CHANGES IN DNA METHYLATION DURING DEVELOPMENT IN THE CHROMOSOME-B NOR OF THE GRASSHOPPER EYPREPOCNEMIS-PLORANS

Chromosomal patterns of DNA methylation were analysed by in situ digestion with restriction endonucleases in different stages of the life cycle in the grasshopper Eyprepocnemis plorans: 10-day-old embryos, last instar male nymphs and adults of both sexes. The results show that the nucleolus organizing region (NOR) located distally on the B chromosome 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 in embryos. Despite variation in methylation status through the life cycle, rRNA genes contained in the B-NOR were never observed to be active, which indicates that DNA methylation is not the direct cause of their inactivity. Other causes such as chromatin structure or repression by genes on A chromosomes are suggested.