Par6b Regulates the Dynamics of Apicobasal Polarity during Development of the Stratified Xenopus Epidermis

Abstract

During early vertebrate development, epithelial cells establish and maintain apicobasal polarity, failure of which can cause developmental defects or cancer metastasis. This process has been mostly studied in simple epithelia that have only one layer of cells, but is poorly understood in stratified epithelia. In this paper we address the role of the polarity protein Partitioning defective-6 homolog beta (Par6b) in the developing stratified epidermis of Xenopus laevis. At the blastula stage, animal blastomeres divide perpendicularly to the apicobasal axis to generate partially polarized superficial cells and non-polarized deep cells. Both cell populations modify their apicobasal polarity during the gastrula stage, before differentiating into the superficial and deep layers of epidermis. Early differentiation of the epidermis is normal in Par6b-depleted embryos; however, epidermal cells dissociate and detach from embryos at the tailbud stage. Par6b-depleted epidermal cells exhibit a significant reduction in basolaterally localized E-cadherin. Examination of the apical marker Crumbs homolog 3 (Crb3) and the basolateral marker Lethal giant larvae 2 (Lgl2) after Par6b depletion reveals that Par6b cell-autonomously regulates the dynamics of apicobasal polarity in both superficial and deep epidermal layers. Par6b is required to maintain the “basolateral” state in both epidermal layers, which explains the reduction of basolateral adhesion complexes and epidermal cells shedding.

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“…Interestingly, it was demonstrated that in Xenopus epidermis, Par6b autonomously regulates the dynamics of apicobasal polarity, as it is required to maintain the “basolateral” state in both epidermal layers. This supports the idea that the Nichoid recapitulates the characteristics of a Niche-like structure [ 95 ] ( Figure 6 A). Itga6 (integrin alpha 6) was found downregulated by log 2 FC= −1.56 in NPCs grown inside the Nichoid ( Figure 6 A).…”

Radial WNT5A-Guided Post-mitotic Filopodial Pathfinding Is Critical for Midgut Tube Elongation

“…Midguts were fixed in 4% PFA at RT for 2 hrs or at 4°C overnight. For vibratome sectioning, fixed midguts were embedded in 4–6% low-melting point agarose and sectioned at thickness of 100μm as previously described (Wang et al, 2013). Vibratome sections were permeabilized in 0.5% TritonX-100 in PBS for 20 min at RT while rocking and washed with PBS 5 min, three times.…”

Getting to know your neighbor: Cell polarization in early embryos

“…Despite substantial differences in the mechanisms that establish radial polarity in frog and worm embryos, the PAR proteins aPKC and Par6b develop an analogous localization to the apical cortex in Xenopus ( Chalmers et al, 2003 ; Wang et al, 2013 ). aPKC promotes the localization of apical polarity regulator Crb3/Crumbs and antagonizes the localization of basolateral regulators Par1 and Lgl2 ( Fig.…”