PAR-6, but not E-cadherin and β-integrin, is necessary for epithelial polarization in C. elegans

Abstract

Cell polarity is a fundamental characteristic of epithelial cells. Classical cell biological studies have suggested that establishment and orientation of polarized epithelia depend on outside-in cues that derive from interactions with either neighboring cells or the substratum (Akhtar and Streuli, 2013; Chen and Zhang, 2013; Chung and Andrew, 2008; McNeill et al., 1990; Nejsum and Nelson, 2007; Nelson et al., 2013; Ojakian and Schwimmer, 1994; Wang et al., 1990; Yu et al., 2005). This paradigm has been challenged by examples of epithelia generated in the absence of molecules that mediate cell-cell or cell-matrix interactions, notably E-cadherin and integrins (Baas et al., 2004; Choi et al., 2013; Costa et al., 1998; Harris and Peifer, 2004; Raich et al., 1999; Roote and Zusman, 1995; Vestweber et al., 1985; Williams and Waterston, 1994; Wu et al., 2009). Here we explore an alternative hypothesis, that cadherins and integrins function redundantly to substitute for one another during epithelium formation (Martinez-Rico et al., 2010; Ojakian et al., 2001; Rudkouskaya et al., 2014; Weber et al., 2011). We use C. elegans, which possesses a single E-cadherin (Costa et al., 1998; Hardin et al., 2013; Tepass, 1999) and a single β-integrin (Gettner et al., 1995; Lee et al., 2001), and analyze the arcade cells, which generate an epithelium late in embryogenesis (Portereiko and Mango, 2001; Portereiko et al., 2004), after most maternal factors are depleted. Loss of E-cadherinHMR-1 in combination with β-integrinPAT-3 had no impact on the onset or formation of the arcade cell epithelium, nor the epidermis or digestive tract. Moreover, β-integrinPAT-3 was not enriched at the basal surface of arcades, and the candidate PAT-3 binding partner β-lamininLAM-1 was not detected until after arcade cell polarity was established and exhibited no obvious polarity defect when mutated. Instead, the polarity protein par-6 (Chen and Zhang, 2013; Watts et al., 1996) was required to polarize the arcade cells, and par-6 mutants exhibited mislocalized or absent apical and junctional proteins. We conclude that the arcade cell epithelium polarizes by a PAR-6-mediated pathway that is independent of E-cadherin, β-integrin and β-laminin.

Epidermal PAR-6 and PKC-3 are essential for postembryonic development ofCaenorhabditis elegansand control non-centrosomal microtubule organization

“…Depletion of PAR-6 and PKC-3 in the epidermis resulted in a fragmented appearance of the hyp7/seam and seam/seam junctions, similar to previous observations in embryonic epithelia (Montoyo-Rosario et al, 2020;Totong et al, 2007;Von Stetina and Mango, 2015;Von Stetina et al, 2017). Our data therefore further demonstrate a general requirement for PAR-6 and PKC-3 in junction formation or maintenance.…”

“…Intestinal and epidermal cells depleted of PAR-6 or PKC-3 using the ZF1 system still show apicobasal polarization, as evidenced by apical localization of junctional and cytoskeletal proteins (Montoyo-Rosario et al, 2020;Totong et al, 2007). However, in the arcade cells of the pharynx, most PAR-6 depleted animals show no apical enrichment of junctional or apical cytoskeletal markers (Von Stetina and Mango, 2015). These data further highlight that the requirements for PAR-6 and PKC-3 can vary between tissues.…”

“…PAR-6 appears to be required for apical junction formation in all epithelia, including the epidermis, intestine, foregut, and pharyngeal arcade cells (Montoyo-Rosario et al, 2020;Totong et al, 2007;Von Stetina and Mango, 2015;Von Stetina et al, 2017). However, while arcade cells show a complete lack of polarization upon PAR-6 loss, foregut, intestinal, and epidermal epithelial cells still establish an apical domain (Totong et al, 2007;Von Stetina and Mango, 2015). PAR-3 is required for apical junction formation in embryonic intestinal and pharyngeal epithelia, but not in epidermal epithelial cells (Achilleos et al, 2010).…”

Multi-tissue patterning drives anterior morphogenesis of theC. elegansembryo

“…Apically formed rosettes are typically highly stable and ultimately give rise to lumens (Lecaudey et al, 2008;Nechiporuk and Raible, 2008). Interestingly, the anterior arcade cells remain distinct from the large pharyngeal cyst, yet must polarize to form a contiguous lumen (Portereiko and Mango, 2001;Portereiko et al, 2004;Mango 2009;Von Stetina and Mango, 2015). These cells must be precisely positioned in line with the more posterior pharyngeal cells and the anterior epidermal cells, but as indicated earlier, it is not clear how they do this.…”

“…Anterior to the cyst are the arcade cells, which migrate anteriorly then move back into the embryo (Portereiko and Mango, 2001;Portereiko et al, 2004;Mango 2009). They also polarize and coordinate with the epidermal cells for epithelialization of the anterior pharynx, but it is not clear how this occurs (Von Stetina and Mango, 2015). During anterior morphogenesis, the neuroblasts presumably also undergo specific movements and patterning, but this has not been studied.…”