A novel hypomorphic allele of Spag17 causes primary ciliary dyskinesia phenotypes in mice.

Zakia Abdelhamed,Heymut Omran,Sandra Cindric,Saima Ali,Marshall Lukacs,Rolf W Stottmann

doi:10.1242/dmm.045344

Abstract

ABSTRACTPrimary ciliary dyskinesia (PCD) is a human condition of dysfunctional motile cilia characterized by recurrent lung infection, infertility, organ laterality defects and partially penetrant hydrocephalus. We recovered a mouse mutant from a forward genetic screen that developed many of the hallmark phenotypes of PCD. Whole-exome sequencing identified this primary ciliary dyskinesia only (Pcdo) allele to be a nonsense mutation (c.5236A>T) in the Spag17 coding sequence creating a premature stop codon (K1746*). The Pcdo variant abolished several isoforms of SPAG17 in the Pcdo mutant testis but not in the brain. Our data indicate differential requirements for SPAG17 in different types of motile cilia. SPAG17 is essential for proper development of the sperm flagellum and is required for either development or stability of the C1 microtubule structure within the central pair apparatus of the respiratory motile cilia, but not the brain ependymal cilia. We identified changes in ependymal ciliary beating frequency, but these did not appear to alter lateral ventricle cerebrospinal fluid flow. Aqueductal stenosis resulted in significantly slower and abnormally directed cerebrospinal fluid flow, and we suggest that this is the root cause of the hydrocephalus. The Spag17Pcdo homozygous mutant mice are generally viable to adulthood but have a significantly shortened lifespan, with chronic morbidity. Our data indicate that the c.5236A>T Pcdo variant is a hypomorphic allele of Spag17 that causes phenotypes related to motile, but not primary, cilia. Spag17Pcdo is a useful new model for elucidating the molecular mechanisms underlying central pair PCD pathogenesis in the mouse.This article has an associated First Person interview with the first author of the paper.

Highlights

Cilia are centriole-derived, microtubule-based membranous extensions that exist in almost every cell (Gilula and Satir 1972, Satir 2005, Pedersen, Veland et al 2008)
We identified the primary ciliary dyskinesia only (Pcdo) mutant in a mouse ENU mutagenesis forward genetic screen for recessive alleles leading to organogenesis phenotypes
In order to identify the causal variant in Pcdo mutants, we performed whole exome sequencing on three phenotypic mutants, (Supplementary table 1)

Summary

Introduction

Cilia are centriole-derived, microtubule-based membranous extensions that exist in almost every cell (Gilula and Satir 1972, Satir 2005, Pedersen, Veland et al 2008). The primary cilia have a “9+0” structure of the axoneme (Nogales, Whittaker et al.1999, Satir 2005) because they lack the central pair of microtubules and other molecular motors such as dynein arms and radial spokes which are responsible for ciliary movement. The well documented function of the motile cilia is a coordinated rhythmic beating to move different body fluids in the brain, respiratory tract and the male and female genital ducts (Brightman and Palay 1963, Dirksen 1971, Jeffery and Reid 1975). This is consistent with the localized tissue distribution of motile cilia in these organs

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Conclusion