Temporally different poly(adenosine diphosphate‐ribosylation) signals are required for DNA replication and cell division in early embryos of sea urchins

To analyze the temporal relationship of poly(adenosine diphosphate [ADP]‐ribosylation) signal with DNA replication and cell divisions, the effect of 3 aminobenzamide (3ABA), an inhibitor of the poly(ADP‐ribose)synthetase, was determined in vivo during the first cleavage division of sea urchins. The incorporation of ³H‐thymidine into DNA was monitored and cleavage division was examined by light microscopy. The poly(ADP‐ribose) neosynthesized on CS histone variants was measured by labeling with ³H‐adenosine during the two initial embryonic cell cycles and the inhibitory effect of 3ABA on this poly(ADP‐ribosylation) was determined. The results obtained indicate that the CS histone variants are poly(ADP‐ribosylated) de novo during the initial cell cycles of embryonic development. The synthesis of poly(ADP‐ribose) is decreased but not abolished by 20 mM of 3ABA. The incubation of zygotes in 3ABA at the entrance into S1 phase decreased ³H‐thymidine incorporation into DNA in phase S2, while S1 was unaltered. Alternatively, when the same treatment was applied to zygotes at the exit of S1 phase, a block of the first cleavage division and a retardation of S2 phase were observed. The inhibitory effect of 3ABA on both DNA replication and cell division was totally reversible by a release of the zygotes from this inhibition. Taking together these observations it may be concluded that the poly(ADP‐ribosylation) signals related to embryonic DNA replication are not contemporaneous with S phase progression but are a requirement before its initiation. These results also indicate that a poly(ADP‐ribosylation) signal is required for cell division; such signal is temporally different from that related to S phase initiation and occurs at the exit of S phase. © 1993 Wiley‐Liss, Inc.