p53-mediated biliary defects caused by knockdown of cirh1a, the zebrafish homolog of the gene responsible for North American Indian Childhood Cirrhosis

• Published in: PloS one Vol. 8; no. 10; p. e77670
• Main Authors: Wilkins, Benjamin J, Lorent, Kristin, Matthews, Randolph P, Pack, Michael
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 11.10.2013; Public Library of Science (PLoS)
• Subjects: Analysis; Anemia; Animals; Apoptosis; Bile; Biopsy; Biosynthesis; Birth defects; Cell cycle; Cellular stress response; Children; Cirrhosis; Congenital defects; Congenital diseases; Cytology; Danio rerio; Defects; Disease; Embryos; Epithelial cells; Evolution; Fluorescence; Gallbladder diseases; Gene expression; Genetic aspects; Genetic disorders; Hepatocytes; Hepatocytes - metabolism; Homology; Humans; Hypertension; In Situ Hybridization; Larva - metabolism; Larvae; Liver; Liver - cytology; Liver - metabolism; Liver cirrhosis; Liver Cirrhosis, Biliary - genetics; Liver Cirrhosis, Biliary - metabolism; Medicine; Metabolism; Missense mutation; Mutation; Mutation, Missense - genetics; Native Americans; Native North Americans; Nucleoli; Oligonucleotides; p53 Protein; Pathogenesis; Physiological aspects; Proteins; Ribonucleic acid; Ribonucleoproteins - genetics; Ribosomal RNA; RNA; RNA processing; rRNA; Transcription; Tumor proteins; Tumor Suppressor Protein p53 - genetics; Tumor Suppressor Protein p53 - metabolism; Yeast; Zebrafish; Zebrafish Proteins - genetics; Zebrafish Proteins - metabolism; United States > US; Pennsylvania
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0077670

North American Indian Childhood Cirrhosis (NAIC) is a rare, autosomal recessive, progressive cholestatic disease of infancy affecting the Cree-Ojibway first Nations of Quebec. All NAIC patients are homozygous for a missense mutation (R565W) in CIRH1A, the human homolog of the yeast nucleolar protein Utp4. Utp4 is part of the t-Utp subcomplex of the small subunit (SSU) processome, a ribonucleoprotein complex required for ribosomal RNA processing and small subunit assembly. NAIC has thus been proposed to be a primary ribosomal disorder (ribosomopathy); however, investigation of the pathophysiologic mechanism of this disease has been hindered by lack of an animal model. Here, using a morpholino oligonucleotide (MO)-based loss-of-function strategy, we have generated a model of NAIC in the zebrafish, Danio rerio. Zebrafish Cirhin shows substantial homology to the human homolog, and cirh1a mRNA is expressed in developing hepatocytes and biliary epithelial cells. Injection of two independent MOs directed against cirh1a at the one-cell stage causes defects in canalicular and biliary morphology in 5 dpf larvae. In addition, 5 dpf Cirhin-deficient larvae have dose-dependent defects in hepatobiliary function, as assayed by the metabolism of an ingested fluorescent lipid reporter. Previous yeast and in vitro studies have shown that defects in ribosome biogenesis cause stabilization and nuclear accumulation of p53, which in turn causes p53-mediated cell cycle arrest and/or apoptosis. Thus, the nucleolus appears to function as a cellular stress sensor in some cell types. In accordance with this hypothesis, transcriptional targets of p53 are upregulated in Cirhin-deficient zebrafish embryos, and defects in biliary function seen in Cirhin-deficient larvae are completely abrogated by mutation of tp53. Our data provide the first in vivo evidence of a role for Cirhin in biliary development, and support the hypothesis that congenital defects affecting ribosome biogenesis can activate a cellular stress response mediated by p53.