Stress and stress associated gene expression and regulation; Biomarkers; DNA damage and repair 

Summary of research

Dr. D. Kar Chowdhuri’s group is interested in understanding the role of stress and stress associated genes and their regulation in the context of cellular toxicity mounted by environmental chemicals. His laboratory uses Drosophila as a model organism to address these issues. His group also addresses the mechanism of DNA damage response caused by environmental chemicals.

Stress proteins in cellular stress response against environmental chemicals: transgenic approach using Drosophila

Heat shock proteins (Hsps) are a ubiquitous feature of cells in which these proteins cope with stress induced denaturation of other proteins. Among the different families of Hsps, the 70kDa family (hsp70) is the most highly conserved and has been most extensively studied. Apart from their primary role in cellular defense under stress condition, a number of studies in recent years have shown the immense potential of hsp70 in pollution monitoring using even transgenic approach both in vivo and in vitro. We have been exploiting this quality of hsp70 to examine the cellular toxicity of environmental chemicals using Drosophila as a model organism that was made transgenic for hsp70. We have shown in the past that hsp70 expression can be used as a first tier bio-indicator of cellular toxicity (our publication in this area was included in one of the ECVAM publications). In the process, we could determine the NOAEL, LOAEL of one of the universal solvents.

We have been exploring the status of other members of stress protein family when hsp70 becomes either refractory or regressed after a peak induction. While in the recent publications we showed that other chaperone like hsps (hsp60, hsp90) can complement the cellular homeostasis under these circumstances, small hsps (hsp22, hsp26 and hsp27) too play significant roles.

Using genome wide expression profiling studies, we were able to identify not only these stress genes mis-regulated but also among other, a gene called methusalah, a member of GRCR family. Mutation in this gene is reported to provide resistance to the organism against oxidative stress We have been exploring the role of methusalah along with other members of stress gene family both under normal, deficiency and over expression state to explore the role of stress genes and methusalah when organisms are exposed to environmental chemicals. We explore their roles both at sub-organismal and organismal levels to find out whether they are beneficial to the organism.

Along with stress genes, oxidative stress genes are reported to be mis-regulated in the organisms that are exposed to environmental chemicals. We are exploring the cooperative response of these genes and stress genes using Drosophila as a model organism. Using chemical inhibitors, genetic (RNAi, deficiencies, point mutation, GAL4-UAS systems), biochemical, imaging and molecular biology techniques, we are currently examining the fine tune of the stress response operational in the exposed organism.

DNA damage and response   

Environmental chemicals have been reported to generate DNA damage in the exposed organism and the damage evident is the deficiency in the total DNA damage vis a vis DNA repair. We developed and validated alkaline Comet assay in brain and midgut cells of Drosophila larvae to score total DNA damage. We were able to show that under different environmental chemicals exposures regime different kinds of DNA damage occur in the exposed organism and identified different types of repair systems being targeted by the environmental chemicals. Using genome wide expression profiling data and imaging, genetic and biochemical techniques, we are exploring the role of different molecules in the DNA repair pathways being affected due to the exposure of the environmental chemicals to the organism.

Innate immune response

Immune system is the first line of defence mechanism in all metazoans. Hence, it is likely to be the primary target of environmental chemicals. Considering the importance of this system, there is growing concern to elucidate the detrimental effects of the chemicals on the immune system of exposed organism. A large number of evidences are now available to show that environmental chemicals can adversely affect the immune system of the exposed organism leading to chemical induced immunological disorders. Drosophila melanogaster, belonging to the dipteran class of insects, relies only on evolutionary conserved multiple innate immune mechanisms for its defense. The immune mechanisms in Drosophila comprise cellular and humoral responses. The cellular immune response is mediated by hemocytes or blood cells which shows extensive homology with vertebrate myeloid lineage especially with mammalian leukocytes and are supposed to be involved in both cellular as well as humoral immune response. They are responsible for phagocytosis of invading micro-organisms, encapsulation of large foreign bodies and also for tissue remodelling during metamorphosis. Therefore, reduced hemocyte population might lead to immuno-compromised situation which in turn may weaken the cellular defence of the exposed organism. We are exploring the effect of environmental chemicals on innate immune response of the organism and the underlying mechanism by using genetic, biochemical and imaging and molecular biology techniques.