Transcription of tandemly repeated genes in embryonal and larval tissues of Calliphora erythrocephala

The transcription of rRNA genes in C. erythrocephala embryonal and larval fat bodies and guts was analyzed by electron microscopy. A gradual increase in the number of active genes and in the RNA polymerase density was observed in both tissues in the hours preceding hatching. Despite this increase, the rRNA genes at hatching are not fully loaded with RNA polymerase molecules. An additional increase in rRNA synthesis is characteristic of the first two days of larval development. This increase in rRNA synthesis is accomplished by an increase in RNA polymerase density, by activation of previously inactive rRNA genes and by activation of newly replicated rRNA genes.