Identification of a putative ribosomal protein mRNA in Chironomus riparius and its response to cadmium, heat shock, and actinomycin D.

A putative ribosomal protein (rp) mRNA in Chironomus riparius has been found using differential display (DD). Its sequence has 84.8% identity with mosquito rp L8, Aedes albopictus, and is approximately 0.9 kb. Studies were undertaken in order to evaluate rp as a control for environmentally relevant genes. Responses of Drosophila heat shock 70 gene (hsp70) were used to establish heat shock temperatures and cadmium (Cd) concentrations for Chironomus experiments and to validate DD. Expression of hsp70 was induced over control by 28 degrees C at 30 minutes and 1 mM Cd at 24 hours (p< or =0.05). For Chironomus, DD, Northern blot, and nuclease sensitivity were used to measure responses to two stressors: heat shock for 30 minutes and Cd for 24 or 48 hours. Differential display and nuclease sensitivity assays found expression of rp mRNA at 37 degrees C and 16 mM Cd to be similar to controls. Northern blots indicated statistically significant effects for heat shock (p = 0.046) but not Cd (p = 0.406). However, mRNA levels at 37 degrees C were increased only 1.72-fold over controls. A concentration of 24 nM actinomycin D suppressed rp expression as measured by nuclease sensitivity assays. Stressors should not affect rp mRNA levels below their LC-50s.