Ankrd6 is a mammalian functional homolog of Drosophila planar cell polarity gene diego and regulates coordinated cellular orientation in the mouse inner ear

Abstract

The coordinated polarization of neighboring cells within the plane of the tissue, known as planar cell polarity (PCP), is a recurring theme in biology. It is required for numerous developmental processes for the form and function of many tissues and organs across species. The genetic pathway regulating PCP was first discovered in Drosophila, and an analogous but distinct pathway is emerging in vertebrates. It consists of membrane protein complexes known as core PCP proteins that are conserved across species. Here we report that the over-expression of the murine Ankrd6 (mAnkrd6) gene that shares homology with Drosophila core PCP gene diego causes a typical PCP phenotype in Drosophila, and mAnkrd6 can rescue the loss of function of diego in Drosophila. In mice, mAnkrd6 protein is asymmetrically localized in cells of the inner ear sensory organs, characteristic of components of conserved core PCP complexes. The loss of mAnkrd6 causes PCP defects in the inner ear sensory organs. Moreover, canonical Wnt signaling is significantly increased in mouse embryonic fibroblasts from mAnkrd6 knockout mice in comparison to wild type controls. Together, these results indicated that mAnkrd6 is a functional homolog of the Drosophila diego gene for mammalian PCP regulation and act to suppress canonical Wnt signaling.

Live imaging of hair bundle polarity acquisition demonstrates a critical timeline for transcription factor Emx2

“…Each macula can be divided by a line of polarity reversal (LPR) into two regions, across which the hair bundles are arranged in opposite orientations ( Figure 1A ; Flock, 1964 ). Although proper alignment of the hair bundles in sensory organs requires the Wnt signaling pathway and the core planar cell polarity pathway ( Dabdoub et al, 2003 ; Goodrich and Strutt, 2011 ; Jones et al, 2014 ; Lee et al, 2012 ; Montcouquiol et al, 2003 ; Montcouquiol et al, 2006 ), the LPR in the maculae is generated by the transcription factor Emx2. The restricted expression of Emx2 to one side of the LPR causes hair bundles within to reverse their orientation by 180° ( Figure 1A , green color; Jiang et al, 2017 ; Holley et al, 2010 ).…”

The spatio-temporal domains of Frizzled6 action in planar polarity control of hair follicle orientation

“…In mice, mutation of these genes demonstrates their central role in controlling polarity in a wide variety of contexts, including neural tube closure (Wang et al, 2006b; Torban et al, 2008; Curtin et al, 2003), axon guidance (Wang et al, 2002; Lyuksyutova et al, 2003; Tissir et al, 2005; Zhou et al, 2008; Hua et al, 2013, 2014b), and the orientations of motile cilia (Tissir et al, 2010; Vladar et al 2012; Boutin et al, 2014; Ohata et al, 2014; Shi et al, 2014), inner ear sensory hair cells (Montcouquiol et al, 2003; Wang et al, 2005, 2006b; Jones et al, 2014), hair follicles (Guo et al, 2004; Wang et al, 2006a; Devenport and Fuchs, 2008; Ravni et al, 2009), and lingual papillae (Hua et al, 2014a). …”

Retracing the path of planar cell polarity

“…For instance, Ankyrin repeats are one of the most common protein-protein interaction motifs in eukaryotes [ 40 – 42 ], resulting in bias in TBLASTN analyses to detect Invs. In addition, if we admit that diego is the Drosophila functional equivalent of ankrd6 or invs (as proposed in Clytia ) [ 18 ], this means that the encoded protein would have a highly divergent domain composition (only 6 ANK repeats and no IQ domain in Dgo) in addition to a low amino acid conservation, without affecting its function [ 43 ].…”

“…As recently reviewed by Hale and Strutt (2015) [ 12 ], the function of the PCP core proteins in epithelial cell orientation is well documented in various developmental processes across planulozoans (bilaterians + cnidarians) [ 14 , 15 ]. Among those commonly used to study the planar polarized tissues in Drosophila are the alignment of actin hairs on the abdomen, the alignment of wing sensory bristles, and the arrangement of eye facet systems [ 16 – 18 ]. A further example of reliance on the PCP pathway can be found in the orientation of inner ear sensory hair cells and of hair follicles of vertebrate skin (Fig.…”

“…A further example of reliance on the PCP pathway can be found in the orientation of inner ear sensory hair cells and of hair follicles of vertebrate skin (Fig. 1c ) [ 18 – 21 ]. Although the study of the planar polarity genes have been mainly focused on Drosophila and mammalians, some lines of evidence strongly support as well the involvement of the core PCP in cilia orientation in less conventional models.…”