Transgenic mice, mammalian cell lines, and model organisms
control mechanism
Cre recombinase recognition of 34-bp loxP sites (tissue-specific promoters or tamoxifen-gated CreERT2)
pioneer
Brian Sauer (Cre recombination in mammalian cells, late 1980s); Jamey Marth and Klaus Rajewsky (conditional T-cell knockouts, 1994)
Core Principles & Analysis
Bacteriophage P1 Cre recombinase recognizes a pair of directional 34-base-pair loxP sequences (two palindromic 13-bp repeats flanking an asymmetric 8-bp spacer) without requiring ATP or host cofactors.
When two loxP sites flank a target exon ("floxed" allele) in the same orientation, Cre excises the intervening DNA; when oriented in opposite directions, Cre inverts the segment, bypassing embryonic lethality by restricting knockout to cells expressing a tissue-specific Cre driver.
Fusing Cre to a mutated human estrogen receptor ligand-binding domain (CreER / CreERT2) sequesters the enzyme in the cytoplasm until administration of tamoxifen (metabolized to 4-hydroxytamoxifen) triggers nuclear translocation and timed recombination.