We are well aware that our N2IC-expressing mouse models by no means FK506 manufacturer represent a physiological condition when normally exact timing of fine-tuned Notch dosages navigates developmental cell fates. However, our results provide a proof of principle that adult mouse hepatocytes are capable to undergo rapid biliary transdifferentiation in vivo when embryonic signaling pathways are reactivated. It has been a debate

on principles whether biliary transdifferentiation of hepatocytes happens in vivo and whether this represents a general regeneration mechanism in response to injury.1, 33 Numerous studies have demonstrated the capability of isolated hepatocytes to undergo biliary transformation in vitro (for review, see Ref.1). However, Tanespimycin data that unambiguously show hepatocyte transdifferentiation in vivo are scarce. Only

by generating chimeric rats by hepatocyte transplantation and combining bile duct ligation with the application of a biliary toxin one group was able to demonstrate that transplanted hepatocytes can give rise to bile ductules.4 Zong et al.6 demonstrated that inducible transgenic Notch1IC (N1IC) expression using the AlbCreERT2 promoter resulted in the appearance of some ectopic tubular structures of biliary phenotype when 6-day-old mice were subjected to repetitive tamoxifen injections for 3 weeks. Their findings were suggestive that the sensitivity of embryonic hepatoblasts to Notch signals extends to young hepatocytes shortly after birth; however, in that study it could not be ruled out that progenitor cells gave rise to the ectopic biliary structures observed. In another recent study by Fan et al.,34 the adenoviral delivery of N1IC together with constitutively active AKT1 led to the lobular appearance of singular hepatobiliary selleckchem hybrid cells that, however, rapidly clonally expanded to give rise to invasive cholangiocytic tumors. After combining this model with hepatocyte lineage tracing using adenoviral transfer

of transthyretin-Cre into R26EYFP reporter animals the authors concluded that the biliary tumors were of hepatocyte origin. This conclusion supports the concept that adult hepatocytes may change cell fates upon stimulation with N1IC. Nevertheless, some concerns with this adenoviral hepatocyte fate-tracing model remain in terms of possible Cre expression in the biliary compartment during malignant transformation. In our study, we used the HNF1βCreERT2 mouse line to specifically direct N2IC expression to the biliary and facultative progenitor compartment. Using this approach, we show that the lobular biliary structures in R26N2ICMxCre animals were not the progeny of N2IC-expressing biliary cells or progenitors, thereby circumventing potential confounding variables that may arise from hepatocyte transplantation or adenoviral models. In comparison to the above-mentioned studies by Zong et al. and Fan et al.