The H2B-TRAP allele (Translating Ribosome Affinity Purification) has a loxP-flanked STOP preventing transcription of two individual components that are separated by a self-cleaving viral 2A peptide:
[i] H2B/mCherry (the human histone 1 H2bj fused to mCherry) and [ii] EGFP/L10a (the 60S ribosomal subunit L10a fused to EGFP).

Although under control of the endogenous Gt(ROSA)26Sor promoter/enhancer regions and the CAG hybrid promoter, widespread expression of the two components should be prevented by the floxed-STOP cassette. The donating investigator reports they observe no mCherry or EGFP expression prior to the introduction of Cre recombinase.
Mice heterozygous for the H2B-TRAP allele are viable and fertile with no reported gross physical or behavioral abnormalities. To date (January 2017), it has not been attempted to make this strain homozygous.

Upon exposure to Cre recombinase, the H2B-TRAP allele co-expresses H2B/mCherry and EGFP/L10a.
The H2B/mCherry protein allows nuclei-labeling with mCherry (direct fluorescence) - this enables nuclear isolation by fluorescence-based purification.
Furthermore, EGFP/L10a fluorescently tags the translating mRNA polysome complex (direct fluorescence in the cytoplasm and nucleolus) - this enables isolation of RNAs that are actively engaged by ribosomes.


Specifically, H2B-TRAP mice may be bred to have Cre recombinase expression in hepatocytes (via Albumin-Cre ; Stock No. 003574), agouti-related protein-secreting neurons (via Agrp-Ires-cre; see Stock No. 012899) or active populations of neurons in the brain (via Arc^CreERT2 ; Stock No. 021881). The resulting Alb-H2B-TRAP, AgRP-H2B-TRAP or ArcTRAP mice (respectively) showed mCherry and EGFP-labeling in the expected cell types, with no abnormal phenotypes reported.


In addition, when bred to have adipocyte-specific Cre recombinase expression (via Adiponectin-Cre ; Stock No. 010803), the resulting Ad-H2B-TRAP mice show brown adipose tissue (BAT) adipocytes have H2B/mCherry-labeled nuclei and EGFP/L10a-labeled ribosomes in cytoplasm. However, Ad-H2B-TRAP mice were profoundly lipodystrophic in all white adipose tissue (WAT) depots and failed to gain weight on high-fat diet, as compared to similarly treated control animals. As such, the donating investigator does not recommend using H2B-TRAP mice for work in adipocytes - suggesting instead that adipocyte studies may better utilize their NuTRAP mouse line (Stock No. 029899).

Of note, the frt sites flanking the H2B-TRAP allele allow for additional targeted replacement of the reporter sequences through FLP-mediated recombination, if so desired. Also, the AttB/AttP-flanked selection cassette may be removed by introduction of the site-specific bacteriophage PhiC31 integrase, if so desired.