The term ciliopathy refers to a group of over 35 rare disorders characterized by defective cilia and many overlapping clinical features, such as hydrocephalus, cerebellar vermis hypoplasia, polydactyly, and retinopathy. Even though many genes have been implicated in ciliopathies, the genetic pathogenesis in certain cases remains still undisclosed. Here, we identified a homozygous truncating variant in WDR31 in a patient with a typical ciliopathy phenotype encompassing congenital hydrocephalus, polydactyly and renal agenesis. WDR31 is an evolutionarily conserved protein that localizes to the cilium and cilia-related compartment. Analysis from zebrafish supports the role of WDR31 in regulating the cilia morphology. The CRISPR/Cas9 knock-in (p.Arg261del) C. elegans model of the patient variant (p.Arg268*) reproduced several cilia-related defects observed in wdr-31 null mutants. Mechanistic analysis from C. elegans revealed that WDR-31 functions redundantly with ELDM-1 (ELMOD protein) and RPI-2 (RP2) to regulate the IFT trafficking through controlling the cilia entry of the BBSome. This work revealed WDR31 as a new ciliopathy protein that regulates IFT and BBSome trafficking.

The term “ciliopathy” refers to a group of over 35 rare disorders characterized by defective cilia and many overlapping clinical features, such as hydrocephalus, cerebellar vermis hypoplasia, polydactyly, and retinopathy. Even though many genes have been implicated in ciliopathies, the genetic pathogenesis in certain cases remains still undisclosed. Here, we identified a homozygous truncating variant in WDR31 in a patient with a typical ciliopathy phenotype encompassing congenital hydrocephalus, polydactyly, and renal agenesis. WDR31 is an evolutionarily conserved protein that localizes to the cilium and cilia-related compartment. Analysis from zebrafish supports the role of WDR31 in regulating the cilia morphology. The CRISPR/Cas9 knock-in (p.Arg261del) C. elegans model of the patient variant (p.Arg268*) reproduced several cilia-related defects observed in wdr-31 null mutants. Mechanistic analysis from C. elegans revealed that WDR-31 functions redundantly with ELDM-1 (ELMOD protein) and RPI-2 (RP2) to regulate the IFT trafficking through controlling the cilia entry of the BBSome. This work revealed WDR31 as a new ciliopathy protein that regulates IFT and BBSome trafficking.

The correct intraflagellar transport (IFT) assembly at the ciliary base and the IFT turnaround at the ciliary tip are key for the IFT to perform its function, but we still have poor understanding about how these processes are regulated. Here, we identify WDR31 as a new ciliary protein, and analysis from zebrafish andCaenorhabditis elegansreveals the role ofWDR31in regulating the cilia morphology. We find that loss of WDR-31 together with RP-2 and ELMD-1 (the sole ortholog ELMOD1-3) results in ciliary accumulations of IFT Complex B components and KIF17 kinesin, with fewer IFT/BBSome particles traveling along cilia in both anterograde and retrograde directions, suggesting that the IFT/BBSome entry into the cilia and exit from the cilia are impacted. Furthermore, anterograde IFT in the middle segment travels at increased speed inwdr-31;rpi-2;elmd-1. Remarkably, a non-ciliary protein leaks into the cilia ofwdr-31;rpi-2;elmd-1, possibly because of IFT defects. This work reveals WDR31–RP-2–ELMD-1 as IFT and BBSome trafficking regulators.

Discovering the entire list of human ciliary genes would help in the diagnosis of cilia-related human disorders known as ciliopathy, but at present the genetic diagnosis of many ciliopathies (over 30%) is far from complete (Bachmann-Gagescu et al., 2015; Knopp et al., 2015; Paff et al., 2018). In a theory, many independent approaches may uncover the whole list of ciliary genes, but 30% of the genes on the ciliary gene list are still ciliary candidate genes (van Dam et al., 2019; Vasquez et al., 2021). All of these cutting-edge techniques, however, have relied on a different single strategy to discover ciliary candidate genes. Because different methodologies demonstrated distinct capabilities with varying quality, categorizing the ciliary candidate genes in the ciliary gene list without further evidence has been difficult. Here, we present a method for predicting ciliary capacity of each human gene that incorporates diverse methodologies (single-cell RNA sequencing, protein-protein interactions (PPIs), comparative genomics, transcription factor (TF)-network analysis, and text mining). By integrating multiple approaches, we reveal previously undiscovered ciliary genes. Our method, CilioGenics, outperforms other approaches that are dependent on a single method. Our top 500 gene list contains 256 new candidate ciliary genes, with 31 experimentally validated. Our work suggests that combining several techniques can give useful evidence for predicting the ciliary capability of all human genes.

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