Expression of creERT2 in TPOCreER transgenic mice is directed by the human thyroid peroxidase (TPO) promoter in the thyroid. TPO encodes an enzyme essential for thyroid gland function. Restricted to the cytoplasm, Cre-ERT2 can only gain access to the nuclear compartment after exposure to tamoxifen. Homozygotes 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
B6.129P2(Cg)-Braftm1Mmcm/J mice (Stock No. 017837), which express the V600E mutant Braf allele after cre recombination, resulting TB offspring develop papillary thyroid carcinomas (PTCs) in a tamoxifen-dependent manner. These mice, however, lack extrathyroidal invasion and cervical lymph node metastases.
When TB mice are further crossed to B6.129S4-Trp53tm3.1Tyj/J mice (Stock No. 008182), which express the R270H missense mutant Trp53 allele, resulting offspring displayed accelerated and aggressive PTCs and had decreased survival time after tamoxifen induction.
