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Lookup NU author(s): Dr Jolanta Kisielewska
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Zygotes of the fucoid brown algae provide excellent models for addressing fundamental questions about zygotic symmetry breaking. Although the acquisition of polarity is tightly coordinated with the timing and orientation of the first asymmetric division - with zygotes having to pass through a G1/5-phase checkpoint before the polarization axis can be fixed -the mechanisms behind the interdependence of polarization and cell cycle progression remain unclear. In this study, we combine in vivo Ca2+ imaging, single cell monitoring of S-phase progression and multivariate analysis of high-throughput intracellular Call buffer loading to demonstrate that Ca2+ signals coordinate polarization and cell cycle progression in the Fucus serratus zygote. Consistent with earlier studies on this organism, and in contrast to animal models, we observe no fast Ca2+ wave following fertilization. Rather, we show distinct slow localized Call elevations associated with both fertilization and S-phase progression, and we show that both S-phase and zygotic polarization are dependent on pre-S-phase Ca2+ increases. Surprisingly, this Ca2+ requirement cannot be explained by co-dependence on a single G1/S-phase checkpoint, as S phase and zygotic polarization are differentially sensitive to pre-S-phase Ca2+ elevations and can be uncoupled. Furthermore, subsequent cell cycle progression through M phase is independent of localized actin polymerization and zygotic polarization. This absence of a morphogenesis checkpoint, together with the observed Ca2+-dependences of S phase and polarization, show that the regulation of zygotic division in the brown algae differs from that in other eukaryotic model systems, such as yeast and Drosophila.
Author(s): Bothwell JHF, Kisielewska J, Genner MJ, McAinsh MR, Brownlee C
Publication type: Article
Publication status: Published
Journal: Development
Year: 2008
Volume: 135
Issue: 12
Pages: 2173-2181
ISSN (print): 0950-1991
ISSN (electronic): 1477-9129
Publisher: The Company of Biologists Ltd.
URL: http://dx.doi.org/10.1242/dev.017558
DOI: 10.1242/dev.017558
PubMed id: 18480164
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