The Microcephaly-Associated Protein Wdr62/CG7337 Is Required to Maintain Centrosome Asymmetry in Drosophila Neuroblasts

Abstract

Centrosome asymmetry has been implicated in stem cell fate maintenance in both flies and vertebrates, but the underlying molecular mechanisms are incompletely understood. Here, we report that loss of CG7337, the fly ortholog of WDR62, compromises interphase centrosome asymmetry in fly neural stem cells (neuroblasts). Wdr62 maintains an active interphase microtubule-organizing center (MTOC) by stabilizing microtubules (MTs), which are necessary for sustained recruitment of Polo/Plk1 to the pericentriolar matrix (PCM) and downregulation of Pericentrin-like protein (Plp). The loss of an active MTOC in wdr62 mutants compromises centrosome positioning, spindle orientation, and biased centrosome segregation. wdr62 mutant flies also have an ∼40% reduction in brain size as a result of cell-cycle delays. We propose that CG7337/Wdr62, a microtubule-associated protein, is required for the maintenance of interphase microtubules, thereby regulating centrosomal Polo and Plp levels. Independent of this function, Wdr62 is also required for the timely mitotic entry of neural stem cells.

Glial-Specific Functions of Microcephaly Protein WDR62 and Interaction with the Mitotic Kinase AURKA Are Essential for Drosophila Brain Growth

“…The bipolar mitotic spindle must be properly orientated, bisecting the apical and basal crescents of the polarity factors inherited by daughter cells, to ensure timely mitotic progression and asymmetric division of NBs (Knoblich, 2008). Worniu- GAL4 driven depletion of wdr62 caused spindle misorientation (Figure S1E), consistent with previous reports of spindle alignment defects in wdr62 loss-of-function mutants (Nair et al., 2016). However, further studies are required to determine if this contributes to the increased mitotic index in wdr62 loss-of-function NBs as spindle misorientation alone is not sufficient to cause cell-cycle delay (Homem and Knoblich, 2012).…”

“…However, potential contribution(s) of individual brain lineage(s) (NB or glia) to the defective brain growth associated with global depletion of wdr62 or aurka is currently unclear. Here, we confirm that WDR62 is required for spindle orientation in NBs (Nair et al., 2016), however, wdr62 depletion specifically in NBs does not significantly retard brain growth. Rather, control of brain growth predominantly depends upon glial lineage function, as depletion of either aurka or wdr62 specifically in the glial lineage significantly reduces brain volume.…”

“…As a consequence, mutant aurka causes NB overproliferation and tissue overgrowth (Atwood and Prehoda, 2009, Smith et al., 2007, Wirtz-Peitz et al., 2008). The WDR62 ortholog in Drosophila (dWDR62) is required for brain growth (Nair et al., 2016), but whether signaling between WDR62 and AURKA modulates brain development has not been reported.…”

Disruptions in asymmetric centrosome inheritance and WDR62-Aurora kinase B interactions in primary microcephaly

“…3). The underlying mechanism remains unknown, but the Drosophila Wdr62 ortholog also plays a role in maintaining centrosome asymmetry in neuroblasts and is required for microtubule stabilization and maintenance of microtubule organizing center activity on the apical interphase centrosome70. WDR62 disruption in patient-derived fibroblasts has no obvious impact on spindle or centrosome formation and proper localization of many pericentrosomal and centrosomal proteins; the localization of (endogenous or overexpressed) disease-associated mutant forms of WDR62 to the spindles poles, however, is impaired.…”

The Centrioles,Centrosomes, Basal Bodies, and Cilia ofDrosophila melanogaster

“…Another player is Wdr62, the fly homolog of WDR62/MCPH2 in vertebrates, that regulate neurogenesis in rat by controlling symmetric and asymmetric divisions and interacts with Aurora A kinase (Chen et al 2014). Wdr62 maintains an active interphase MTOC by stabilizing MTs, which are necessary for recruitment of Polo to the PCM and downregulation of DPlp (Ramdas Nair et al 2016). …”