Reconstruction of Par-dependent polarity in apolar cells reveals a dynamic process of cortical polarization

Abstract

Cellular polarization is fundamental for various biological processes. The Par network system is conserved for cellular polarization. Its core complex consists of Par3, Par6, and aPKC. However, the general dynamic processes that occur during polarization are not well understood. Here, we reconstructed Par-dependent polarity using non-polarized Drosophila S2 cells expressing all three components endogenously in the cytoplasm. The results indicated that elevated Par3 expression induces cortical localization of the Par-complex at the interphase. Its asymmetric distribution goes through three steps: emergence of cortical dots, development of island-like structures with dynamic amorphous shapes, repeating fusion and fission, and polarized clustering of the islands. Our findings also showed that these islands contain a meshwork of unit-like segments. Furthermore, Par-complex patches resembling Par-islands exist in Drosophila mitotic neuroblasts. Thus, this reconstruction system provides an experimental paradigm to study features of the assembly process and structure of Par-dependent cell-autonomous polarity.

A balance between antagonizing PAR proteins specifies the pattern of asymmetric and symmetric divisions in C. elegans embryogenesis

“…The striking conservation of the function of PAR proteins in both invertebrates and vertebrates raises a possibility that the self-organizing PAR system is a conserved executor of the specification between the two division modes. Consistent with this model, a recent study also revealed that overexpression of Drosophila PAR-3, Bazooka, is sufficient to trigger the segregation of other PAR proteins and fate determinants in S2 cells (Kono et al, 2019). Interestingly, the ratios of PAR proteins can be modified dynamically during development.…”

Liquid-Liquid Phase Separation in Neuronal Development and Synaptic Signaling

“…Interestingly, when the imaging focal plane is perpendicular to the apical-basal axis and focused on the apical side of NBs, each component of the Par complex showed a patch-like distribution with clearly visible individual puncta within the patches (Liu et al, 2020b). Such patch-like Par complex formation has also been observed when Drosophila S2 cells were induced to polarize with overexpression of Baz, and the small puncta are dynamic and can fuse into larger ones (Kono et al, 2019). All these observations suggest that the Par complex in NBs or in induced polar S2 cells may be formed via LLPS.…”

“…Extensive studies in the past several decades have revealed that distinct molecular complexes are required for these two processes (Wen and Zhang, 2018;Bergstralh et al, 2017;di Pietro et al, 2016;Taverna et al, 2014;Knoblich, 2010;Siller and Doe, 2009). Emerging evidence in the last few years indicate that some of these complexes may be assem-bled via LLPS to form condensed molecular networks in distinct cellular compartments (Liu et al, 2020a(Liu et al, , 2020bKono et al, 2019;Shan et al, 2018).…”

Phase Separation and Mechanical Forces in Regulating Asymmetric Cell Division of Neural Stem Cells

“…The formation of such dynamic PAR condensates is mainly driven by oligomerization of Baz/Par3 via its N-terminal domain (NTD) ( Figure 2 B). Supporting this notion, the overexpression of Baz/Par3 in a non-polarized Drosophila S2 cell induced the formation of cortical Baz/Par3 patches, which had a liquid-like property [ 49 ]. Par-6 could be enriched in the Baz/Par3 condensates by binding to Baz/Par3 PDZ3 via its PDZ binding motif (PBM), and Par-6 could self-associate through its PB1 domain, which further enhances the multivalence of the Baz/Par3–Par-6 complex as well as its LLPS property ( Figure 2 B) [ 17 ].…”