The Stress-Response Network in Animals: Proposals to Develop a Predictive Mathematical Model

Abstract

Abstract:Increasing evidence indicates that numerous genetic pathways responding to environmental stress in animals are regulated co-ordinately as well as independently. These stress-response systems should therefore be viewed in holistic terms as a network. As such, their behaviour is susceptible to mathematical modelling using a systems biology approach. This review outlines relevant evidence and describes a newly launched project to develop just such a model using stressresponse data from multiple transgenic strains of C. elegans and D. melanogaster. We hope that our eventual model will be capable of predicting the effects of simple stressor mixtures with reasonable accuracy. To maximise the effectiveness and scope of this model, we appeal for help from colleagues to share reagents and data relevant to this project. We also present preliminary data where RNA interference has implicated the key transcription factor DAF-16 in an unexpected upregulation of cyp-34A9 reporter expression by high cadmium. STRESS RESPONSES AND MIXTURE TOXICITYIn multicellular organisms, the defensive cellular responses evoked by environmental stresses do not result from simple linear pathways, but rather from a network of interlinked pathways with multiple outputs. This makes it difficult to predict the biological effects of multiple stressors acting together, even though this is the normal situation for industrial pollution of soil or water, where several different contaminants are usually present together. There are few studies and no useful predictive models describing the molecular responses of multicellular organisms to several toxicants acting in concert. This is essentially a systems biology problem, requiring integration of complex molecular and toxicological information. Under the auspices of a Major Award from the UK-India Education and Research Initiative (UK-IERI), we intend to develop an in silico model describing the principal elements of a consensus stress response network (SRN) and its in vivo responses to single stressors, using data from two invertebrate model systems, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. This model will be used to predict the likely SRN responses to stressor mixtures, and such predictions will then be tested experimentally in both species so that the model can be refined accordingly. Since the SRN core pathways are highly conserved among animal taxa, general features of this model should find wider application in ecotoxi-*Address correspondence to this author at the School of Biology, Nottingham University, Nottingham NG7 2RD, UK; Tel: (0044) 115 951 3250; Fax: (0044) 115 951 3251; E-mail: david.depomerai@nottingham.ac.uk cology. The dynamic aspects of this model, and in particular its ability to integrate multiple toxicant inputs for predicting likely SRN outputs, distinguish this from a simple map of the regulatory gene-circuits comprising the SRN. THE C. ELEGANS STRESS-RESPONSE NETWORKThe free-living soil nematode, C. elegans, is particularly suitable fo...

Transgenic nematodes as biosensors for metal stress in soil pore water samples

“…Far greater detail would be obtainable using gene-arrays to investigate global or pathway-specific patterns of gene expression (transcriptome analysis), but this would be prohibitively expensive for testing many different toxicants at multiple doses and time points, let alone extending such work to mixtures. GFP-reporter responses can be used for initial screening to identify unusual or interesting patterns of response (whether to single toxicants or mixtures), which could then be further investigated using gene arrays (de Pomerai et al 2008 ). The responses described here are robust, reproducible and easily measured in a microplate format, lending themselves readily to high-throughput screening methods.…”

“…Another master regulator controlling multiple stress-response pathways is the zinc-finger transcription factor SLR-2 (Kirienko and Fay 2010 ). Testing multiple output genes simultaneously allows insight into the patterns of stress response within the test organism, and this approach is greatly facilitated by the use of green fluorescent protein (GFP) reporters (Chalfie et al 1994 ; de Pomerai et al 2008 ). Although hitherto applied only to single output genes, similar tests can also be used to assess the toxicity of field samples of metal-contaminated water and soils (Mutwakil et al 1997 ; Power and de Pomerai 1999 ), and have previously demonstrated synergistic effects for metal mixtures (Power et al 1998 ; Chu and Chow 2002 ).…”

High-throughput analysis of multiple stress pathways using GFP reporters inC. elegans

“…Other strains were supplied as integrated promoter::GFP fusions by the Baillie Genome GFP Project (Simon Fraser University, Burnaby, Vancouver, Canada), each containing about 3 kb of upstream promoter sequence (apart from BC20306 which contains only the 250 bp of promoter separating the cyp-34A9 gene from its upstream neighbour cyp-34A10) [2,13]. These are:-BC17553 (T09A12.2 glutathione peroxidase designated GPA::GFP), BC20303 (hsp-6::GFP), BC20305 (C11E4.1 glutathione peroxidise designated GPB::GFP), BC20306 (cyp-34A9::GFP), BC20308 (hsp-3::GFP), BC20309 (mtl-1::GFP), BC20314 (elt-2::GFP), BC20316 (gst-1::GFP), BC20329 (skn-1::GFP), BC20330 (gst-4::GFP), BC20333 (sod-4::GFP), BC20334 (cyp-29A2::GFP), BC20336 (ctl-2::GFP), BC20337 (hsf-1::GFP), BC20342 (mtl-2::GFP), BC20343 (hsp-60::GFP), BC20349 (C12C8.1 hsp-70 designated cHSP70::GFP) and BC20350 (sod-1::GFP).…”

“…Several of these pathways can be activated by a single agent: cadmium (Cd) is genotoxic, binds to reduced glutathione thus increasing ROS levels, and is a potent inducer of hsp expression. Paradoxically, cadmium can also induce the expression of multiple cytochrome P450 (cyp) genes, as revealed by gene-array studies in the nematode C. elegans [1]; we and others have demonstrated that for the cyp-34A9 gene at least, Cd regulation is probably mediated by the DAF-16 transcription factor regulating longevity [2,3]. Indeed, DAF-16 acts as a positive regulator for many other stress-response genes, including sod-3 (mitochondrial superoxide dismutase) and mtl-1 (metal-binding metallothionein) as well as hsp-16.1 and hsp-16.2 (encoding small hsp's) [3].…”

Inactivation of GABAA receptor is related to heat shock stress response in organism model Caenorhabditis elegans

“…The IIS pathway comprises a receptor that signals to a PI3 kinase/AKT conserved pathway which, finally, downregulates to DAF-16 activity by inhibiting its translocation into the nucleus. Thus, the major downstream target of IIS is DAF-16, the sole C. elegans ortholog of the FOXO family of transcription factors, and its translocation induces the expression of cytoprotective proteins such as heat shock proteins (HSPs), some antioxidant enzymes (superoxide dismutase and catalase), and other proteins against stress (de Pomerai et al 2008;Hsu et al 2003). HSPs are evolutionarily conserved chaperones present in all cellular compartments and classified according to their molecular weight.…”