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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 and Caeno-rhabditis elegans reveals the role of WDR31 in 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 accumu-lations 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 in wdr-31;rpi-2;elmd-1. Remarkably, a non-ciliary protein leaks into the cilia of wdr-31;rpi-2;elmd-1, possibly because of IFT de-fects. This work reveals WDR31-RP-2-ELMD-1 as IFT and BBSome trafficking regulators. National Institutes of Health (NIH) - USA P40 OD010440 Abdullah Gul University Scienti fic Research Project Coordination Unit TOA-2018-110 German Research Foundation (DFG) INST 2388/62-1

Human growth is a complex trait. A considerable number of gene defects have been shown to cause short stature, but there are only few examples of genetic causes of non-syndromic tall stature. Besides rare variants with large effects and common risk alleles with small effect size, oligogenic effects may contribute to this phenotype. Exome sequencing was carried out in a tall male (height 3.5 SDS) and his parents. Filtered damaging variants with high CADD scores were validated by Sanger sequencing in the trio and three other affected and one unaffected family members. Network analysis was carried out to assess links between the candidate genes, and the transcriptome of murine growth plate was analyzed by microarray as well as RNA Seq. Heterozygous gene variants in CEP104, CROCC, NEK1, TOM1L2, and TSTD2 predicted as damaging were found to be shared between the four tall family members. Three of the five genes (CEP104, CROCC, and NEK1) belong to the ciliary gene family. All genes are expressed in mouse growth plate. Pathway and network analyses indicated close functional connections. Together, these data expand the spectrum of genes with a role in linear growth and tall stature phenotypes.

Inherited retinal diseases (IRDs) are a group of diseases that are caused by dysfunction or loss of photoreceptors or retinal pigment epithelium. They are amongst the most frequent causes of early-onset blindness and account for 5% of blindness worldwide. However, still 30-50% of patients diagnosed with IRD have an incomplete molecular diagnosis. The latter becomes increasingly important given the era of therapies for IRD. Moreover, apart from a molecular diagnosis, insight into the underlying pathogenic mechanisms is highly needed. The general aim of this doctoral work was to identify and functionally characterize new genes and variants involved in syndromic and non- syndromic IRD. First, autozygosity mapping combined with whole exome sequencing (WES) in a consanguineous family with syndromic IRD revealed a homozygous missense variant in RCBTB1. Further data mining of WES data revealed four additional homozygous missense variants in five unrelated families with non-syndromic and syndromic IRD. Overall, this study allowed to put forward RCBTB1 as new gene for autosomal recessive IRD (Paper 1). A stable knockout model of rcbtb1 was generated in Xenopus tropicalis, a diploid amphibian, to study the pathogenesis of RCBTB1-associated IRD. In the CRISPR/Cas9-mediated knockout model the effects of rcbtb1 loss-of-function on retinal structures were evaluated and compared with the retinal features of RCBTB1-associated IRD in human. In addition, stress response was studied in vivo and in vitro using an RCBTB1 knock-down human cellular model. This study resulted in Paper 2. A third study focused on CEP78, a gene in which inactivating variants have recently been found to cause cone‐rod dystrophy with hearing loss (CRDHL). We identified and functionally characterized the first CEP78 missense variant in three unrelated CRDHL families, to evaluate if a ‘milder allele’ in CEP78 could underlie the same phenotype so far only associated with inactivating variants. This study resulted in Paper 3. Given the occurrence of a complex structural variant (SV) of the CEP78 region in a patient with CRDHL, we further investigated the role of SVs in unsolved CRDHL patients. In two unrelated individuals we identified a total and partial gene deletion in a heterozygous and homozygous state, respectively. This study emphasized the importance of SV identification and characterization in Mendelian diseases and resulted in Paper 4.

AIM To evaluate the genetic defects of ciliary genes causing the loss of primary cilium in autosomal dominant polycystic kidney disease (ADPKD). METHODS We analyzed 191 structural and functional genes of the primary cilium using next-generation sequencing analysis. We analyzed the kidney samples, which were obtained from 7 patients with ADPKD who underwent nephrectomy. Each sample contained polycystic kidney tissue and matched normal kidney tissue. RESULTS In our study, we identified genetic defects in the 5 to 15 genes in each ADPKD sample. The most frequently identified defects were found in genes encoding centrosomal proteins (PCM1, ODF2, HTT and CEP89) and kinesin family member 19 (KIF19), which are important for ciliogenesis. In addition, pathogenic mutations in the PCM1 and KIF19 genes were found in all ADPKD samples. Interestingly, mutations in the genes encoding the intraflagellar transport proteins, which are the basis of animal models of ADPKD, were only rarely detected. CONCLUSION The results of our study revealed the actual state of structural ciliary genes in human ADPKD tissues and provided valuable indications for further research.

The cilium is an essential organelle at the surface of mammalian cells whose dysfunction causes a wide range of genetic diseases collectively called ciliopathies. The current rate at which new ciliopathy genes are identified suggests that many ciliary components remain undiscovered. We generated and rigorously analyzed genomic, proteomic, transcriptomic and evolutionary data and systematically integrated these using Bayesian statistics into a predictive score for ciliary function. This resulted in 285 candidate ciliary genes. We generated independent experimental evidence of ciliary associations for 24 out of 36 analyzed candidate proteins using multiple cell and animal model systems (mouse, zebrafish and nematode) and techniques. For example, we show that OSCP1, which has previously been implicated in two distinct non-ciliary processes, causes ciliogenic and ciliopathy-associated tissue phenotypes when depleted in zebrafish. The candidate list forms the basis of CiliaCarta, a comprehensive ciliary compendium covering 956 genes. The resource can be used to objectively prioritize candidate genes in whole exome or genome sequencing of ciliopathy patients and can be accessed at http://bioinformatics.bio.uu.nl/john/syscilia/ciliacarta/. This work was supported by the European Community’s Seventh Framework Programme [241955, 278568 to MU and KB, 602273 to RS]; the Virgo consortium, funded by the Dutch government [FES0908 to TvD, RvdL and MAH]; the Netherlands Genomics Initiative [050-060-452 to TvD, RvdL and MAH]; the Canadian Institutes of Health Research [MOP-142243, MOP-82870 and PJT-156042 to MRL]; Michael Smith Foundation for Health Research to MRL and VLJ; Kidney Research Scientist Core Education and National Training fellowship to VLJ; The Foundation Fighting Blindness [PPA-0717-0719-RAD to UW, RR, and MU]; the Dutch Kidney Foundation “KOUNCIL” consortium [CP11.18 to RHG, PLB and RR]; The Deutsche Forschungsgemeinschaft [Excellence grant CellNetworks to RBR and QL, CRC1140 “Kidney Disease – From Genes to Mechanisms” to MS, collaborative research center grant SFB-1411 KIDGEM to MS]; Metakids Foundation to RS; the National Institute for Health Research to PLB and VH-H. PLB is an NIHR Senior Investigator; Radboudumc Hypatia Tenure Track Fellowship, Radboud Universiteit excellence fellowship, ERC starting grant TREATCilia, grant agreement no. 716344 to MS; and the Netherlands Organization for Scientific Research [NWO Vici-865.12.005 to RR].

Background Evolutionarily conserved RFX transcription factors (TFs) regulate their target genes through a DNA sequence motif called the X-box. Thereby they regulate cellular specialization and terminal differentiation. Here, we provide a comprehensive analysis of all the eight human RFX genes (RFX1–8), their spatial and temporal expression profiles, potential upstream regulators and target genes. Results We extracted all known human RFX1–8 gene expression profiles from the FANTOM5 database derived from transcription start site (TSS) activity as captured by Cap Analysis of Gene Expression (CAGE) technology. RFX genes are broadly (RFX1–3, RFX5, RFX7) and specifically (RFX4, RFX6) expressed in different cell types, with high expression in four organ systems: immune system, gastrointestinal tract, reproductive system and nervous system. Tissue type specific expression profiles link defined RFX family members with the target gene batteries they regulate. We experimentally confirmed novel TSS locations and characterized the previously undescribed RFX8 to be lowly expressed. RFX tissue and cell type specificity arises mainly from differences in TSS architecture. RFX transcript isoforms lacking a DNA binding domain (DBD) open up new possibilities for combinatorial target gene regulation. Our results favor a new grouping of the RFX family based on protein domain composition. We uncovered and experimentally confirmed the TFs SP2 and ESR1 as upstream regulators of specific RFX genes. Using TF binding profiles from the JASPAR database, we determined relevant patterns of X-box motif positioning with respect to gene TSS locations of human RFX target genes. Conclusions The wealth of data we provide will serve as the basis for precisely determining the roles RFX TFs play in human development and disease. Electronic supplementary material The online version of this article (10.1186/s12864-018-4564-6) contains supplementary material, which is available to authorized users.