Ribonucleic acid treatment alters gene expression in diploid strains of Aspergillus nidulans

Physical and chemical agents that promote DNA damage can induce high levels of mitotic crossing-over in eukaryotic diploid cells. Similarly, foreign DNA segments introduced by transformation processes, in the cell genome, can also induce mitotic crossing-over as an outcome of the reactions leading to chromosomic balance or due to the mechanisms aiming at the integration of the exogenous DNA. Zucchi et al. have described a system showing that RNA treatments are capable of inducing changes in the genome of haploid receptor strains of Aspergillus nidulans. To verify the genetic consequences of this process in diploid cells, conidia from two strains of this fungus were protoplastized, treated with homologous RNA and analyzed. Alterations in the gene expression and in the mitotic crossing-over frequencies between linked markers were detected. Among the main observed effects there was a generalized alteration in gene expression which was very likely caused by a reversible gene inactivation mechanism due to the methylation of cytosine residues. This was confirmed by treating the haploid segregants with the hypomethylating agent 5-azacytidine, that restored the original gene activity. The presence of a duplicated segment in the chromosome I of one of the treated diploids, interfered with the RNA general effects on its genome.