Polarity establishment requires dynamic actin in fucoid zygotes

Brown algae (Phaeophyceae) are an important algal class that play a range of key ecological roles. They are often important components of rocky shore communities. A number of members of the Fucales and Ectocarpales have provided models for the study of multicellular evolution, reproductive biology and polarized development. Indeed the fucoid algae exhibit the unusual feature of inducible embryo polarization, allowing many classical studies of polarity induction. The potential of further studies of brown algae in these important areas has been increasingly hindered by the absence of tools for manipulation of gene expression that would facilitate further mechanistic analysis and gene function studies at a molecular level. The aim of this study was to establish a method that would allow the analysis of gene function through RNAi-mediated gene knockdown. We show that injection of double-stranded RNA (dsRNA) corresponding to an α-tubulin gene into Fucus serratus Linnaeus zygotes induces the loss of a large proportion of the microtubule cytoskeleton, leading to growth arrest and disruption of cell division. Injection of dsRNA targeting β-actin led to reduced rhizoid growth, enlarged cells and the failure to develop apical hair cells. The silencing effect on actin expression was maintained for 3 months. These results indicate that the Fucus embryo possesses a functional RNA interference system that can be exploited to investigate gene function during embryogenesis.

supporting

confidence: 80%

mentioning

confidence: 99%

Gene silencing inFucusembryos: developmental consequences ofRNAi‐mediated cytoskeletal disruption

Farnham

Strittmatter

Coelho

et al. 2013

“…In brown algae, actin filaments have been observed using fluorescence microscopy following labeling with phalloidin or detection of actin molecules bound to antibody (Brawley and Robinson 1985, Kropf et al 1989, Bouget et al 1996, Alessa and Kropf 1999, Karyophyllis et al 2000, Hable et al 2003, Bisgrove and Kropf 2004. The distribution of actin filaments changes during the cell cycle (Brawley and Robinson 1985, Bouget et al 1996, Karyophyllis et al 2000, Bisgrove et al 2003, Hable et al 2003, Bisgrove and Kropf 2004. At interphase, actin filaments are distributed at the surface of the cytoplasm and colocalize with spindle MTs from metaphase to early telophase (Karyophyllis et al 2000).…”

mentioning

confidence: 99%

“…In Fucus distichus, this expansion was coincident with the outgrowth of the new cell partition membrane (Belanger and Quatrano 2000). Pharmacological reagents that disrupt actin filaments, such as latrunculin B and cytochalasin B or D, have been used to investigate the function of actin filaments in the progression of cytokinesis (Allen and Kropf 1992, Karyophyllis et al 2000, Hable et al 2003. In the presence of these reagents, mitosis occurs, but not cytokinesis, indicating that actin filaments have an important function during the latter process.…”

mentioning

confidence: 99%

EFFECT OF LATRUNCULIN B AND BREFELDIN A ON CYTOKINESIS IN THE BROWN ALGA SCYTOSIPHON LOMENTARIA (SCYTOSIPHONALES, PHAEOPHYCEAE)¹

Nagasato

Motomura

2009

In zygotes of the brown alga Scytosiphon lomentaria (Lyngb.) Link, cytokinesis proceeds by growth of membranous sacs, which are formed by fusion of Golgi vesicles and flat cisternae accumulated at the future cytokinetic plane. It has been reported that depolymerization of actin filaments by latrunculin B does not inhibit mitosis. However, this molecule prevents the formation of the actin plate, which appears at the region of intermingled microtubules from each centrosome just before and during cytokinesis. In this study, zygotes treated with latrunculin B were observed using EM. Remarkably, this reagent inhibited the formation of flat cisternae. Golgi vesicles gathered around the midzone between the two daughter nuclei and fused with the plasma membrane there. As a result, the plasma membrane invaginated, in a complicated manner, into the cytoplasm. However, these invaginations of the plasma membrane never produced a continuous partition membrane. The ultrastructure of zygotes treated with brefeldin A, which prevents Golgi-mediated secretion, was also examined. Flat cisternae appeared at the future cytokinetic plane, and a new cell partition membrane was formed. However, the partition membrane became thick, because it was filled with amorphous material rather than the normal rigid fibrous material. These results suggested that actin is involved in the formation of flat cisternae, where it is necessary for completion of the new cell partition membrane, and that Golgi vesicles may play an important role in the deposition of cell wall material.

“…Myosin uses the hydrolysis of ATP to translocate organelles or actin along actin filaments (Herrmann et al 1992). While the involvement of the cytoskeleton in cellular processes is well established in green and brown algae (Grolig 1990, Braun and Wasteneys 1998, Karyophyllis et al 2000, Hable et al 2003, the function of actin in red algal cells has not been thoroughly investigated.…”

mentioning

confidence: 99%

ACTIN AND MYOSIN REGULATE PSEUDOPODIA OFPORPHYRA PULCHELLA(RHODOPHYTA) ARCHEOSPORES¹

Ackland

West

Pickett‐Heaps

2007

Archeospores of Porphyra pulchella Ackland, J. A. West et Zuccarello (Rhodophyta) display amoeboid and gliding motility. Time-lapse videomicroscopy revealed that amoeboid cells extend and retract pseudopodia as they translocate through the media. We investigated the involvement of actin and myosin in generating the force for amoeboid motility using immunofluorescence, time-lapse videomicroscopy, and cytoskeletal inhibitors. Actin filaments were seen as short and long rodlike bundles around the periphery of spores. The actin inhibitors cytochalasin D (CD) and latrunculin B (Lat B), and the myosin inhibitor butanedione monoxime (BDM) disrupted the actin filament network and reversibly inhibited pseudopodial activity, resulting in the rounding and immobilization of spores. It was uncertain whether forward translocation of archeospores resumed following drug removal. These results demonstrate that actin and myosin have a role in generating force for pseudopodial activity. This is the first report of cytoskeletal involvement in red algal cell movement. The involvement of actin and myosin in forward translocation of amoeboid archeospores can only be speculated upon.