Comparative genomics identifies genes mediating cardiotoxicity in the embryonic zebrafish heart
Jing Chen1, Sara A Carney, Richard E Peterson
1Pharmaceutical Sciences Division, School of Pharmacy, University of Wisconsin, Madison, Wisconsin 53705, USA.
Abstract:
Retinoic acid (RA) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) activate distinct ligand-dependent transcription factors, and both cause cardiac malformation and heart failure in zebrafish embryos. We hypothesized that they cause this response by hyperactivating a common set of genes critical for heart development. To test this, we used microarrays to measure transcript changes in hearts isolated from zebrafish embryos 1, 2, 4, and 12 h after exposure to 1 muM RA. We used hierarchical clustering to compare the transcriptional responses produced in the embryonic heart by RA and TCDD. We could identify no early responses in common between the two agents. However, at 12 h both treatments produced a dramatic downregulation of a common cluster of cell cycle progression genes, which we term the cell cycle gene cluster. This was associated with a halt in heart growth. These results suggest that RA and TCDD ultimately trigger a common transcriptional response associated with heart failure, but not through the direct activation of a common set of genes. Among the genes rapidly induced by RA was Nr2F5, a member of the COUP-TF family of transcriptional repressors. We found that induction of Nr2F5 was both necessary and sufficient for the cardiotoxic response to RA.
Insights
Retinoic acid (RA) and TCDD cause zebrafish heart failure by halting cell growth. While not initially activating common genes, both agents eventually downregulate cell cycle genes, leading to cardiac defects.
Area of Science:
- Developmental Biology
- Toxicology
- Molecular Biology
Background:
- Retinoic acid (RA) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are teratogens known to cause cardiac malformations and heart failure in zebrafish embryos.
- Both agents activate distinct ligand-dependent transcription factors, suggesting different initial mechanisms of action.
Purpose of the Study:
- To investigate whether RA and TCDD induce cardiac malformations by hyperactivating a common set of genes critical for heart development.
- To compare the early and late transcriptional responses in zebrafish embryonic hearts following exposure to RA and TCDD.
Main Methods:
- Zebrafish embryos were exposed to 1 muM RA, and transcript changes in isolated hearts were measured using microarrays at 1, 2, 4, and 12 hours post-exposure.
- Hierarchical clustering was employed to compare the transcriptional profiles induced by RA and TCDD.
Main Results:
- No common transcriptional responses were observed between RA and TCDD at early time points (1-4 hours).
- At 12 hours post-exposure, both RA and TCDD treatments resulted in a significant downregulation of a common cluster of cell cycle progression genes, termed the cell cycle gene cluster.
- This downregulation of cell cycle genes was associated with a cessation of heart growth.
Conclusions:
- RA and TCDD ultimately trigger a common transcriptional response leading to heart failure, but not through the direct activation of shared genes.
- The induction of Nr2F5, a transcriptional repressor, by RA was identified as both necessary and sufficient for the cardiotoxic effects of RA.
