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In contrast to the deregulated hepatocellular division that is a feature of many hepatic diseases and malignancies, physiologic liver growth during embryonic development and after partial hepatectomy (PH) in adults is characterized by tightly controlled cell proliferation. We used forward genetic screening in zebrafish to test the hypothesis that a similar genetic program governs physiologic liver growth during hepatogenesis and regeneration after PH. We identified the uhrf1 gene, a cell cycle regulator and transcriptional activator of top2a expression, as required for hepatic outgrowth and embryonic survival. By developing a methodology to perform PH on adult zebrafish, we found that liver regeneration in uhrf1+/- adult animals is impaired. uhrf1 transcript levels dramatically increase after PH in both mice, and zebrafish and top2a is not up-regulated in uhrf1+/- livers after PH. This indicates that uhrf1 is required for physiologic liver growth in both embryos and adults and illustrates that zebrafish livers regenerate. [ABSTRACT FROM AUTHOR]