Conditional bicistronic Cre reporter line expressing both firefly luciferase and β-galactosidase

Development of two mouse strains conditionally expressing bright luciferases with distinct emission spectra as new tools for in vivo imaging

In vivo bioluminescence imaging (BLI) has been an invaluable noninvasive method to visualize molecular and cellular behaviors in laboratory animals. Bioluminescent reporter mice harboring luciferases for general use have been limited to a classical luciferase, Luc2, from Photinus pyralis, and have been extremely powerful for various in vivo studies. However, applicability of reporter mice for in vivo BLI could be further accelerated by increasing light intensity through the use of other luciferases and/or by improving the biodistribution of their substrates in the animal body. Here we created two Cre-dependent reporter mice incorporating luciferases oFluc derived from Pyrocoeli matsumurai and Akaluc, both of which had been reported previously to be brighter than Luc2 when using appropriate substrates; we then tested their bioluminescence in neural tissues and other organs in living mice. When expressed throughout the body, both luciferases emitted an intense yellow (oFluc) or far-red (Akaluc) light easily visible to the naked eye. oFluc and Akaluc were similarly bright in the pancreas for in vivo BLI; however, Akaluc was superior to oFluc for brain imaging, because its substrate, AkaLumine-HCl, was distributed to the brain more efficiently than the oFluc substrate, D-luciferin. We also demonstrated that the lights produced by oFluc and Akaluc were sufficiently spectrally distinct from each other for dual-color imaging in a single living mouse. Taken together, these novel bioluminescent reporter mice are an ideal source of cells with bright bioluminescence and may facilitate in vivo BLI of various tissues/organs for preclinical and biomedical research in combination with a wide variety of Cre-driver mice.

Development of dual reporter vector system for estimating translational activity of regulatory elements

BACKGROUND

For the needs of modern biotechnology, a quantitative approach to the control of regulatory elements at all stages of gene expression has long become indispensable. Such a control regime is impossible without a quantitative analysis of the role of each regulatory element or pattern used. Therefore, it seems important to modify and develop the accuracy, reproducibility, and availability of methods for quantifying the contribution of each regulatory code to the implementation of genetic information.

RESULTS

A new vector system for transient expression in plants is described; this system is intended for quantitative analysis of the contribution of regulatory elements to transcription and translation efficiencies. The proposed vector comprises two expression cassettes carrying reporter genes (of the Clostridium thermocellum thermostable lichenase and E. coli β-glucuronidase) under the control of different promoters. Herewith we also propose a new method for quantification of the effect of tested regulatory elements on expression, which relies on assessment of the enzyme activities of reporter proteins taking into account the transcription of their genes.

CONCLUSIONS

In our view, this approach makes it possible to precisely determine the amounts of reporter proteins and their transcripts at all stages of expression. The efficiency of the proposed system has been validated by the analysis of the roles of known translation enhancers at the stages of transcription and translation.

Cre recombinase toxicity in podocytes: a novel genetic model for FSGS in adolescent mice

Here, we show that inducible overexpression of Cre recombinase in glomerular podocytes but not in parietal epithelial cells may trigger focal segmental glomerulosclerosis (FSGS) in juvenile transgenic homocygous Pod-rtTA/LC1 mice. Administration of doxycycline shortly after birth, but not at any other time point later in life, resulted in podocyte injury and development of classical FSGS lesions in these mice. Sclerotic lesions were formed as soon as 3 wk of age, and FSGS progressed with low variability until 13 wk of age. In addition, our experiments identified Cre toxicity as a potentially relevant limitation for studies in podocytes of transgenic animals. In summary, our study establishes a novel genetic model for FSGS in mice, which exhibits low variability and manifests already at a young age.

Rapid, Single-Cell Analysis and Discovery of Vectored mRNA Transfection In Vivo with a loxP-Flanked tdTomato Reporter Mouse

mRNA therapeutics hold promise for the treatment of diseases requiring intracellular protein expression and for use in genome editing systems, but mRNA must transfect the desired tissue and cell type to be efficacious. Nanoparticle vectors that deliver the mRNA are often evaluated using mRNA encoding for reporter genes such as firefly luciferase (FLuc); however, single-cell resolution of mRNA expression cannot generally be achieved with FLuc, and, thus, the transfected cell populations cannot be determined without additional steps or experiments. To more rapidly identify which types of cells an mRNA formulation transfects in vivo, we describe a Cre recombinase (Cre)-based system that permanently expresses fluorescent tdTomato protein in transfected cells of genetically modified mice. Following in vivo application of vectored Cre mRNA, it is possible to visualize successfully transfected cells via Cre-mediated tdTomato expression in bulk tissues and with single-cell resolution. Using this system, we identify previously unknown transfected cell types of an existing mRNA delivery vehicle in vivo and also develop a new mRNA formulation capable of transfecting lung endothelial cells. Importantly, the same formulations with mRNA encoding for fluorescent protein delivered to wild-type mice did not produce sufficient signal for any visualization in vivo, demonstrating the significantly improved sensitivity of our Cre-based system. We believe that the system described here may facilitate the identification and characterization of mRNA delivery vectors to new tissues and cell types.

Development and Characterization of Cell-Specific Androgen Receptor Knockout Mice

Conditional gene targeting has revolutionized molecular genetic analysis of nuclear receptor proteins, however development and analysis of such conditional knockouts is far from simple, with many caveats and pitfalls waiting to snare the novice or unprepared. In this chapter, we describe our experience of generating and analyzing mouse models with conditional ablation of the androgen receptor (AR) from tissues of the reproductive system and other organs. The guidance, suggestions, and protocols outlined in the chapter provide the key starting point for analyses of conditional-ARKO mice, completing them as described provides an excellent framework for further focussed project-specific analyses, and applies equally well to analysis of reproductive tissues from any mouse model generated through conditional gene targeting.

Autophagy Protects against Colitis by the Maintenance of Normal Gut Microflora and Secretion of Mucus

Genome-wide association studies of inflammatory bowel diseases identified susceptible loci containing an autophagy-related gene. However, the role of autophagy in the colon, a major affected area in inflammatory bowel diseases, is not clear. Here, we show that colonic epithelial cell-specific autophagy-related gene 7 (Atg7) conditional knock-out (cKO) mice showed exacerbation of experimental colitis with more abundant bacterial invasion into the colonic epithelium. Quantitative PCR analysis revealed that cKO mice had abnormal microflora with an increase of some genera. Consistently, expression of antimicrobial or antiparasitic peptides such as angiogenin-4, Relmβ, intelectin-1, and intelectin-2 as well as that of their inducer cytokines was significantly reduced in the cKO mice. Furthermore, secretion of colonic mucins that function as a mucosal barrier against bacterial invasion was also significantly diminished in cKO mice. Taken together, our results indicate that autophagy in colonic epithelial cells protects against colitis by the maintenance of normal gut microflora and secretion of mucus.

NF-κB activity in perinatal brain during infectious and hypoxic-ischemic insults revealed by a reporter mouse

Infants suffering from infection or hypoxia-ischemia around the time of birth can develop brain damage resulting in life-long impairment such as cerebral palsy, epilepsy and cognitive disability. Inflammation appears to be an important contributor irrespective of whether the primary event is infection or hypoxia-ischemia. Activation of the transcription factor NF-κB is a hallmark of inflammation. To study perinatal brain inflammation, we developed a transgenic reporter mouse for imaging NF-κB activity in live animals and tissue samples. The reporter genes firefly luciferase and a destabilized version of enhanced GFP (dEGFP) were regulated by common NF-κB sites using a bidirectional promoter. Luciferase activity was imaged in vivo, while dEGFP was detected at cellular level in tissue sections. In newborn mice subjected to experimental models of infections or hypoxia-ischemia; luciferase signal increased in brains of live animals. In brain sections dEGFP expression, revealing NF-κB activation was observed in the endothelial cells of the blood-brain barrier in all disease models. In meningitis and hypoxia-ischemia expression of dEGFP was also induced in perivascular astrocytes. In conclusion, by using this transgenic reporter mouse in experimental models of perinatal complications, we could assess NF-κB activity in vivo and subsequently determine the cellular origin in the tissues.

Applications of molecular imaging

Today molecular imaging technologies play a central role in clinical oncology. The use of imaging techniques in early cancer detection, treatment response, and new therapy development is steadily growing and has already significantly impacted on clinical management of cancer. In this chapter, we overview three different molecular imaging technologies used for the understanding of disease biomarkers, drug development, or monitoring therapeutic outcome. They are (1) optical imaging (bioluminescence and fluorescence imaging), (2) magnetic resonance imaging (MRI), and (3) nuclear imaging (e.g., single-photon emission computed tomography (SPECT) and positron emission tomography (PET)). We review the use of molecular reporters of biological processes (e.g., apoptosis and protein kinase activity) for high-throughput drug screening and new cancer therapies, diffusion MRI as a biomarker for early treatment response and PET and SPECT radioligands in oncology.

[Issues and solutions of conditional gene targeting]

Conditional gene targeting, based on the site-specific recombination system such as Cre-loxP, plays a vital role in the study of gene functions and the generation of disease mouse models. It was always under consideration that there were problems in the Cre-loxP recombination system, such as illegal expression pattern of Cre transgene, variation of Cre recombination efficiency and toxicity of Cre recombinase, as well as the potential influences of genetic background, breeding strategy, experimental control and gene compensation. Oversights of these issues may have a profound influence on the accuracy of gene functional dissection and conditional gene targeting mice phenotypic interpretation. Accordingly, solutions should be adopted including delicate regulative control of temporal-spatial specific Cre expression, detailed detection of Cre recombination efficiency, reduction of Cre toxicity, simplification of mouse genetic background, optimization of breeding, setting up of proper control and combined conditional gene targeting.

A Cre-reporter transgenic mouse expressing the far-red fluorescent protein Katushka

Cre/loxP-dependent expression of fluorescent proteins represents a powerful biological tool for cell lineage, fate-mapping, and genetic analysis. Live tissue imaging has significantly improved with the development of far-red fluorescent proteins, with optimized spectral characteristics for in vivo applications. Here, we report the generation of the first transgenic mouse line expressing the far-red fluorescent protein Katushka, driven by the hybrid CAG promoter upon Cre-mediated recombination. After germ line or tissue-specific Cre-driven reporter activation, Katushka expression is strong and ubiquitous, without toxic effects, allowing fluorescence detection in fresh and fixed samples from all tissues examined. Moreover, fluorescence can be detected by in vivo noninvasive whole-body imaging when Katuhska is expressed exclusively in a specific cell population deep within the animal body such as pancreatic beta cells. Thus, this reporter model enables early, widespread, and sensitive in vivo detection of Cre activity and should provide a versatile tool for a wide spectrum of fluorescence and live-imaging applications.