Comparison of the Opn-CreER and Ck19-CreER Drivers in Bile Ducts of Normal and Injured Mouse Livers

Inducible cyclization recombinase (Cre) transgenic mouse strains are powerful tools for cell lineage tracing and tissue-specific knockout experiments. However, low efficiency or leaky expression can be important pitfalls. Here, we compared the efficiency and specificity of two commonly used cholangiocyte-specific Cre drivers, the Opn-iCreER^T2 and Ck19-CreER^T drivers, using a tdTomato reporter strain. We found that Opn-iCreER^T2 triggered recombination of the tdTomato reporter in 99.9% of all cholangiocytes while Ck19-CreER^T only had 32% recombination efficiency after tamoxifen injection. In the absence of tamoxifen, recombination was also induced in 2% of cholangiocytes for the Opn-iCreER^T2 driver and in 13% for the Ck19-CreER^T driver. For both drivers, Cre recombination was highly specific for cholangiocytes since recombination was rare in other liver cell types. Toxic liver injury ectopically activated Opn-iCreER^T2 but not Ck19-CreER^T expression in hepatocytes. However, ectopic recombination in hepatocytes could be avoided by applying a three-day long wash-out period between tamoxifen treatment and toxin injection. Therefore, the Opn-iCreER^T2 driver is best suited for the generation of mutant bile ducts, while the Ck19-CreER^T driver has near absolute specificity for bile duct cells and is therefore favorable for lineage tracing experiments.

SgIGSF is a novel biliary-epithelial cell adhesion molecule mediating duct/ductule development

Spermatogenic immunoglobulin superfamily (SgIGSF) is an intercellular adhesion molecule of the nectin-like family. While screening its tissue distribution, we found that it was expressed in fetal liver but not adult liver. In the present study, we examined which cells in developing and regenerating liver express SgIGSF via immunohistochemistry and Western blot analysis. In developing mouse liver, SgIGSF expression was transiently upregulated at perinatal ages and was restricted to the lateral membrane of biliary epithelial cells (BECs). In regenerating rat livers from the 2-acetylaminofluorene/partial hepatectomy model, SgIGSF was detected exclusively in oval cells that aligned in ductal and trabecular patterns by the second week posthepatectomy. In human livers, fetal and newborn bile ducts and cirrhotic bile ductules were clearly positive for SgIGSF, whereas disease-free adult bile ducts were negative. To investigate the role of SgIGSF in bile duct/ductule formation, we used an in vitro model in which rat hepatocyte aggregates embedded in collagen gels containing insulin and epidermal growth factor extend epithelial sheets and processes in the first week and form ductules within a month. The process and ductular cells were continuously positive for SgIGSF and cytokeratin 19, a BEC marker. When the aggregate culture was started in the presence of a function-blocking anti-SgIGSF antibody, the number of epithelial processes per aggregate was reduced by 80%.

CONCLUSION

We propose that SgIGSF is a novel and functional BEC adhesion molecule that is expressed for a limited time during active bile duct/ductule formation.

[Bootstrapping algorithm approach reveals inherent regulatory pattern in 550 invasive breast cancer cases: CK5/6/CK14 and CK8/18/CK19 builds an antagonistic set]

All the preliminary observations on a lot of marker sets defining different stages in the tumor development are building a framework of work hypothesis which can be verified in characterising large pools of histological uniform rated paraffin probes. We developed a bootstrapping algorithm based on correlation measures to uncover regulatory patterns of immunohistochemical characterized tissue arrays with 550 invasive breast cancer cases. The algorithm is implemented in 'S' a computer language used to model mathematical solutions. Focussing on the Cytokeratins versus a set of prominent markers in breast cancer differentiation it will be obvious that markers which are known to appear in early (progenitor) forms conform to CK5/6 and CK14 while others associated with late stages conform to CK8/18 and CK19. Markers examined are among others EGFR, EMA, erb-B2, Vimentin, p53, ER and PR. The developed approach is an elegant and complete procedure to reveal the real regulatory patterns which are enclosed in a certain experimental design. The statistical significance of the results calculated by our algorithm is generally high and in the presented experimental design smaller than 0.6 * 10E-6.