Wac: a new Augmin subunit required for chromosome alignment but not for acentrosomal microtubule assembly in female meiosis

Abstract

The bipolar spindle forms without centrosomes naturally in female meiosis and by experimental manipulation in mitosis. Augmin is a recently discovered protein complex required for centrosome-independent microtubule generation within the spindle in Drosophila melanogaster cultured cells. Five subunits of Augmin have been identified so far, but neither their organization within the complex nor their role in developing organisms is known. In this study, we report a new Augmin subunit, wee Augmin component (Wac). Wac directly interacts with another Augmin subunit, Dgt2, via its coiled-coil domain. Wac depletion in cultured cells, especially without functional centrosomes, causes severe defects in spindle assembly. We found that a wac deletion mutant is viable but female sterile and shows only a mild impact on somatic mitosis. Unexpectedly, mutant female meiosis showed robust microtubule assembly of the acentrosomal spindle but frequent chromosome misalignment. For the first time, this study establishes the role of an Augmin subunit in developing organisms and provides an insight into the architecture of the complex.

Genomic and clinical characteristics of six patients with partially overlapping interstitial deletions at 10p12p11

“…Wac depletion in cultured Drosophila S2 cells has been shown to cause severe defects in spindle assembly. 13,14 In developing Drosophila, WAC is required for cell proliferation, but its homozygous or heterozygous deletions were not found to be lethal. Instead, in somatic cells, the deletion of WAC resulted in delayed mitotic progression with a proper chromosome segregation in general.…”

Microtubule nucleation and organization in dendrites

“…20,35 Golgi outposts provide a local guide for microtubule nucleation in dendrites, and they interact with other nucleation sites in order to fine-tune the amplitude and polarity of dendrite microtubule nucleation events. 20,35,57 Dendrite microtubules themselves may also act as a nucleation site through the activity of the Augmin complex, 20,62 an important question for further study. Diversity in neuron arbors can be achieved by modulating the dendrite nucleation machinery, for example by regulating the activity of Golgi outposts as nucleation sites.…”

“…3B). 20 Microtubule nucleation is catalyzed from the sides of microtubules during the maturation of the mitotic spindle by the Augmin complex, 61 and loss of the Drosophila Augmin component Wee Augmin (Wac) 62 leads to a specific reduction of the additional anterograde polymerization events that are caused when nucleation is decoupled from Golgi. 20 Augmin nucleates new microtubules with the same polarity as the pre-existing microtubule template 61 ( Fig.…”

50 ways to build a spindle: the complexity of microtubule generation during mitosis

“…Genetic removal of Augmin from larval neuroblasts appears to have no effect on the shape or size of the mitotic spindle, as assessed by indirect immunofluorescence of metaphase cells (Meireles et al 2009;Wainman et al 2009). In contrast, the mitotic spindles of syncytial blastoderm embryos laid by this same mutant are less dense and longer than their wild-type counterparts, with apparently larger MT asters (Wainman et al 2009).…”

“…Null mutants of the Augmin subunit, Wac, are viable, albeit showing a small, but significant, impact on somatic mitosis (Meireles et al 2009). However, Augmin is essential for the fast and synchronous early embryonic divisions that occur in the embryo of the fly.…”