Tamoxifen-induced gene expression

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Tamoxifen-induced gene expression is a method used in molecular biology and neuroscience to activate transcription of a specific gene by application of the drug tamoxifen. It is based on the expression of a mutated estrogen receptor (ERT2) fused to Cre recombinase. [1] In the absence of tamoxifen, the receptor is inactive and sequestered in the cytoplasm. When tamoxifen is administered, it binds to ERT2, causing the Cre-ERT2 fusion protein to move into the cell's nucleus, where it can perform its recombination function. The gene of interest, encoding e.g. the fluorescent protein GFP, contains a LoxP-flanked stop cassette that prevents expression unless it is excised by Cre recombinase. [2]

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When used in mice, the Cre-ERT2 system allows for excellent temporal control: Administration of tamoxifen triggers genetic changes at a precise time point in development or adult life. However, depending on the type of target cell, the gene of interest may not be successfully activated in every cell, leading to mosaic expression.

TRAP2 mice to label active neurons

Function of the TRAP mouse: Neuronal activity activates the Fos promoter, producing CreER that is sequestered in the cytoplasm. Upon tamoxifen binding, CreER enters the nucleus and excises the Lox-stop-Lox cassette from the gene of interest (here GFP). As a result, active neurons become fluorescent. TRAP2.jpg
Function of the TRAP mouse: Neuronal activity activates the Fos promoter, producing CreER that is sequestered in the cytoplasm. Upon tamoxifen binding, CreER enters the nucleus and excises the Lox-stop-Lox cassette from the gene of interest (here GFP). As a result, active neurons become fluorescent.

The Cre-ERT2 system has been harnessed to express genes of interest, e.g. fluorescent markers or optogenetic tools, in highly active neurons. For this purpose, it is driven by the immediate early gene Fos. [3] [4] This approach, called Targeted Recombination in Active Populations (TRAP, TRAP2), is used to investigate learning and memory in mice on the cellular level. [5] [6] [7]

See also

References

  1. ↑ Zhao, Jing; Nassar, Mohammed A.; Gavazzi, Isabella; Wood, John N. (2006). "Tamoxifen-inducible Na V 1.8-CreERT2 recombinase activity in nociceptive neurons of dorsal root ganglia". Genesis. 44 (8): 364–371. doi:10.1002/dvg.20224. ISSN   1526-954X. PMID   16850455.
  2. ↑ Sapkota, Darshan; Dougherty, Joseph D. (2020-02-20). "An inducible Cre mouse line to sparsely target nervous system cells, including Remak Schwann cells". Neural Development. 15 (1) 2. doi: 10.1186/s13064-020-00140-y . ISSN   1749-8104. PMC   7031956 . PMID   32079539.
  3. ↑ Allen, William E.; DeNardo, Laura A.; Chen, Michael Z.; Liu, Cindy D.; Loh, Kyle M.; Fenno, Lief E.; Ramakrishnan, Charu; Deisseroth, Karl; Luo, Liqun (2017-09-15). "Thirst-associated preoptic neurons encode an aversive motivational drive". Science. 357 (6356): 1149–1155. Bibcode:2017Sci...357.1149A. doi:10.1126/science.aan6747. ISSN   0036-8075. PMC   5723384 . PMID   28912243.
  4. ↑ Guenthner, Casey J; Miyamichi, Kazunari; Yang, Helen H; Heller H, Craig; Luo, Liqun (2013). "Permanent Genetic Access to Transiently Active Neurons via TRAP: Targeted Recombination in Active Populations". Neuron. 78 (5): 773–784. doi:10.1016/j.neuron.2013.03.025. PMC   3782391 . PMID   23764283.
  5. ↑ DeNardo, Laura A.; Liu, Cindy D.; Allen, William E.; Adams, Eliza L.; Friedmann, Drew; Fu, Lisa; Guenthner, Casey J.; Tessier-Lavigne, Marc; Luo, Liqun (2019). "Temporal evolution of cortical ensembles promoting remote memory retrieval". Nature Neuroscience. 22 (3): 460–469. doi:10.1038/s41593-018-0318-7. ISSN   1097-6256. PMC   6387639 . PMID   30692687.
  6. ↑ Chen, Michelle B.; Jiang, Xian; Quake, Stephen R.; Südhof, Thomas C. (2020-11-11). "Persistent transcriptional programmes are associated with remote memory". Nature. 587 (7834): 437–442. Bibcode:2020Natur.587..437C. doi:10.1038/s41586-020-2905-5. ISSN   0028-0836. PMC   9097329 . PMID   33177708.
  7. ↑ Mocle, Andrew J.; Ramsaran, Adam I.; Jacob, Alexander D.; Rashid, Asim J.; Luchetti, Alessandro; Tran, Lina M.; Richards, Blake A.; Frankland, Paul W.; Josselyn, Sheena A. (2024). "Excitability mediates allocation of pre-configured ensembles to a hippocampal engram supporting contextual conditioned threat in mice". Neuron. 112 (9): 1487–1497.e6. doi:10.1016/j.neuron.2024.02.007. ISSN   0896-6273. PMC   11065628 . PMID   38447576.
  8. ↑ Xu, Ru-Xia; Liao, Shi-Han; Wang, Nan; Jiang, Wen-Ying; Wang, Xun; Li, Xiao-Wen; Gao, Tian-Ming; Yang, Jian-Ming (2025-12-10). "Sex-dependent effects of tamoxifen on mouse behavior". Behavioral and Brain Functions. doi: 10.1186/s12993-025-00312-y . ISSN   1744-9081. PMID   41366492.
  9. ↑ Han, H. J.; Allen, C. C.; Buchovecky, C. M.; Yetman, M. J.; Born, H. A.; Marin, M. A.; Rodgers, S. P.; Song, B. J.; Lu, H.-C.; Justice, M. J.; Probst, F. J.; Jankowsky, J. L. (2012-08-01). "Strain Background Influences Neurotoxicity and Behavioral Abnormalities in Mice Expressing the Tetracycline Transactivator". Journal of Neuroscience. 32 (31): 10574–10586. doi:10.1523/JNEUROSCI.0893-12.2012. ISSN   0270-6474. PMID   22855807.
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