Regulation of Translation Initiation in Mussels ( Mytilus Galloprovincialis , Lam.) Following Contamination Stress

Abstract

The use of mussels (Mytilus sp.) as bioindicators of the aquatic environment is a valuable approach to monitor environmental contamination. Applying batteries of biomarkers is an essential prerequisite, since the complexity of environmental contaminants can induce in mussels a variety of structural and functional responses, which are not necessarily correlated. In an attempt to correlate translation responses to contamination stress, the sedimentation profiles of runoff ribosomes isolated from digestive gland cells of control or contaminated Mediterranean mussels (Mytilus galloprovincialis, Lam.) were examined and the efficiency of these ribosomes to accomplish protein synthesis was determined. While the major species of ribosomal material was 80S monomers, native 60S and 40S ribosomal subunits were also detected independently of the contamination level in the surrounding waters. However, concomitant with the increase of contamination stress, the level of 80S ribosomes was reduced in favor of free ribosomal subunits. In addition, ribosomes isolated from contaminated mussels and programmed with poly(U) were less efficient to enzymatically bind AcPhe-tRNA, compared with ribosomes from control samples. These results suggest that the contamination stress causes stoichiometric aberrations in the ribosomal particle pool and reduction of translation machinery capability to initiate protein synthesis. Data support the notion that downregulation of translation is an important component of the cellular stress response and may be exploited as a biomarker of environmental contamination.