Expression in this Cre-ERT2 transgenic line is directed by the T (brachyury) promoter/enhancer regions. T encodes a nuclear transcription factor active in progenitor cells that reside within the primitive streak and tail bud, and lineages that emerge from these tissues as the embryonic axis extends. This protein is essential to axis extension and somitogenesis. These mice express Cre-ERT2 protein in all cells emerging from the primitive streak or tail bud throughout development. Restricted to the cytoplasm, Cre-ERT2 can only gain access to the nuclear compartment after exposure to tamoxifen. Mice homozygous for the TCreERT2 transgene are viable and fertile. When these mice are bred with mice containing loxP-flanked sequence, tamoxifen-inducible, Cre-mediated recombination will result in deletion of the floxed sequences in the Cre-expressing cells of the offspring.
For example, when bred to mice carrying Gt(ROSA)26Sortm1Sor (see Stock No. 003474), 24 hours after tamoxifen induction, widespread βgal activity is seen only in tissues recently emerged from the primitive streak at E7.5 and E8.5 or tailbud at E9.5–13.5. 48 hours after induction, TCreERT2;R26R embryos from E9.5–E12.5 display βgal activity that extends more rostrally.
When bred with B6.129-Ctnnb1tm2Kem/KnwJ (Stock No. 003474), E8.5 and E10.5 embryos show disruption of somite patterning 48 after tamoxifen administration.
