Browsing by Author "Yen, Jerry"

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Dynamic zebrafish interactome reveals transcriptional mechanisms of dioxin toxicity.
(PloS one, 2010) Alexeyenko, Andrey; Wassenberg, Deena M; Lobenhofer, Edward K; Yen, Jerry; Linney, Elwood; Sonnhammer, Erik LL; Meyer, Joel N
BACKGROUND: In order to generate hypotheses regarding the mechanisms by which 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) causes toxicity, we analyzed global gene expression changes in developing zebrafish embryos exposed to this potent toxicant in the context of a dynamic gene network. For this purpose, we also computationally inferred a zebrafish (Danio rerio) interactome based on orthologs and interaction data from other eukaryotes. METHODOLOGY/PRINCIPAL FINDINGS: Using novel computational tools to analyze this interactome, we distinguished between dioxin-dependent and dioxin-independent interactions between proteins, and tracked the temporal propagation of dioxin-dependent transcriptional changes from a few genes that were altered initially, to large groups of biologically coherent genes at later times. The most notable processes altered at later developmental stages were calcium and iron metabolism, embryonic morphogenesis including neuronal and retinal development, a variety of mitochondria-related functions, and generalized stress response (not including induction of antioxidant genes). Within the interactome, many of these responses were connected to cytochrome P4501A (cyp1a) as well as other genes that were dioxin-regulated one day after exposure. This suggests that cyp1a may play a key role initiating the toxic dysregulation of those processes, rather than serving simply as a passive marker of dioxin exposure, as suggested by earlier research. CONCLUSIONS/SIGNIFICANCE: Thus, a powerful microarray experiment coupled with a flexible interactome and multi-pronged interactome tools (which are now made publicly available for microarray analysis and related work) suggest the hypothesis that dioxin, best known in fish as a potent cardioteratogen, has many other targets. Many of these types of toxicity have been observed in mammalian species and are potentially caused by alterations to cyp1a.
Open Access
Organophosphorus Pesticide Exposure Effects on Neurobehavioral Development of Zebrafish and Characterization of Developmental Switch Between Two Cation-chloride Cotransporters (zfnkcc1 and zfkcc2)
(2012) Yen, Jerry
Organophosphorus pesticides (OPs) are neuroactive compounds that can affect the development of the nervous system and behavior. Using zebrafish, we compared the effectiveness of three different OPs, chlorpyrifos (CPF), diazinon (DZN) and parathion (PA) on survival, AChE inhibition and larval motility. We conclude that at equimolar concentrations CPF is the most effective OP of the three tested. 300nM CPF inhibited AChE when measured at 5 days post fertilization (dpf) by 80%, which correlated to a 35% decrease in larval motility when measured at 6 dpf.
We isolated the cDNA of zfkcc2, which encodes for an important cation-chloride cotransporter responsible for establishing a chloride gradient that allows for the neurotransmitter GABA to become inhibitory for a subset of neurons. By isolating the cDNA of zfkcc2, we were able to characterize its expression pattern up to 4 dpf. Using qRT-PCR, we showed that the expression of zfkcc2 rises from 2 to 96 hours post fertilization (hpf). The expression of zfkcc2 is found at 1 dpf in the forebrain, midbrain and hindbrain in a distinct pattern. By 3 dpf, zfkcc2 expression is found throughout most of the developing zebrafish brain. We were then able to characterize the expression pattern of zfnkcc1, which encodes for a cation-chloride cotransporter that works opposite to zfkcc2 and establishes a chloride gradient allowing GABA to be excitatory during development. Expression of zfnkcc1 is found at 1 dpf throughout most of the developing zebrafish head including in some non-neural tissue, but appears concentrated to the otic vesicle at 3 dpf. Using double in situ hybridization, we investigated the nature of the developmental switch from zfnkcc1 to zfkcc2 by looking at regions where there was an interaction between both genes' expression patterns in the developing zebrafish nervous system.
We preliminarily examined how affecting nicotinic signaling with exposures to nicotinic agonists/antagonists can affect the expression of zfnkcc2 and zfkcc2. While there were no apparent changes in the expression pattern from any of the exposures at 2 dpf, we found that by 3 dpf nicotine and CPF exposures resulted in an incomplete expression pattern for zfkcc2 that seemed to be delayed. However, the expression of zfnkcc1 at the otic vesicle was unaffected by exposure.
Our results suggest that disrupting nicotinic signaling during development can affect the expression of an important cation-chloride cotransporter, zfkcc2, that plays a major role in establishing the necessary chloride gradient for the proper functioning of GABA during development. Future studies should focus on investigating the nature of the developmental switch between zfnkcc1 and zfkcc2 to see if the possibility of their regulation being coupled is a target for exposures.