Pins is not required for spindle orientation in the Drosophila wing disc.

Dan T Bergstralh,Samantha Cooper,Holly E Lovegrove,Daniel St Johnston,Nicole S Dawney,Jinwei Zhu,Rongguang Zhang,Izabela Kujawiak

doi:10.1242/dev.135475

Dan T Bergstralh, Samantha Cooper + Show 6 more

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https://doi.org/10.1242/dev.135475

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Abstract

In animal cells, mitotic spindles are oriented by the dynein/dynactin motor complex, which exerts a pulling force on astral microtubules. Dynein/dynactin localization depends on Mud/NUMA, which is typically recruited to the cortex by Pins/LGN. In Drosophila neuroblasts, the Inscuteable/Baz/Par-6/aPKC complex recruits Pins apically to induce vertical spindle orientation, whereas in epithelial cells Dlg recruits Pins laterally to orient the spindle horizontally. Here we investigate division orientation in the Drosophila imaginal wing disc epithelium. Live imaging reveals that spindle angles vary widely during prometaphase and metaphase, and therefore do not reliably predict division orientation. This finding prompted us to re-examine mutants that have been reported to disrupt division orientation in this tissue. Loss of Mud misorients divisions, but Inscuteable expression and aPKC, dlg and pins mutants have no effect. Furthermore, Mud localizes to the apical-lateral cortex of the wing epithelium independently of both Pins and cell cycle stage. Thus, Pins is not required in the wing disc because there are parallel mechanisms for Mud localization and hence spindle orientation, making it a more robust system than in other epithelia.

Highlights

Spindle orientation has been extensively examined in asymmetrically dividing cells, less attention has been given to orientation in symmetrically dividing epithelia
Consistent with reported results using the aPKCTS allele, extensive apoptotic cell death was observed at the basal surface of these discs, indicating that atypical Protein kinase C (aPKC) function was compromised (Guilgur et al, 2012). These findings show that aPKC does not regulate spindle orientation in the imaginal wing disc, and are consistent with previous studies in the chick neuroepithelium and the Drosophila notum and follicular epithelium (Bergstralh et al, 2013b; Peyre et al, 2011; Rosa et al, 2015)
We explored the possibility that the failure of Inscuteable to reorient divisions in the wing disc, as it does in other Drosophila epithelia, could be attributed to aPKC

Summary

Introduction

Spindle orientation has been extensively examined in asymmetrically dividing cells, less attention has been given to orientation in symmetrically dividing epithelia. The orientation of division is determined by the orientation of the mitotic spindle This orientation depends on a conserved pathway that includes Partner of Inscuteable (Pins; GPR-1/2 in C. elegans, LGN or GPSM2 in vertebrates), which anchors Mushroom body defect (Mud; LIN-5 in C. elegans, NuMA or NUMA1 in vertebrates) to. This pathway is thought to work in every mitotic cell type and organism

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