Elwood Linney, PhD
This laboratory is using the zebrafish model to study a molecular mechanism of gene repression during embryonic development. This mechanism is based upon the role of enzymes that are normally considered as general metabolizing enzymes (Phase I enzymes) as having a definitive role on embryonic development: dehydrogenases that produce endogenous retinoic acid and cytochrome p450 enzymes that metabolize retinoic acid.
The hypothesis, based upon substantial mammalian cell culture work, is that retinoic acid receptors are allosteric regulators of gene expression where their OFF position includes a retinoic acid receptor-corepressor (smrt/ncor2)-histone deacetylase complex represses genes in the absence of endogenous retinoic acid–and that this is the ground state before mammalian embryonic genes are activated (or ON) as retinoic acid is presented to regions of the embryo. During development as retinaldehyde dehydrogenase produces retinioic acid at different times and places, the retinoic acid recepter goes through an allosteric change eliminating the corepressor and its associated histone deacetylase and forms a transcriptional coactivator binding site that can result in histone acetylation and communication with the transcriptional complex causing gene activation.
We are using RNAseq technology to investigate the expression of genes within the first 10 hours post-fertilization to examine what genes are upregulated via ectopic retinoic acid exposure and how the natural expression of these genes might be affected by down-regulating individual complex components with either anti-sense morpholinos or a combination of compounds that can affect the retinoic acid corepressor interaction. Along with RNAseq analysis of gene expression changes induced by these manipulations, we are using a battery of fluorescent, transgenics embryos to investigate the cellular phenotype of these induced changes followed by ChIPseq analysis to confirm changes at retinoic acid receptor response elements (RAREs) in the promoter regions of these genes.
This hypothesis can explain the teratogenic properties of retinoic acid and how retinoid based acne medicines that have been reported to create teratogenic effects in many model vertebrates and in human fetuses.
An associated study has compared the effects of different triazole compounds on embryonic development. These compounds, used as pesticides, body-building compounds (to inhibit aromatase and raise testosterone levels), fungal creams, and pharmaceuticals can have the effect of inhibiting the activity of cytochrome p450 enzymes that naturally metabolize retinoic acid to a non-functional retinoic acid receptor ligand. We have been comparing their individual potency through RNAseq analysis and fluorescent transgenic analysis.