Abstract
Rats (Rattus norvegicus) have been widely utilized as model animals due to their physiological characteristics, making them suitable for surgical and long-term studies. They have played a crucial role in biomedical research, complementing studies conducted in mice. The advent of genome editing technologies has facilitated the generation of genetically modified rat strains, advancing studies in experimental animals. Among these innovations, Cre-driver rat models have emerged as powerful tools for spatiotemporal control of gene expression. However, their development and characterization remain less advanced compared to mouse models. In this study, we developed liver-targeting Cre knock-in rats and reporter knock-in rats to evaluate Cre recombinase expression profiles in different genetic contexts. Our results revealed that insertion orientation and promoter origin significantly influence Cre expression patterns. Notably, forward insertion of the Albumin (Alb) promoter-driven Cre sequence at the ROSA26 locus resulted in ubiquitous Cre expression, while reverse insertion confined Cre expression predominantly to the liver. Interestingly, Cre expression under an endogenous Alb promoter unexpectedly induced expression in non-liver tissues, which may suggest a potential link to the in vivo dynamics of albumin. These findings underscore the importance of rigorous characterization in Cre-based transgenic systems. By elucidating the roles of promoter origin, insertion site, and orientation, our study provides valuable insights for optimizing Cre-driver rat models. These findings pave the way for refining genetic strategies to enhance tissue specificity and reliability in functional genomics and disease modeling.