Asymmetric Division in Fucoid Zygotes Is Positioned by Telophase Nuclei

Abstract

The relative contributions of cell polarity and nuclear position in specifying the plane of asymmetric division in fucoid zygotes were investigated. In zygotes developing normally, telophase nuclei were positioned parallel to the polar growth axis, and the division plane bisected both axes. To assess division plane specification, the colinearity of the nuclear and growth axes was uncoupled by treatment with pharmacological agents. Spatial correlations between the growth axis, telophase nuclei, and the division plane were analyzed in the treated zygotes. In all cases, cytokinesis was oriented transverse to the telophase mitotic array and was less well aligned with the growth axis. Telophase nuclei also played a predominant role in positioning the division plane in polyspermic zygotes. Microtubules from the telophase nuclei interdigitated throughout the plane of subsequent cytokinesis, and we speculate that they specify the division plane. Morphological markers of the division plane were not observed before telophase; the earliest division marker detected was a plate of actin that assembled in the zone of microtubule overlap late in telophase. These findings are consistent with division plane specification at cytoplast boundaries.

Membrane fusion process and assembly of cell wall during cytokinesis in the brown alga, Silvetia babingtonii (Fucales, Phaeophyceae)

“…The appearance of an actin plate at the future cytokinetic plane is a distinctive feature in brown algae (Brawley and Robinson 1985;Bouget et al 1996;Karyophyllis et al 2000;Bisgrove et al 2003;Hable et al 2003;Bisgrove and Kropf 2004;Nagasato and Motomura 2009). In Silvetia and fucoid zygotes, the actin plate expanded centrifugally, and this expansion correlates with the outgrowth of the new cell partition membrane (Belanger and Quatrano 2000;Bisgrove and Kropf 2004).…”

“…The first cell division always arise perpendicular to the growth axis. Cytokinesis occurs where microtubules (MTs) from each centrosome intermingle (Nagasato and Motomura 2002a;Bisgrove et al 2003), and the centrosomes rotate so that cytokinesis occurs across the appropriate plane after mitosis. As a result of the asymmetrical division of the zygote, the thallus and rhizoid cells are formed.…”

Germline-Specific MATH-BTB Substrate Adaptor MAB1 Regulates Spindle Length and Nuclei Identity in Maize

“…First, the establishment of an internal cell asymmetry is required; and second, the positioning of the division plane and the spindle apparatus with respect to the axis is defined by the polarity of the cell. Accordingly, cytokinesis results in the asymmetric distribution of cellular components (Bisgrove et al, 2003) and presumably cell fate determinants. In mammalian cells, it has been shown that asymmetric mitosis is achieved by asymmetric labeling of peripheral centrosomal proteins for degradation when centrioles separate and migrate to opposite poles (Fuentealba et al, 2008).…”

“…In mammalian cells, it has been shown that asymmetric mitosis is achieved by asymmetric labeling of peripheral centrosomal proteins for degradation when centrioles separate and migrate to opposite poles (Fuentealba et al, 2008). Moreover, in cases where the site of cytokinesis is not predetermined by a PPB, the cell division plane will bisect the spindle axis (Bisgrove et al, 2003). A PPB marks the position of the first mitotic division of the zygote (Webb and Gunning, 1991).…”

Effect of GeO2on embryo development and photosynthesis in Fucus vesiculosus (Phaeophyceae)

“…Polarity can be observed within 14-16 h AF when the rhizoid protuberance appears on the zygote surface. The rhizoid appearance is preceded by a series of processes, including asymmetric ion fluxes (Homblé and Léonetti 2007), redistribution of cytoskeletal elements (e.g., Bisgrove and Kropf 2001a, Bisgrove et al 2003) and targeted vesicular secretion (Kropf 1997). Subsequently, the zygote has a single axis of symmetry that defines the embryo growth axis, and normally the first division of the zygote is perpendicular to this axis and positioned by telophase nuclei (Bisgrove and Kropf 2004).…”