Inducible, tightly regulated and non-leaky neuronal gene expression in mice

Sterilization of Channel Catfish (Ictalurus punctatus) via Overexpression of bax Gene Regulated by a Tet-off System in the Primordial Germ Cells

Transgenic technologies have been used for genetic improvement of catfish performance with notable success. However, these developments are useless from a commercialization standpoint without extremely efficient confinement. Transgenic sterilization has the potential to accomplish 100% reproductive confinement and avoid genetic exchange between transgenic or domestic genotypes and wild populations. The present study reports a novel sterilization method for channel catfish by overexpressing the pro-apoptosis gene bax, specifically in the primordial germ cells, to inhibit their proliferation. Three transgenic constructs were electroporated into channel catfish one-cell embryos, including Nanos-nanos, Nanos-dnd, and Dazl-vasa. Transgene integration, gonad development, and sex ratio were evaluated in P1 and F1 generations. The transgene was successfully integrated into the channel catfish genome, with variable rates depending on each construct. Mosaicism of transgene integration was widely evident in the P1 fish, as expected. All three constructs showed similar efficacy for sterilizing P1 male channel catfish, with approximately half of all males showing little to no gonadal development, resulting in a significantly lower (p < 0.05) gonadosomatic index (GSI) when compared to the control at four years of age. The same trend occurred but with lower efficacy in P1 females, with approximately one-third showing little gonadal development at four years of age. This technology is potentially useful for generating sterile male fish, where the overexpression of the bax gene can lead to reduced or no gonadal development, presumably due to the death of primordial germ cells.

PLP1-Targeting Antisense Oligonucleotides Improve FOXG1 Syndrome Mice

FOXG1 syndrome is a rare neurodevelopmental disorder of the telencephalon, for which there is no cure. Underlying heterozygous pathogenic variants in the Forkhead Box G1 (FOXG1) gene with resulting impaired or loss of FOXG1 function lead to severe neurological impairments. Here, we report a patient with a de novo pathogenic single nucleotide deletion c.946del (p.Leu316Cysfs*10) of the FOXG1 gene that causes a premature protein truncation. To study this variant in vivo, we generated and characterized Foxg1 c946del mice that recapitulate hallmarks of the human disorder. Accordingly, heterozygous Foxg1 c946del mice display neurological symptoms with aberrant neuronal networks and increased seizure susceptibility. Gene expression profiling identified increased oligodendrocyte- and myelination-related gene clusters. Specifically, we showed that expression of the c946del mutant and of other pathogenic FOXG1 variants correlated with overexpression of proteolipid protein 1 (Plp1), a gene linked to white matter disorders. Postnatal administration of Plp1-targeting antisense oligonucleotides (ASOs) in Foxg1 c946del mice improved neurological deficits. Our data suggest Plp1 as a new target for therapeutic strategies mitigating disease phenotypes in FOXG1 syndrome patients.

Targeting 14-3-3θ-mediated TDP-43 pathology in amyotrophic lateral sclerosis and frontotemporal dementia mice

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by cytoplasmic deposition of the nuclear TAR-binding protein 43 (TDP-43). Although cytoplasmic re-localization of TDP-43 is a key event in the pathogenesis of ALS/FTD, the underlying mechanisms remain unknown. Here, we identified a non-canonical interaction between 14-3-3θ and TDP-43, which regulates nuclear-cytoplasmic shuttling. Neuronal 14-3-3θ levels were increased in sporadic ALS and FTD with TDP-43 pathology. Pathogenic TDP-43 showed increased interaction with 14-3-3θ, resulting in cytoplasmic accumulation, insolubility, phosphorylation, and fragmentation of TDP-43, resembling pathological changes in disease. Harnessing this increased affinity of 14-3-3θ for pathogenic TDP-43, we devised a gene therapy vector targeting TDP-43 pathology, which mitigated functional deficits and neurodegeneration in different ALS/FTD mouse models expressing mutant or non-mutant TDP-43, including when already symptomatic at the time of treatment. Our study identified 14-3-3θ as a mediator of cytoplasmic TDP-43 localization with implications for ALS/FTD pathogenesis and therapy.

Tetracycline response element driven Cre causes ectopic recombinase activity independent of transactivator element

OBJECTIVE

Tamoxifen is widely used for inducible Cre-LoxP systems but has several undesirable side effects for researchers investigating metabolism or energy balance, including weight loss, lipoatrophy, and drug incorporation into lipid stores. For this reason, we sought to determine whether a doxycycline-inducible system would be more advantageous for adipocyte-specific Cre mouse models, but serendipitously discovered widespread ectopic tetracycline response element Cre (TRE-Cre) recombinase activity.

METHODS

Adipocyte-specific tamoxifen- and doxycycline-inducible Cre mice were crossed to fluorescent Cre reporter mice and visualized by confocal microscopy to assess efficiency and background activity. TRE-Cre mice were crossed to stop-floxed diphtheria toxin mice to selectively ablate cells with background Cre activity.

RESULTS

Tamoxifen- and doxycycline-inducible systems performed similarly in adipose tissues, but ectopic Cre recombination was evident in numerous other cell types of the latter, most notably neurons. The source of ectopic Cre activity was isolated to the TRE-Cre transgene, driven by the pTet (tetO7) tetracycline-inducible promoter. Ablation of cells with ectopic recombination in mice led to stunted growth, diminished survival, and reduced brain mass.

CONCLUSIONS

These results indicate that tamoxifen- and doxycycline-inducible adipocyte-specific Cre mouse models are similarly efficient, but the TRE-Cre component of the latter is inherently leaky. TRE-Cre background activity is especially pronounced in the brain and peripheral nerve fibers, and selective ablation of these cells impairs mouse development and survival. Caution should be taken when pairing TRE-Cre with floxed alleles that have defined roles in neural function, and additional controls should be included when using this model system.

Microinjection of Zygotes for CRISPR/Cas9-Mediated Insertion of Transgenes into the Murine Rosa26 Safe Harbor

Genetically modified (GM) mice are widely used in biomedical research because they can address complex questions in an in-vivo setting that could not otherwise be addressed in-vitro. Microinjection of zygotes remains the most common technique to generate GM animals to date. Here, we describe the targeted insertion (knock-in) of transgenes by microinjection of 1-cell or 2-cell stage embryos into the murine Rosa26 safe harbor.

Disruption of PAK3 Signaling in Social Interaction Induced cFos Positive Cells Impairs Social Recognition Memory

P21-activated kinase 3 (PAK3) gene mutations are linked to several neurodevelopmental disorders, but the underlying mechanisms remain unclear. In this study, we used a tetracycline-inducible system to control the expression of a mutant PAK3 (mPAK3) protein in immediate early gene, namely cFos, positive cells to disrupt PAK signaling, specifically in cells activated by social interaction in transgenic mice. We show that the expression of mPAK3-GFP proteins was in cFos-expressing excitatory and inhibitory neurons in various brain regions, such as the cortex and hippocampus, commonly activated during learning and memory. Basal expression of mPAK3-GFP proteins in cFos-positive cells resulted in social recognition memory deficits in the three-chamber social interaction test, without affecting locomotor activity or other forms of memory. The social memory deficit was rescued by doxycycline to halt the mPAK3-GFP transgene expression. In addition, we show that the expression of mPAK3-GFP proteins in a subset of cFos-positive cells, induced by an antecedent short social interaction, termed social pairing, was sufficient to impair social recognition memory. These results indicate that normal PAK signaling in cFos-positive cells activated during social interaction is critical for social memory.

Naproxen inhibits spontaneous lung adenocarcinoma formation in KrasG12V mice

•

Naproxen inhibits the adenocarcinoma by 64% in Kras^G12V mice.

•

Naproxen inhibits serum PGE₂/CXCR4 levels in Kras^G12V mice.

•

Naproxen inhibits the progression of adenocarcinoma in Kras^G12V mice.

Lung cancer is the leading cause of cancer related deaths worldwide. The present study investigated the effects of naproxen (NSAID) on lung adenocarcinoma in spontaneous lung cancer mouse model. Six-week-old transgenic Kras^G12V mice (n = 20; male + female) were fed modified AIN-76A diets containing naproxen (0/400 ppm) for 30 wk and euthanized at 36 wk of age. Lungs were evaluated for tumor incidence, multiplicity, and histopathological stage (adenoma and adenocarcinoma). Lung tumors were noticeable as early as 12 wk of age exclusively in the Kras^G12V mice. By 36 wk age, 100% of Kras^G12V mice on control diet developed lung tumors, mostly adenocarcinomas. Kras^G12V mice fed control diet developed 19.8 ± 0.96 (Mean ± SEM) lung tumors (2.5 ± 0.3 adenoma, 17.3 ± 0.7 adenocarcinoma). Administration of naproxen (400 ppm) inhibited lung tumor multiplicity by ∼52% (9.4 ± 0.85; P < 0001) and adenocarcinoma by ∼64% (6.1 ± 0.6; P < 0001), compared with control-diet-fed mice. However, no significant difference was observed in the number of adenomas in either diet, suggesting that naproxen was more effective in inhibiting tumor progression to adenocarcinoma. Biomarker analysis showed significantly reduced inflammation (COX-2, IL-10), reduced tumor cell proliferation (PCNA, cyclin D1), and increased apoptosis (p21, caspase-3) in the lung tumors exposed to naproxen. Decreased serum levels of PGE₂ and CXCR4 were observed in naproxen diet fed Kras^G12V mice. Gene expression analysis of tumors revealed a significant increase in cytokine modulated genes (H2-Aa, H2-Ab1, Clu), which known to further modulate the cytokine signaling pathways. Overall, the results suggest a chemopreventive role of naproxen in inhibiting spontaneous lung adenocarcinoma formation in Kras^G12V mice.

Photoactivatable Cre knock-in mice for spatiotemporal control of genetic engineering in vivo

Although the Cre-loxP recombination system has been extensively used to analyze gene function in vivo, spatiotemporal control of Cre activity is a critical limitation for easy and precise recombination. Here, we established photoactivatable-Cre (PA-Cre) knock-in (KI) mice at a safe harbor locus for the spatial and temporal regulation of Cre recombinase activity. The mice showed whole-body Cre recombination activity following light exposure for only 1 h. Almost no leaks of Cre recombination activity were detected in the KI mice under natural light conditions. Spot irradiation could induce locus-specific recombination noninvasively, enabling us to compare phenotypes on the left and right sides in the same mouse. Furthermore, long-term irradiation using an implanted wireless LED substantially improved Cre recombination activity, especially in the brain. These results demonstrate that PA-Cre KI mice can facilitate the spatiotemporal control of genetic engineering and provide a useful resource to elucidate gene function in vivo with Cre-loxP.

Neurodegeneration and Motor Deficits in the Absence of Astrogliosis upon Transgenic Mutant TDP-43 Expression in Mature Mice

Amyotrophic lateral sclerosis is a rapidly progressing and fatal disease characterized by muscular atrophy due to loss of upper and lower motor neurons. Pathogenic mutations in the TARDBP gene encoding TAR DNA binding protein-43 (TDP-43) have been identified in familial amyotrophic lateral sclerosis. We have previously reported transgenic mice with neuronal expression of human TDP-43 carrying the pathogenic A315T mutation (iTDP-43^A315T mice) using a tetracycline-controlled inducible promotor system. Constitutive expression of transgenic TDP-43^A315T in the absence of doxycycline resulted in pronounced early-onset and progressive neurodegeneration, and motor and memory deficits. Here, delayed transgene expression of TDP-43^A315T by oral doxycycline treatment of iTDP-43^A315T mice from birth till weaning was analyzed. After doxycycline withdrawal, transgenic TDP-43^A315T expression gradually increased and resulted in cytoplasmic TDP-43, widespread ubiquitination, and cortical and hippocampal atrophy. In addition, these mice developed motor and gait deficits with underlying muscle atrophy, similar to that observed in the constitutive iTDP-43^A315T mice. Surprisingly, in contrast to the constitutive iTDP-43^A315T mice, these mice did not develop astrogliosis. In summary, delayed activation coupled with gradual increase in TDP-43^A315T expression in the central nervous system of mature mice resulted in progressive functional deficits with neuron and muscle loss, but in the absence of a glial response. This suggests that astrocytosis does not contribute to functional deficits and neuronal loss upon TDP-43^A315T expression in mature mice.

Constitutive and Inducible Systems for Genetic In Vivo Modification of Mouse Hepatocytes Using Hydrodynamic Tail Vein Injection

In research models of liver cancer, regeneration, inflammation, and fibrosis, flexible systems for in vivo gene expression and silencing are highly useful. Hydrodynamic tail vein injection of transposon-based constructs is an efficient method for genetic manipulation of hepatocytes in adult mice. In addition to constitutive transgene expression, this system can be used for more advanced applications, such as shRNA-mediated gene knock-down, implication of the CRISPR/Cas9 system to induce gene mutations, or inducible systems. Here, the combination of constitutive CreER expression together with inducible expression of a transgene or miR-shRNA of choice is presented as an example of this technique. We cover the multi-step procedure starting from the preparation of sleeping beauty-transposon constructs, to the injection and treatment of mice, and the preparation of liver tissue for analysis by immunostaining. The system presented is a reliable and efficient approach to achieve complex genetic manipulations in hepatocytes. It is specifically useful in combination with Cre/loxP-based mouse strains and can be applied to a variety of models in the research of liver disease.

Overexpression of miR-210 and its significance in ischemic tissue damage

Hypoxia-induced miR-210 displays a pro-survival, cytoprotective and pro-angiogenic role in several in vitro systems. In vivo, we previously found that miR-210 inhibition increases ischemic damage. Here we describe the generation of a versatile transgenic mouse model allowing the evaluation of miR-210 therapeutic potential in ischemic cardiovascular diseases. We generated a Tet-On miR-210 transgenic mouse strain (TG-210) by targeted transgenesis in the ROSA26 locus. To functionally validate miR-210 transgenic mice, hindlimb ischemia was induced by femoral artery dissection. Blood perfusion was evaluated by power Doppler while tissue damage and inflammation were assessed by histological evaluation. We found that miR-210 levels were rapidly increased in TG-210 mice upon doxycycline administration. miR-210 overexpression was maintained over time and remained within physiological levels in multiple tissues. When hindlimb ischemia was induced, miR-210 overexpression protected from both muscular and vascular ischemic damage, decreased inflammatory cells density and allowed to maintain a better calf perfusion. In conclusion, we generated and functionally validated a miR-210 transgenic mouse model. Albeit validated in the context of a specific cardiovascular ischemic disease, miR-210 transgenic mice may also represent a useful model to assess the function of miR-210 in other physio-pathological conditions.

Synthetic circuits that process multiple light and chemical signal inputs

Background

Multi-signal processing circuits are essential for rational design of sophisticated synthetic systems with good controllability and modularity, therefore, enable construction of high-level networks. Moreover, light-inducible systems provide fast and reversible means for spatiotemporal control of gene expression.

Results

Here, in HEK 293 cells, we present combinatory genetic circuits responding to light and chemical signals, simultaneously. We first constructed a dual input circuit converting different light intensities into varying of the sensitivity of the promoter to a chemical inducer (doxycycline). Next, we generated a ternary input circuit, which responded to light, doxycycline and cumate. This circuit allowed us to use different combinations of blue light and the two chemical inducers to generate gradual output values over two orders of magnitude.

Conclusions

Overall, in this study, we devise genetic circuits sensing and processing light and chemical inducers. Our work may provide insights into bio-computation and fine-tuning expression of the transgene.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-016-0384-y) contains supplementary material, which is available to authorized users.

A Tet-on and Cre-loxP Based Genetic Engineering System for Convenient Recycling of Selection Markers in Penicillium oxalicum

The lack of selective markers has been a key problem preventing multistep genetic engineering in filamentous fungi, particularly for industrial species such as the lignocellulose degrading Penicillium oxalicum JUA10-1(formerly named as Penicillium decumbens). To resolve this problem, we constructed a genetic manipulation system taking advantage of two established genetic systems: the Cre-loxP system and Tet-on system in P. oxalicum JUA10-1. This system is efficient and convenient. The expression of Cre recombinase was activated by doxycycline since it was controlled by Tet-on system. Using this system, two genes, ligD and bglI, were sequentially disrupted by loxP flanked ptrA. The successful application of this procedure will provide a useful tool for genetic engineering in filamentous fungi. This system will also play an important role in improving the productivity of interesting products and minimizing by-product when fermented by filamentous fungi.

Expression of A152T human tau causes age-dependent neuronal dysfunction and loss in transgenic mice

A152T-variant human tau (hTau-A152T) increases risk for tauopathies, including Alzheimer's disease. Comparing mice with regulatable expression of hTau-A152T or wild-type hTau (hTau-WT), we find age-dependent neuronal loss, cognitive impairments, and spontaneous nonconvulsive epileptiform activity primarily in hTau-A152T mice. However, overexpression of either hTau species enhances neuronal responses to electrical stimulation of synaptic inputs and to an epileptogenic chemical. hTau-A152T mice have higher hTau protein/mRNA ratios in brain, suggesting that A152T increases production or decreases clearance of hTau protein. Despite their functional abnormalities, aging hTau-A152T mice show no evidence for accumulation of insoluble tau aggregates, suggesting that their dysfunctions are caused by soluble tau. In human amyloid precursor protein (hAPP) transgenic mice, co-expression of hTau-A152T enhances risk of early death and epileptic activity, suggesting copathogenic interactions between hTau-A152T and amyloid-β peptides or other hAPP metabolites. Thus, the A152T substitution may augment risk for neurodegenerative diseases by increasing hTau protein levels, promoting network hyperexcitability, and synergizing with the adverse effects of other pathogenic factors.

Structure-function integrity of the adult hippocampus depends on the transcription factor Bcl11b/Ctip2

The dentate gyrus is one of the only two brain regions where adult neurogenesis occurs. Throughout life, cells of the neuronal stem cell niche undergo proliferation, differentiation and integration into the hippocampal neural circuitry. Ongoing adult neurogenesis is a prerequisite for the maintenance of adult hippocampal functionality. Bcl11b, a zinc finger transcription factor, is expressed by postmitotic granule cells in the developing as well as adult dentate gyrus. We previously showed a critical role of Bcl11b for hippocampal development. Whether Bcl11b is also required for adult hippocampal functions has not been investigated. Using a tetracycline‐dependent inducible mouse model under the control of the forebrain‐specific CaMKIIα promoter, we show here that the adult expression of Bcl11b is essential for survival, differentiation and functional integration of adult‐born granule cell neurons. In addition, Bcl11b is required for survival of pre‐existing mature neurons. Consequently, loss of Bcl11b expression selectively in the adult hippocampus results in impaired spatial working memory. Together, our data uncover for the first time a specific role of Bcl11b in adult hippocampal neurogenesis and function.

Short-term suppression of A315T mutant human TDP-43 expression improves functional deficits in a novel inducible transgenic mouse model of FTLD-TDP and ALS

The nuclear transactive response DNA-binding protein 43 (TDP-43) undergoes relocalization to the cytoplasm with formation of cytoplasmic deposits in neurons in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Pathogenic mutations in the TDP-43-encoding TARDBP gene in familial ALS as well as non-mutant human TDP-43 have been utilized to model FTD/ALS in cell culture and animals, including mice. Here, we report novel A315T mutant TDP-43 transgenic mice, iTDP-43(A315T), with controlled neuronal over-expression. Constitutive expression of human TDP-43(A315T) resulted in pronounced early-onset and progressive neurodegeneration, which was associated with compromised motor performance, spatial memory and disinhibition. Muscle atrophy resulted in reduced grip strength. Cortical degeneration presented with pronounced astrocyte activation. Using differential protein extraction from iTDP-43(A315T) brains, we found cytoplasmic localization, fragmentation, phosphorylation and ubiquitination and insolubility of TDP-43. Surprisingly, suppression of human TDP-43(A315T) expression in mice with overt neurodegeneration for only 1 week was sufficient to significantly improve motor and behavioral deficits, and reduce astrogliosis. Our data suggest that functional deficits in iTDP-43(A315T) mice are at least in part a direct and transient effect of the presence of TDP-43(A315T). Furthermore, it illustrates the compensatory capacity of compromised neurons once transgenic TDP-43 is removed, with implications for future treatments.