CHANGES IN DNA METHYLATION DURING DEVELOPMENT IN THE CHROMOSOME-B NOROF THE GRASSHOPPER EYPREPOCNEMIS-PLORANS

Chromosomal patterns of DNA methylation were analysed by in situ diges tion with restriction endonucleases in different stages of the life cy cle in the grasshopper Eyprepocnemis plorans: 10-day-old embryos, last instar male nymphs and adults of both sexes. The results show that th e nucleolus organizing region (NOR) located distally on the B chromoso me is not methylated in embryos or in gastric caeca of adult males and females, but it is methylated in ovariole cells and spermatocytes in both last instar nymphs and adults. Demethylation of the B-NOR during early embryogenesis is proposed for the observed methylation pattern i n embryos. Despite variation in methylation status through the life cy cle, rRNA genes contained in the B-NOR were never observed to be activ e, which indicates that DNA methylation is not the direct cause of the ir inactivity. Other causes such as chromatin structure or repression by genes on A chromosomes are suggested.