Glutathione S-Transferase (GST) Gene Diversity in the Crustacean Calanus finmarchicus – Contributors to Cellular Detoxification

Abstract

Detoxification is a fundamental cellular stress defense mechanism, which allows an organism to survive or even thrive in the presence of environmental toxins and/or pollutants. The glutathione S-transferase (GST) superfamily is a set of enzymes involved in the detoxification process. This highly diverse protein superfamily is characterized by multiple gene duplications, with over 40 GST genes reported in some insects. However, less is known about the GST superfamily in marine organisms, including crustaceans. The availability of two de novo transcriptomes for the copepod, Calanus finmarchicus, provided an opportunity for an in depth study of the GST superfamily in a marine crustacean. The transcriptomes were searched for putative GST-encoding transcripts using known GST proteins from three arthropods as queries. The identified transcripts were then translated into proteins, analyzed for structural domains, and annotated using reciprocal BLAST analysis. Mining the two transcriptomes yielded a total of 41 predicted GST proteins belonging to the cytosolic, mitochondrial or microsomal classes. Phylogenetic analysis of the cytosolic GSTs validated their annotation into six different subclasses. The predicted proteins are likely to represent the products of distinct genes, suggesting that the diversity of GSTs in C. finmarchicus exceeds or rivals that described for insects. Analysis of relative gene expression in different developmental stages indicated low levels of GST expression in embryos, and relatively high expression in late copepodites and adult females for several cytosolic GSTs. A diverse diet and complex life history are factors that might be driving the multiplicity of GSTs in C. finmarchicus, as this copepod is commonly exposed to a variety of natural toxins. Hence, diversity in detoxification pathway proteins may well be key to their survival.

Transcriptomic responses of the calanoid copepod Calanus finmarchicus to the saxitoxin producing dinoflagellate Alexandrium fundyense

“…The Calanus finmarchicus reference transcriptome used in this study included more then 200 of genes involved in detoxification such as superoxide dismutases (SOD), ferritins, catalases, cytochromes P450, aldehyde dehydrogenases and 39 glutathione S-transferase 18 21 . Surprisingly, detoxification was not a major component of the C. finmarchicus response to the toxic dinoflagellate: only a small number of DEGs were involved in detoxification with the majority of them being down-regulated ( Fig.…”

Glutathione S-Transferase Regulation in Calanus finmarchicus Feeding on the Toxic Dinoflagellate Alexandrium fundyense

“…In C . finmarchicus , the diversity of the GST family exceeds that of many insects [ 16 ]. A total of 41 different GST unigenes have been predicted for C .…”

Complementary mechanisms for neurotoxin resistance in a copepod

“…50 genes involved in the MXR response and ca. 200 genes involved in either phase I or phase II detoxification 27 , 28 , 39 . Searching for these genes among the DEGs in nauplii showed that only 2% of genes involved in these two defense mechanisms (MXR and detoxification, phases I and II) were regulated in response to the dinoflagellate.…”