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cytokinesis (for reviews see Bowerman and Severson, 1999; O'Halloran, 2000;
Finger and White, 2002). Consistent with proteins involved in vesicle
tra cking and/or cytoskeletal processes being involved in cytokinesis, we
recently demonstrated that Dyn2 localizes to the spindle midzone and plays a
role in the late stages of cytokinesis (Thompson et al., 2002). Using
fluorescence and immunoelectron microscopy, we noted an intense staining
of Dyn2 at the microtubule-rich intercellular bridge proximal to the dense
midbody matrix (Figure 12.1C). However, Dyn2 staining was not observed
along cytoplasmic microtubule bundles induced by paralitaxel treatment,
suggesting a specific localization of Dyn2 to the intercellular bridge during
cytokinesis and not to microtubule bundles in general. In support of these
morphological data, we were able to detect a 30- to 50-fold enrichment of
Dyn2 in isolated spindle midbody extracts as compared with interphase
extracts. To test for a functional role for dynamin in cytokinesis, the nematode
Caenorhabditis elegans was used. Importantly, an antibody recognizing
C. elegans dynamin localized this protein to the ingressing cleavage furrow
as well as to the midbody of dividing embryos. Finally, using either a
temperature-sensitive dynamin mutant strain of C. elegans or wildtype
embryos depleted of dynamin protein through RNAi treatment, we were
able to demonstrate that dynamin function is necessary for the late stages of
cytokinesis. In both cases, disruption of dynamin function did not block
mitosis or the initiation of cleavage furrow ingression. However, just before
the final separation of the two daughter cells, cleavage furrow ingression was
aborted and the cells became multinucleate. Interestingly, dynamin ortho-
logues in plants (Gu and Verma, 1996; Lauber et al., 1997), fungi (Wienke et
al., 1999), flies (Swanson and Poodry, 1981) and zebrafish (Feng et al., 2002)
have also been implicated in cytokinesis. Thus, this could be a conserved
function for dynamin family members across a variety of species. Though the
exact role of dynamin in cytokinesis is not known, it could be involved in
multiple aspects of this process, such as membrane remodelling, vesicle
tracking or coordinating interactions between cleavage furrow membranes
and the microtubule and actin cytoskeletons. The role of dynamin in
cytokinesis and its regulation during this process are areas of
Dynamin and dendritic spine morphogenesis
Although most mammalian tissues only express a single isoform of dynamin,
Dyn2, neurons produce all three forms. Of these three, previous studies in
neurons have focused almost exclusively on the brain-specific isoform Dyn1,
and its role in synaptic vesicle recycling (Takei et al., 1996; Shupliakov et al.,
1997). Additional experiments have since demonstrated a postsynaptic
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