A novel keratin18 promoter that drives reporter gene expression in the intrahepatic and extrahepatic biliary system allows isolation of cell-type specific transcripts from zebrafish liver

• A novel keratin18 promoter marks all biliary cells in transgenic zebrafish.
• TRAP methodology can be used to recover polysome RNA from specific liver cell types.
• These tools allow cell lineage tracing and gene profiling during zebrafish liver development and in zebrafish disease models.

Heritable and acquired biliary disorders are an important cause of acute and chronic human liver disease. Biliary development and physiology have been studied extensively in rodent models and more recently, zebrafish have been used to uncover pathogenic mechanisms and potential therapies for these conditions. Here we report development of novel transgenic lines labeling the intrahepatic and extrahepatic biliary system of zebrafish larvae that can be used for lineage tracing and isolation of biliary-specific RNAs from mixed populations of liver cells. We show that GFP expression driven by a 4.4 kilobase promoter fragment from the zebrafish keratin18 (krt18) gene allows visualization of all components of the developing biliary system as early as 3 days post-fertilization. In addition, expression of a ribosomal fusion protein (EGFP-Rpl10a) in krt18:TRAP transgenic fish allows for enrichment of translated biliary cell mRNAs via translating ribosome affinity purification (TRAP). Future studies utilizing these reagents will enhance our understanding of the morphologic and molecular processes involved in biliary development and disease.