Explorer HEATR 2 Plays a Conserved Role in Assembly of the Ciliary Motile Apparatus

Cilia are highly conserved microtubule-based structures that perform a variety of sensory and motility functions during development and adult homeostasis. In humans, defects specifically affecting motile cilia lead to chronic airway infections, infertility and laterality defects in the genetically heterogeneous disorder Primary Ciliary Dyskinesia (PCD). Using the comparatively simple Drosophila system, in which mechanosensory neurons possess modified motile cilia, we employed a recently elucidated cilia transcriptional RFX-FOX code to identify novel PCD candidate genes. Here, we report characterization of CG31320/HEATR2, which plays a conserved critical role in forming the axonemal dynein arms required for ciliary motility in both flies and humans. Inner and outer arm dyneins are absent from axonemes of CG31320 mutant flies and from PCD individuals with a novel splice-acceptor HEATR2 mutation. Functional conservation of closely arranged RFXFOX binding sites upstream of HEATR2 orthologues may drive higher cytoplasmic expression of HEATR2 during early motile ciliogenesis. Immunoprecipitation reveals HEATR2 interacts with DNAI2, but not HSP70 or HSP90, distinguishing it from the client/chaperone functions described for other cytoplasmic proteins required for dynein arm assembly such as DNAAF1-4. These data implicate CG31320/HEATR2 in a growing intracellular pre-assembly and transport network that is necessary to deliver functional dynein machinery to the ciliary compartment for integration into the motile axoneme. Citation: Diggle CP, Moore DJ, Mali G, zur Lage P, Ait-Lounis A, et al. (2014) HEATR2 Plays a Conserved Role in Assembly of the Ciliary Motile Apparatus. PLoS Genet 10(9): e1004577. doi:10.1371/journal.pgen.1004577 Editor: Susan K. Dutcher, Washington University School of Medicine, United States of America Received November 22, 2013; Accepted July 3, 2014; Published September 18, 2014 Copyright: 2014 Diggle et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: DJM is supported by a BBSRC studentship and GM is supported by an EGRS scholarship and CMVM studentship. MS is supported by an Action Medical Research UK Clinical Training Fellowship (RTF-1411) and acknowledges funding from the Dutch Kidney Foundation (CP11.18). HMM is supported by grants from the Milena Carvajal Pro-Kartagener Foundation, Action Medical Research (GN2101) and Newlife Foundation for Disabled Children UK (10-11/15). This work was supported by grants to BD from the Fondation pour la Recherche Médicale (équipe FRM, DEQ2000329168) and the ANR (Ciliopath-X), and to WR from the Swiss National Science Foundation. AGM and AvK are supported by funding through Science Foundation Ireland’s funding award 06/CE/B1129. APJ and PzL are supported by the Medical Research Council of Great Britain (MR/K018558/10). MRH, PG, PLY, IJJ and PM are supported by core funding from the Medical Research Council of Great Britain. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: e.sheridan@leeds.ac.uk (ES); andrew.jarman@ed.ac.uk (APJ); pleasantine.mill@igmm.ed.ac.uk (PM) . These authors contributed equally to this work. " These authors jointly supervised this work.