Spatial re-organisation of cortical microtubules in vivo during polarisation and asymmetric division ofFucuszygotes

Abstract

IntroductionMicrotubules perform a variety of essential functions within the cell. The mitotic spindle supports chromosome segregation and determines the position of cleavage in animals (Ahringer, 2003). This array is focused at centrosomes in animals although other non-centrosomal arrays exist that are mostly involved in polarised morphologies of specialised animal cells (Keating and Borisy, 1999). In animals, cortical microtubule (MT) arrays have been described only in very specific cases, such as starfish or Xenopus oocytes and zebrafish zygotes, where they are involved in the establishment of the dorsoventral axis (Jesuthasan and Stahle, 1997;Schroeder and Gard, 1992;Schroeder and Otto, 1984).By contrast, cortical MTs are a common feature of vegetative plant cells, in which they play a key role in shaping the cell by directing deposition of cellulose microfibrils (Mfs) in the cell wall and thereby cell growth (Lloyd and Chan, 2004). In plants the interphase MT array in G1 consists of cortical MTs linked to the plasmalemma and is replaced in G2 by the pre-prophase band cortical array that marks the position of the division plane. This array disappears in late prophase and is followed in succession by the mitotic apparatus and the phragmoplast. The perinuclear MT array is in continuity with the cortical array although it is still not clear whether cortical MTs arise from the translocation of perinuclear MTs or are nucleated de novo at cortical sites or both since there is evidence for both mechanisms (Burk and Ye, 2002;Cyr and Palevitz, 1995;Shaw et al., 2003).Rather less is known about MT distributions in zygotes and embryos of higher plants, owing to their general inaccessibility for direct study. Zygotes of fucoid algae (Fucus, Silvetia) have long served as a cellular model to study fertilisation, polarisation and cell division. Oospheres are initially spherical with no detectable polarity (Jaffe, 1958). After fertilisation (AF) Fucus zygotes deposit a cell wall within minutes and establish an axis of polarity in response to external cues (such as unidirectional light) that becomes fixed in space (14-18 hours AF) and leads to the germination of a rhizoid at the side facing away from the incident light (16-20 hours AF) (Henry et al., 1996;Love et al., 1997;Novotny and Forman, 1974). Concomitantly zygotes progress through the first cell cycle and divide perpendicularly to the growth axis (Corellou et al., 2001). The first asymmetrical division gives rise to the rhizoid and thallus cells with distinct developmental fates . The rhizoid remains the only site of growth of the embryos during several rounds of division. The primary division planes in the rhizoid are oriented transverse to the polar axis whereas the first thallus cell 2723Fucus zygotes polarise and germinate a rhizoid before their first asymmetrical division. The role of microtubules (MTs) in orienting the first division plane has been extensively studied by immunofluorescence approaches. In the present study, the re-organisation of MT arrays during...

Phospholipid signaling during stramenopile development

“…In F. serratus, a closely related brown alga, injection of fluorescent tubulin visualized centrosomal MT arrays as well as arrays residing solely in the cortex. 23 Together, these data suggest that (1) MT arrays can be stabilized by interactions with the plasma membrane, and (2) the plasma membrane may be capable of MT nucleation. Interestingly, cortical MT nucleation and MT stabilization by interaction with the plasma membrane are both characteristic of higher plant interphase MTs.…”

Radial endoplasmic reticulum arrays co-localize with radial F-actin in polarizing cells of brown algae

“…It should be noted that Corellou et al (2005) recently described the organisation of cortical Mt arrays during the development of Fucus zygotes, after microinjection of fluorescent tubulin. During zygote germination, these arrays undergo re-organization and converge towards the site of rhizoid emergence.…”

Life-cycle-generation-specific developmental processes are modified in theimmediate uprightmutant of the brown algaEctocarpus siliculosus

“…Initial cell (zygote) photopolarisation has been extensively studied in members of the Fucales group (Corellou et al, 2005;Robinson and Miller, 1997;Fowler et al, 2004;Brownlee and Bouget, 1998). In this group, photopolarisation causes the zygote to germinate in a negatively phototropic manner, emitting a rhizoid on the side opposite the light source.…”