A new light on DNA replication from the inactive X chromosome.
While large portions of the mammalian genome are known to replicate sequentially in a distinct, tissue-specific order, recent studies suggest that the inactive X chromosome is duplicated rapidly via random, synchronous DNA synthesis at numerous adjacent regions. The rapid duplication of the inactive X chromosome was observed in high-resolution studies visualizing DNA replication patterns in the nucleus, and by allele-specific DNA sequencing studies measuring the extent of DNA synthesis. These studies conclude that inactive X chromosomes complete replication earlier than previously thought and suggest that the strict order of DNA replication detected in the majority of genomic regions is not preserved in non-transcribed, "silent" chromatin. These observations alter current concepts about the regulation of DNA replication in non-transcribed portions of the genome in general and in the inactive X-chromosome in particular.
Developmental Therapeutic Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, USA.
Mirit I
MI
Aladjem
Haiqing
H
Fu
D000818:Animals; D004261:DNA Replication; D042522:DNA Replication Timing; D044127:Epigenesis, Genetic; D042822:Genomic Instability; D006801:Humans; D014960:X Chromosome / Q000235:genetics*; D049951:X Chromosome Inactivation / Q000235:genetics*
DNA replication; cell cycle; chromatin; epigenetics; inactive X chromosome