Gene expression profiling as a tool for sediment risk assessment: a pilot study using Caenorhabditis elegans whole genome microarrays

Toxicity of river sediments are assessed using whole sediment toxicity tests with benthic organisms. The challenge, however, is the differentiation between multiple effects caused by complex contaminant mixtures and the unspecific toxicity endpoints such as survival, growth or reproduction. Moreover, natural sediment properties, such as grain size distribution and organic carbon content, can influence the test parameters by masking pollutant toxicity. The use of gene expression profiling facilitates the identification of transcriptional changes at the molecular level that are specific to the bioavailable fraction of pollutants. The nematode Caenorhabditis elegans is ideally suited for these purposes, as (i) it can be exposed to whole sediments, and (ii) its genome is fully sequenced and widely annotated. In this pilot study we exposed C. elegans for 48 h to three sediments varying in degree of contamination with e.g. heavy metals and organic pollutants. Following the exposure period, gene expression was profiled using a whole genome DNA-microarray approach.

Interplay between mitochondria and diet mediates pathogen and stress resistance in Caenorhabditis elegans.

To understand the impact of a diet on host health, we performed a number of assays with C. elegans reared on OP50 or HT115 E. coli. We observed that HT115 provided a substantial increase in resistance to Liquid Killing and abiotic stresses (e.g., heat shock, oxidative stress). This phenomenon was independent of the worms innate immune system. In the absence of any other obvious candidates, we turned to microarray transcriptional profiling to gain an unbiased picture of the differences that result from feeding C. elegans with HT115 instead of OP50. To our surprise, there was a relatively small number of genes differentially expressed between worms fed OP50 and HT115. Amongst them were several mitochondrially-associated genes, suggesting that the relevant difference may involve this organelle. Using a variety of approaches, we determined that worms fed HT115 exhibit increased mitochondrial health than their OP50 counterparts. Furthermore, supplementation of growing OP50 with cobalamin recapitulated virtually all of the HT115 phenotypes.

Cell-specific microarray profiling of the C. elegans nervous system.

Background: With its fully sequenced genome and simple, well-defined nervous system, the nematode C. elegans offers a unique opportunity to correlate gene expression with neuronal differentiation. The lineal origin, cellular morphology and synaptic connectivity of each of the 302 neurons are known. In many instances, specific behaviors can be attributed to particular neurons or circuits. Here we describe microarray-based methods that monitor gene expression in C. elegans neurons and thereby link comprehensive profiles of neuronal transcription to key developmental and functional attributes of the nervous system. Results: We employed complementary microarray-based strategies to profile gene expression in the embryonic and larval nervous systems. In the MAPCeL (Micro-Array Profiling C. elegans Cells) method, we used Fluorescence Activated Cell Sorting (FACS) to isolate GFP-tagged embryonic neurons for microarray analysis. To profile the larval nervous system, we used the mRNA-tagging technique in which an epitope-labeled mRNA binding protein (FLAG-PAB-1) was transgenically expressed in neurons for immunoprecipitation of cell-specific transcripts. These combined approaches identified approximately 2,500 mRNAs that are highly enriched in either the embryonic or larval C. elegans nervous system. These data are validated in part by the detection of gene classes (e.g. transcription factors, ion channels, synaptic vesicle components) with established roles in neuronal development or function. In addition to utilizing these profiling approaches to define stage specific gene expression, we also applied the mRNA-tagging method to fingerprint a specific neuron type, the A-class group of cholinergic motor neurons, during early larval development. A comparison of these data to a MAPCeL profile of embryonic A-class motor neurons identified genes with common functions in both types of A-class motor neurons as well as transcripts with roles specific to each motor neuron type. Conclusion: We describe microarray-based strategies for generating expression profiles of embryonic and larval C. elegans neurons. These methods can be applied to particular neurons at specific developmental stages and therefore provide an unprecedented opportunity to obtain spatially and temporally defined snapshots of gene expression in a simple model nervous system. Keywords: nervous system, development