1C, top). Cre expression was found only in albNScko livers and showed a prominent peak at 2 weeks of age (Fig. 1C, bottom). Histologically, albNScko livers appeared no different from NSflx/flx

livers up to 1 week of age, but began to show increased cellularity around bile ducts at 2 weeks of age (Supporting Fig. 2A-D). When albNScko mice reached 3-4 weeks of age, the liver surface displayed a nodular appearance (Fig. 1D) and showed areas of extensive bile duct hyperplasia (BDH; Fig. 1E1,E2 and Supporting Fig. 2E,F), portal and periportal fibrosis (Supporting Fig. 2G), and necrotic foci in parenchyma (Fig. 1E3). The liver/body weight ratio of albNScko selleck products mice began to exceed that of NSflx/flx mice at 3 weeks (Fig. 1F). These results demonstrate that NS deletion caused liver parenchymal damage and BDH. To establish onset of NS deletion and cell type(s) involved, we examined selleck kinase inhibitor NS expression in

albNScko livers from postnatal day 1 (P1D) to 3 weeks of age. Though a significant number of albNScko hepatocytes still retained their NS expression at P1D, almost all of them lost their NS expression at 1 and 2 weeks of age (Fig. 2A). These findings are consistent with a previous report that differentiated hepatocytes functionally expressing Alb-Cre are rare and distribute in a mosaic pattern in fetal livers.[15] In 2- to 3-week-old albNScko livers, NS-positive cells were mostly confined to the hyperplastic ductular epithelium (Fig. 2B, left panels) and the regenerative hepatic nodules (Fig. 3D1). Contrarily, MCE in the 3-week-old NSflx/flx liver, NS signals were found only in scattered hepatocytes, but not in bile duct epithelial

cells (BECs; Fig. 2B, right panels). Although we cannot exclude the expression of Alb-Cre in subsets of BECs, these results indicate that expression of NS is depleted predominantly in the hepatocytic lineage by albNScko from 1 week of age, but is maintained in the hyperplastic BECs. The time sequence of NSKO-induced events was determined by measuring onset of DNA damage, cell death, and hepatic regeneration in albNScko livers. DNA damage in vivo was detected by the foci formation of phosphorylated histone H2AX (γ-H2AX), which plays a key role in assembling DNA damage response and repair proteins at the damage sites and provides a rapid, sensitive way to detect the DNA damage event.[18] Our results showed that γ-H2AX+ hepatocytes are increased by albNScko as early as 1 week of age (Fig. 3A). This event peaks at 2 weeks and gradually declines afterward, coinciding with the temporal pattern of Cre expression. TUNEL assays showed that the increase of cell death occurs after the DNA damage event and peaks at 3 weeks (Fig. 3B).