Chromosomal ‘Puffing’ and Undercondensed Segments-additional Indicators of Chromosome Fragility

抄録

Fragile sites are known to represent single stranded gaps resulting from despiralization of DNA due to failure of compact folding in metaphase chromosomes. During routine cytogenetic investigation we have observed a “puff”-like appearance and varying degrees of undercondensation in chromosomes 4 and 12 in a case of hairy cell leukemia and chromosome 17 in a case of non-specific mental retardation. The regions involved include previously reported fragile sites. In our view, these unique features represent additional aspects of folate sensitive fragile regions on chromosomes. The possible mechanism(s) that might have led to the origin of undercondensed segments has been discussed in view of the recent understanding of the role of histone and non-histone proteins, divalent cations and the DNA structure in chromatin packaging.