engleski

FISH analyses of replication timing of human subtelomeric regions

Recent studies have shown that DNA replication timing is correlated with transcriptional activity of genes. Synchronous replication of alleles was demonstrated for genes with a biallelic and asynchronous replication for those with a monoallelic mode of expression. Alteration of replication order has been associated with aneuploidy and genetic instability, while asynchronous replication with the formation of the 22q11 deletion. No data on replication timing of subtelomeric regions (SR) are available so far. SRs are highly unstable and rearrangements have been reported in ~7% of patients with mental retardation. The objective of this study was to determine the replication timing of human SR. The replication pattern of SR of chromosomes 5, 7, 8 and 20 was investigated using FISH method in lymphocytes of 4 healthy donors. At least 200 cells per probe per person were analysed. The replication status of a locus was classified as unreplicated (&#8220; s&#8221; -single signal) and replicated (&#8220; d&#8221; - doubled signal). The results showed that each SR had a characteristic timing of replication, and that 20q (ss: 47.8&#177; 3.1% ; dd: 18&#177; 1.8%) was the first of examined SRs to replicate, whereas 5q (ss: 75.9&#177; 1.8% ; dd: 4.3&#177; 0.5%) was the last (p<0.001). The analysis revealed variable level of replication synchrony of homologous SR. The frequency of sd cells hybridized with the probes for the 5p, 7p, 8q, 20q (30.1&#177; 2.6%) was significantly higher (p<0.02) compared to 5q, 7q, 8p, 20p (20.6&#177; 2.0%). These results suggest that replication pattern might contribute to the non-random involvement of specific SR in the aetiology of mental retardation

FISH; replication; subtelomers

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