10 F.-Y.Bougetetal.
tified in cell cycle genes involved at various stages of cell cycle progression
(Table 1), suggesting that the transcription of several cell cycle genes may be
regulated by circadian clock components such as CCA1/LHY. A highly specu-
lative view of how such a regulation of the clock may regulate cell division is
represented in Fig. 2.
5
Conclusion: A Future for Unicellular Algae in Circadian Studies of Cell Cycle?
The circadian regulation of cell division has been known for a long time in
unicellular algae of the green lineage. Recently, the genomes of two green
algae, the PrasinophytaOstreococcus tauriand the ChlorophytaChlamy-
domonas, have been sequenced (Derelle et al. 2006). Genetic tools are avail-
able in both species and luciferase reporter allows automated monitoring of
in vivo expression of circadian clock and CDC genes inOstreococcus(our
unpublished results). Both organisms display a minimum set of cell cycle
genes, most cyclins, CDK and regulating kinases and phosphatases being
present as a single copy (Bisova et al. 2005; Robbens et al. 2005). These
genes are regulated by light/dark cycles inChlamydomonas. Interestingly,
bothChlamydomonasandOstreococcuscontain plant-specific CDC proteins
such as a B-type CDK, which plays a major role in the control of mitosis in
Ostreococcus(Corellou et al. 2005).In silicoanalysis, has revealed the pres-
ence of CCA1/LHY and TOC1-like protein homologues inChlamydomonas
andOstreococcus(Breton and Kay 2006, our unpublished data).
These unique features of green algae may promote them as models of
choice to study circadian regulation of cell division.
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