticity. Lentiviral expression of either TRPC1 or TRPC5 turns classic synaptic depression of wild-type neurons into STE, demonstrating that TRPCs are instrumental in regulating synaptic plasticity. Presynaptic Ca²⁺ imaging shows that TRPC activity strongly boosts synaptic Ca²⁺ dynamics, showing that TRPC channels provide an additional presynaptic Ca²⁺ entry pathway, which efficiently regulates synaptic strength and plasticity.

Transient receptor potential (TRP) proteins can form non-selective cation channels, but their role in synaptic transmission is poorly understood. This study shows that calcium-permeable TRPC channels provide an additional calcium entry pathway at presynaptic sites and are efficient regulators of synaptic strength and plasticity.

Pathogenic FAM83G palmoplantar keratoderma mutations inhibit the PAWS1:CK1α association and attenuate Wnt signalling

Background: Two recessive mutations in the FAM83G gene, causing A34E and R52P amino acid substitutions in the DUF1669 domain of the PAWS1 protein, are associated with palmoplantar keratoderma (PPK) in humans and dogs respectively. We have previously reported that PAWS1 associates with the Ser/Thr protein kinase CK1α through the DUF1669 domain to mediate canonical Wnt signalling. Methods: Co-immunoprecipitation was used to investigate possible changes to PAWS1 interactors caused by the mutations. We also compared the stability of wild-type and mutant PAWS1 in cycloheximide-treated cells. Effects on Wnt signalling were determined using the TOPflash luciferase reporter assay in U2OS cells expressing PAWS1 mutant proteins. The ability of PAWS1 to induce axis duplication in Xenopus embryos was also tested. Finally, we knocked-in the A34E mutation at the native gene locus and measured Wnt-induced AXIN2 gene expression by RT-qPCR. Results: We show that these PAWS1 ^A34E and PAWS1 ^R52P mutants fail to interact with CK1α but, like the wild-type protein, do interact with CD2AP and SMAD1. Like cells carrying a PAWS1 ^F296A mutation, which also abolishes CK1α binding, cells carrying the A34E and R52P mutants respond poorly to Wnt signalling to an extent resembling that observed in FAM83G gene knockout cells. Consistent with this observation, these mutants, in contrast to the wild-type protein, fail to induce axis duplication in Xenopus embryos. We also found that the A34E and R52P mutant proteins are less abundant than the native protein and appear to be less stable, both when overexpressed in FAM83G-knockout cells and when knocked-in at the native FAM83G locus. Ala ³⁴ of PAWS1 is conserved in all FAM83 proteins and mutating the equivalent residue in FAM83H (A31E) also abolishes interaction with CK1 isoforms. Conclusions: We propose that mutations in PAWS1 cause PPK pathogenesis through disruption of the CK1α interaction and attenuation of Wnt signalling.

Tagger-A Swiss army knife for multiomics to dissect cell type-specific mechanisms of gene expression in mice

A deep understanding of how regulation of the multiple levels of gene expression in mammalian tissues give rise to complex phenotypes has been impeded by cellular diversity. A handful of techniques were developed to tag-select nucleic acids of interest in specific cell types, thereby enabling their capture. We expanded this strategy by developing the Tagger knock-in mouse line bearing a quad-cistronic transgene combining enrichment tools for nuclei, nascent RNA, translating mRNA, and mature microRNA (miRNA). We demonstrate that Tagger can capture the desired nucleic acids, enabling multiple omics approaches to be applied to specific cell types in vivo using a single transgenic mouse line.

This Methods and Resources paper describes Tagger, a knock-in mouse line bearing a quad-cistronic transgene that enables the capture of translating mRNAs, mature miRNAs, pulse-labeled total RNA, and the nucleus, all from specific cells of complex tissues.

Bundling mRNA Strands to Prepare Nano-Assemblies with Enhanced Stability Towards RNase for In Vivo Delivery

Ribonuclease (RNase)-mediated degradation of messenger RNA (mRNA) poses a huge obstruction to in vivo mRNA delivery. Herein, we propose a novel strategy to protect mRNA by structuring mRNA to prevent RNase attack through steric hinderance. Bundling of mRNA strands through hybridization of RNA oligonucleotide linkers allowed the preparation of mRNA nano-assemblies (R-NAs) comprised of 7.7 mRNA strands on average, mostly below 100 nm in diameter. R-NA formation boosted RNase stability by around 100-fold compared to naïve mRNA and preserved translational activity, allowing protein production. A mechanistic analysis suggests that an endogenous mRNA unwinding mechanism triggered by 5'-cap-dependent translation may induce selective R-NA dissociation intracellularly, leading to smooth translation. R-NAs showed efficient mRNA transfection in mouse brain, demonstrating the feasibility for in vivo administration.

New α- and SIN γ-retrovectors for safe transduction and specific transgene expression in pancreatic β cell lines

BACKGROUND

Viral vectors are invaluable tools to transfer genes and/or regulatory sequences into differentiated cells such as pancreatic cells. To date, several kinds of viral vectors have been used to transduce different pancreatic cell types, including insulin-producing β cells. However, few studies have used vectors derived from « simple » retroviruses, such as avian α- or mouse γ-retroviruses, despite their high experimental convenience. Moreover, such vectors were never designed to specifically target transgene expression into β cells.

RESULTS

We here describe two novel α- or SIN (Self-Inactivating) γ-retrovectors containing the RIP (Rat Insulin Promoter) as internal promoter. These two retrovectors are easily produced in standard BSL2 conditions, rapidly concentrated if needed, and harbor a large multiple cloning site. For the SIN γ-retrovector, either the VSV-G (pantropic) or the retroviral ecotropic (rodent specific) envelope was used. For the α-retrovector, we used the A type envelope, as its receptor, termed TVA, is only naturally present in avian cells and can efficiently be provided to mammalian β cells through either exogenous expression upon cDNA transfer or gesicle-mediated delivery of the protein. As expected, the transgenes cloned into the two RIP-containing retrovectors displayed a strong preferential expression in β over non-β cells compared to transgenes cloned in their non-RIP (CMV- or LTR-) regulated counterparts. We further show that RIP activity of both retrovectors mirrored fluctuations affecting endogenous INSULIN gene expression in human β cells. Finally, both α- and SIN γ-retrovectors were extremely poorly mobilized by the BXV1 xenotropic retrovirus, a common invader of human cells grown in immunodeficient mice, and, most notably, of human β cell lines.

CONCLUSION

Our novel α- and SIN γ-retrovectors are safe and convenient tools to stably and specifically express transgene(s) in mammalian β cells. Moreover, they both reproduce some regulatory patterns affecting INSULIN gene expression. Thus, they provide a helpful tool to both study the genetic control of β cell function and monitor changes in their differentiation status.

Real-Time Temporal Dynamics of Bicistronic Expression Mediated by Internal Ribosome Entry Site and 2A Cleaving Sequence

Multicistronic elements, such as the internal ribosome entry site (IRES) and 2A-like cleavage sequence, serve crucial roles in the eukaryotic ectopic expression of exogenous genes. For utilization of multicistronic elements, the cleavage efficiency and order of elements in multicistronic vectors have been investigated; however, the dynamics of multicistronic element-mediated expression remains unclear. Here, we investigated the dynamics of encephalomyocarditis virus (EMCV) IRES- and porcine teschovirus-1 2A (p2A)-mediated expression. By utilizing real-time fluorescent imaging at a minute-level resolution, we monitored the expression of fluorescent reporters bridged by either EMCV IRES or p2A in two independent cultured cell lines, HEK293 and Neuro2a. We observed significant correlations for the two fluorescent reporters in both multicistronic elements, with a higher correlation coefficient for p2A in HEK293 but similar coefficients for IRES-mediated expression and p2A-mediated expression in Neuro2a. We further analyzed the causal relationship of multicistronic elements by convergent cross mapping (CCM). CCM revealed that in all four conditions examined, the expression of the preceding gene causally affected the dynamics of the subsequent gene. As with the cross correlation, the predictive skill of p2A was higher than that of IRES in HEK293, while the predictive skills of the two multicistronic elements were indistinguishable in Neuro2a. To summarize, we report a significant temporal correlation in both EMCV IRES- and p2A-mediated expression based on the simple bicistronic vector and real-time fluorescent monitoring. The current system also provides a valuable platform to examine the dynamic aspects of expression mediated by diverse multicistronic elements under various physiological conditions.

Acute Suppression of LH Secretion by Prolactin in Female Mice Is Mediated by Kisspeptin Neurons in the Arcuate Nucleus

Hyperprolactinemia causes infertility, but the specific mechanism is unknown. It is clear that elevated prolactin levels suppress pulsatile release of GnRH from the hypothalamus, with a consequent reduction in pulsatile LH secretion from the pituitary. Only a few GnRH neurons express prolactin receptors (Prlrs), however, and thus prolactin must act indirectly in the underlying neural circuitry. Here, we have tested the hypothesis that prolactin-induced inhibition of LH secretion is mediated by kisspeptin neurons, which provide major excitatory inputs to GnRH neurons. To evaluate pulsatile LH secretion, we collected serial blood samples from diestrous mice and measured LH levels by ultrasensitive ELISA. Acute prolactin administration decreased LH pulses in wild-type mice. Kisspeptin neurons in the arcuate nucleus and in the rostral periventricular area of the third ventricle (RP3V) acutely responded to prolactin, but prolactin-induced signaling in kisspeptin neurons was up to fourfold higher in the arcuate nucleus when compared with the RP3V. Consistent with this, conditional knockout of Prlr specifically in arcuate nucleus kisspeptin neurons prevented prolactin-induced suppression of LH secretion. Our data establish that during hyperprolactinemia, suppression of pulsatile LH secretion is mediated by Prlr on arcuate kisspeptin neurons.

Rapid production of a chimeric antibody-antigen fusion protein based on 2A-peptide cleavage and green fluorescent protein expression in CHO cells

To enable large-scale antibody production, the creation of a stable, high producer cell line is essential. This process often takes longer than 6 months using standard limited dilution techniques and is very labor intensive. The use of a tri-cistronic vector expressing green fluorescent protein (GFP) and both antibody chains, separated by a GT2A peptide sequence, allows expression of all proteins under a single promotor in equimolar ratios. By combining the advantages of 2A peptide cleavage and single cell sorting, a chimeric antibody-antigen fusion protein that contained the variable domains of mouse IgG with a porcine IgA constant domain fused to the FedF antigen could be produced in CHO-K1 cells. After transfection, a strong correlation was found between antibody production and GFP expression (r = 0.69) using image analysis of formed monolayer patches. This enables the rapid selection of GFP-positive clones using automated image analysis for the selection of high producer clones. This vector design allowed the rapid selection of high producer clones within a time-frame of 4 weeks after transfection. The highest producing clone had a specific antibody productivity of 2.32 pg/cell/day. Concentrations of 34 mg/L were obtained using shake-flask batch culture. The produced recombinant antibody showed stable expression, binding and minimal degradation. In the future, this antibody will be assessed for its effectiveness as an oral vaccine antigen.

Chemical Biology Gateways to Mapping Location, Association, and Pathway Responsivity

Here we discuss, how by applying chemical concepts to biological problems, methods have been developed to map spatiotemporal regulation of proteins and small-molecule modulation of proteome signaling responses. We outline why chemical-biology platforms are ideal for such purposes. We further discuss strengths and weaknesses of chemical-biology protocols, contrasting them against classical genetic and biochemical approaches. We make these evaluations based on three parameters: occupancy; functional information; and spatial restriction. We demonstrate how the specific choice of chemical reagent and experimental set-up unite to resolve biological problems. Potential improvements/extensions as well as specific controls that in our opinion are often overlooked or employed incorrectly are also considered. Finally, we discuss some of the latest emerging methods to illuminate how chemical-biology innovations provide a gateway toward information hitherto inaccessible by conventional genetic/biochemical means. Finally, we also caution against solely relying on chemical-biology strategies and urge the field to undertake orthogonal validations to ensure robustness of results.

Preclinical Assessment of Suitable Natural Killer Cell Sources for Chimeric Antigen Receptor Natural Killer-Based "Off-the-Shelf" Acute Myeloid Leukemia Immunotherapies

The introduction of chimeric antigen receptors (CARs) to augment the anticancer activity of immune cells represents one of the major clinical advances in recent years. This work demonstrates that sorted CAR natural killer (NK) cells have improved antileukemia activity compared to control NK cells that lack a functional CAR. However, in terms of viability, effectiveness, risk of side effects, and clinical practicality and applicability, an important question is whether gene-modified NK cell lines represent better CAR effector cells than primary human donor CAR-NK (CAR-dNK) cells. Comparison of the functional activities of sorted CAR-NK cells generated using the NK-92 cell line with those generated from primary human dNK cells demonstrated that CAR-NK-92 cells had stronger cytotoxic activity against leukemia cells compared to CAR-dNK cells. CAR-NK-92 and CAR-dNK cells had similar CD107a surface expression upon co-incubation with leukemia cells. However, CAR-NK-92 cells secreted higher granzyme A and interleukin-17A levels, while CAR-dNK cells secreted more tumor necrosis factor alpha, interferon gamma, and granulysin. In addition, CAR-NK-92 cells revealed a significantly higher potential for adverse side effects against nonmalignant cells. In short, this work shows the feasibility for further development of CAR-NK strategies to treat leukemia.

Basic Concepts in Viral Vector-Mediated Gene Therapy

Today any researcher with the desire can easily purchase a viral vector. However, despite the availability of viral vectors themselves, the requisite knowledge that is absolutely essential to conducting a gene therapy experiment remains somewhat obscure and esoteric. To utilize viral vectors to their full potential, a large number of decisions must be made, in some instances prior to even obtaining the vector itself. For example, critical decisions include selection of the proper virus, selection of the proper expression cassette, whether to produce or purchase a viral vector, proper viral handling and storage, the most appropriate delivery method, selecting the proper controls, how to ensure your virus is expressing properly, and many other complex decisions that are essential to performing a successful gene therapy experiment. The need to make so many important decisions can be overwhelming and potentially prohibitive, especially to the novice gene therapist. In order to aid in this challenging process, here we provide an overview of basic gene therapy modalities and a decision tree that can be used to make oneself aware of the options available to the beginning gene therapist. This information can be used as a road map to help navigate the complex and perhaps confusing process of designing a successful gene therapy experiment.

Hnrnpab regulates neural cell motility through transcription of Eps8

Cell migration requires a complicated network of structural and regulatory proteins. Changes in cellular motility can impact migration as a result of cell-type or developmental stage regulated expression of critical motility genes. Hnrnpab is a conserved RNA-binding protein found as two isoforms produced by alternative splicing. Its expression is enriched in the subventricular zone (SVZ) and the rostral migratory stream within the brain, suggesting possible support of the migration of neural progenitor cells in this region. Here we show that the migration of cells from the SVZ of developing Hnrnpab^-/- mouse brains is impaired. An RNA-seq analysis to identify Hnrnpab-dependent cell motility genes led us to Eps8, and in agreement with the change in cell motility, we show that Eps8 is decreased in Hnrnpab^-/- SVZ tissue. We scrutinized the motility of Hnrnpab^-/- cells and confirmed that the decreases in both cell motility and Eps8 are restored by ectopically coexpressing both alternatively spliced Hnrnpab isoforms, therefore these variants are surprisingly nonredundant for cell motility. Our results support a model where both Hnrnpab isoforms work in concert to regulate Eps8 transcription in the mouse SVZ to promote the normal migration of neural cells during CNS development.

Pathogenic FAM83G palmoplantar keratoderma mutations inhibit the PAWS1:CK1α association and attenuate Wnt signalling

Background: Two recessive mutations in the FAM83G gene, causing A34E and R52P amino acid substitutions in the DUF1669 domain of the PAWS1 protein, are associated with palmoplantar keratoderma (PPK) in humans and dogs respectively. We have previously reported that PAWS1 associates with the Ser/Thr protein kinase CK1α through the DUF1669 domain to mediate canonical Wnt signalling. Methods: Co-immunoprecipitation was used to investigate possible changes to PAWS1 interactors caused by the mutations. We also compared the stability of wild-type and mutant PAWS1 in cycloheximide-treated cells. Effects on Wnt signalling were determined using the TOPflash luciferase reporter assay in U2OS cells expressing PAWS1 mutant proteins. The ability of PAWS1 to induce axis duplication in Xenopus embryos was also tested. Finally, we knocked-in the A34E mutation at the native gene locus and measured Wnt-induced AXIN2 gene expression by RT-qPCR. Results: We show that these PAWS1 ^A34E and PAWS1 ^R52P mutants fail to interact with CK1α but, like the wild-type protein, do interact with CD2AP and SMAD1. Like cells carrying a PAWS1 ^F296A mutation, which also abolishes CK1α binding, cells carrying the A34E and R52P mutants respond poorly to Wnt signalling to an extent resembling that observed in FAM83G gene knockout cells. Consistent with this observation, these mutants, in contrast to the wild-type protein, fail to induce axis duplication in Xenopus embryos. We also found that the A34E and R52P mutant proteins are less abundant than the native protein and appear to be less stable, both when overexpressed in FAM83G-knockout cells and when knocked-in at the native FAM83G locus. Ala ³⁴ of PAWS1 is conserved in all FAM83 proteins and mutating the equivalent residue in FAM83H (A31E) also abolishes interaction with CK1 isoforms. Conclusions: We propose that mutations in PAWS1 cause PPK pathogenesis through disruption of the CK1α interaction and attenuation of Wnt signalling.

Modifying inter-cistronic sequence significantly enhances IRES dependent second gene expression in bicistronic vector: Construction of optimised cassette for gene therapy of familial hypercholesterolemia

Internal ribosome entry site (IRES) sequences have become a valuable tool in the construction of gene transfer and therapeutic vectors for multi-cistronic gene expression from a single mRNA transcript. The optimal conditions for effective use of this sequence to construct a functional expression vector are not precisely defined but it is generally assumed that the internal ribosome entry site dependent expression of the second gene in such as cassette is less efficient than the cap-dependent expression of the first gene. Mainly tailoring inter-cistronic sequence significantly enhances IRES dependent second gene expression in bicistronic vector further in construction of optimised cassette for gene therapy of familial hypercholesterolemia. We tailored the size of the inter-cistronic spacer sequence at the 5′ region of the internal ribosome entry site sequence using sequential deletions and demonstrated that the expression of the 3′ gene can be significantly increased to similar levels as the cap-dependent expression of the 5’ gene. Maximum expression efficiency of the downstream gene was obtained when the spacer is composed of 18–141 base pairs. In this case a single mRNA transcriptional unit containing both the first and the second Cistron was detected. Whilst constructs with spacer sequences of 216 bp or longer generate a single transcriptional unit containing only the first Cistron. This suggests that long spacers may affect transcription termination. When the spacer is 188 bp, both transcripts were produced simultaneously in most transfected cells, while a fraction of them expressed only the first but not the second gene. Expression analyses of vectors containing optimised cassettes clearly confirm that efficiency of gene transfer and biological activity of the expressed transgenic proteins in the transduced cells can be achieved. Furthermore, Computational analysis was carried out by molecular dynamics (MD) simulation to determine the most emerges as viable containing specific binding site and bridging of 5′ and 3′ ends involving direct RNA-RNA contacts and RNA-protein interactions. These results provide a mechanistic basis for translation stimulation and RNA resembling for the synergistic stimulation of cap-dependent translation.

A systematic analysis of the expression of the anti-HIV VRC01 antibody in Pichia pastoris through signal peptide optimization

Pichia pastoris (Komagataella phaffi) has been used for recombinant protein production for over 30 years with over 5000 proteins reported to date. However, yields of antibody are generally low. We have evaluated the effect of secretion signal peptides on the production of a broadly neutralizing antibody (VRC01) to increase yield. Eleven different signal peptides, including the murine IgG1 signal peptide, were combinatorially evaluated for their effect on antibody titer. Strains using different combinations of signal peptides were identified that secreted approximately 2-7 fold higher levels of VRC01 than the previous best secretor, with the highest yield of 6.50 mg L-1 in shake flask expression. Interestingly it was determined that the highest yields were achieved when the murine IgG1 signal peptide was fused to the light chain, with several different signal peptides leading to high yield when fused to the heavy chain. Finally, we have evaluated the effect of using a 2A signal peptide to create a bicistronic vector in the attempt to reduce burden and increase transformation efficiency, but found it to give reduced yields compared to using two independent vectors.

Assembling multiple xenoprotective transgenes in pigs

This review gives a brief overview of the genetic modifications necessary for grafted porcine tissues and organs to overcome rejection in human recipients. It then focuses on the problem of generating and breeding herds of donor pigs carrying modified endogenous genes and multiple xenoprotective transgenes. A xenodonor pig optimised for human clinical use could well require the addition of ten or more xenoprotective transgenes. It is impractical to produce the required combination of transgene by cross-breeding animals bearing individual transgenes at unlinked genetic loci, because independent segregation means that huge numbers of pigs would be required to produce relatively few donor animals. A better approach is to colocate groups of transgenes at a single genomic locus. We outline current methods to assemble transgene arrays and consider their pros and cons. These include polycistronic expression systems, in vitro recombination of large DNA fragments in PAC and BAC vectors, transposon vectors, classical gene targeting by homologous recombination at permissive loci such as ROSA26, targeted transgene placement aided by gene editing systems such as CRISPR/Cas9, and transgene placement by site-specific recombination such as Min-tagging using the Bxb1recombinase.

Neutralizing Anti-Hemagglutinin Monoclonal Antibodies Induced by Gene-Based Transfer Have Prophylactic and Therapeutic Effects on Influenza Virus Infection

Hemagglutinin (HA) of influenza virus is a major target for vaccines. HA initiates the internalization of the virus into the host cell by binding to host sialic acid receptors; therefore, inhibition of HA can significantly prevent influenza virus infection. However, the high diversity of HA permits the influenza virus to escape from host immunity. Moreover, the vaccine efficacy is poor in some high-risk populations (e.g., elderly or immunocompromised patients). Passive immunization with anti-HA monoclonal antibodies (mAbs) is an attractive therapy; however, this method has high production costs and requires repeated inoculations. To address these issues, several methods for long-term expression of mAb against influenza virus have been developed. Here, we provide an overview of methods using plasmid and viral adeno-associated virus (AAV) vectors that have been modified for higher expression of neutralizing antibodies in the host. We also examine two methods of injection, electro-transfer and hydrodynamic injection. Our results show that antibody gene transfer is effective against influenza virus infection even in immunocompromised mice, and antibody expression was detected in the serum and upper respiratory tract. We also demonstrate this method to be effective following influenza virus infection. Finally, we discuss the perspective of passive immunization with antibody gene transfer for future clinical trials.

Efficient Generation of Transgenic Buffalos (Bubalus bubalis) by Nuclear Transfer of Fetal Fibroblasts Expressing Enhanced Green Fluorescent Protein

The possibility of producing transgenic cloned buffalos by nuclear transfer of fetal fibroblasts expressing enhanced green fluorescent protein (EGFP) was explored in this study. When buffalo fetal fibroblasts (BFFs) isolated from a male buffalo fetus were transfected with pEGFP-N1 (EGFP is driven by CMV and Neo is driven by SV-40) by means of electroporation, Lipofectamine-LTX and X-tremeGENE, the transfection efficiency of electroporation (35.5%) was higher than Lipofectamine-LTX (11.7%) and X-tremeGENE (25.4%, P < 0.05). When BFFs were transfected by means of electroporation, more embryos from BFFs transfected with pEGFP-IRES-Neo (EGFP and Neo are driven by promoter of human elongation factor) cleaved and developed to blastocysts (21.6%) compared to BFFs transfected with pEGFP-N1 (16.4%, P < 0.05). A total of 72 blastocysts were transferred into 36 recipients and six recipients became pregnant. In the end of gestation, the pregnant recipients delivered six healthy calves and one stillborn calf. These calves were confirmed to be derived from the transgenic cells by Southern blot and microsatellite analysis. These results indicate that electroporation is more efficient than lipofection in transfecting exogenous DNA into BFFs and transgenic buffalos can be produced effectively by nuclear transfer of BFFs transfected with pEGFP-IRES-Neo.

Human rhinovirus internal ribosome entry site element enhances transgene expression in transfected CHO-S cells

Chinese hamster ovary (CHO) cells are mainly used for recombinant protein production. However, the unstable transgene expression and lower transgene copy numbers are the major issues need to be resolved. Here, eleven internal ribosome entry site (IRES) elements from viral and cellular IRES were evaluated for foreign gene expression in CHO-S cells. We constructed eleven fusing plasmids containing different IRES sequences downstream of the enhanced green fluorescent protein (EGFP) gene. EGFP expression was detected by flow cytometry and the transgene copy number was evaluated by quantitative PCR. The erythropoietin (EPO) protein was also used to assess the stronger IRES. The results showed that IRES from human rhinovirus (HRV) exhibited the highest EGFP expression level under transient and stable transfections. The EGFP expression level of vector with IRES from HRV was related to the gene copy number in stably transfected CHO-S cells. Moreover, IRES from HRV induced higher expression level of EPO compared with one mutant IRES from EMCV in transfected cells. In conclusion, IRES from HRV can function as a strong IRES element for stable expression in CHO-S cells, which could potentially guide more effective foreign gene expression in CHO-S cells.

Efficient Therapeutic Protein Expression Using Retroviral Replicating Vector with 2A Peptide in Cancer Models

Toca 511, a retroviral replicating vector (RRV), uses an internal ribosomal entry site (IRES) to express an optimized yeast cytosine deaminase (yCD2), which converts 5-fluorocytosine to 5-fluorouracil. This configuration is genetically stable in both preclinical mouse models and human clinical trials. However, the use of IRES (∼600 bp) restricts choices of therapeutic transgenes due to limits in RRV genome size. This study replaced IRES with 2A peptides derived from picornaviruses with or without a GSG linker. The data show that GSG-linked 2A (g2A) peptide resulted in higher polyprotein separation efficiency than non-GSG linked 2A peptide. The study also shows that RRV can tolerate insertion of two separate 2A peptides to allow expression of two transgenes without compromising the assembly and function of the virus in addition to insertion of a single 2A peptide to confirm genetic stability with yCD2, green fluorescent protein, and HSV-1 thymidine kinase. In a parallel comparison of the RRV-IRES-yCD2 and RRV-g2A-yCD2 configurations, the study shows the yCD2 protein expressed from RRV-g2A-yCD2 has higher activity, resulting in a higher survival benefit in an intracranial tumor mouse model. These data enable a wider range of potential product candidates that could be developed using the RRV platform.

Expression of a Constitutively Active Human Insulin Receptor in Hippocampal Neurons Does Not Alter VGCC Currents

Memory and cognitive decline are the product of numerous physiological changes within the aging brain. Multiple theories have focused on the oxidative, calcium, cholinergic, vascular, and inflammation hypotheses of brain aging, with recent evidence suggesting that reductions in insulin signaling may also contribute. Specifically, a reduction in insulin receptor density and mRNA levels has been implicated, however, overcoming these changes remains a challenge. While increasing insulin receptor occupation has been successful in offsetting cognitive decline, alternative molecular approaches should be considered as they could bypass the need for brain insulin delivery. Moreover, this approach may be favorable to test the impact of continued insulin receptor signaling on neuronal function. Here we used hippocampal cultures infected with lentivirus with or without IRβ, a constitutively active, truncated form of the human insulin receptor, to characterize the impact continued insulin receptor signaling on voltage-gated calcium channels. Infected cultures were harvested between DIV 13 and 17 (48 h after infection) for Western blot analysis on pAKT and AKT. These results were complemented with whole-cell patch-clamp recordings of individual pyramidal neurons starting 96 h post-infection. Results indicate that while a significant increase in neuronal pAKT/AKT ratio was seen at the time point tested, effects on voltage-gated calcium channels were not detected. These results suggest that there is a significant difference between constitutively active insulin receptors and the actions of insulin on an intact receptor, highlighting potential alternate mechanisms of neuronal insulin resistance and mode of activation.

Simian Immunodeficiency Virus (SIV)-Specific Chimeric Antigen Receptor-T Cells Engineered to Target B Cell Follicles and Suppress SIV Replication

There is a need to develop improved methods to treat and potentially cure HIV infection. During chronic HIV infection, replication is concentrated within T follicular helper cells (Tfh) located within B cell follicles, where low levels of virus-specific CTL permit ongoing viral replication. We previously showed that elevated levels of simian immunodeficiency virus (SIV)-specific CTL in B cell follicles are linked to both decreased levels of viral replication in follicles and decreased plasma viral loads. These findings provide the rationale to develop a strategy for targeting follicular viral-producing (Tfh) cells using antiviral chimeric antigen receptor (CAR) T cells co-expressing the follicular homing chemokine receptor CXCR5. We hypothesize that antiviral CAR/CXCR5-expressing T cells, when infused into an SIV-infected animal or an HIV-infected individual, will home to B cell follicles, suppress viral replication, and lead to long-term durable remission of SIV and HIV. To begin to test this hypothesis, we engineered gammaretroviral transduction vectors for co-expression of a bispecific anti-SIV CAR and rhesus macaque CXCR5. Viral suppression by CAR/CXCR5-transduced T cells was measured in vitro, and CXCR5-mediated migration was evaluated using both an in vitro transwell migration assay, as well as a novel ex vivo tissue migration assay. The functionality of the CAR/CXCR5 T cells was demonstrated through their potent suppression of SIV_mac239 and SIV_E660 replication in in vitro and migration to the ligand CXCL13 in vitro, and concentration in B cell follicles in tissues ex vivo. These novel antiviral immunotherapy products have the potential to provide long-term durable remission (functional cure) of HIV and SIV infections.

A novel bicistronic gene design couples stable cell line selection with a fucose switch in a designer CHO host to produce native and afucosylated glycoform antibodies

The conserved glycosylation site Asn²⁹⁷ of a monoclonal antibody (mAb) can be decorated with a variety of sugars that can alter mAb pharmacokinetics and recruitment of effector proteins. Antibodies lacking the core fucose at Asn²⁹⁷ (afucosylated mAbs) show enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) and increased efficacy. Here, we describe the development of a robust platform for the manufacture of afucosylated therapeutic mAbs by engineering a Chinese hamster ovary (CHO) host cell line to co-express a mAb with GDP-6-deoxy-D-lyxo-4-hexulose reductase (RMD), a prokaryotic enzyme that deflects an intermediate in the de novo synthesis of fucose to a dead-end product, resulting in the production of afucosylated mAb (GlymaxX™ Technology, ProBioGen). Expression of the mAb and RMD genes was coordinated by co-transfection of separate mAb and RMD vectors or use of an internal ribosome entry site (IRES) element to link the translation of RMD with either the glutamine synthase selection marker or the mAb light chain. The GS-IRES-RMD vector format was more suitable for the rapid generation of high yielding cell lines, secreting afucosylated mAb with titers exceeding 6.0 g/L. These cell lines maintained production of afucosylated mAb over 60 generations, ensuring their suitability for use in large-scale manufacturing. The afucosylated mAbs purified from these RMD-engineered cell lines showed increased binding in a CD16 cellular assay, demonstrating enhancement of ADCC compared to fucosylated control mAb. Furthermore, the afucosylation in these mAbs could be controlled by simple addition of L-fucose in the culture medium, thereby allowing the use of a single cell line for production of the same mAb in fucosylated and afucosylated formats for multiple therapeutic indications.

Biosynthesis of Orthogonal Molecules Using Ferredoxin and Ferredoxin-NADP+ Reductase Systems Enables Genetically Encoded PhyB Optogenetics

Transplanting metabolic reactions from one species into another has many uses as a research tool with applications ranging from optogenetics to crop production. Ferredoxin (Fd), the enzyme that most often supplies electrons to these reactions, is often overlooked when transplanting enzymes from one species to another because most cells already contain endogenous Fd. However, we have shown that the production of chromophores used in Phytochrome B (PhyB) optogenetics is greatly enhanced in mammalian cells by expressing bacterial and plant Fds with ferredoxin-NADP+ reductases (FNR). We delineated the rate limiting factors and found that the main metabolic precursor, heme, was not the primary limiting factor for producing either the cyanobacterial or plant chromophores, phycocyanobilin or phytochromobilin, respectively. In fact, Fd is limiting, followed by Fd+FNR and finally heme. Using these findings, we optimized the PCB production system and combined it with a tissue penetrating red/far-red sensing PhyB optogenetic gene switch in animal cells. We further characterized this system in several mammalian cell lines using red and far-red light. Importantly, we found that the light-switchable gene system remains active for several hours upon illumination, even with a short light pulse, and requires very small amounts of light for maximal activation. Boosting chromophore production by matching metabolic pathways with specific ferredoxin systems will enable the unparalleled use of the many PhyB optogenetic tools and has broader implications for optimizing synthetic metabolic pathways.

Generation of Hutat2:Fc Knockin Primary Human Monocytes Using CRISPR/Cas9

The ability of monocytes to travel through the bloodstream, traverse tissue barriers, and aggregate at disease sites endows these cells with the attractive potential to carry therapeutic genes into the nervous system. However, gene editing in primary human monocytes has long been a challenge. Here, we applied the CRISPR/Cas9 system to deliver the large functional Hutat2:Fc DNA fragment into the genome of primary monocytes to neutralize HIV-1 transactivator of transcription (Tat), an essential neurotoxic factor that causes HIV-associated neurocognitive disorder (HAND) in the nervous system. Following homology-directed repair (HDR), ∼10% of the primary human monocytes exhibited knockin of the Hutat2:Fc gene in the AAVS1 locus, the "safe harbor" locus of the human genome, without selection. Importantly, the release of Hutat2:Fc by these modified monocytes protected neurons from Tat-induced neurotoxicity, reduced HIV replication, and restored T cell homeostasis. Moreover, compared with lentiviral transfection, CRISPR-mediated knockin had the advantage of maintaining the migrating function of monocytes. These results establish CRISPR/Cas9-mediated Hutat2:Fc knockin monocytes and provide a potential method to cross the blood-brain barrier for HAND therapy.

Strong xenoprotective function by single-copy transgenes placed sequentially at a permissive locus

BACKGROUND

Multiple xenoprotective transgenes are best grouped at a single locus to avoid segregation during breeding and simplify production of donor animals.

METHODS

We used transgene stacking to place a human CD55 transgene adjacent to a human heme oxygenase 1 construct at the porcine ROSA26 locus. A transgenic pig was analyzed by PCR, RT-PCR, droplet digital PCR, immunohistochemistry, immunofluorescence, and flow cytometry. Resistance to complement-mediated cell lysis and caspase 3/7 activation were determined in vitro.

RESULTS

The ROSA26 locus was retargeted efficiently, and animals were generated by nuclear transfer. RNA and protein analyses revealed abundant expression in all organs analyzed, including pancreatic beta cells. Transgenic porcine kidney fibroblasts were almost completely protected against complement-mediated lysis and showed reduced caspase 3/7 activation.

CONCLUSION

Step-by-step placement enables highly expressed single-copy xenoprotective transgenes to be grouped at porcine ROSA26.

Useful Bicistronic Reporter System for Studying Poly(A) Site-Defining cis Elements and Regulation of Alternative Polyadenylation

The link between polyadenylation (pA) and various biological, behavioral, and pathological events of eukaryotes underlines the need to develop in vivo polyadenylation assay methods for characterization of the cis-acting elements, trans-acting factors and environmental stimuli that affect polyadenylation efficiency and/or relative usage of two alternative polyadenylation (APA) sites. The current protein-based CAT or luciferase reporter systems can measure the polyadenylation efficiency of a single pA site or candidate cis element but not the choice of two APA sites. To address this issue, we developed a set of four new bicistronic reporter vectors that harbor either two luciferase or fluorescence protein open reading frames connected with one Internal Ribosome Entry Site (IRES). Transfection of single or dual insertion constructs of these vectors into mammalian cells demonstrated that they could be utilized not only to quantify the strength of a single candidate pA site or cis element, but also to accurately measure the relative usage of two APA sites at both the mRNA (qRT-PCR) and protein levels. This represents the first reporter system that can study polyadenylation efficiency of a single pA site or element and regulation of two APA sites at both the mRNA and protein levels.

Introduction of Exogenous HSV-TK Suicide Gene Increases Safety of Keratinocyte-Derived Induced Pluripotent Stem Cells by Providing Genetic "Emergency Exit" Switch

Since their invention in 2006, induced Pluripotent Stem (iPS) cells remain a great promise for regenerative medicine circumventing the ethical issues linked to Embryonic Stem (ES) cell research. iPS cells can be generated in a patient-specific manner as an unlimited source of various cell types for in vitro drug screening, developmental biology studies and regenerative use. Having the capacity of differentiating into the cells of all three primary germ layers, iPS cells have high potential to form teratoma tumors. This remains their main disadvantage and hazard which, until resolved, prevents utilization of iPS cells in clinic. Here, we present an approach for increasing iPS cells safety by introducing genetic modification—exogenous suicide gene Herpes Simplex Virus Thymidine Kinase (HSV-TK). Its expression results in specific vulnerability of genetically modified cells to prodrug—ganciclovir (GCV). We show that HSV-TK expressing cells can be eradicated both in vitro and in vivo with high specificity and efficiency with low doses of GCV. Described strategy increases iPS cells safety for future clinical applications by generating “emergency exit” switch allowing eradication of transplanted cells in case of their malfunction.