title: Hypoxia-inducible factor 2 alpha is essential for hepatic outgrowth and functions via the regulation of leg1 transcription in the zebrafish embryo.
abstract: The liver plays a vital role in metabolism, detoxification, digestion, and the maintenance of homeostasis. During development, the vertebrate embryonic liver undergoes a series of morphogenic processes known as hepatogenesis. Hepatogenesis can be separated into three interrelated processes: endoderm specification, hepatoblast differentiation, and hepatic outgrowth. Throughout this process, signaling molecules and transcription factors initiate and regulate the coordination of cell proliferation, apoptosis, differentiation, intercellular adhesion, and cell migration. Hifs are already recognized to be essential in embryonic development, but their role in hepatogenesis remains unknown. Using the zebrafish embryo as a model organism, we report that the lack of Hif2-alpha but not Hif1-alpha blocks hepatic outgrowth. While Hif2-alpha is not involved in hepatoblast specification, this transcription factor regulates hepatocyte cell proliferation during hepatic outgrowth. Furthermore, we demonstrated that the lack of Hif2-alpha can reduce the expression of liver-enriched gene 1 (leg1), which encodes a secretory protein essential for hepatic outgrowth. Additionally, exogenous mRNA expression of leg1 can rescue the small liver phenotype of hif2-alpha morphants. We also showed that Hif2-alpha directly binds to the promoter region of leg1 to control leg1 expression. Interestingly, we discovered overrepresented, high-density Hif-binding sites in the potential upstream regulatory sequences of leg1 in teleosts but not in terrestrial mammals. We concluded that hif2-alpha is a key factor required for hepatic outgrowth and regulates leg1 expression in zebrafish embryos. We also proposed that the hif2-alpha-leg1 axis in liver development may have resulted from the adaptation of teleosts to their environment.
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Tzung-Yi
authors.initials: TY
authors.lastname: Lin
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Chi-Fu
authors.initials: CF
authors.lastname: Chou
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Hsin-Yu
authors.initials: HY
authors.lastname: Chung
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Chia-Yin
authors.initials: CY
authors.lastname: Chiang
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Chung-Hao
authors.initials: CH
authors.lastname: Li
authors.affiliation: Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan.
authors.forename: Jen-Leih
authors.initials: JL
authors.lastname: Wu
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Han-Jia
authors.initials: HJ
authors.lastname: Lin
authors.affiliation: Department of Computer Science and Engineering, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Tun-Wen
authors.initials: TW
authors.lastname: Pai
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Chin-Hwa
authors.initials: CH
authors.lastname: Hu
authors.affiliation: Department of Life Sciences, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Wen-Shyong
authors.initials: WS
authors.lastname: Tzou
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D003035:Cobalt / Q000494:pharmacology; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D055785:Gene Knockdown Techniques; D017228:Hepatocyte Growth Factor / Q000378:metabolism; D007422:Intestines / Q000196:embryology; D008099:Liver / Q000166:cytology / Q000196:embryology*; D009929:Organ Size / Q000187:drug effects; D046790:Pancreas, Exocrine / Q000196:embryology; D010641:Phenotype; D011401:Promoter Regions, Genetic / Q000235:genetics; D020218:Response Elements / Q000235:genetics; D014158:Transcription, Genetic; D060449:Wnt Signaling Pathway / Q000187:drug effects; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics*; D029961:Zebrafish Proteins / Q000235:genetics*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D003035:Cobalt; D005346:Fibroblast Growth Factors; D017228:Hepatocyte Growth Factor; D029961:Zebrafish Proteins; D000099162:Endothelial PAS Domain-Containing Protein 1; C569822:leg1.1 protein, zebrafish; C569823:leg1.2 protein, zebrafish; C018021:cobaltous chloride