Out of Sight, but Aligned: Dynamic Planar Cell Polarity in Eyelid Morphogenesis

Abstract

The development of multicellular organisms requires highly coordinated tissue movements that depend on the precise alignment of cells within an epithelial plane. Planar cell polarity (PCP) is a conserved signaling pathway that establishes this directional organization through the asymmetric localization of core protein complexes at opposing cell-cell junctions, propagating intercellular asymmetry across entire tissue sheets to guide oriented migration, cell division, and cytoskeletal remodeling. Despite its well-established role in morphogenetic processes ranging from neural tube closure to cochlear patterning, how asymmetric PCP localization is translated into directed cytoskeletal organization remains poorly understood, particularly in mammalian systems. Eyelid closure in the mouse embryo offers an accessible model to address this question. Closure proceeds through localized cell intercalations at the epithelial front that advance the tissue over the cornea, and disruption of PCP produces a fully penetrant eyes-open-at-birth phenotype with disorganized actin arrays and failed fusion. Despite this clear requirement, PCP has never been directly characterized within the eyelid epithelium. Its spatial distribution, layer specificity, and relationship to the actin cytoskeleton remain entirely unexamined. This study provides the first characterization of PCP organization in this system, investigating how core PCP protein localization relates to actomyosin dynamics at the advancing epithelial front. Using Fz6, Celsr1, and Vangl2 reporter mice alongside layer-specific markers, I find that PCP expression is largely restricted to the basal epithelial layer of the outer eyelid, suggesting a spatially regionalized role during closure. Phalloidin staining further reveals that F-actin does not co-localize with any of the three core PCP proteins, instead accumulating apically as a continuous cable at the leading edge, altogether revealing a spatially compartmentalized architecture of PCP-cytoskeletal coupling with implications for wound healing and tissue repair.