Characterization of TMEM14 Proteins in the Context of Zebrafish PCP AND Ciliogenesis

The planar cell polarity (PCP) pathway regulates key developmental processes which include convergence and extension (C) movements and the planar organization of motile cilia (1–3). Central members of the PCP pathway include transmembrane proteins such as Van Gogh-like (Vangl). However, despite a large body of research characterizing the PCP pathway, the intracellular trafficking of each factor is poorly understood. This knowledge gap has led to a search for additional factors that act in the regulation of PCP components. In this work, I expand on the characterization of the trans-Golgi network (TGN) localized protein, Tmem14A, an unpublished novel interactor of Vangl1/2 in the context zebrafish PCP and ciliogenesis. Curiously, I found that the loss of Tmem14A in both zygotic and maternal zygotic (MZ) tmem14A mutants did not severely impact the morphogenesis of zebrafish embryos. However, in my analysis of MZtmem14A floor plate (FP) neuroepithelia, I show the planar polarity of motile cilia to be disrupted and the localization of Vangl2 to the basolateral membranes of FP cells to be reduced. This analysis supports the hypothesis that Tmem14A can regulate PCP, possibly through the intracellular transport of Vangl2 from the TGN. The absence of severe developmental defects in MZtmem14A mutants suggests that Tmem14A function may be dispensable in the context of embryonic development. Interestingly, a recent study has provided evidence to suggest that the loss of gene function can be rescued by the upregulation of a functionally related gene, induced by a novel non-sense mediated decay (NMD)-dependent compensatory mechanism (4,5). Intriguingly, I show that MZtmem14A mutants have a near 2-fold upregulation of tmem14cB, an uncharacterized zebrafish-specific Tmem14 family member, suggesting that loss of Tmem14A may be rescued by Tmem14cB. Interestingly, contrary to my initial hypothesis of Tmem14cB alleviating the loss of Tmem14A, MZtmem14A;MZtmem14cB mutants did not develop morphological defects. Remarkably, the loss of Tmem14cB rescued the translational polarity and basolateral Vangl2 defects of FP cells in MZtmem14A mutants. These observations suggest that the upregulation of tmem14cB in MZtmem14A mutants has a deleterious effect on FP planar polarity and implicates Tmem14cB as a novel regulator of Vangl2 and zebrafish planar polarity.Ph.D