Separable mechanisms drive local and global polarity establishment in the C. elegans intestinal epithelium

Abstract

Apico-basolateral polarization is essential for epithelial cells to function as selective barriers and transporters, and to provide mechanical resiliency to organs. Epithelial polarity is established locally, within individual cells to establish distinct apical, junctional, and basolateral domains, and globally, within a tissue where cells coordinately orient their apico-basolateral axes. Using live imaging of endogenously tagged proteins and tissue specific protein depletion in the C. elegans embryonic intestine, we found that local and global polarity establishment are temporally and genetically separable. Local polarity is initiated prior to global polarity and is robust to perturbation. PAR-3 is required for global polarization across the intestine but is not required for local polarity establishment as small groups of cells are able to correctly establish polarized domains in PAR-3 depleted intestines in an HMR-1/E-cadherin dependent manner. Despite belonging to the same apical protein complex, we additionally find that PAR-3 and PKC-3/aPKC have distinct roles in the establishment and maintenance of local and global polarity. Together, our results indicate that different mechanisms are required for local and global polarity establishment in vivo.SUMMARY STATEMENTLive-imaging and intestine specific protein depletion reveal that apico-basolateral polarity establishment can be temporally and genetically separated at the local level of individual cells and globally, across a tissue.

E-cadherin/HMR-1 and PAR-3 break symmetry at stable cell contacts in a developing epithelium

“…We note that some non-migratory AFD-1 foci still localized to lateral membranes during this midline enrichment, suggesting that distinct subpopulations of AFD-1 may exist with differing mobilities. By E20, midline-associated AFD-1 began assembling into junctional rings as previously reported (Pickett et al, 2021).…”

“…We next investigated whether HMR-1 and PAR-3 are required for tissue symmetry breaking, when LPCs migrate and spread along the intestinal midline at E16. We observed HMR-1 localization in PAR-3 gut(-) embryos and PKC-3 in HMR-1 gut(-) embryos because PAR-3 fluorescence was too dim to reliably track and PKC-3 and PAR-3 always colocalize at this stage (Pickett et al, 2021). By E16, PKC-3 and HMR-1 became brighter in HMR-1 gut(-) and PAR-3 gut(-) embryos, respectively, although still localizing as small foci rather than large LPCs.…”

“…PAR proteins co-localize and co-migrate with adherens junction (AJ) proteins at E16 (Pickett et al, 2021; Totong et al, 2007). Consistently, E-cadherin/HMR-1, β-catenin/HMP-2, α-catenin/HMP-1, and afadin/AFD-1 were all found in E4 foci and sometimes colocalized with or were adjacent to PAR-3 before enriching together into LPCs at the E8 stage (Fig.…”

Won’t You be My Neighbor: How Epithelial Cells Connect Together to Build Global Tissue Polarity

“…At a global scale across a tissue and even across entire organ systems such as a through gut digestive tract, this local polarity must be coordinated into a global apico-basolateral polarity that is consistent across all connected epithelial cells, regardless of their origin or their polarity establishment mechanisms ( Figure 1A ). Recent in vivo work has found that local and global polarity establishment are temporally and genetically separable during the development of the C. elegans intestine ( Pickett et al, 2021 ). In the absence of PAR-3, local pockets of apical proteins align between neighboring cells in a HMR-1/E-cadherin-dependent manner, leading to a cystic, non-functional intestine that lacks global polarity ( Pickett et al, 2021 ).…”

“…Recent in vivo work has found that local and global polarity establishment are temporally and genetically separable during the development of the C. elegans intestine ( Pickett et al, 2021 ). In the absence of PAR-3, local pockets of apical proteins align between neighboring cells in a HMR-1/E-cadherin-dependent manner, leading to a cystic, non-functional intestine that lacks global polarity ( Pickett et al, 2021 ). Global coordination of apical membrane initiation sites to one common lumen involves the location of the midbody after oriented cell divisions and cadherin-mediated mechanisms that are independent of cell division ( Jewett and Prekeris, 2018 ; Buckley and St Johnston, 2022 ), as shown in cultured cells ( Schluter et al, 2009 ; Li et al, 2014 ; Lujan et al, 2016 ; Liang et al, 2022 ) and zebrafish development ( Tawk et al, 2007 ; Zigman et al, 2011 ; Rathbun et al, 2020 ).…”