M. Hola et al., INDIVIDUAL NUCLEI DIFFER IN THEIR SENSITIVITY TO THE CYTOPLASMIC INDUCERS OF DNA-SYNTHESIS - IMPLICATIONS FOR THE ORIGIN OF CELL-CYCLE VARIABILITY, Experimental cell research, 229(2), 1996, pp. 350-359
Nuclei of multinucleate cells generally initiate DNA synthesis simulta
neously, suggesting that the timing of DNA synthesis depends upon the
appearance of a cytoplasmic signal. In contrast, intact nuclei from qu
iescent mammalian cells initiate DNA synthesis asynchronously in cell-
free extracts of Xenopus eggs, despite the common environment. Here we
show that the two nuclei of permeabilized binucleate cells enter DNA
synthesis coordinately in egg extracts, as they do in vivo, with diffe
rent pairs of nuclei initiating replication at different times. This i
ndicates that. the two nuclei of a binucleate cell are identical in th
eir sensitivity to the inducers of DNA synthesis in egg extracts; this
sensitivity varies in general between the nuclei of unrelated cells,
The asynchrony of DNA synthesis shown by unrelated nuclei in egg extra
cts is therefore not an artifact of the cell-free system but a reflect
ion of genuine differences preexisting within the intact cell, Evidenc
e that these differences between nuclei are responsible for a substant
ial fraction of G(1) variability in Living cells is presented. (C) 199
6 Academic Press, Inc.