Decreased replication origin activity in temporal transition regions.
In the mammalian genome, early- and late-replicating domains are often separated by temporal transition regions (TTRs) with novel properties and unknown functions. We identified a TTR in the mouse immunoglobulin heavy chain (Igh) locus, which contains replication origins that are silent in embryonic stem cells but activated during B cell development. To investigate which factors contribute to origin activation during B cell development, we systematically modified the genetic and epigenetic status of the endogenous Igh TTR and used a single-molecule approach to analyze DNA replication. Introduction of a transcription unit into the Igh TTR, activation of gene transcription, and enhancement of local histone modifications characteristic of active chromatin did not lead to origin activation. Moreover, very few replication initiation events were observed when two ectopic replication origin sequences were inserted into the TTR. These findings indicate that the Igh TTR represents a repressive compartment that inhibits replication initiation, thus maintaining the boundaries between early and late replication domains.
Guan
Zeqiang
Z
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA. zguan@aecom.yu.edu
Hughes
Christina M
CM
Kosiyatrakul
Settapong
S
Norio
Paolo
P
Sen
Ranjan
R
Fiering
Steven
S
Allis
C David
CD
Bouhassira
Eric E
EE
Schildkraut
Carl L
CL
D000818:Animals; D004261:DNA Replication / Q000502:physiology*; D053595:Embryonic Stem Cells; D018507:Gene Expression Regulation, Developmental; D006657:Histones / Q000378:metabolism; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D011993:Recombinant Fusion Proteins / Q000032:analysis; D018741:Replication Origin; D015533:Transcriptional Activation
D006657:Histones; D007143:Immunoglobulin Heavy Chains; D011993:Recombinant Fusion Proteins