Ribosomal DNA and its expression in Drosophila melanogaster during growth and development.

Ribosomal DNA content has been determined in several adult and larval tissues of Drosophila melanogaster. Underreplication of rRNA genes was observed in polytenic salivary glands of larvae. On the contrary, polytenic/polyploid ovaries showed no decrease in rDNA. It is concluded that polyteny is not necessarily associated with underreplication of rDNA. No other tissue examined displayed any change in rDNA redundancy. Third-instar-larvae showed a decrease in rDNA amount which might be partly accounted for by underreplication of rDNA in salivary glands. No such decrease was seen in pupae. Bobbed genotypes were essentially similar to wild type in all tissues except salivary glands. In this case, it was found that the extent of underreplication is less in bobbed as compared to wild genotypes. Ribosomal DNA activity was examined in various tissues of Drosophila melanogaster. The rates of rRNA synthesis vary greatly between various tissues. It is concluded that a control at the level of gene activity operates as differences in the amount of precursor rRNA synthesized can be observed both in flies of varying rDNA contents as well as in various tissues of the same genotype.