By precisely inserting the IRES-iCre expression box downstream of the stop codon and upstream of the 3’UTR of the mouse Alb gene, the Alb-IRES-iCre knock-in allele was successfully constructed. In this model, Alb and iCre are co-transcribed from the same transcript; the IRES element mediates the independent translation of the downstream iCre open reading frame, allowing the Alb protein and the iCre recombinase to be expressed as independent functional proteins without forming an Alb-iCre fusion protein or relying on a P2A self-cleavage mechanism. iCre is an improved Cre recombinase optimized with mammalian codons, which helps enhance its expression in mouse cells and the recombination efficiency of loxP sites.

The Alb gene encodes serum albumin, which is an important marker gene and major secretory protein of mature hepatocytes, playing a role in maintaining plasma colloid osmotic pressure and participating in the transport of endogenous and exogenous molecules. Because Alb is activated during hepatocyte differentiation and expressed primarily in hepatic parenchymal cells, Alb-driven Cre systems have been widely used in hepatocyte-specific conditional gene knockout and knock-in studies. Unlike Alb-CreERT2, Alb-IRES-iCre is a constitutive Cre-driving model and generally does not require tamoxifen induction. When crossed with mice carrying floxed alleles, it can mediate loxP site recombination in Alb-positive cells and their developmental progeny, achieving conditional genetic modification of hepatocyte-related genes. Because Alb can be expressed during embryonic and perinatal liver development stages, this model may undergo gene recombination before adulthood; therefore, it is suitable for studies on hepatocyte development, liver metabolism, liver injury repair, liver fibrosis, liver tumors, and drug metabolism. It should be noted that the recombination range mediated by Alb-Cre may be affected by the expression of Alb at developmental stages and the lineage of hepatic progenitor cells. For experiments requiring strict limitation to adult mature hepatocytes, the recombination efficiency and cell specificity should be verified using the Rosa26 reporter system alongside hepatocyte and cholangiocyte markers.