Genomic organization and transcriptional modulation in response to endocrine disrupting chemicals of three vitellogenin genes in the self-fertilizing fish Kryptolebias marmoratus

Vitellogenin (Vtg) is the precursor of egg yolk proteins, and its expression has been used as a reliable biomarker for estrogenic contamination in the aquatic environment. To examine the biomarker potential of the self-fertilizing killifish Kryptolebias marmoratus Vtgs (Km-Vtgs), full genomic DNAs of Km-Vtgs-Aa, Km-Vtgs-Ab, and Km-Vtgs-C were cloned, sequenced, and characterized. Three Vtg genes in K. marmoratus are tandemly placed in a 550 kb section of the same chromosome. In silico analysis of promoter regions revealed that both the Km-Vtgs-Aa and Km-Vtgs-Ab genes had an estrogen response element (ERE), but the Km-Vtgs-C gene did not. However, all three Km-Vtgs genes had several ERE-half sites in their promoter regions. Phylogenetic analysis demonstrated that the three deduced amino acid residues were highly conserved with conventional Vtgs protein, forming distinctive clades within teleost Vtgs. Liver tissue showed the highest expression of Km-Vtg transcripts in all tested tissues (brain/pituitary, eye, gonad, intestine, skin, and muscle) in response to endocrine disrupting chemical (EDC)-exposed conditions. Km-Vtg transcripts were significantly increased in response to 17β-estradiol (E2), tamoxifen (TMX), 4-n-nonylphenol (NP), bisphenol A (BPA), and octylphenol (OP) over 24 hr exposure. The Km-Vtg-A gene was highly expressed compared to the control in response to NP and OP. EDC-induced modulatory patterns of Km-Vtg gene expression were different depending on tissue, gender, and isoforms.

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