588 Discussion In this study, we compare the growth pattern and the expression of proteins involved in cell adhesion, to cell-to- cell communication and cell migration in two different populations of clonally expanding hepatocytes: namely, hepatocytes isolated from a normal untreated liver and hepatocytes isolated from carcinogen-induced liver nod- ules. In a former study, we already observed that neither cell type was able to proliferate to any signiﬁcant extent upon transplantation into syngeneic, untreated normal hosts (Laconi et al. 2001a). However, both normal and nodular hepatocytes underwent selective clonal expansion follow- ing injection into the liver of rats pre-treated with RS. Furthermore, we observed that the biological outcome was radically different following transplantation of either cell type in RS-treated recipients, as expected (Laconi et al. 2001a, b). In fact, the selective proliferation of normal transplanted hepatocytes resulted in liver repopulation, reproducing a seemingly normal tissue architecture, with Histochem Cell Biol (2011) 135:581–591 Fig. 6 Expression of MMP-2 RNA in normal and nodular hepatocyte preparations. Triplicates of both cell preparations were processed. A marked reduction in gene expression is evident in nodular cells (upper lanes); in the lower lanes the expression of the beta-2- microglobulin gene is presented for comparison. The experiment was repeated twice with similar pattern of results. See ‘‘Materials and methods’’ for details no evidence of pre-neoplastic and/or neoplastic lesions (Laconi et al. 2001b). In contrast, the transplantation of nodular hepatocytes was consistently associated with their failure to integrate in the host liver and the formation of liver nodules. Moreover, such nodules had the potential to progress to hepatocellular carcinoma (Laconi et al. 2001a), as also conﬁrmed in this study (data not presented). Fig. 5 Immunoﬂuorescence colocalization of DPPIV (red) and MMP-2 (green) in clusters of normal (a, b, c, g) and nodular (d, e, f, h). Normal hepatocyte clusters display decreased ﬂuorescence staining for MMP-2 compared to surrounding host liver (a–c). However, low levels of expression are detected (g). In contrast, no MMP-2 protein is detectable inside nodular hepatocyte clusters, while intense expression is noted in the surrounding liver (d, e, f, h). See ‘‘Materials and methods’’ for details 123