Tetracycline Transactivator Research Articles

Inducible and reversible SOD2 knockdown in mouse skeletal muscle drives impaired pyruvate oxidation and reduced metabolic flexibility.

Skeletal muscle mitochondrial dysfunction is a key characteristic of aging muscle and contributes to age related diseases such as sarcopenia, frailty, and type 2 diabetes. Mitochondrial oxidative distress has been implicated as a driving factor in these age-related diseases, however whether it is a cause, or a consequence of mitochondrial dysfunction remains to be determined. The development of more flexible genetic models is an important tool to test the mechanistic role of mitochondrial oxidative stress on skeletal muscle metabolic dysfunction. We characterize a new model of inducible and reversible mitochondrial redox stress using a tetracycline controlled skeletal muscle specific short hairpin RNA targeted to superoxide dismutase 2 (iSOD2). iSOD2 KD and control (CON) animals were administered doxycycline for 3- or 12- weeks and followed for up to 24 weeks and mitochondrial respiration and muscle contraction were measured to define the time course of SOD2 KD and muscle functional changes and recovery. Maximum knockdown of SOD2 protein occurred by 6 weeks and recovered by 24 weeks after DOX treatment. Mitochondrial aconitase activity and maximum mitochondrial respiration declined in KD muscle by 12 weeks and recovered by 24 weeks. There were minimal changes in gene expression between KD and CON muscle. Twelve-week KD showed a small, but significant decrease in muscle fatigue resistance. The primary phenotype was reduced metabolic flexibility characterized by impaired pyruvate driven respiration when other substrates are present. The pyruvate dehydrogenase kinase inhibitor dichloroacetate partially restored pyruvate driven respiration, while the thiol reductant DTT did not. We use a model of inducible and reversible skeletal muscle SOD2 knockdown to demonstrate that elevated matrix superoxide reversibly impairs mitochondrial substrate flexibility characterized by impaired pyruvate oxidation. Despite the bioenergetic effect, the limited change in gene expression suggests that the elevated redox stress in this model is confined to the mitochondrial matrix.

Dissociable dorsal medial prefrontal cortex ensembles are necessary for cocaine seeking and fear conditioning in mice

The dorsal medial prefrontal cortex (dmPFC) plays a dual role in modulating drug seeking and fear-related behaviors. Learned associations between cues and drug seeking are encoded by a specific ensemble of neurons. This study explored the stability of a dmPFC cocaine seeking ensemble over 2 weeks and its influence on persistent cocaine seeking and fear memory retrieval. In the first series of experiments, we trained TetTag c-fos-driven-EGFP mice in cocaine self-administration and tagged strongly activated neurons with EGFP during the initial day 7 cocaine seeking session. Subsequently, a follow-up seeking test was conducted 2 weeks later to examine ensemble reactivation between two seeking sessions via c-Fos immunostaining. In the second series of experiments, we co-injected viruses expressing TRE-cre and a cre-dependent inhibitory PSAM-GlyR into the dmPFC of male and female c-fos-tTA mice to enable “tagging” of cocaine seeking ensemble or cued fear ensemble neurons with inhibitory chemogenetic receptors. These c-fos-tTA mice have the c-fos promoter that drives expression of the tetracycline transactivator (tTA). The tTA can bind to the tetracycline response element (TRE) site on the viral construct, resulting in the expression of cre-recombinase, which enables the expression of cre-dependent inhibitory chemogenetic receptors and fluorescent reporters. Then we investigated ensemble contribution to subsequent cocaine seeking and fear recall during inhibition of the tagged ensemble by administering uPSEM792s (0.3 mg/kg), a selective ligand for PSAM-GlyR. In both sexes, there was a positive association between the persistence of cocaine seeking and the proportion of reactivated EGFP+ neurons within the dmPFC. More importantly, inhibition of the cocaine seeking ensemble suppressed cocaine seeking, but not recall of fear memory, while inhibition of the fear ensemble reduced conditioned freezing but not cocaine seeking. The results demonstrate that cocaine and fear recall ensembles in the dmPFC are stable, but largely exclusive from one another.

Tissue-specific inducible IL-33 expression elicits features of eosinophilic esophagitis

BackgroundIL-33 is a type 2 inflammatory cytokine that is elevated in the esophageal epithelium of EoE subjects. We previously developed a mouse model of EoE dependent on constitutive overexpression of IL-33 from the esophageal epithelium (EoE33). ObjectiveOur objective was to develop an inducible, IL-33-dependent model of EoE and examine induction of EoE-associated pathology. MethodsWe utilized a tetracycline-inducible system to express IL-33 in the esophagus by generating two transgenic mice. The first (iSophagus) expresses a reverse tetracycline transactivator (rtTA) from the esophageal epithelium. The second (TRE33) features a tetracycline-response element driving expression of IL-33. When crossed, these mice generate an inducible model of EoE (iEoE33). Mice were administered doxycycline-infused chow for up to 2 weeks. Cytokines were assessed by ELISA or bead-based multiplex. T cells were assessed by flow cytometry. Pathology was assessed by histology and immunohistochemistry for IL-33, eosinophil peroxidase, CD4, and Ki-67. iEoE33 was treated with steroids and crossed with IL-13-/- mice. For detailed Methods, please see the Methods section in this article's Online Repository at www.jacionline.org. ResultsDoxycycline-treated iEoE33 mice demonstrated expression of IL-33 in the esophageal epithelium, and esophageal pathology including eosinophilia, CD4+ cell infiltrate, basal zone hyperplasia, and dilated intercellular spaces. These findings became pronounced on day 7 of induction, were accompanied by weight loss and esophageal thickening, and were steroid responsive and IL-13 dependent. ConclusionInducible IL-33 expression in the esophageal epithelium elicited features pathognomonic of EoE. iEoE33 enables investigation of EoE disease mechanisms as well as initiation, progression, and resolution.

Identification of a gene promoter active in Lucilia sericata larval salivary glands using a rapid transient expression assay

Tissue-specific gene promoters are desired as they provide the specificity needed for control of gene expression in transgenic animals. Here we describe a relatively rapid two-component transient expression assay that was used to identify a gene promoter active in the larval salivary glands of the green blow fly, Lucilia sericata. Sterile L.sericata maggots are widely used for wound debridement. A larval salivary gland gene promoter could be used to make maggots that secrete factors for enhanced wound therapy. Embryos from a line that carry a tetracycline transactivator (tTA)-activated red fluorescent protein gene were injected with plasmid DNA with the tTA gene driven by a constitutive or tissue-specific gene promoter. The hatched larvae were reared on diet and then examined for red fluorescence. A promoter from the LsCG30371 gene was active in the larval salivary glands. The tissue-specificity of the promoter was subsequently confirmed with stable transgenic lines that carried the LsCG30371-tTA gene. The relatively rapid transient expression assay could potentially be used to determine the tissue-specificity of other gene promoters. Further, the stable LsCG30371-tTA lines could be used to make sterile maggots that secrete factors from the salivary glands for enhanced wound healing.

Generation of three iPSC lines with inducible systems to be used in Angelman syndrome research

The neurodevelopmental disorder Angelman syndrome (AS) has an incidence of 1:15.000 live births and is caused by absence of UBE3A protein, showing imprinted gene expression in the brain. Imprinted genes are controlled by differentially methylated regions resulting in parent-of-origin dependent gene expression. Two iPS cell lines derived from patients with AS and one healthy control iPSC line were used to integrate a 3rd generation reverse tetracycline transactivator protein (rtTA3) into the AAVS1 locus on chromosome 19. The rtTA allows tetracycline-dependent activation of an inducible promoter that can be introduced at a position of interest in the cell lines described here.

Abstract 2968: TWIST1-induced suppression of oncogene-induced senescence in non-small cell lung cancer requires the transactivation domain of TWIST1

Abstract Non-small cell lung carcinoma (NSCLC) is a major cause of cancer mortality. High expression of the epithelial-to-mesenchymal transition transcription factor TWIST1 is strongly associated with metastatic cancers and treatment resistance. Additionally, TWIST1 can upregulate O-GlcNAcylation which (1) is required to suppress fail-safe programs such as oncogene (KRasG12D)-induced senescence (OIS) to accelerate tumorigenesis in primary NSCLC tumors, and (2) is a potential modulator of DNA repair/radiation response. To decipher the domains and transcriptional targets required for tumorigenicity and radioresistance, we created a novel genetically engineered mouse model (GEMM) allowing tetracycline-inducible expression in the lung epithelium (via lung specific CCSP-reverse tetracycline transactivator (C)) of KRasG12D (R) with Twist1wt (T) or with Twist1F191G transactivation-null mutant (F). CRT mice had shorter tumor-free survival and more aggressive tumors compared to CR/CRF mice indicating that the Twist1 transactivation domain is required for Twist1-dependent tumorigenesis acceleration. Also, Twist1wt expression promoted radioresistance in cell lines and GEMMs. Contrary to CRT, CRF showed a progressive loss of Twist1F191G expression over time suggesting no functionality/no selective advantage. CRT lung tumors had higher proliferation (Ki67) and lower cell-cycle arrest (p16) compared to CR/CRF suggesting that the transactivation domain of Twist1 is important for the suppression of OIS. Supporting these data, we observed in non-cancer Human Bronchial Epithelial Cell (HBEC) that the co-expression of human TWIST1wt (HBEC-TWIST1wt) could suppress HRasG12V-induced senescence while the transactivation-null TWIST1F187G mutant (HBEC-TWIST1F187G) could not. Additionally, HBEC expressing HRasG12V-TWIST1wt had enhanced tumorigenic/invasive programs. Interestingly, we observed that the inhibition of O-GlcNAcylation rescued OIS in HBEC-HRasG12V-TWIST1wt while the stimulation of O-GlcNAcylation in HBEC-HRasG12V-TWIST1F187G suppressed OIS. Furthermore, TWIST1wt expression with HRasG12V modulated MYC downstream targets and the inhibition of MYC activity using the novel MYC inhibitor MYCi975 in HBEC-HRasG12V-TWIST1wt also rescued OIS induction. Altogether, these results suggest that TWIST1 may suppress OIS via MYC signaling and nominate MYCi975 as a means to activate latent OIS programs. In this context, MYC inhibiting strategies could serve as a therapeutic sensitizer for TWIST1-positive NSCLC. This work and our future studies on TWIST1 toward the control of OIS, O-GlcNAcylation and of mechanisms of radioresistance may help to identify new potential NSCLC therapeutic strategies. Citation Format: Audrey M. Lafargue, Hailun Wang, Sivarajan T. Chettiar, Rajendra P. Gajula, Amol C. Shetty, Yang Song, Brian W. Simons, Triet Nguyen, Christine Lam, Francesca A. Carrieri, Caleb Smack, Nick Connis, Dipanwita Dutta Chowdhury, Jinhee Chang, Danielle Council, Katriana Nugent, Ismaeel Siddiqui, Kekoa Taparra, Mohammad Rezaee, Natasha Zachara, Zachary S. Morris, Christopher McFarland, Sarki Abba Abdulkadir, Christine L. Hann, Phuoc T. Tran. TWIST1-induced suppression of oncogene-induced senescence in non-small cell lung cancer requires the transactivation domain of TWIST1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2968.

Doxycycline for transgene control disrupts gut microbiome diversity without compromising acute neuroinflammatory response

The tetracycline transactivator (tTA) system provides controllable transgene expression through oral administration of the broad-spectrum antibiotic doxycycline. Antibiotic treatment for transgene control in mouse models of disease might have undesirable systemic effects resulting from changes in the gut microbiome. Here we assessed the impact of doxycycline on gut microbiome diversity in a tTA-controlled model of Alzheimer’s disease and then examined neuroimmune effects of these microbiome alterations following acute LPS challenge. We show that doxycycline decreased microbiome diversity in both transgenic and wild-type mice and that these changes persisted long after drug withdrawal. Despite the change in microbiome composition, doxycycline treatment had minimal effect on basal transcriptional signatures of inflammation the brain or on the neuroimmune response to LPS challenge. Our findings suggest that central neuroimmune responses may be less affected by doxycycline at doses needed for transgene control than by antibiotic cocktails at doses used for experimental microbiome disruption.

Construction of foot-and-mouth disease virus like particles-induced expression vectors and screening of BHK-21 cell pools

Transient expression is the major method to express foot-and-mouth disease virus (FMDV) capsid proteins in mammalian cells. To achieve stable expression of FMDV capsid proteins and efficient assembly of virus like particles (VLPs) in cells, the plasmids of piggyBac (PB) transposon-constitutive expression and PB transposon-tetracycline (Tet) inducible expression vectors were constructed. The function of the plasmids was tested by fluorescent proteins. By adding antibiotics, the constitutive cell pools (C-WT, C-L127P) expressing P12A3C (WT/L127P) genes and the inducible cell pools (I-WT, I-L127P) expressing P12A3C (WT/L127P) genes were generated. The genes of green fluorescent protein, 3C protease and reverse tetracycline transactivator (rtTA) were integrated into chromosome, which was confirmed by fluorescence observation and PCR testing. The cell pool I-L127P has a stronger production capacity of capsid proteins and VLPs, which was confirmed by Western blotting and enzyme linked immunosorbent assay (ELISA), respectively. In conclusion, inducing the chromosomal expression of FMDV capsid proteins was firstly reported, which may facilitate the technical process of mammalian production of FMDV VLPs vaccine and the construction of mammalian inducible expression systems for other proteins.

In vivo recording of the circadian calcium rhythm in Prokineticin 2 neurons of the suprachiasmatic nucleus

Prokineticin 2 (Prok2) is a small protein expressed in a subpopulation of neurons in the suprachiasmatic nucleus (SCN), the primary circadian pacemaker in mammals. Prok2 has been implicated as a candidate output molecule from the SCN to control multiple circadian rhythms. Genetic manipulation specific to Prok2-producing neurons would be a powerful approach to understanding their function. Here, we report the generation of Prok2-tTA knock-in mice expressing the tetracycline transactivator (tTA) specifically in Prok2 neurons and an application of these mice to in vivo recording of Ca2+ rhythms in these neurons. First, the specific and efficient expression of tTA in Prok2 neurons was verified by crossing the mice with EGFP reporter mice. Prok2-tTA mice were then used to express a fluorescent Ca2+ sensor protein to record the circadian Ca2+ rhythm in SCN Prok2 neurons in vivo. Ca2+ in these cells showed clear circadian rhythms in both light–dark and constant dark conditions, with their peaks around midday. Notably, the hours of high Ca2+ nearly coincided with the rest period of the behavioral rhythm. These observations fit well with the predicted function of Prok2 neurons as a candidate output pathway of the SCN by suppressing locomotor activity during both daytime and subjective daytime.

Progressive tauopathy disrupts breathing stability and chemoreflexes during presumptive sleep in mice.

Rationale: Although sleep apnea occurs in over 50% of individuals with Alzheimer's Disease (AD) or related tauopathies, little is known concerning the potential role of tauopathy in the pathogenesis of sleep apnea. Here, we tested the hypotheses that, during presumptive sleep, a murine model of tauopathy (rTg4510) exhibits: 1) increased breathing instability; 2) impaired chemoreflex function; and 3) exacerbation of these effects with tauopathy progression. Methods: rTg4510 mice initially develop robust tauopathy in the hippocampus and cortex, and eventually progresses to the brainstem. Type I and II post-sigh apnea, Type III (spontaneous) apnea, sigh, and hypopnea incidence were measured in young adult (5-6months; n = 10-14/group) and aged (13-15months; n = 22-24/group) non-transgenic (nTg), monogenic control tetracycline transactivator, and bigenic rTg4510 mice using whole-body plethysmography during presumptive sleep (i.e., eyes closed, curled/laying posture, stable breathing for >200 breaths) while breathing room air (21% O2). Peripheral and central chemoreceptor sensitivity were assessed with transient exposures (5min) to hyperoxia (100% O2) or hypercapnia (3% and 5% CO2 in 21% O2), respectively. Results: We report significant increases in Type I, II, and III apneas (all p < 0.001), sighs (p = 0.002) and hypopneas (p < 0.001) in aged rTg4510 mice, but only Type III apneas in young adult rTg4510 mice (p < 0.001) versus age-matched nTg controls. Aged rTg4510 mice exhibited profound chemoreflex impairment versus age matched nTg and tTA mice. In rTg4510 mice, breathing frequency, tidal volume and minute ventilation were not affected by hyperoxic or hypercapnic challenges, in striking contrast to controls. Histological examination revealed hyperphosphorylated tau in brainstem regions involved in the control of breathing (e.g., pons, medullary respiratory column, retrotrapezoid nucleus) in aged rTg4510 mice. Neither breathing instability nor hyperphosphorylated tau in brainstem tissues were observed in young adult rTg4510 mice. Conclusion: Older rTg4510 mice exhibit profound impairment in the neural control of breathing, with greater breathing instability and near absence of oxygen and carbon-dioxide chemoreflexes. Breathing impairments paralleled tauopathy progression into brainstem regions that control breathing. These findings are consistent with the idea that tauopathy per se undermines chemoreflexes and promotes breathing instability during sleep.

Uniform transgene activation in Tet-On systems depends on sustained rtTA expression

Application of the tetracycline-inducible gene expression system (Tet-On) in human induced pluripotent stem cells (hiPSCs) has become a fundamental transgenic tool owing to its regulatable gene expression. One of the major hurdles in hiPSC application is non-uniform transgene activation. Here, we report that the supplementation of reverse tetracycline transactivator (rtTA) in polyclonal hiPSCs populations can achieve the uniform transgene activation of Tet-On. Furthermore, the choice of antibiotic selection markers connected by an internal ribosomal entry site (IRES) can influence the expression of upstream transgenes. In particular, expression of the rtTA is more uniform in cell populations when linked to puromycin as compared to neomycin, obviating the need for sub-cloning or supplementation of rtTA. Finally, to expand the range of applications, we adopted our findings to tetracycline-inducible MyoD vector (Tet-MyoD). Our Tet-MyoD promises efficient, robust, and reproducible directed myogenic differentiation of hiPSCs.

#4976 DIFFERENTIAL ROLES OF REGNASE3 IN RESIDENT MACROPHAGE VERSUS TUBULAR EPITHELIAL CELLS IN THE HEALTHY OR POSTISCHEMIC KIDNEY

Abstract Background and Aims Acute kidney injury (AKI) is a prevalent yet severe condition that occurs in clinical settings. The prognosis for AKI is poor, with many patients progressing to AKD, CKD, and even ESKD especially in those who were admitted to the ICU. RNA-binding proteins (RBPs) are a class of proteins that play a vital role in regulating gene expression and have been implicated in a wide range of diseases. Regnase3 is a member of the Regnase RBPs family and has been shown to promote inflammation by increasing TNF in macrophages. Despite this knowledge, the full extent of the role played by Regnase3 in AKI remains unknown. Therefore, we hypothesized that Regnase3 plays a role in both macrophages and tubular epithelial cells, influencing inflammation and tubular repair in AKI. Method In order to investigate the role of Regnase3 in kidney injury, a series of genetically-modified mice were developed on the C57BL/6J genetic background. These mice included the paired box gene 8 (Pax8)-reverse tetracycline transactivator (rTtA, Pax8rTtA), tetracycline resistance protein (TetO)-Cre (TetOCre), transgenic receptor activator of nuclear factor kappa-Β (Rank)-Cre (RankCre), and Regnase3 floxed (Regnase-3fl/fl) mice. Using these genetically modified mice, we applied a range of experimental animal models to study the effects of Regnase3 on kidney injury, including unilateral kidney ischemia-reperfusion surgery with or without nephrectomy and nephrocalcinosis-related kidney injury. Additionally, we employed in vitro models utilizing primary cells to study Regnase3 on the cellular level. Furthermore, we utilized scRNA-seq and RNA-seq to investigate the underlying mechanisms of Regnase3’s function. Results We conducted a thorough investigation and discovered that the Regnase3 is highly expressed in macrophages located within the kidney after AKI. The scRNA-seq showed the expression Regnase3 positively correlated with the phagocytosis, chemokines, and monocyte maturation. Furthermore, Rank-Regnase3 mice suffered from more inflammation and kidney injury after AKI, characterized by an increase in CCR2 positive leukocyte infiltration. Additionally, in vitro experiments revealed that Regnase3 is involved in modulating macrophage behavior, acting as a regulator of macrophage polarization towards an M1 and M2 phenotype and influencing the capacity of cell migration. These findings indicate that Regnase3 is essential in the migration of macrophages after AKI, which contribute to both early phase inflammation and progression towards AKI- CKD. Next, we aimed to examine the role of Regnase3 in the context of renal tubule injury. We observed that Regnase3 is highly expressed in healthy renal tubules, but its expression is reduced following injury. Through in silico, in vivo and in vitro experiments, we found that Regnase3 controls early apoptosis, cell death, proliferation, and wound healing capability of tubular epithelial cells. These effects contribute to kidney injury in postischemic kidneys. Additionally, we discovered that the deletion of Regnase3 provides protection against ischemic AKI (Figure 1). Mechanistically, Regnase3 targets pre-RNA and modulates alternative splicing by increasing the proportion of targeted skipped exon events and decreasing the probability of targeted retained intron events. Overall, our findings indicate that Regnase3 plays a vital role in tubular epithelial cells in the response to kidney injury by regulating alternative splicing. Conclusion In summary, our findings indicate that Regnase3 contributes to kidney injury in postischemic kidneys. However, the impact of Regnase3 is contingent upon the specific cell lineage in question. The Rank-Regnase3 leads to an exacerbation of kidney injury by increasing macrophage recruitment, whereas the Pax8-Regnase3 leads to an improvement in kidney injury through its effects on cell death and wound healing capability of tubular epithelial cells. Therefore, the role of Regnase3 in kidney injury is dependent on the cell lineage, which ultimately determines the detrimental or beneficial impact on kidney injury.

Development of transgenic corn planthopper Peregrinus maidis that express the tetracycline transactivator.

The corn planthopper, Peregrinus maidis, is a vector of several maize viruses and is consequently a significant agricultural pest in many tropical and subtropical regions. As P. maidis has developed resistance to insecticides, the aim of this study was to develop transgenic P. maidis strains that could be used for future genetic biocontrol programs. To facilitate the identification of transgenic P. maidis, we isolated and characterized the promoters for the P. maidis ubiquitin-like and profilin genes. Transient expression assays with P. maidis embryos showed that both promoters were active. Transgenic lines were established using piggyBac vectors and fluorescent protein marker genes. The lines carried an auto-regulated tetracycline transactivator (tTA) gene, which has been widely used to establish conditional lethal strains in other insect species. The transgenic lines showed low levels of tTA expression but were viable on diet with or without doxycycline, which inhibits the binding of tTA to DNA. We discuss possible modifications to the tTA overexpression system that could lead to the successful development of conditional lethal strains. To our knowledge, this is the first report of a transgenic Hemiptera. The approach we have taken could potentially be applied to other Hemiptera and, for P. maidis, the technology will facilitate future functional genomics studies.

Effects of antibiotics on the in vitro expression of tetracycline-off constructs and the performance of Drosophila suzukii female-killing strains.

Genetic control strategies such as the Release of Insects Carrying a Dominant Lethal (RIDL) gene and Transgenic Embryonic Sexing System (TESS) have been demonstrated in the laboratory and/or deployed in the field. These strategies are based on tetracycline-off (Tet-off) systems which are regulated by antibiotics such as Tet and doxycycline (Dox). Here, we generated several Tet-off constructs carrying a reporter gene cassette mediated by a 2A peptide. Different concentrations (0.1, 10, 100, 500, and 1,000μg/mL) and types (Tet or Dox) of antibiotics were used to evaluate their effects on the expression of the Tet-off constructs in the Drosophila S2 cells. One or both of the two concentrations, 100 and 250μg/mL, of Tet or Dox were used to check the influence on the performances of a Drosophila suzukii wild-type strain and female-killing (FK) strains employing TESS. Specifically, the Tet-off construct for these FK strains contains a Drosophila suzukii nullo promoter to regulate the tetracycline transactivator gene and a sex-specifically spliced pro-apoptotic gene hid Ala4 to eliminate females. The results suggested that the in vitro expression of the Tet-off constructs was controlled by antibiotics in a dose-dependent manner. ELISA experiments were carried out identifying Tet at 34.8ng/g in adult females that fed on food supplemented with Tet at 100μg/mL. However, such method did not detect Tet in the eggs produced by antibiotic-treated flies. Additionally, feeding Tet to the parents showed negative impact on the fly development but not the survival in the next generation. Importantly, we demonstrated that under certain antibiotic treatments females could survive in the FK strains with different transgene activities. For the strain V229_M4f1 which showed moderate transgene activity, feeding Dox to fathers or mothers suppressed the female lethality in the next generation and feeding Tet or Dox to mothers generated long-lived female survivors. For the strain V229_M8f2 which showed weak transgene activity, feeding Tet to mothers delayed the female lethality for one generation. Therefore, for genetic control strategies employing the Tet-off system, the parental and transgenerational effects of antibiotics on the engineered lethality and insect fitness must be carefully evaluated for a safe and efficient control program.

Painting memory engram by biologically active messengers –The molecular time travel for the search of memory

Using MRI and PET methods, neuroscience has made significant progress in understanding the episodic events of the human brain under varied cognitive situations throughout the last century. However, the higher resolutions of the memory locus, which consists of a neuro-glial ensemble for episodic memory, are unclear and must be clarified. Additionally, attempts have been made to create new nano technologies for mapping complete brains and related engrams with single neuro-glial accuracy and resolution in the hopes of unlocking the secrets of the brain by delving into Brain Activity Map (BAM). This hypothetical research is the first of its kind to suggest a novel method for understanding episodic memory in mouse brains by mapping brain activity at the functional connectome (engram) level and focused on neuro-glia-ECM (Extracellular Matrix). I propose to paint the memory engram at the neuro glia-ECM canvas of the mouse brain by engineering and inserting novel "Biologically Active Messengers: Bidirectional Messengers (BM)s/ Alternative Clones (AC)s and Transcriptional/ Translational Messenger (TM)s" coupled with different colour tags into transgenic mice via Transposon and Recombination, followed by behavioural analysis and Clarity. The BMs will be produced in all neuro-glial cells via a bicistronic promoter (Neuro-glia specific promoter + Tetracycline Responsive Element) led by a tetracycline transactivator gene driven by an immediate early gene (c-Fos/ Arc), whereas the TMs will be expressed via an endogenous promoter. The viability of all constructions (BMs, ACs, and TMs) as well as the process of painting will be tested in cortical/ hippocampal culture by chemically generating long term potentiation (cLTP). Fear consolidation (Fear context and Recall by contextual cue) tests will be administered to adult transgenic mice, followed by Clarity coupled Immunostaining to investigate the neuro-glia-ECM ensemble after whole brain imaging using a Light Sheet Microscope. Finally, the steady state behaviour of normal mice will be compared to the episodic picture of a colourful painted engram. At both the functional connectome and activity levels, this holistic painting method will highlight cognition over multiple timelines of a working memory region. Bidirectional Messenger (Biological Boomerang) has huge implications in neuropsychiatric illness, generation of artificial blood, cancer treatment, and regenerative medicine in the near future, according to my intuition.

Limiting Transactivator Amounts Contribute to Transgene Mosaicism in Tet-On All-in-One Systems.

MicroRNAs play an essential role in cell homeostasis and have been proposed as therapeutic agents. One strategy to deliver microRNAs is to genetically engineer target cells to express microRNAs of interest. However, to control dosage and timing, as well as to limit potential side-effects, microRNAs' expression should ideally be under exogenous, inducible control. Conditional expression of miRNA-based short hairpin RNAs (shRNAmirs) via gene regulatory circuits such as the Tet-system is therefore a promising strategy to control shRNAmirs' expression in research and therapy. Single vector approaches like Tet-On all-in-one designs are more compatible with potential clinical applications by providing the Tet-On system components in a single round of genetic engineering. However, all-in-one systems often come at the expense of heterogeneous and unstable expression. In this study, we aimed to understand the causes that lead to such erratic transgene expression. By using a reporter cell, we found that the degree of heterogeneity mostly correlated with reverse tetracycline transactivator (rtTA) expression levels. Moreover, the targeted integration of a potent rtTA expression cassette into a genomic safe harbor locus functionally rescued previously silenced rtTA-responsive transcription units. Overall, our results suggest that ensuring homogenous and stable rtTA expression is essential for the robust and reliable performance of future Tet-On all-in-one designs.

Broadly Applicable, Virus-Free Dual Reporter Assay to Identify Compounds Interfering with Membrane Fusion: Performance for HSV-1 and SARS-CoV-2.

Membrane fusion constitutes an essential step in the replication cycle of numerous viral pathogens, hence it represents an important druggable target. In the present study, we established a virus-free, stable reporter fusion inhibition assay (SRFIA) specifically designed to identify compounds interfering with virus-induced membrane fusion. The dual reporter assay is based on two stable Vero cell lines harboring the third-generation tetracycline (Tet3G) transactivator and a bicistronic reporter gene cassette under the control of the tetracycline responsive element (TRE3G), respectively. Cell–cell fusion by the transient transfection of viral fusogens in the presence of doxycycline results in the expression of the reporter enzyme secreted alkaline phosphatase (SEAP) and the fluorescent nuclear localization marker EYFPNuc. A constitutively expressed, secreted form of nanoluciferase (secNLuc) functioned as the internal control. The performance of the SRFIA was tested for the quantification of SARS-CoV-2- and HSV-1-induced cell–cell fusion, respectively, showing high sensitivity and specificity, as well as the reliable identification of known fusion inhibitors. Parallel quantification of secNLuc enabled the detection of cytotoxic compounds or insufficient transfection efficacy. In conclusion, the SRFIA reported here is well suited for high-throughput screening for new antiviral agents and essentially will be applicable to all viral fusogens causing cell–cell fusion in Vero cells.

Lineage Tracing of Inducible Fluorescently-Labeled Stem Cells in the Adult Mouse Brain.

A telomerase reverse transcriptase (Tert) lineage-tracing mouse line was developed to investigate the behavior and fate of adult tissue stem cells, by crossing the 'Tet-On' system oTet-Cre mouse with a novel reverse tetracycline transactivator (rtTA) transgene linked to the Tert promoter, which we have demonstrated marks a novel population of adult brain stem cells. Here, administration of the tetracycline derivative doxycycline to mTert-rtTA::oTet-Cre mice will indelibly mark a population of cells that express a 4.4 kb fragment of the promoter region of the gene Tert. When combined the Rosa-mTmG reporter, mTert-rtTA::oTet-Cre::Rosa-mTmG mice will express membrane tdTomato (mTomato) until doxycycline treatment induces the replacement of mTomato expression with membrane EGFP (mGFP) in cells that also express Tert. Therefore, when these triple-transgenic lineage tracing mice receive doxycycline (the "pulse" period during which TERT expressing cells are marked), these cells will become indelibly marked mGFP+ cells, which can be tracked for any desirable amount of time after doxycycline removal (the "chase" period), even if Tert expression is subsequently lost. Brains are then perfusion-fixed and processed for immunofluorescence and other downstream applications in order to interpret changes to stem cell activation, proliferation, lineage commitment, migration to various brain niches, and differentiation to mature cell types. Using this system, any rtTA mouse can be mated to oTet-Cre and a Rosa reporter to conduct doxycycline-inducible "pulse-chase" lineagetracing experiments using markers of stem cells.

Generation of a human extended pluripotent stem cell line (SKLRMe002-A) carrying a doxycycline-inducible Cas9 expression cassette

Human extended pluripotent stem cell (hEPS) is a novel type of pluripotent stem cell, which possesses bi-potency towards both embryonic and extraembryonic lineages. Here, we generated a hEPS cell line (hEPS1-iCas9-B) from the cell line named hEPS1, carrying a doxycycline-inducible Cas9 expression cassette along with a constitutive reverse tetracycline transactivator (M2rtTA) expression cassette at the AAVS1 locus, thus we could efficiently generate genetically modified hEPS for studies. This cell lined remained self-renewal, differentiation potential and normal karyotype. Meanwhile, it showed robust transcriptional expression of Cas9 with doxycycline induction and could target the site where the sgRNA guided.

Cell Type-Specific Genetic Manipulation and Impaired Circadian Rhythms in Vip tTA Knock-In Mice.

The suprachiasmatic nucleus (SCN), the central circadian clock in mammals, is a neural network consisting of various types of GABAergic neurons, which can be differentiated by the co-expression of specific peptides such as vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP). VIP has been considered as a critical factor for the circadian rhythmicity and synchronization of individual SCN neurons. However, the precise mechanisms of how VIP neurons regulate SCN circuits remain incompletely understood. Here, we generated Vip tTA knock-in mice that express tetracycline transactivator (tTA) specifically in VIP neurons by inserting tTA sequence at the start codon of Vip gene. The specific and efficient expression of tTA in VIP neurons was verified using EGFP reporter mice. In addition, combined with Avp-Cre mice, Vip tTA mice enabled us to simultaneously apply different genetic manipulations to VIP and AVP neurons in the SCN. Immunostaining showed that VIP is expressed at a slightly reduced level in heterozygous Vip tTA mice but is completely absent in homozygous mice. Consistently, homozygous Vip tTA mice showed impaired circadian behavioral rhythms similar to those of Vip knockout mice, such as attenuated rhythmicity and shortened circadian period. In contrast, heterozygous mice demonstrated normal circadian behavioral rhythms comparable to wild-type mice. These data suggest that Vip tTA mice are a valuable genetic tool to express exogenous genes specifically in VIP neurons in both normal and VIP-deficient mice, facilitating the study of VIP neuronal roles in the SCN neural network.