After 2 months, we examined the liver samples of the surviving 3 rats under a fluorescence microscope before and after performing IF staining for albumin and fluorescence in situ hybridization (FISH) for Y-chromosome. Unstained sections revealed the presence of PKH+ cell clusters (approximately

1% of all cells) morphologically consistent with biliary ductal cells and hepatocytes (Fig. 7A-C). To confirm this finding, we then proceeded with IF staining for albumin and FISH for Y-chromosome, which showed the presence of male hepatocytes (Fig. 7D-F; Supporting Fig. 4C) in approximately 0.2% of the cells examined. This is not an insignificant DMXAA nmr number, in view of the fact that even in our positive control, male rat liver, (Supporting Fig. 4B) only 2% of cells were positive for Y-chromosome. Taken together, our findings strongly suggested that LDPCs had engrafted and differentiated into hepatocytes in the recipient animals. The main aim of this study was to identify the origin of LDPC, which are unique bipotential adult hepatic progenitors that were first isolated and characterized by us.18 LDPCs, which are capable of forming mature hepatocytes both in vitro and in vivo, are generated in culture from normal liver tissues that have

not been exposed to chemicals or any type of injury. selleck This is in contrast to the many published protocols used to generate the quintessential hepatic progenitor oval cells. Therefore, LDPCs have a unique clinical application potential in humans. However, the source or the origin of these cells, and, therefore, their lineage relationship to other cells in the liver, is essentially unknown. It is now well established that many adult tissues harbor stem cells or progenitors, which are capable of generating some or all of the cell types found in that particular tissue. Commonly referred

to as “tissue-specific stem cells,” these cells have been identified in tissues including, but not limited to, heart, skin, brain, small intestine, mammary medchemexpress gland, and teeth.26-31 In the adult liver, however, the situation is a bit more complex. This results from an extensive proliferative capacity of mature hepatocytes, which can regenerate the original liver mass even after 90% hepatectomy. However, when the degree of liver injury is very severe or when the liver has been exposed to certain toxins or chemicals, hepatocytes are unable to proliferate. It is under these conditions that the hepatic stem/progenitor compartment is activated. The most widely known and characterized liver progenitors are oval cells. They are believed to have primary hepatic origin and are thought to reside in small numbers in the terminal bile ducts. It is widely accepted, and perhaps even assumed, that hepatocytes do not contribute directly to this progenitor or stem cell compartment.