VISUALIZING THE TRANSIENT REMODELING OF PLANAR CELL POLARITY PROTEINS DURING CELL DIVISION IN THE MAMMALIAN EPIDERMIS

Abstract

Polarity is a fundamental feature of cells across unicellular and multicellular organisms and is essential for generating diverse cellular functions. It is defined by the asymmetric localization of polarity proteins and components to opposing regions of a cell where they act on downstream factors to direct polarized cell behaviors. Deciphering how polarity proteins are transported to and retained at their asymmetric positions is therefore central to our understanding of how cells establish and regulate a polarized state. Here we study how planar cell polarity (PCP) is transiently lost and regained during cellular division in the murine embryonic epidermis. By live-imaging endogenously-tagged PCP reporter mouse lines, we can monitor the “core” PCP proteins, Celsr1, Fz6 and Vangl2 as they are dynamically redistributed in mitosis. We show that mitotic internalization of PCP proteins coincides with a dramatic increase in the lateral mobility of PCP proteins that remain at the plasma membrane, and that this mobility is promoted by the cell cycle kinase, Polo-like kinase 1. Consistent with prior data in fixed epidermal tissues, we find that endocytic vesicles containing each of the transmembrane PCP components enter the cell unequally from opposite sides but are partitioned evenly in daughters. Surprisingly, PCP-protein containing vesicles are not redelivered to the membrane in a polarized manner that immediately results restores their asymmetric state. Rather, their localization must be further refined following cytokinesis. We find that find PCP proteins continued to be highly mobile within the plasma membrane during cytokinesis. The increase in mobility allows PCP proteins to laterally diffuse within the membrane after being delivered there, presumably to be captured and stabilized by the PCP proteins within their neighbors. Subsequently, we find that Celsr1 is required non-autonomously to asymmetrically localize and cluster Fz6 and Vangl2 at A-P cell borders during interphase. All together, these data demonstrate that PCP proteins transition between mobile and stable states in coordination with cell cycle progression. We propose that a transient, laterally diffusive state in mitosis allows for flexibility and robustness in polarity as dividing cells change shape and rearrange.