CLA MP/Spef1 regulates planar cell polarity signaling and asymmetric microtubule accumulation in the Xenopus ciliated epithelia

Most epithelial cells polarize along the axis of the tissue, a feature known as planar cell polarity (PCP). The initiation of PCP requires cell-cell signaling via the noncanonical Wnt/PCP pathway. Additionally, changes in the cytoskeleton both facilitate and reflect this polarity. We have identified CLA MP/Spef1 as a novel regulator of PCP signaling. In addition to decorating microtubules (MTs) and the ciliary rootlet, a pool of CLA MP localizes at the apical cell cortex. Depletion of CLA MP leads to the loss of PCP protein asymmetry, defects in cilia polarity, and defects in the angle of cell division. Additionally, depletion of CLA MP leads to a loss of the atypical cadherin-like molecule Celrs2, suggesting that CLA MP facilitates the stabilization of junctional interactions responsible for proper PCP protein localization. Depletion of CLA MP also affects the polarized organization of MTs. We hypothesize that CLA MP facilitates the establishment of cell polarity and promotes the asymmetric accumulation of MTs downstream of the establishment of proper PCP.