Abstract
Polyploidy, the existence of cells containing more than one pair of chromosomes, is a well-known feature of mammalian hepatocytes. Polyploid hepatocytes are found either as cells with a single polyploid nucleus or as multinucleated cells with diploid or even polyploid nuclei. In this study, we evaluate the degree of polyploidy in the murine liver by accounting both DNA content and number of nuclei per cell. We demonstrate that mouse hepatocytes with diploid nuclei have distinct metabolic characteristics compared to cells with polyploid nuclei. In addition to strong differential gene expression, comprising metabolic as well as signaling compounds, we found a strongly decreased insulin binding of nuclear polyploid cells. Our observations were associated with nuclear ploidy but not with total ploidy within a cell. We therefore suggest ploidy of the nuclei as an new diversity factor of hepatocytes and hypothesize that hepatocytes with polyploid nuclei may have distinct biological functions than mono-nuclear ones. This diversity is independent from the well-known heterogeneity related to the cells' position along the porto-central liver-axis.
Highlights
Somatic eukaryotic cells are usually diploid, i.e., have a pair (2n) for each set of n chromosomes
In order to differentiate between binuclear diploid and mononuclear 4n polyploid hepatocytes, cells were fixed after overnight culture to allow cell adherence and repolarization and stained with DAPI at saturating concentration to visualize the nuclei and ß-catenin was labeled with AlexaFluor 546 for visualizing the membrane by High-Content Screening (HCS, Figure 1B)
By combining flow cytometry and HCS we were able to identify, quantitate and characterize different entities of hepatocytes in the liver of mice based on the number of nuclei per cell and their respective ploidy status
Summary
Somatic eukaryotic cells are usually diploid, i.e., have a pair (2n) for each set of n chromosomes. Cells may possess greater than two sets of chromosomes, a condition which has been termed polyploidy. Such polyploid cells can either be mononuclear or binuclear. Polyploid cells with 4n in a single nucleus occur if karyokinesis has failed for a diploid cell, whereas two diploid nuclei (2∗2n) emerge in the case of failure of cytokinesis. Since both events may occur repeatedly and can succeed each other, further combinations like 8n, or multinucleated cells with polyploidy nuclei, e.g., 2∗4n, can occur. Genome duplication is considered a driving force in the early evolution of vertebrates (Panopoulou and Poustka, 2005), including primates (Bailey et al, 2002)
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