Abstract
BackgroundIn the interphase nucleus of metazoan cells DNA is organized in supercoiled loops anchored to a nuclear matrix (NM). There is varied evidence indicating that DNA replication occurs in replication factories organized upon the NM and that DNA loops may correspond to the actual replicons in vivo. In normal rat liver the hepatocytes are arrested in G0 but they synchronously re-enter the cell cycle after partial-hepatectomy leading to liver regeneration in vivo. We have previously determined in quiescent rat hepatocytes that a 162 kbp genomic region containing members of the albumin gene family is organized into five structural DNA loops.ResultsIn the present work we tracked down the movement relative to the NM of DNA sequences located at different points within such five structural DNA loops during the S phase and after the return to cellular quiescence during liver regeneration. Our results indicate that looped DNA moves sequentially towards the NM during replication and then returns to its original position in newly quiescent cells, once the liver regeneration has been achieved.ConclusionsLooped DNA moves in a sequential fashion, as if reeled in, towards the NM during DNA replication in vivo thus supporting the notion that the DNA template is pulled progressively towards the replication factories on the NM so as to be replicated. These results provide further evidence that the structural DNA loops correspond to the actual replicons in vivo.
Highlights
In the interphase nucleus of metazoan cells DNA is organized in supercoiled loops anchored to a nuclear matrix (NM)
We have previously shown that specific DNA sequences located in different chromosomes, representing several territories within the interphase nucleus, change their original position relative to the NM during liver regeneration, becoming quite proximal to the NM during the peak of DNA synthesis at 24 h after partial hepatectomy and recover their original positions once the liver regeneration has been achieved and the hepatocytes return to quiescence [10,13]
Our results suggest that looped DNA moves in a sequential fashion, as if reeled in, towards the NM during DNA replication in vivo and returns to its original position in newly quiescent cells, once the liver regeneration has been achieved, providing further evidence that the structural DNA loops correspond to the actual replicons in vivo
Summary
In the interphase nucleus of metazoan cells DNA is organized in supercoiled loops anchored to a nuclear matrix (NM). Theoretical implications resulting from considering the topology of DNA and the actual size of the replication complexes that include enormous polymerizing machines that dwarf the DNA template, suggest that replication of mammalian DNA in vivo involves fixed polymerases in replication foci that reel in their templates as they extrude newly made DNA [20]. This coupled to varied experimental evidence suggests that the NM is the structural support of DNA replication [21]
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