It is possible that the biliary cells derived from hepatocytes will suspend the expression of DPPIV as the restoration process come to an end. It can be argued that the biliary cells from the donor liver are the source of new biliary cells observed in the chimeric liver. However, after collagenase perfusion of the donor liver only <5% contamination

of small admixture of nonparenchymal cells including biliary, stellate, endothelial, and other cell types was noticed as in routine hepatocyte preparations. In addition, the chimeric rats are treated with DAPM that targets biliary cells specifically. Therefore it is unlikely that newly appearing biliary cells originate from the very small if any biliary contamination engrafted in the chimeric

liver. In the chimeric rats, after a thorough examination, PF-3084014 in vitro not a single DPPIV-positive bile duct epithelial cell was observed in total 45 portal triads examined in the sections taken randomly. DPPIV positive biliary cells are observed in the chimeric liver only after the DAPM treatment regimen. During liver development both hepatocytes and BECs differentiate from hepatoblasts. The lineage-specific differentiation is regulated by cell-specific gene expression in turn controlled primarily by distinct sets of transcription factors [30, 31]. Altered patterns of cell specificity in the expression of the transcription factors between hepatocytes and BECs has been observed under severe Inositol monophosphatase 1 hepatic necrosis and chronic biliary disease in human patients [9, 26] as well as in experimental conditions of 2AAF

+ PHx treatment HSP990 mouse [29]. In the present study, expression of the hepatocyte-specific transcription factor HNF4α was observed in the newly repairing NU7026 ductules after DAPM + BDL and repeated DAPM injury. The newly repaired biliary ductules showed appearance of hepatocyte-like cells carrying HNF4α expression. It is interesting to note that the level of the HNF4α expression in repairing ductular cells was lower compared to normal hepatocytes suggesting its gradual loss during reprogramming towards biliary phenotype. Consistent with that notion, HNF4α expressing ductular cells also expressed HNF1β, a BEC-specific transcription factor. Specific inactivation of Hnf1β gene in hepatocytes and bile duct cells using the Cre/loxP system results in abnormalities of the gallbladder and intrahepatic bile ducts, suggesting an essential function of Hnf1β in bile duct morphogenesis [17]. Gain of expression of HNF1β by the hepatocytes normally expressing HNF4α indicates switch to the biliary specification of these cells. In order to examine if the mechanisms that govern the differentiation of hepatoblasts into BECs are recapitulated during transdifferentiation of mature hepatocytes into BECs, expression of TGFβ1 and Onecut factor HNF6 were assessed. During liver embryogenesis, a gradient of TGFβ signaling has been shown to control ductal plate hepatoblasts differentiation [20].