Abstract
DNA replication initiates at specific positions termed replication origins. Genome-wide studies of human replication origins have shown that origins are organized into replication initiation zones. However, only few replication initiation zones have been described so far. Moreover, few origins were mapped in other mammalian species besides human and mouse. Here we analyzed pattern of short nascent strands in the X inactivation center (XIC) of vole Microtus levis in fibroblasts, trophoblast stem cells, and extraembryonic endoderm stem cells and confirmed origins locations by ChIP approach. We found that replication could be initiated in a significant part of XIC. We also analyzed state of XIC chromatin in these cell types. We compared origin localization in the mouse and vole XIC. Interestingly, origins associated with gene promoters are conserved in these species. The data obtained allow us to suggest that the X inactivation center of M. levis is one extended replication initiation zone.
Highlights
DNA replication is required for duplication of the genome and subsequent cell division
We generated 30 primer pairs and probes located throughout the vole X inactivation center (XIC) with mean interval of 2 kb except for the repeat containing regions and Xist exons 5, 6, and 7 (Fig 1A and S1 Table)
We identified four SNS peaks that located in the exon 1 of Xist, near the Xist 3’ end, in the Tsix promoter (Fig 1D)
Summary
DNA replication is required for duplication of the genome and subsequent cell division. First stage of this process is initiation, which occurs at specific sites termed replication origins. Several evidences have shown that origins are nonuniformly distributed in the genome and organized into broad zones of replication [2]. Such organization of mammalian origins was reported in earlier studies of the Chinese hamster DHFR locus and mouse β-globin and IgH loci [3,4,5,6]. How origins are regulated within the replication zones and PLOS ONE | DOI:10.1371/journal.pone.0128497 June 3, 2015
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