p73 regulates ependymal planar cell polarity by modulating actin and microtubule cytoskeleton

Abstract

Planar cell polarity (PCP) and intercellular junctional complexes establish tissue structure and coordinated behaviors across epithelial sheets. In multiciliated ependymal cells, rotational and translational PCP coordinate cilia beating and direct cerebrospinal fluid circulation. Thus, PCP disruption results in ciliopathies and hydrocephalus. PCP establishment depends on the polarization of cytoskeleton and requires the asymmetric localization of core and global regulatory modules, including membrane proteins like Vangl1/2 or Frizzled. We analyzed the subcellular localization of select proteins that make up these modules in ependymal cells and the effect of Trp73 loss on their localization. We identify a novel function of the Trp73 tumor suppressor gene, the TAp73 isoform in particular, as an essential regulator of PCP through the modulation of actin and microtubule cytoskeleton dynamics, demonstrating that Trp73 is a key player in the organization of ependymal ciliated epithelia. Mechanistically, we show that p73 regulates translational PCP and actin dynamics through TAp73-dependent modulation of non-musclemyosin-II activity. In addition, TAp73 is required for the asymmetric localization of PCP-core and global signaling modules and regulates polarized microtubule dynamics, which in turn set up the rotational PCP. Therefore, TAp73 modulates, directly and/or indirectly, transcriptional programs regulating actin and microtubules dynamics and Golgi organization signaling pathways. These results shed light into the mechanism of ependymal cell planar polarization and reveal p73 as an epithelial architect during development regulating the cellular cytoskeleton.

Biology of multiciliated cells

“…Interestingly, it was suggested that p73 marks some basal cells in airway epithelium for MCC differentiation, lending to it a role as a pioneer or competence factor [8]. Further supporting the importance of p73, it was also reported that it regulates ependymal MCC polarity through maintenance of actin and microtubule cytoskeletal networks [10]. It is important to mention that the MCC identity is inherently labile, as its maintenance requires constant FoxJ1 transcriptional activity, at least in murine ependymal MCCs [11].…”

Tissue-specific roles of p73 in development and homeostasis

“…Mechanistically, TAp73 regulates translational PCP (asymmetrical polarization of cilia clusters at the anterior apical surface) by directly inducing transcription of Mlck kinase (also known as Mylk), which modulates non-muscle myosin-II activity, thereby affecting the dynamics of actin and microtubulebased transport and Golgi organization. TAp73 is also required for the asymmetric membrane localization of PCP core proteins Vangl2, Prickle2 and Fzd3 (Fuertes-Alvarez et al, 2018). Interestingly, ciliary axonemes in TAp73KO ECs appear less disheveled than in p73KO counterparts.…”

“…Thus, p73 is required for ependymal maturation and neurogenic SVZ cytoarchitecture (Fujitani et al, 2017;Gonzalez-Cano et al, 2016). TAp73KO ECs exhibit the same PCP and basalbody anchoring defects, identifying TAp73 as the regulator of PCP (Fuertes-Alvarez et al, 2018). Mechanistically, TAp73 regulates translational PCP (asymmetrical polarization of cilia clusters at the anterior apical surface) by directly inducing transcription of Mlck kinase (also known as Mylk), which modulates non-muscle myosin-II activity, thereby affecting the dynamics of actin and microtubulebased transport and Golgi organization.…”

“…Interestingly, ciliary axonemes in TAp73KO ECs appear less disheveled than in p73KO counterparts. The latter suggests a compensatory role for DNp73 in TAp73KO ependymal cells, even though DNp73KO brains have normal ECs and lack PCP defects (Fuertes-Alvarez et al, 2018). But does the ciliogenic defect of p73KO ECs causally contribute to the severe hydrocephalus of p73KO brains?…”

Brain ependymocytes in neurogenesis and maintaining integrity of blood-cerebrospinal fluid barrier

“…Тар73 является важным регулятором и координатором вращательных и поступательных движений ресничек и, таким образом, участвует в прямой циркуляции ликвора. Указанный механизм реализуется посредством модуляции взаимодействия актина и белков микротрубочек с мембранными белками, участвующими в обеспечении полярности клеток и движения ресничек [12].…”