Investigating the role of CEP164 in ciliopathies through characterisation of a novel Cep164 mouse model

Abstract

Ciliopathies are a group of rare, genetic disorders caused by mutations affecting the biogenesis, functioning or maintenance of the ciliary complex. Cilia are found on almost all cell types in the mammalian body where they orchestrate a multitude of cellular processes. There are two main classes of cilia, primary cilia, and motile cilia, which function through their respective roles in signal transduction and motility. Accordingly, ciliopathies are associated with a plethora of overlapping, multi-system, clinical manifestations. Moreover, ciliopathies display an extensive genotype-phenotype heterogeneity, which remains poorly understood. CEP164 was initially identified as encoding a centrosomal distal appendage protein, essential for ciliogenesis. Subsequently, CEP164 mutations have been found in patients with nephronophthisis (NPHP)–related ciliopathies. These patients have NPHP, a fibrotic cortico-medullary cystic kidney disease that can lead to end-stage kidney disease, associated with retinal degeneration and neurological defects. More recently, CEP164 has been implicated in wider ciliopathy phenotypes, providing a paradigm for understanding the genetic complexity of multisystem ciliopathies. CEP164 expression in human and mouse development revealed that CEP164 expression correlates with tissues affected in CEP164-ciliopathy patients, and that the expression pattern of CEP164 is conserved between human and mouse. To examine the role of Cep164, an inducible Cep164 knockout mouse was developed that revealed a mixed-ciliopathy phenotype, affecting both primary and motile cilia, which are traditionally associated with separate disease syndromes. Specifically, inactivation of Cep164 resulted in a number of phenotypes including: cystic kidney disease, retinal dystrophy, abnormal cerebellar folding, obesity and male infertility. Many of these phenotypes were consistent with the expanding human CEP164-disease spectrum, confirming specific roles for CEP164 in organ development and an ongoing requirement in adult tissue homeostasis. The murine obesity phenotype and male infertility guided interrogation of wider patient cohorts to assess the contribution of CEP164 alleles in common disease phenotypes. These data reveal that Cep164 is involved in primary and motile cilia function and that Cep164 mutations alone can lead to complex mixed-ciliopathy phenotypes, potentially including non-syndromic and adult-onset disease. This serves as a striking example of the phenotypic heterogeneity that can be caused by a single gene, and the importance of functional analyses to inform genetic interpretation of ciliopathies.