aPKC-mediated displacement and actomyosin-mediated retention polarize Miranda in Drosophila neuroblasts

Abstract

Cell fate assignment in the nervous system of vertebrates and invertebrates often hinges on the unequal distribution of molecules during progenitor cell division. We address asymmetric fate determinant localization in the developing Drosophila nervous system, specifically the control of the polarized distribution of the cell fate adapter protein Miranda. We reveal a stepwise polarization of Miranda in larval neuroblasts and find that Miranda's dynamics and cortical association are differently regulated between interphase and mitosis. In interphase, Miranda binds to the plasma membrane. Then, before nuclear envelope breakdown, Miranda is phosphorylated by aPKC and displaced into the cytoplasm. This clearance is necessary for the subsequent establishment of asymmetric Miranda localization. After nuclear envelope breakdown, actomyosin activity is required to maintain Miranda asymmetry. Therefore, phosphorylation by aPKC and differential binding to the actomyosin network are required at distinct phases of the cell cycle to polarize fate determinant localization in neuroblasts.

The last-born daughter cell contributes to division orientation of Drosophila larval neuroblasts

“… 55 for a review). Septins 56 , Cindr, Roughest 39 and Flare 37 can be linked in one way or another to the regulation of actomyosin, and at least the maintenance of Baz localization in mitotic NBs is also actin-dependent 57 . Intracellular long-range control of polarization has been further observed in eight-cell stage mouse blastomeres, where cell–cell contacts induce apical polarization at the opposite end of the cell 58 .…”

Switching states: dynamic remodelling of polarity complexes as a toolkit for cell polarization

“…A shared characteristic of numerous polarity-related proteins, these domains are often the direct targets of regulatory kinases, allowing membrane association to be regulated in time and space. Miranda, Numb, Lgl and PAR-2 membrane binding domains are direct targets of the polarity-related kinase aPKC, providing a mechanism for exclusion from aPKC-enriched domains [32,34,36,37].…”

aPKC: the Kinase that Phosphorylates Cell Polarity

“…For instance, aPKC phosphorylation could induce conformation changes or protein interactions that hinder the polybasic domain from binding to PM. In addition, a recent study showed that although aPKC phosphorylation of the polybasic domain clears Mir from PM at interphase in asymmetrically dividing neuroblasts, at metaphase phosphorylation of the polybasic domain may actually enhance the actomyosin-dependent anchoring of Mir to basal PM 41 .…”