Structural-functional rearrangements in chromosome G in Chironomus riparius (Diptera, Chironomidae) collected from a heavy metal-polluted area near Turin, Italy

A natural population of Chironomus riparius from the heavy metal-polluted P iedmont station (Italy) was analysed. Chromosome G, on which the Balbiani r ings BRa, BRb and BRc are located, was very sensitive to the pollution. The BR system was considered to be an interesting model for studying the respo nse of the genome to the heavy metal pollution. Together, with a standard a ctivity of BRs (BRc > BRb), we observed a clear reversed, level of activity of BRb and BRc: BRc was repressed while BRb became activated. Also, there were a number of cells in which BRb and BRc were collapsed. A change in the activity of the nucleolar organizing region (N) was found, from a very hig h activity till completely collapsed. For the first time it was established that there was an activation at the telomere region of chromosome G. Addit ional active sites in sections Dc and E2de were observed. The conjugation o f both homologues was often disturbed. A high frequency of ectopic pairings was also observed. In addition, structural rearrangements as inversions an d deletions were found. Some deletions led to the formation of pompon-like chromosome G. Chromosome G of C. riparius is suggested to be used to test f or the presence of genotoxic concentrations of polluting agents in an aquat ic ecosystem. (C) 1998 Elsevier Science Ltd. All rights reserved.