Cre-lox Lineage-Tracing Reporter Model
Materials Required
Principle
Cre-lox lineage tracing labels cells that express Cre recombinase by excising a loxP-flanked STOP cassette in a reporter allele, causing permanent reporter expression in the recombined cell and its descendants[1][2][3].
Inducible CreERT2 models add temporal control because tamoxifen activates CreERT2-dependent recombination, allowing cells expressing a selected promoter at a chosen time point to be fate-mapped during development, homeostasis, injury, or disease[4][5].
Reporter readouts include β-galactosidase, EYFP/ECFP, tdTomato, membrane GFP, and multicolor fluorescent proteins; these readouts detect recombined cells by histology, fluorescence microscopy, flow cytometry, or tissue imaging[2][3][6][7][8].
MCE has not independently verified the accuracy of these methods. They are for reference only.
Experimental Materials
Reagents and chemicals
• Use a Cre or CreERT2 driver line, a loxP-STOP-loxP reporter line, tamoxifen for inducible CreERT2 activation, and standard tissue-fixation and staining reagents appropriate for the reporter readout[1][2][3][5][6].Antibodies, probes, dyes, or kits
• Use reporter-compatible detection reagents such as X-gal for lacZ reporters, fluorescence detection for fluorescent reporters, and cell-type marker antibodies to verify whether labeled cells match the intended lineage[1][2][3][6][9].Equipment and instruments
• Use animal breeding and genotyping equipment, tissue-processing instruments, fluorescence or confocal microscopy for spatial readout, and flow cytometry when quantitative cell-type labeling analysis is required[3][5][9][10].Experimental Procedure
Preparation Steps
• Generate experimental animals by crossing the selected Cre or CreERT2 driver with a Cre-responsive reporter strain, and include Cre-negative reporter controls, no-tamoxifen CreERT2 controls, and tamoxifen-treated CreERT2 controls when inducible systems are used[1][2][5][11][12].• Before lineage interpretation, validate driver specificity and reporter activation in the tissue of interest because different Cre lines, reporter alleles, breeding strategies, and genetic backgrounds can alter recombination patterns[9][11][13].
Operation Steps
• For constitutive lineage tracing, breed Cre-positive reporter animals, collect target tissue at the planned developmental or experimental endpoint, and detect reporter-positive cells as the lineage-labeled population[1][2][3].• For inducible lineage tracing, administer tamoxifen to CreERT2 reporter animals at the selected labeling time, collect tissue after the pulse or after a chase period, and interpret reporter-positive cells as cells that expressed the driver during the induction window and their descendants[4][5][10].
• For clonal or multicolor lineage tracing, use reporter systems that generate distinct fluorescent labels after Cre recombination, then analyze spatially separated labeled clones or color-coded cell populations over time[7][8].
Data Acquisition and Analysis
• Quantify reporter-positive cells within anatomically defined regions or purified cell populations, co-localize reporter signal with lineage or differentiation markers, and compare labeling between induced animals and negative controls to distinguish true lineage labeling from background recombination[5][9][11][12].• Interpret lineage tracing as evidence of ancestry from the originally labeled Cre-expressing population, not as direct proof of ongoing promoter expression at the endpoint, because reporter activation is permanent after recombination[1][2][5].
Troubleshooting
Problem: Reporter-positive cells appear without tamoxifen.
• Possible Cause: Basal CreERT2 activity or reporter susceptibility to leaky recombination.• Literature-supported Solution: Include no-tamoxifen CreERT2 reporter controls and consider reporter choice, because Ai14/Ai3 reporters showed higher susceptibility to basal recombination than mTmG or R26R-EYFP in tested CreERT2 lines[11][12].
Problem: Labeled cells do not match the expected lineage.
• Possible Cause: Cre-driver expression is broader than assumed or varies by reporter system, tissue, background, or breeding strategy.• Literature-supported Solution: Validate recombination with cell-type markers in the specific experimental tissue and model before interpreting fate-mapping results[9][13].
Problem: Tamoxifen-treated CreERT2 animals show unexpected pathology.
• Possible Cause: Tamoxifen-activated CreERT2 can produce toxicity in some models.• Literature-supported Solution: Include tamoxifen-treated CreERT2 animals lacking the floxed experimental allele, because young Rosa26CreERT2 mice developed hematological toxicity after tamoxifen exposure[14].
Problem: Local induction labels broader tissue than intended.
• Possible Cause: Tamoxifen or 4-hydroxytamoxifen can produce systemic recombination despite local administration.• Literature-supported Solution: Verify labeling distribution with whole-animal or multi-tissue reporter analysis, because localized 4-hydroxytamoxifen injection in an inducible reporter fracture model produced labeling comparable to systemic induction[10].
References:
- [1]. Soriano P. Generalized lacZ expression with the ROSA26 Cre reporter strain. Nat Genet. 1999;21(1):70-71. [Content Brief]
- [2]. Srinivas S, et al. Cre reporter strains produced by targeted insertion of EYFP and ECFP into the ROSA26 locus. BMC Dev Biol. 2001;1:4. [Content Brief]
- [3]. Madisen L, Zwingman TA, Sunkin SM, Oh SW, Zariwala HA, Gu H, et al. A robust and high-throughput Cre reporting and characterization system for the whole mouse brain. Nat Neurosci. 2010;13(1):133-140. [Content Brief]
- [4]. Danielian PS, et al. Modification of gene activity in mouse embryos in utero by a tamoxifen-inducible form of Cre recombinase. Curr Biol. 1998;8(24):1323-1326. [Content Brief]
- [5]. Feil S, et al. Genetic inducible fate mapping in adult mice using tamoxifen-dependent Cre recombinases. Methods Mol Biol. 2014;1194:113-139. [Content Brief]
- [6]. Muzumdar MD, et al. A global double-fluorescent Cre reporter mouse. Genesis. 2007;45(9):593-605. [Content Brief]
- [7]. Livet J, Weissman TA, Kang H, Draft RW, Lu J, Bennis RA, et al. Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system. Nature. 2007;450(7166):56-62. [Content Brief]
- [8]. Snippert HJ, van der Flier LG, Sato T, van Es JH, van den Born M, Kroon-Veenboer C, et al. Intestinal crypt homeostasis results from neutral competition between symmetrically dividing Lgr5 stem cells. Cell. 2010;143(1):134-144. [Content Brief]
- [9]. Rovira M, et al. Hnf1b-CreER, a model used for fate mapping pancreatic lineages, achieves efficient Cre-mediated recombination in duct and islet δ cells. Islets. 2021;13(5-6):122-128. [Content Brief]
- [10]. Seime T, et al. Inducible cell labeling and lineage tracking during fracture repair. Dev Growth Differ. 2015;57(1):10-23. [Content Brief]
- [11]. Álvarez-Aznar A, et al. Tamoxifen-independent recombination of reporter genes limits lineage tracing and mosaic analysis using CreERT2 lines. Transgenic Res. 2020;29(1):53-68. [Content Brief]
- [12]. Van Hove H, et al. Identifying the variables that drive tamoxifen-independent CreERT2 recombination: implications for microglial fate mapping and gene deletions. Eur J Immunol. 2020;50(3):459-463. [Content Brief]
- [13]. Gil-Sanz C, Espinosa A, Fregoso SP, Bluske KK, Cunningham CL, Martínez-Garay I, et al. Lineage tracing using Cux2-Cre and Cux2-CreERT2 mice. Neuron. 2015;86(5):1091-1099. [Content Brief]
- [14]. Rossi M, et al. Warning regarding hematological toxicity of tamoxifen activated CreERT2 in young Rosa26CreERT2 mice. Sci Rep. 2023;13(1):6204. [Content Brief]
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