TCF/Lef:H2B-GFP transgenic mice express an H2B-EGFP fusion protein (coding sequence for the human HIST1H2BB gene [histone 1 H2bb] followed C-terminally by Enhanced Green Fluorescent Protein gene) under the control of six copies of a T cell specific transcription factor/lymphoid enhancer-binding factor 1 (TCF/Lef1) response element and a heat shock protein 1B (Hspa1b) minimal promoter. Mice homozygous for the transgene are viable, fertile, and normal in size. Wnt (wingless-related MMTV) family members are required for triggering embryonic axis formation and for proper development. Wnt signaling results in phosphorylation and nuclear localization of β-catenin, a transcriptional co-activator protein, which, together with the TCF/Lef family of transcription factors, induces the transcription of downstream genes. TCF/Lef:H2B-GFP transgenic mice contain 6 copies of nuclear localized TCF/Lef1 DNA binding sites, which provides increased sensitivity to Wnt/&beta-catenin signaling and drives single-cell resolution of GFP expression at sites of active signaling. Specifically, GFP expression is evident in cells of the extraembryonic visceral endoderm, the primitive streak, the mature node, presomitic mesoderm and newly formed somites, posterior neural plate, cranial neural crest, face, and branchial arches. By E12.5 fluorescence is also seen in the kidney, gonads, and some neuronal subsets in the brain.
