Abstract
The Drosophila Centrosomin (Cnn) protein is an essential core component of centrosomes in the early embryo. We have expressed a Cnn-GFP fusion construct in cleavage stage embryos, which rescues the maternal effect lethality of cnn mutant animals. The localization patterns seen with GFP-Cnn are identical to the patterns we see by immunofluorescent staining with anti-Cnn antibodies. Live imaging of centrosomes with Cnn-GFP reveals surprisingly dynamic features of the centrosome. Extracentrosomal particles of Cnn move radially from the centrosome and frequently change their direction. D-TACC colocalized with Cnn at these particles. We have named these extrusions 'flares'. Flares are dependent on microtubules, since disruption of the microtubule array severs the movement of these particles. Movement of flare particles is cleavage-cycle-dependent and appears to be attributed mostly to their association with dynamic astral microtubules. Flare activity decreases at metaphase, then increases at telophase and remains at this higher level of activity until the next metaphase. Flares appear to be similar to vertebrate PCM-1-containing 'centriolar satellites' in their behavior. By injecting rhodamine-actin, we observed that flares extend no farther than the actin cage. Additionally, disruption of the microfilament array increased the extent of flare movement. These observations indicate that centrosomes eject particles of Cnn-containing pericentriolar material that move on dynamic astral microtubules at a rate that varies with the cell cycle. We propose that flare particles play a role in organizing the actin cytoskeleton during syncytial cleavage.
Highlights
The centrosome is the major microtubule-organizing center (MTOC) in most animal cells, but its functions are still relatively obscure (Palazzo and Schatten, 2000)
A Drosophila cell line that lacks centrosomes can be perpetually maintained, a delay at cytokinesis is observed (Debec and Abbadie, 1989; Piel et al, 2001). These results demonstrate that bipolar spindle assembly can occur efficiently without centrosomes in vivo and in vitro
Using antibodies directed toward the Cnn protein, we observed that Cnn is localized at the perimeter of the centrosome, as is characteristic of components of the centrosome pericentriolar material (PCM), producing an image with a doughnut-shaped structure (Fig. 1A)
Summary
The centrosome is the major microtubule-organizing center (MTOC) in most animal cells, but its functions are still relatively obscure (Palazzo and Schatten, 2000). In the absence of centrosomes, the bipolar spindle assembles by an alternate, anastral, pathway where the microtubules are nucleated on the chromosomes and subsequently organized into the bipolar spindle with the minus ends of the microtubules focused at the poles (Hyman, 2000; Compton, 2000). This process involves the coordinate activities of motor proteins (Wittmann et al, 2001; Walczak, 2000; Heald, 2000; Sharp et al, 2000; Compton, 2000). Since centrioles are degraded during oogenesis in many species, this alternate spindle assembly pathway appears to act exclusively during female meiosis (Theurkauf and Hawley, 1992; Rieder et al, 1993; McKim and Hawley, 1995; Megraw and Kaufman, 2000; Compton, 2000)
Sign-in/Register to view highlights & summary 
Paper version not known (
Free)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call