title: Characterization and expression of C/EPB-like genes in the liver of Rana catesbeiana tadpoles during spontaneous and thyroid hormone-induced metamorphosis.
abstract: Tissue-specific changes in gene expression occur in the liver of Rana catesbeiana tadpoles undergoing metamorphosis. Many of these changes can be induced precociously by administration of thyroid hormone (TH) to a tadpole or to cultured tadpole liver. While the precise molecular means by which TH exerts a tissue-specific response is unknown, recent studies suggest that the expression of genes which are liver-specific and characteristic of the adult liver phenotype may rely on TH-induction of tissue-specific transcription factors, as well as the thyroid hormone receptor proteins. Guided by this notion, we screened our Rana catesbeiana liver cDNA library and isolated clones, RcC/EBP-1 and -2, encoding Rana homologues of a mammalian transcription factor, C/EBP (CCAAT/enhancer core binding protein), implicated in the expression of liver-specific genes and terminal differentiation of hepatocytes. Gel mobility shift assays demonstrate that the proteins synthesized from these cDNAs bind specifically to the consensus binding site for C/EBP-related proteins. Characterization of the amino acid sequence in the bZIP DNA-binding domains of these proteins suggests that RcC/EBP-1 and -2 encode Rana homologues of C/EBP alpha and delta, respectively. Hybridization analyses demonstrate that the amount of RcC/EBP-2 mRNAs in tadpole liver remains constant throughout metamorphosis, whereas RcC/EBP-1 mRNAs are up-regulated during both spontaneous and TH-induced metamorphosis. The TH-induced up-regulation of RcC/EBP-1 mRNAs precedes the up-regulation of liver-specific urea cycle enzyme mRNAs by 6 to 12 hours. These results, coupled with in situ hybridization studies, suggest that RcC/EBP-1 mRNAs encode a transcription factor which may play an early role(s) in the terminal differentiation and/or reprogramming of gene expression in this tadpole's liver cells during both spontaneous and TH-induced metamorphosis.
authors.affiliation: Department of Zoology, University of Western Ontario, London, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Hu
authors.forename: B G
authors.initials: BG
authors.lastname: Atkinson
mesh_terms: D000595:Amino Acid Sequence; D029845:Amphibian Proteins; D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D022763:CCAAT-Enhancer-Binding Protein-alpha; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation; D016384:Consensus Sequence; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D051790:G-Box Binding Factors; D005786:Gene Expression Regulation; D005812:Genes, Switch; D007814:Larva; D016350:Leucine Zippers / Q000235:genetics; D008099:Liver / Q000166:cytology / Q000254:growth & development*; D008675:Metamorphosis, Biological / Q000187:drug effects / Q000235:genetics*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D009928:Organ Specificity; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis; D011892:Rana catesbeiana / Q000196:embryology / Q000235:genetics* / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D013963:Thyroid Hormones / Q000502:physiology*; D013974:Thyroxine / Q000502:physiology; D014018:Tissue Distribution; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics; D014284:Triiodothyronine / Q000494:pharmacology / Q000502:physiology
chemical_list: D029845:Amphibian Proteins; D050976:Basic-Leucine Zipper Transcription Factors; C089571:C-EBP-1 protein, Rana catesbeiana; C089572:C-EBP-2 protein, Rana catesbeiana; D022763:CCAAT-Enhancer-Binding Protein-alpha; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051790:G-Box Binding Factors; D009687:Nuclear Proteins; D012333:RNA, Messenger; D013963:Thyroid Hormones; D014157:Transcription Factors; D014284:Triiodothyronine; D051743:CCAAT-Enhancer-Binding Protein-delta; D013974:Thyroxine