Induction of hepatic choriogenin mRNA expression in male marine medaka: a highly sensitive biomarker for environmental estrogens.
Teleost choriogenins, precursors of the inner layer subunits of egg envelope, have been recently introduced as sensitive biomarkers for exposure to estrogenic compounds. In this study, two full-length cDNAs-ojChgH and ojChgL which encode the choriogenin H and L forms, respectively, were cloned from the marine medaka, Oryzias javanicus. The deduced protein sequences of ojChgH and ojChgL are highly similar to the corresponding homologues in the freshwater medaka (O. latipes) with identities of 77.2 and 87.6%, respectively. Phylogenetic analysis indicated that ojChgH and ojChgL are members of two different classes of liver-specific ZP-domain containing proteins (ZPB and ZPC, respectively). Computer analysis of ca. 2 kb of the 5'-flanking sequences of ojChgH and ojChgL revealed that both genes contain a number of putative estrogen response elements (EREs) and/or half-site EREs. In vivo mRNA expression patterns of the genes were examined by quantitative real-time RT-PCR. ojChgH is expressed exclusively in the liver while ojChgL is co-expressed in the liver (major) and ovary (minor). Exposure of fish to waterborne 17beta-estradiol (E2) at environmentally relevant concentrations (1, 5, 10 and 100 ng/L) resulted in dose-dependent induction of both genes in the liver, with higher sensitivity and magnitude of induction in males than in females. In the male liver, induction of ojChgH is more sensitive to E2 than that of ojChgL and two other estrogen-responsive genes, estrogen receptor alpha (ojERalpha) and vitellogenin (ojVTG). The lowest-observed-effect concentration (LOEC) of E2 on induction of hepatic ojChgH mRNA is 1 ng/L. In the ovary, expression of ojChgL is non-responsive to E2 treatment. In conclusion, the present study suggested that induction of hepatic ojChgH mRNA in male fish may be a highly sensitive biomarker for exposure to environmental estrogens.
Yu
Richard Man Kit
RM
Department of Biology and Chemistry, Centre for Marine Environmental Research and Innovative Technology, MERIT, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong.
Wong
Minnie Man Lai
MM
Kong
Richard Yuen Chong
RY
Wu
Rudolf Shiu Sun
RS
Cheng
Shuk Han
SH
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D015415:Biomarkers / Q000032:analysis; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D004527:Egg Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics; D004784:Environmental Monitoring; D047628:Estrogen Receptor alpha / Q000032:analysis / Q000187:drug effects / Q000235:genetics; D004967:Estrogens / Q000633:toxicity*; D005260:Female; D029941:Fish Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009990:Oryzias / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D011498:Protein Precursors / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D050436:Regulatory Elements, Transcriptional / Q000235:genetics; D014819:Vitellogenins / Q000032:analysis / Q000187:drug effects / Q000235:genetics; D014874:Water Pollutants, Chemical / Q000633:toxicity
D015415:Biomarkers; D004527:Egg Proteins; D047628:Estrogen Receptor alpha; D004967:Estrogens; D029941:Fish Proteins; C092024:L-SF protein, Oryzias latipes; D011498:Protein Precursors; D012333:RNA, Messenger; D014819:Vitellogenins; D014874:Water Pollutants, Chemical; C104950:choriogenin H