A. Almeida et al., HYPOMETHYLATION OF CLASSICAL SATELLITE DNA AND CHROMOSOME INSTABILITYIN LYMPHOBLASTOID CELL-LINES, Human genetics, 91(6), 1993, pp. 538-546
To determine possible relationships between DNA hypomethylation and ch
romosome instability, human lymphoblastoid cell lines from different g
enetic constitutions were studied with regard to 1) uncoiling and rear
rangements, which preferentially affect the heterochromatic segments o
f chromosomes 1 and 16; 2) the methylation status of the tandemly repe
titive sequences (classical satellite and alphoid DNAs) from chromosom
es 1 and 16, and of the L1Hs interspersed repetitive sequences. The me
thylation status largely varied from cell line to cell line, but for a
given cell line, the degree of methylation was similar for all the re
petitive DNAs studied. Two cell lines, one obtained from a Fanconi ane
mia patient and the other from an ataxia telangiectasia patient were f
ound to be heavily hypomethylated. The heterochromatic segments of the
ir chromosomes 1 and 16 were more frequently elongated and rearranged
than those from other cell lines, which were found to be less hypometh
ylated. Thus, in these lymphoblastoid cell lines, alterations characte
rized by uncoiling and rearrangements of heterochromatic segments from
chromosomes 1 and 16 seem to correlate with the hypomethylation of th
eir repetitive DNAs. Two-color in situ hybridizations demonstrated tha
t these elongations and rearrangements involved only classical satelli
te-DNA-containing heterochromatin. This specificity may be related to
the excess of breakages affecting the chromosomes carrying these struc
tures in a variety of pathological conditions.