Hepatocyte genomic loxP sites (loxP)

Hepatocyte genomic loxP sites are synthetic 34-base pair DNA sequences (5'-ATAACTTCGTATA-GCATACAT-TATACGAAGTTAT-3') integrated into the genome of liver cells to enable site-specific DNA recombination (Nagy, 2000, Genesis). These sites are specifically recognized by the Cre recombinase enzyme, which catalyzes the deletion, inversion, or translocation of DNA segments flanked by two loxP sites, a process known as "floxing" (Sauer, 1998, Methods). In hepatology research, this system is a fundamental tool for creating conditional knockout mouse models, allowing for the study of gene function specifically within hepatocytes to avoid embryonic lethality or systemic effects (Yanger et al., 2014, Genes & Dev). While not a traditional therapeutic target for small molecules, these sites serve as the substrate for Cre-expressing viral vectors, such as Adeno-associated viruses (AAVs) utilizing liver-specific promoters like Albumin or TBG. The system is widely used to model human diseases including hepatocellular carcinoma, non-alcoholic steatohepatitis (NASH), and various metabolic disorders (Schmidt-Supprian & Rajewsky, 2007, Nat Immunol). However, challenges include "Cre toxicity," where high levels of the enzyme can trigger a DNA damage response and cell cycle arrest (Loonstra et al., 2001, PNAS). Additionally, the presence of endogenous "pseudo-loxP" sites in the mammalian genome can lead to unintended off-target recombination events (Schmidt et al., 2000, PNAS).

Other names

Locus of crossing over in P1Floxed sitesCre-recognition sitesloxP sequence

Cre recombinase binds to two loxP sites and catalyzes a reciprocal recombination event, leading to excision, inversion, or translocation of the intervening DNA sequence depending on the orientation of the sites (Nagy, 2000, Genesis).