Histochem Cell Biol (2011) 135:581–591 DOI 10.1007/s00418-011-0813-3 O R I G I N A L P A P E R The growth pattern of transplanted normal and nodular hepatocytes Silvia Doratiotto • Petra Krause • Maria Paola Serra • Fabio Marongiu • Marcella Sini • Sarah Koenig • Ezio Laconi Accepted: 15 April 2011 / Published online: 29 April 2011 The Author(s) 2011. This article is published with open access at Springerlink.com Abstract Overt neoplasia is often the end result of a long biological process beginning with the appearance of focal lesions of altered tissue morphology. While the putative clonal nature of focal lesions has often been emphasized, increasing attention is being devoted to the possible role of an altered growth pattern in the evolution of carcinogenesis. Here we compare the growth patterns of normal and nodular hepatocytes in a transplantation system that allows their selective clonal proliferation in vivo. Rats were pre-treated with retrorsine, which blocks the growth of resident hepa- tocytes, and were then transplanted with hepatocytes iso- lated from either normal liver or hepatocyte nodules. Both cell types were able to proliferate extensively in the reci- pient liver, as expected. However, their growth pattern was remarkably different. Clusters of normal hepatocytes inte- grated in the host liver, displaying a normal histology; however, transplanted nodular hepatocytes formed new hepatocyte nodules, with altered morphology and sharp demarcation from surrounding host liver. Both the expres- sion and distribution of proteins involved in cell polarity, cell communication, and cell adhesion, including connexin 32, E-cadherin, and matrix metalloproteinase-2, were altered in clusters of nodular hepatocytes. Furthermore, we S. Doratiotto and P. Krause contributed equally to this work. S. Doratiotto M. P. Serra F. Marongiu M. Sini E. Laconi (&) Department of Biomedical Sciences and Biotechnology, Section of Experimental Pathology, University of Cagliari, Via Porcell, 4, 09125 Cagliari, Italy e-mail: elaconi@unica.it P. Krause S. Koenig Department of General Surgery, University Medical Centre Goettingen, Go¨ttingen, Germany were able to show that down-regulation of connexin 32 and E-cadherin in nodular hepatocyte clusters was independent of growth rate. These results support the concept that a dominant pathway towards neoplastic disease in several organs involves defect(s) in tissue pattern formation. Keywords Liver nodules Growth pattern Cell transplantation Focal growth Introduction Many human solid cancers, including hepatocellular car- cinoma, often arise from discrete focal lesions that long precede the overt clinical appearance of the disease. In fact, it is well established that such lesions represent a common precursor site for overt neoplasia (Clark et al. 1984; Foulds 1975; Hruban et al. 2000; Hytiroglou et al. 2007; Montironi et al. 2002; Noffsinger 2009; Schreer and Lu¨ ttges 2005; Su et al. 1997), thus implying that gaining insights into their biology and pathogenesis bears direct relevance to our understanding of the natural history of neoplastic disease. Historically, the salient feature of cancer precursor lesions has been considered to reside in their putative clonal nature, and this notion still forms the basis for most of the current theories on the pathogenesis of neoplastic disease (Diallo et al. 2001; Garcia et al. 2000; Iannaccone et al. 1987; Mason et al. 2010). Within this perspective, research efforts continue to be focussed mainly on putative biochemical and molecular changes of rare altered cells that could possibly explain their selective growth, resulting in the emergence of focal proliferative lesions (Hanahan and Weinberg 2000). However, over the past few years increasing attention has been devoted to the analysis of the phenotypic property 123