Levels of liver enzymes such as alanine aminotransferase (ALT), alkaline phosphatase and γ-glutamyl transferase are clinical markers of liver injury, and are used to diagnose and monitor alcoholic liver disease, non-alcoholic fatty liver disease, cirrhosis, hepatitis and drug-induced liver injury

Levels of liver enzymes such as alanine aminotransferase (ALT), alkaline phosphatase and γ-glutamyl transferase are clinical markers of liver injury, and are used to diagnose and monitor alcoholic liver disease, non-alcoholic fatty liver disease, cirrhosis, hepatitis and drug-induced liver injury (Goessling and Friedman, 2005). Plasma concentrations of these enzymes can also be affected by heritable factors (Bathum et al., 2001), and investigating the genes influencing liver enzyme concentrations can shed light on the molecular mechanisms of liver disease. Previous genome-wide association studies (GWAS) have been conducted to uncover genetic loci associated with concentrations of plasma liver enzymes (Chambers et al., 2011; Yuan et al., 2008). Six loci were initially identified in a GWAS of 7715 individuals (Yuan et al., 2008) and 36 additional loci were identified in a second GWAS using a larger population of 61,089 individuals, which increased the likelihood that additional genes reached statistical significance (Chambers et al., 2011). These 42 loci correspond to 69 probable candidate genes, which represent many previously unknown associations and provide a remarkable resource for further investigation and functional insight into the disease mechanisms and molecular mediators involved in maintaining liver homeostasis. However, as with other GWAS, the size of this gene list can hinder further investigation of individual candidate genes owing to the difficulty of selecting the most important or biologically relevant genes at each locus, combined with the lack of rapid and cost-effective screening methods to prioritize genes for follow-up. Zebrafish embryos exhibit many characteristics that are ideal for functional validation of GWAS data, specifically rapid development, high fecundity, and population-level variation similar to humans because zebrafish are not inbred. In this study, we utilize the zebrafish embryo for functional characterization of a subset of genes found to influence liver enzyme levels in human adults. Liver enzyme elevation in human patients is a specific measure, but is reflective of a patient’s susceptibility to injury and their overall liver function. Previous studies revealed that pathways regulating liver homeostasis in the adult are also important for embryonic liver development, indicating the possibility of eliciting organ-relevant phenotypic changes during organogenesis (Goessling et al., 2008). Furthermore, aspects of fatty liver disease and drug-induced liver injury can be modeled in both the zebrafish adult and embryo (North et al., 2010; Passeri et al., 2009). We can also use hematopoieticallyexpressed homeobox protein (hhex) and liver fatty acid binding protein (fabp10a), genes specifying hepatic progenitors and hepatocytes, respectively, as markers of liver growth and maintenance, which are reflective of liver health and homeostasis and can be easily assessed in the zebrafish embryo. We therefore aimed to functionally validate