Oriented cell division is a key regulator of cell fate and linked to the positioning of the spindle in mitosis. However, in mammals the cues that determine planar versus perpendicular positioning of the spindle remain largely unclear. One candidate is the polarity protein atypical protein kinase C (aPKC)l, which regulates cell fate and spindle orientation in vivo in the epidermis. To study how aPKC controls mitotic spindle orientation, we developed a minimal keratinocyte culture system in which planar spindle positioning occurs in the absence of intercellular adhesive polarity cues. As in vivo, either loss of aPKC or knockdown of the LGN orthologue AGS-3 increased spindle angle, which was dependent on LGN. Whereas in late mitosis planar spindles were linked to bipolar cortical LGN localization of LGN and similar spreading capacity of future daughters, increased spindle angles showed a monopolar cortical LGN, and differential circularity and spreading of future daughters. To ask how aPKC and AGS-3 control planar positioning and LGN positioning in late mitosis, we then performed SILAC and mass spectrometry. This unbiased screen identified Serine 1221 in the spindle orientation machinery protein NuMA as an aPKC phospho-target. Importantly, the phosphomimetic NuMA-SD, but not the phosphomutant SA, rescued planar spindle orientation upon loss of either aPKC or AGS3. Moreover, NuMA-SD but not NuMA-SA restored bipolar cortical LGN localization, and future daughter circularity in late mitosis. Interactome analysis revealed that NumaSD but not SA interacts with CLASP2, a microtubule binding protein that also may regulate focal adhesion dependent spreading. Together, our results indicate that aPKC-dependent phosphorylation of NuMA couples spindle orientation to differential spreading behavior of future daughter cells through regulation of LGN cortical localization.

ESDR550 - aPKC regulates the spindle orientation machinery to promote planar cell divisons

The scientific meeting of the European Society for Dermatological Research (ESDR) is held yearly, usually in September. With an international attendance of more than 1000 skin scientists from around the globe, the four-day event includes short oral presentations from peer-reviewed abstracts, keynote lectures from international experts, sponsored symposia, satellite programs, educational events as well as an important focus on posters, networking and building collaborations amongst scientists. For more information about this year’s meeting visit our website.