title: Regulation of DNA synthesis: age-dependent cooperation among G1 cells upon fusion.
abstract: The object of this study was to determine whether the inducer(s) of DNA synthesis in mammalian cells accumulates gradually throughout the G1 period or becomes available suddenly at the G1-S transition. HeLa cells, synchronized at various points in the G1 period, were fused by using UV-inactivated Sendai virus. Early G1 cells were fused with mid-G1 or late G1 cells and late G1 cells were fused with mid-G1 cells. The G1 traverse of mono-, bi-, and trinucleated cells was studied. The bi- and trinucleated cells of mid-G1 and late G1 parents traversed the G1 period significantly faster than did their mononucleated counterparts. The reduction in the duration of the G1 period was proportional to the number and age of nuclei at the time of fusion. There was no significant difference between the mono- and binucleated cells of the early G1 parent in their rates of entry into S period. In light of these findings, a model is proposed in which the inducer(s) of DNA synthesis accumulates gradually throughout the G1 period, reaching a critical level at the G1-S boundary when DNA replication is initiated; after reaching a peak during early or mid-S period, it declines to below the critical level when DNA synthesis ceases.
mesh_terms: D002455:Cell Division; D002459:Cell Fusion; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D004247:DNA / Q000096:biosynthesis*; D006367:HeLa Cells; D007700:Kinetics
chemical_list: D004247:DNA
references.citation: Adv Genet. 1976;18:99-177
references.pmid: 181964
references.citation: Exp Cell Res. 1976 Nov;103(1):213-8
references.pmid: 991950
references.citation: Proc Natl Acad Sci U S A. 1975 Mar;72(3):869-73
references.pmid: 1055386
references.citation: J Cell Sci. 1975 Aug;18(3):455-90
references.pmid: 1171873
references.citation: Dev Biol. 1973 Sep;34(1):77-92
references.pmid: 4207056
references.citation: Exp Cell Res. 1972 Jun;72(2):393-403
references.pmid: 4338826
references.citation: Biol Rev Camb Philos Soc. 1971 Feb;46(1):97-155
references.pmid: 4399534
references.citation: Proc Natl Acad Sci U S A. 1967 Aug;58(2):545-52
references.pmid: 5234323
references.citation: Nature. 1970 Jan 10;225(5228):159-64
references.pmid: 5409962
references.citation: Science. 1968 May 17;160(3829):774-6
references.pmid: 5646416
references.citation: Proc Natl Acad Sci U S A. 1967 Mar;57(3):607-14
references.pmid: 16591507