Zebrafish (Danio rerio) life-cycle exposure to chronic low doses of ethinylestradiol modulates p53 gene transcription within the gonads, but not NER pathways

Abstract

Parental full life-cycle exposure to ethinylestradiol (EE₂) significantly affects embryo development and survival. One of the possible mechanisms of action of EE₂ may involve the impairment of an organism's ability to repair DNA damage. DNA repair mechanisms have sophistically evolved to overcome DNA damaging hazards that threaten the integrity of the genome. In the present study, changes in the transcription levels of key genes involved in two of the most thoroughly studied DNA repair systems in mammals were evaluated in adult zebrafish (Danio rerio) gonad upon full life-cycle exposure to chronic environmentally low levels of EE₂ (i.e., 0.5, 1 and 2 ng/L EE₂). Real time PCR was used to analyse the expression levels of nucleotide excision repair genes (NER) as well as the tumor suppressor p53 and downstream selected effectors, i.e., p21 (cyclin-dependent kinase inhibitor), GADD45α (growth arrest and DNA damage induced 45, alpha), bax (bcl2-associated X protein) and p53 key regulator MDM2 (murine double minute 2 protein). NER genes transcription levels in gonads did not differ significantly among treatments. In contrast, the number of transcripts of p53 gene was significantly increased in male gonads at all EE₂ exposure concentrations and in females at 1 ng/L EE₂. Despite the increase in p53 transcripts, transcription levels of p21, GADD45α and bax genes were not affected upon EE₂ treatment, whereas MDM2 gene expression significantly increased in females at the intermediate EE₂ dose (1 ng/L). Overall, the present study indicate that chronic low levels of EE₂ significantly modulates the transcription of p53, a key gene involved in DNA repair, particularly in male zebrafish gonads, which supports the hypothesis of an impact of EE2 in male gonad DNA repair pathways.

Benzo[a]pyrene induced p53-mediated cell cycle arrest, DNA repair, and apoptosis pathways in Chinese rare minnow (Gobiocypris rarus)

“…Similarly, statistically significant differences in mdm2 expression levels were observed in laryngeal carcinoma samples (Hassumi‐Fukasawa et al, ). Our finding that p53 and mdm2 increased upon BaP exposure could be due to the auto‐regulatory feedback loop described in mammals for this complex of proteins (Soares et al, ). However, molecular analysis of zebrafish mdm2 revealed that it seems to lack some key amino acids for DNA binding found in other models (Neel et al, ), and the regulation of p53 activity in fish may not be dependent on mdm2 in the same way or to the same extent as that in mammals (Krumschnabel and Podrabsky, ).…”

“…Based on the sequence and phylogenetic analysis of their predicted amino acid sequences, the new transcripts were classified as p53 , p21 , mdm2 , gadd45α , gadd45β , igfbp‐3 , and bax . In general, the predicted amino acid sequences of the genes exhibited high homology with the same regions in zebrafish (Soares et al, ).…”

“…For example, heavy fuel oil significantly upregulated p53 and gadd45α transcripts in turbot (Ruiz et al, ), BaP and microcystin‐LR significantly induced the expression of p53 and p21 mRNA in whitefish (Brzuzan et al, ). Most previous studies examined the effects of p53 network genes, including p53 , p21 , gadd45α , and mdm2 , in zebrafish (Soares et al, ) and turbot (Ruiz et al, ) exposed to environmental pollutants (e.g., PAHs). However, molecular characterization and the functions of p53 network genes in rare minnow have not been investigated.…”

Screening the Toxicity of Selected Personal Care Products Using Embryo Bioassays: 4-MBC, Propylparaben and Triclocarban

“…This organism has been largely used as a model species for toxicological purposes due to its small size, short life-cycle, high sensitivity to a a range of chemicals, easy maintenance and reproduction in laboratory conditions as well as the availability of tools (full genome sequence, regulatory sequences and expression profile) [44,45]. Furthermore, eggs are translucent, which makes the follow up of embryo development and their manipulation easier [46,47].…”

RNA-Seq-based transcriptome analysis of Korean rose bitterling (Rhodeus uyekii) exposed to synthetic estrogen 17-α-ethinylestradiol (EE2)

“…EE2 also induced apoptotic proteins, such as p53, Bcl-2, and caspase3 in D. rerio and G. gobio (Soares et al, 2012;Nadzialek et al, 2010). The annotation data presented herein showed that treatment with EE2 upregulated the transcription of various apoptotic genes, including apoptosis-stimulating proteins p53-like (comp84557_c0_seq2), BCL2-like 16 (comp89614_c0_seq1), caspase-6 (comp103672_c0_seq10), and WDR36 (comp84426_c0_seq3).…”