Histochem Cell Biol (2011) 135:581–591 585 Fig. 2 Immunoﬂuorescence colocalization of DPPIV (red) and Cx32 (green) in clusters of normal (a, b, c, g) and nodular (d, e, f, h) hepatocytes. a, d DPPIV only; b, e Cx32 staining only; c, f, g, h staining for DPPIV and Cx32 were merged. Note the regular pattern normal hepatocytes (Fig. 2a–c, g). However, in nodular hepatocyte clusters resulting from the transplantation of isolated nodular cells, the expression of Cx32 was nearly absent or greatly reduced (Fig. 2d–f, h). Furthermore, low Cx32 levels were found in nodules with high or low proliferative rates, as indicated by Ki67 labelling ranging from 2% (Fig. 3b) to 34% (Fig. 3f). In contrast, clusters of normal transplanted hepatocytes with high or low Ki67 labelling displayed a normal pattern of Cx32 expression, comparable to or even higher than that of the surrounding host tissue (Fig. 3g–h). No correlation could therefore be established between Cx32 expression and proliferative activity in nodular hepatocyte clusters. The expression of E-cadherin in transplanted normal and nodular hepatocytes Another protein critically involved in the genesis and maintenance of tissue architecture in the liver is E-cad- herin. Cadherins constitute a superfamily of at least 80 of expression of Cx32 in normal hepatocyte clusters (b, c, g), while the gap junction protein is almost undetected in the donor-derived nodular lesion (e, f, h). See ‘‘Materials and methods’’ for details members and are a major component of adherens junc- tion, i.e. the zipper-like seals between adjacent cells. Cadherin–catenin complexes are also at the crossroad of cell signalling coupled with cell adhesion (van Roy and Berx 2008). The epithelial E-cadherin is expressed in the normal liver and is under dynamic regulation during liver regeneration following partial hepatectomy (Monga et al. 2001). In the present study, our aim was to com- pare the levels of expression of E-cadherin in the expanding clusters of transplanted normal and nodular hepatocytes, in light of the phenotypic differences in their growth pattern described above. The results obtained are illustrated in Fig. 4. Clusters of transplanted normal hepatocytes displayed a regular distribution of E-cadherin in the cell membrane (Fig. 4a–d). However, such regular distribution was completely abrogated in nodular hepatocyte clusters (Fig. 4e–h). In fact, the latter displayed an overall decrease and patchy staining of the cell adhesion protein, in line with the altered morphology of nodular lesions. 123