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Generation of a tamoxifen inducible Tnnt2MerCreMer knock-in mouse model for cardiac studies.

ABSTRACT: Tnnt2, encoding thin-filament sarcomeric protein cardiac troponin T, plays critical roles in heart development and function in mammals. To develop an inducible genetic deletion strategy in myocardial cells, we generated a new Tnnt2:MerCreMer (Tnnt2(MerCreMer/+)) knock-in mouse. Rosa26 reporter lines were used to examine the specificity and efficiency of the inducible Cre recombinase. We found that Cre was specifically and robustly expressed in the cardiomyocytes at embryonic and adult stages following tamoxifen induction. The knock-in allele on Tnnt2 locus does not impact cardiac function. These results suggest that this new Tnnt2(MerCreMer/+) mouse could be applied towards the temporal genetic deletion of genes of interests in cardiomyocytes with Cre-LoxP technology. The Tnnt2(MerCreMer/+) mouse model also provides a useful tool to trace myocardial lineage during development and repair after cardiac injury.

SUBMITTER: Yan J

PROVIDER: S-EPMC4480198 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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Generation of a tamoxifen inducible Tnnt2MerCreMer knock-in mouse model for cardiac studies.

Yan Jianyun J Sultana Nishat N Zhang Lu L Park David S DS Shekhar Akshay A Hu Jun J Bu Lei L Cai Chen-Leng CL

Genesis (New York, N.Y. : 2000) 20150613 6

Tnnt2, encoding thin-filament sarcomeric protein cardiac troponin T, plays critical roles in heart development and function in mammals. To develop an inducible genetic deletion strategy in myocardial cells, we generated a new Tnnt2:MerCreMer (Tnnt2(MerCreMer/+)) knock-in mouse. Rosa26 reporter lines were used to examine the specificity and efficiency of the inducible Cre recombinase. We found that Cre was specifically and robustly expressed in the cardiomyocytes at embryonic and adult stages fol ...[more]

PMID: 26010701

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Project description:The tamoxifen-inducible Cre-loxP system is widely used to overcome gene targeting pre-adult lethality, to modify a specific cell population at desired time-points, and to visualize and trace cells in fate-mapping studies. In this study we focused on tamoxifen degradation kinetics, because for all genetic fate-mapping studies, the period during which tamoxifen or its metabolites remain active in the CNS, is essential. Additionally, we aimed to define the tamoxifen administration scheme, enabling the maximal recombination rate together with minimal animal mortality. The time window between tamoxifen injection and the beginning of experiments should be large enough to allow complete degradation of tamoxifen and its metabolites. Otherwise, these substances could promote an undesired recombination, leading to data misinterpretation. We defined the optimal time window, allowing the complete degradation of tamoxifen and its metabolites, such as 4-hydroxytamoxifen, N-desmethyltamoxifen, endoxifen and norendoxifen, in the mouse brain after intraperitoneal tamoxifen injection. We determined the biological activity of these substances in vitro, as well as a minimal effective concentration of the most potent metabolite 4-hydroxytamoxifen causing recombination in vivo. For this purpose, we analyzed the recombination rate in double transgenic Cspg4-cre/Esr1/ROSA26Sortm14(CAG-tdTomato) mice, in which tamoxifen administration triggers the expression of red fluorescent protein in NG2-expressing cells, and employed a liquid chromatography, coupled with mass spectrometry, to determine the concentration of studied substances in the brain. We determined the degradation kinetics of these substances, and revealed that this process is influenced by mouse strains, age of animals, and dosage. Our results revealed that tamoxifen and its metabolites were completely degraded within 8 days in young adult C57BL/6J mice, while the age-matched FVB/NJ male mice displayed more effective degradation. Moreover, aged C57BL/6J mice were unable to metabolize all substances within 8 days. The lowering of initial tamoxifen dose leads to a significantly faster degradation of all studied substances. A disruption of the blood-brain barrier caused no concentration changes of any tamoxifen metabolites in the ipsilateral hemisphere. Taken together, we showed that tamoxifen metabolism in mouse brains is age-, strain- and dose-dependent, and these factors should be taken into account in the experimental design.

Project description:BackgroundE-proteins are transcription factors important for the development of a variety of cell types, including neural, muscle and lymphocytes of the immune system. E2A, the best characterized E-protein family member in mammals, has been shown to have stage specific roles in cell differentiation, lineage commitment, proliferation, and survival. However, due to the complexity of E2A function, it is often difficult to separate these roles using conventional genetic approaches. Here, we have developed a new genetic model for reversible control of E2A protein activity at physiological levels. This system was created by inserting a tamoxifen-responsive region of the estrogen receptor (ER) at the carboxyl end of the tcfe2a gene to generate E2AER fusion proteins. We have characterized and analyzed the efficiency and kinetics of this inducible E2AER system in the context of B cell development.ResultsB cell development has been shown previously to be blocked at an early stage in E2A deficient animals. Our E2AER/ER mice demonstrated this predicted block in B cell development, and E2AER DNA binding activity was not detected in the absence of ligand. In vitro studies verified rapid induction of E2AER DNA binding activity upon tamoxifen treatment. While tamoxifen treatment of E2AER/ER mice showed inefficient rescue of B cell development in live animals, direct exposure of bone marrow cells to tamoxifen in an ex vivo culture was sufficient to rescue and support early B cell development from the pre-proB cell stage.ConclusionThe E2AER system provides inducible and reversible regulation of E2A function at the protein level. Many previous studies have utilized over-expression systems to induce E2A function, which are complicated by the toxicity often resulting from high levels of E2A. The E2AER model instead restores E2A activity at an endogenous level and in addition, allows for tight regulation of the timing of induction. These features make our E2AER ex vivo culture system attractive to study both immediate and gradual downstream E2A-mediated events.

Dataset Information

Generation of a tamoxifen inducible Tnnt2MerCreMer knock-in mouse model for cardiac studies.

Publications

Generation of a tamoxifen inducible Tnnt2MerCreMer knock-in mouse model for cardiac studies.

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