873 Planar cell polarity-disrupting mutations alter Celsr1-mediated cell adhesion and dynamics

Abstract

Planar cell polarity (PCP), the collective and organized polarization of cells along a tissue plane, is fundamental to early embryonic development and tissue organization in complex, multicellular organisms. A striking example of PCP is the ordered alignment of body hairs on mammalian skin. Deficiencies in PCP components leads to neural tube defects, cardiomyopathies, as well as, abnormal hair patterning in the skin. Atypical cadherin Celsr is the principle component of an asymmetric junctional complex that regulates PCP. How Celsr mediates adhesive interactions to coordinate asymmetric PCP protein localization and function remains poorly understood. Using the mammalian epidermis as a model system, along with junctional recruitment and cell aggregation assays, we confirmed that Celsr1 mediates calcium-dependent, homophilic cell adhesion. Interestingly, disease-associated PCP variants Celsr1Crsh and Celsr1Scy, which harbor mutations in the extracellular cadherin domains, still mediated cell aggregation. These mutants lack the ability to enrich at epithelial junctions, suggesting that intercellular adhesion alone cannot explain Celsr1 functions. Surprisingly, Celsr1Crsh aggregates segregated from Celsr1WT clusters when mixed, demonstrating this point mutation generates a novel Celsr variant with altered homophilic binding properties. Further, Celsr1Crsh displayed broader cell surface distribution and reduced junction localization relative to WT even when in adhesive aggregates. Stable association of Celsr1 at the membrane was also substantially reduced in Celsr1Crsh. These observations indicate that perturbing Celsrs homophilic adhesive properties compromises functional PCP. We hypothesize Celsr1Crsh is defective in lateral clustering and that this mutation affects a region required to stabilize and reinforce the adhesive complex. Domain mapping, biochemistry and advanced imaging are ongoing to elucidate how Celsr1 adhesion mediates PCP complex assembly, maturation and functional asymmetry.