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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-1α 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-1α  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.    Conclusion  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.

bmc molecular biology

Hypoxia induces telomerase reverse transcriptase (TERT) gene expression in non-tumor fish tissues in vivo: the marine medaka (Oryzias melastigma) model