Research Models

TREM2-mKATE2 Reporter Mouse

Synonyms: TREM2 Reporter Mouse

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Species: Mouse
Disease Relevance: Alzheimer's Disease, Frontotemporal Dementia, Nasu-Hakola Disease
Strain Name: B6J-Trem2em4(mKate2)Bwef
Genetic Background: C57Bl/6J
Availability: Available through Christian Haass.

Summary

In this mouse, TREM2 and the fluorescent protein mKate2 are co-expressed under the control of the endogenous Trem2 promoter, allowing researchers to indirectly assess expression of TREM2 by measuring mKate2 fluorescence (Feiten et al., 2024).

Bicistronic expression of TREM2 and mKate2 was achieved using a P2A sequence inserted between the endogenous Trem2 gene and the mKate2 transgene. (During translation of the P2A sequence, the ribosome “skips” between two codons without forming a peptide bond, resulting in separation of the two proteins [Donnelly et al., 2001].) Additionally, the KDEL sequence was fused to the C terminus of mKate2 to trap the reporter inside the endoplasmic reticulum.

Reporter mice expressed normal levels of Trem2 mRNA (i.e., levels of Trem2 mRNA were similar in the brains of wild-type mice and carriers of the mKate2 transgene). mKate2 was localized to microglia, consistent with the known expression pattern of TREM2. The transgene did not interfere with the microglial response to controlled cortical impact, a well-studied model of brain injury.

Applications of model

TREM2 reporter mice have been crossed with APPPS1 mice to study microglial responses to amyloidosis. Microglia isolated from the brains of these mice were stratified on the basis of levels of mKate2 fluorescence—as a proxy for TREM2 expression—and transcriptomic, metabolomic and lipidomic analyses were conducted on the microglial subpopulations (Feiten et al., 2024).

The reporter mice have also been used to evaluate how levels of TREM2 expression influence microglial responses to a brain-penetrant TREM2 agonist antibody. For this application, reporter mice were intercrossed with AppSAA knock-in mice, which have a humanized Aβ sequence and the AD-linked Swedish, Arctic, and Austrian mutations within the murine App gene, and mice with a humanized transferrin receptor (Feiten et al., 2024).

Modification details

CRISPR/Cas9 gene editing was used to insert the reporter construct into the mouse Trem2 locus, immediately downstream of exon 5. This construct contained a P2A (peptide 2A) sequence followed by mKate2 with the KDEL endoplasmic reticulum-retention sequence fused to its C terminus.

Silent mutations were also introduced into Trem2 to aid in genotyping.

Last Updated: 17 Oct 2024

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References

Research Models Citations

  1. APPPS1
  2. AppSAA Knock-in

Paper Citations

  1. . TREM2 expression level is critical for microglial state, metabolic capacity and efficacy of TREM2 agonism. 2024 Jul 22 10.1101/2024.07.18.604115 (version 1) bioRxiv.
  2. . Analysis of the aphthovirus 2A/2B polyprotein 'cleavage' mechanism indicates not a proteolytic reaction, but a novel translational effect: a putative ribosomal 'skip'. J Gen Virol. 2001 May;82(Pt 5):1013-1025. PubMed.

Other Citations

  1. Christian Haass

Further Reading