The s phase is discrete and is controlled by the circadian clock in the marine dinoflagellate Gonyaulax polyedra.
Cloned cultures of the dinoflagellate Gonyaulax polyedra grown in a 12-h light-12-h dark cycle (LD 12:12) were synchronized to the beginning of G1 by a two sequential filtration technique. After the second filtration, with the cultures growing in LD 12:12, not many cells had divided after 1 day, but approximately half underwent cell division after 2 days. Flow cytometric measurements of the cells revealed that there is one unique S phase starting about 12 h prior to cell division and lasting for less than 4 h. A majority of cells in cultures synchronized in the same way but maintained in continuous light (LL) after filtration also divided synchronously after 2 days. Just as for the cultures in LD 12:12, those in LL have a similar discrete DNA synthesis phase prior to division. It is concluded that the circadian control of cell division acts before the S phase, giving rise to a discontinuous DNA synthesis phased by the circadian clock.
Homma
K
K
Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138.
Hastings
J W
JW
D000818:Animals; D002453:Cell Cycle; D002455:Cell Division; D002940:Circadian Rhythm; D004247:DNA / Q000032:analysis; D004261:DNA Replication; D004141:Dinoflagellida / Q000166:cytology*; D005434:Flow Cytometry; D007399:Interphase; D007700:Kinetics
D004247:DNA