Non-cell-autonomous planar cell polarity propagation in the auditory sensory epithelium of vertebrates

Abstract

Sensory epithelia of the inner ear require a coordinated alignment of hair cell stereociliary bundles as an essential element of mechanoreceptive function. Hair cell bundle alignment is mediated by core planar cell polarity (PCP) proteins, such as Vangl2, that localize asymmetrically to the circumference of the cell near its apical surface. During early phases of cell orientation in the chicken basilar papilla (BP), Vangl2 is present at supporting cell junctions that lie orthogonal to the polarity axis. Several days later, there is a striking shift in the Vangl2 pattern associated with hair cells that reorient toward the distal (apical) end of the organ. How the localization of PCP proteins transmits planar polarity information across the developing sensory epithelium remains unclear. To address this question, the normal asymmetric localization of Vangl2 was disrupted by overexpressing Vangl2 in clusters of cells. The BP was infected with replication-competent retrovirus encoding Vangl2 prior to hair cell differentiation. Virus-infected cells showed normal development of individual stereociliary bundles, indicating that asymmetry was established at the cellular level. Yet, bundles were misoriented in ears infected with Vangl2 virus but not Wnt5a virus. Notably, Vangl2 misexpression did not randomize bundle orientations but rather generated larger variations around a normal mean angle. Cell clusters with excess Vangl2 could induce non-autonomous polarity disruptions in wildtype neighboring cells. Furthermore, there appears to be a directional bias in the propagation of bundle misorientation that is towards the abneural edge of the epithelium. Finally, regional bundle reorientation was inhibited by Vangl2 overexpression. In conclusion, ectopic Vangl2 protein causes inaccurate local propagation of polarity information, and Vangl2 acts in a non-cell-autonomous fashion in the sensory system of vertebrates.

Principles of planar polarity in animal development

“…Furthermore, at the boundaries of transplants, cells orient their cilia towards low levels of Vangl2 and high levels of Fz3 (Fig. 7) (Mitchell et al, 2009), an effect also seen upon overexpression of Vangl2 in the chick inner ear (Sienknecht et al, 2011). Thus, as in flies, Vangl and Fz provide directional information that allows cells to achieve a uniform polarisation, providing some of the best evidence for nonautonomous signalling in vertebrates, and highlighting the ability of multiple cell types to participate in polarised cell-cell interactions.…”

Evolution and Development of Hair Cell Polarity and Efferent Function in the Inner Ear

“…These proteins are thought to mediate the intercellular transmission of polarity information from cell to cell in a bucket brigade fashion. Such a manifestation of a non-cell-autonomous mechanism of PCP propagation via Vangl2 has been demonstrated in the developing auditory epithelium of chickens [Sienknecht et al, 2011]. It is important to keep in mind that in inner ear sensory epithelia PCP is coordinated across a heterogeneous field of cells.…”

“…In summary, these observations on Vangl2, together with the PCP protein expression data from macular organs, in which the hair cell orientation and the molecular polarity of the cells are inconsistent, highlight the necessity for further investigation to better understand the functional role of PCP proteins. Moreover, our current model of PCP propagation from cell to cell ignores the fact that hair cells apparently do not (or only weakly) express Vangl2 in chicken and mouse ears [Sienknecht et al, 2011;Ezan and Montcouquiol, 2013]. If it turns out that in fact polarity propagation by intercellular PCP protein interaction takes place primarily via supporting cellsupporting cell junctions (and not via hair cell junctions), as indicated in the avian auditory primordium ( fig.…”

“…Thus, apparently the PCP protein Vangl2 changes its location to cell borders having a different alignment. Finally, another shifted Vangl2 expression superimposes on the regional reorientation of hair cells [Sienknecht et al, 2011], meaning that this PCP protein changes its orientation twice during development of the avian auditory epithelium. In summary, these observations on Vangl2, together with the PCP protein expression data from macular organs, in which the hair cell orientation and the molecular polarity of the cells are inconsistent, highlight the necessity for further investigation to better understand the functional role of PCP proteins.…”

Planar cell polarity in moving cells: think globally, act locally

“…1B-D) (Butler and Wallingford, 2015;Chu and Sokol, 2016;Ciruna et al, 2006;Davey et al, 2016;Deans et al, 2007;Devenport et al, 2011;Hashimoto et al, 2010;Vladar et al, 2012;Yin et al, 2008). Altering the expression of Vang or Fz homologs mosaically in the frog skin or in the sensory epithelium of the chick ear disrupts the polarity of adjacent wild-type cells, suggesting that the molecular interactions between core PCP components that amplify and maintain their asymmetric localization are conserved between fly and vertebrate epithelia (Mitchell et al, 2009;Sienknecht et al, 2011). As we discuss later, this paired cell-autonomous and noncell-autonomous function is a deeply conserved characteristic of the pathway even in migrating cells.…”