Hypoxia induces telomerase reverse transcriptase (TERT) gene expression in non-tumor fish tissues in vivo: the marine medaka (Oryzias melastigma) model.
BACKGROUND
Current understanding on the relationships between hypoxia, hypoxia-inducible factor-1 (HIF-1) and telomerase reverse transcriptase (TERT) gene expression are largely based on in vitro studies in human cancer cells. Although several reports demonstrated HIF-1- mediated upregulation of the human TERT gene under hypoxia, conflicting findings have also been reported. Thus far, it remains uncertain whether these findings can be directly extrapolated to non-tumor tissues in other whole animal systems in vivo. While fish often encounter environmental hypoxia, the in vivo regulation of TERT by hypoxia in non-neoplastic tissues of fish remains virtually unknown.


RESULTS
The adult marine medaka (Oryzias melastigma) was employed as a model fish in this study. We have cloned and characterized a 3261-bp full-length TERT cDNA, omTERT, which encodes a protein of 1086 amino acids. It contains all of the functional motifs that are conserved in other vertebrate TERTs. Motif E is the most highly conserved showing 90.9-100% overall identity among the fish TERTs and 63.6% overall identity among vertebrates. Analysis of the 5'-flanking sequence of the omTERT gene identified two HRE (hypoxia-responsive element; nt. - 283 and - 892) cores. Overexpression of the HIF-1alpha induced omTERT promoter activity as demonstrated using transient transfection assays. The omTERT gene is ubiquitously expressed in fish under normoxia, albeit at varying levels, where highest expression was observed in gonads and the lowest in liver. In vivo expression of omTERT was significantly upregulated in testis and liver in response to hypoxia (at 96 h and 48 h, respectively), where concomitant induction of the omHIF-1alpha and erythropoietin (omEpo) genes was also observed. In situ hybridization analysis showed that hypoxic induction of omTERT mRNA was clearly evident in hepatocytes in the caudal region of liver and in spermatogonia-containing cysts in testis.


CONCLUSIONS
This study demonstrates for the first time, hypoxic regulation of TERT expression in vivo in a whole fish system. Our findings support the notion that hypoxia upregulates omTERT expression via omHIF-1 in non-neoplastic fish liver and testis in vivo. Overall, the structure and regulation of the TERT gene is highly conserved in vertebrates from fish to human.
Yu
Richard M K
RM
Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong. bhrichyu@cityu.edu.hk
Chen
Eric X H
EX
Kong
Richard Y C
RY
Ng
Patrick K S
PK
Mok
Helen O L
HO
Au
Doris W T
DW
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D004790:Enzyme Induction; D005136:Eye Proteins / Q000235:genetics; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000201:enzymology* / Q000235:genetics; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology*; D017403:In Situ Hybridization; D008099:Liver / Q000201:enzymology; D008297:Male; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics; D009990:Oryzias / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013094:Spermatozoa / Q000201:enzymology; D019098:Telomerase / Q000096:biosynthesis* / Q000235:genetics; D013737:Testis / Q000201:enzymology; D015533:Transcriptional Activation; D014714:Vertebrates / Q000235:genetics; D014781:Viscera / Q000201:enzymology
D004268:DNA-Binding Proteins; D005136:Eye Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; C509186:TERT protein, human; D019098:Telomerase