Gene transcription profiling in pollutant exposed mussels (Mytilus spp.) using a new low-density oligonucleotide microarray.

A low density oligonucleotide-microarray encompassing 24 mussel genes implicated in both housekeeping and stress related functions was developed to investigate expression profiles in animals challenged for l week with different pollutants at sub-lethal concentrations (Hg, Cd, Cr (VI) and a crude oil preparation, NSO). Hg (150 µg/l) caused activation of the two metallothioneins mt10 and mt20 and histone h2. Conversely, the expression of housekeeping genes (actin, histone hl and mrp2) and components of the humoral immune system, i.e. mytilin-b and myticin-a and lysozyme, was severely reduced. Cd (300 µg/l) shared with Hg the activation of metallothioneins and histone h2, but a congruent number of genes were up-regulated: transporter mrp2, hsp70, defensin-mgd-l, and an ATP dependent RNA helicases, putatively involved in pre-mRNA processing. In addition, the increase of histone hl and h4 transcripts, together with that of h2, might suggest a mitogenic effect of Cd. Cr (VI) exposure (1, 10 and 50 ng/L) caused impaired expression of different gene c1asses: histones, immune response components (mytilin, myticin and mvp) and hsp 70 were down-regulated, while mt20 showed some up-regulation at the highest metal concentration. The crude oil treatment (0.5 ppm) caused down-regulation of several targets: hsp70, mt10, mvp, RNA helicases and p53. As already observed for the Hg treatment, NSO exposure caused the down-regulation of mrp2 and actin, but particular1y that of mytilin-b, and lysozyme. Catalase was the only gene displaying some up-regulation. In conclusion, the developed technique represents a valid tool to improve the knowledge in the field of molecular toxicology. The integration of the biological effects of pollutants with gene (and protein) expression profiles will provide a more correct interpretation of how a stress syndrome takes place and develops in the challenged organism.