Intraflagellar Transport Research Articles

The intraflagellar transport cycle.

Primary and motile cilia are eukaryotic organelles that perform crucial roles in cellular signalling and motility. Intraflagellar transport (IFT) contributes to the formation of the highly specialized ciliary proteome by active and selective transport of soluble and membrane proteins into and out of cilia. IFT is performed by the IFT-A and IFT-B protein complexes, which together link cargoes to the microtubule motors kinesin and dynein. In this Review, we discuss recent structural and mechanistic insights on how the IFT complexes are first recruited to the base of the cilium, how they polymerize into an anterograde IFT train, and how this complex imports cargoes from the cytoplasm. We will describe insights into how kinesin-driven anterograde trains are carried to the ciliary tip, where they are remodelled into dynein-driven retrograde trains for cargo export. We will also present how the interplay between IFT-A and IFT-B complexes, motor proteins and cargo adaptors is regulated for bidirectional ciliary transport.

Glutamylation imbalance impairs the molecular architecture of the photoreceptor cilium.

Microtubules, composed of conserved α/β-tubulin dimers, undergo complex post-translational modifications (PTMs) that fine-tune their properties and interactions with other proteins. Cilia exhibit several tubulin PTMs, such as polyglutamylation, polyglycylation, detyrosination, and acetylation, with functions that are not fully understood. Mutations in AGBL5, which encodes the deglutamylating enzyme CCP5, have been linked to retinitis pigmentosa, suggesting that altered polyglutamylation may cause photoreceptor cell degeneration, though the underlying mechanisms are unclear. Using super-resolution ultrastructure expansion microscopy (U-ExM) in mouse and human photoreceptor cells, we observed that most tubulin PTMs accumulate at the connecting cilium that links outer and inner photoreceptor segments. Mouse models with increased glutamylation (Ccp5-/- and Ccp1-/-) or loss of tubulin acetylation (Atat1-/-) showed that aberrant glutamylation, but not acetylation loss, disrupts outer segment architecture. This disruption includes exacerbation of the connecting cilium, loss of the bulge region, and destabilization of the distal axoneme. Additionally, we found significant impairment in tubulin glycylation, as well as reduced levels of intraflagellar transport proteins and of retinitis pigmentosa-associated protein RPGR. Our findings indicate that proper glutamylation levels are crucial for maintaining the molecular architecture of the photoreceptor cilium.

Collaborative role of two distinct cilium-specific cytoskeletal systems in driving Hedgehog-responsive transcription factor trafficking.

Calibrated transcriptional outputs in cellular signaling require fine regulation of transcription factor activity. In vertebrate Hedgehog (Hh) signaling, the precise output of the final effectors, the GLI (Glioma-associated-oncogene) transcription factors, depends on the primary cilium. In particular, the formation of the activator form of GLI upon pathway initiation requires its concentration at the distal cilium tip. However, the mechanisms underlying this critical step in Hh signaling are unclear. We developed a real-time imaging assay to visualize GLI2, the primary GLI activator isoform, at single particle resolution within the cilium. We observed that GLI2 is a cargo of Intraflagellar Transport (IFT) machinery and is transported with anterograde bias during a restricted time window following pathway activation. Our findings position IFT as a crucial mediator of transcription factor transport within the cilium for vertebrate Hh signaling, in addition to IFT's well-established role in ciliogenesis. Surprisingly, a conserved Hh pathway regulator, the atypical non-motile kinesin KIF7, is critical for the temporal control of GLI2 transport by IFT and the spatial control of GLI2 localization at the cilium tip. This discovery underscores the collaborative role of a motile and a non-motile cilium-specific cytoskeletal system in determining the transcriptional output during Hh signaling.

The Nociceptor Primary Cilium Contributes to Mechanical Nociceptive Threshold and Inflammatory and Neuropathic Pain.

The primary cilium, a single microtubule-based organelle protruding from the cell surface and critical for neural development, also functions in adult neurons. While some dorsal root ganglion neurons elaborate a primary cilium, whether it is expressed by and functional in nociceptors is unknown. Recent studies have shown a role of Hedgehog, whose canonical signaling is primary cilium dependent, in nociceptor sensitization. We establish the presence of primary cilia in soma of rat nociceptors, where they contribute to mechanical threshold, prostaglandin E2 (PGE2)-induced hyperalgesia, and chemotherapy-induced neuropathic pain (CIPN). Intrathecal administration of siRNA targeting Ift88, a primary cilium-specific intra-flagellar transport (IFT) protein required for ciliary integrity, resulted in attenuation of Ift88 mRNA and nociceptor primary cilia. Attenuation of primary cilia was associated with an increase in mechanical nociceptive threshold in vivo, and decrease in nociceptor excitability in vitro, abrogation of hyperalgesia, and nociceptor sensitization induced by both a prototypical pronociceptive inflammatory mediator PGE2 and paclitaxel CIPN, in a sex-specific fashion. siRNA targeting Ift52, another IFT protein, and knockdown of NompB, the Drosophila Ift88 ortholog, also abrogated CIPN and reduced baseline mechanosensitivity, respectively, providing independent confirmation for primary cilia control of nociceptor function. Hedgehog-induced hyperalgesia is attenuated by Ift88 siRNA, supporting a role for primary cilia in Hedgehog-induced hyperalgesia. Attenuation of CIPN by cyclopamine (intradermal and intra-ganglion), which inhibits Hedgehog signaling, supports a role of Hedgehog in CIPN. Our findings support a role of the nociceptor primary cilium in control of mechanical nociceptive threshold and inflammatory and neuropathic pain, the latter Hedgehog-dependent.Significance statement Many neurons have a tiny antenna-like structure, the primary cilium, protruding from their cell body, which processes information about the extracellular environment as well as regulates intracellular signaling. We report experiments aimed at understanding the role of the primary cilium in pain sensory neurons (nociceptors), including in the setting of inflammatory and neuropathic pain. We establish that nociceptors bear a primary cilium and show that this organelle regulates detection of noxious stimuli and contributes to nociceptor sensitization, using both the rat and the fruit fly as model organisms to manipulate primary cilia in pain states. We also identify primary cilium dependence of the contribution of Hedgehog to pain states.

The human ciliopathy protein RSG1 links the CPLANE complex to transition zone architecture.

Cilia are essential organelles and variants in genes governing ciliary function result in ciliopathic diseases. The Ciliogenesis and PLANar polarity Effectors (CPLANE) protein complex is essential for ciliogenesis in animals models but remains poorly defined. Notably, all but one subunit of the CPLANE complex have been implicated in human ciliopathy. Here, we identify three families in which variants in the remaining CPLANE subunit CPLANE2/RSG1 also cause ciliopathy. These patients display cleft palate, tongue lobulations and polydactyly, phenotypes characteristic of Oral-Facial-Digital Syndrome. We further show that these alleles disrupt two vital steps of ciliogenesis, basal body docking and recruitment of intraflagellar transport proteins. Moreover, APMS reveals that Rsg1 binds the CPLANE and also the transition zone protein Fam92 in a GTP-dependent manner. Finally, we show that CPLANE is generally required for normal transition zone architecture. Our work demonstrates that CPLANE2/RSG1 is a causative gene for human ciliopathy and also sheds new light on the mechanisms of ciliary transition zone assembly.

Vinblastine Resistance Is Associated with Nephronophthisis 3-Mediated Primary Cilia via Intraflagellar Transport Protein 88 and Apoptosis-Antagonizing Transcription Factor.

Primary cilia (PC) are microtubule-based organelles that function as cellular antennae to sense and transduce extracellular signals. Nephronophthisis 3 (NPHP3) is localized in the inversin compartment of PC. Mutations in NPHP3 are associated with renal-hepatic-pancreatic dysplasia. In this study, we investigated whether vinblastine (VBL), a microtubule destabilizer, induces anticancer drug resistance through NPHP3-associated PC formation in HeLa human cervical cancer cells. A considerable increase in PC frequency was observed in HeLa cells under serum-deprived (SD) conditions, which led to the inhibition of VBL-induced cell death. VBL-resistant cells were established by repetitive treatments with VBL and showed an increase in PC frequency. NPHP3 expression was also increased by VBL treatment under serum starvation as well as in VBL-resistant cells. NPHP3 expression and PC-associated resistance were positively correlated with apoptosis-antagonizing transcription factor (AATF) and negatively correlated with inhibition of NPHP3. In addition, AATF-mediated NPHP3 expression is associated with PC formation via the regulation of intraflagellar transport protein 88 (IFT88). VBL resistance ability was reduced by treating with ciliobrevin A, a well-known ciliogenesis inhibitor. Collectively, cancer cell survival following VBL treatment is regulated by PC formation via AATF-mediated expression of IFT88 and NPHP3. Our data suggest that the activation of AATF and IFT88 could be a novel regulator to induce anticancer drug resistance through NPHP3-associated PC formation.

Evolutionary trajectory for nuclear functions of ciliary transport complex proteins.

SUMMARYCilia and the nucleus were two defining features of the last eukaryotic common ancestor. In early eukaryotic evolution, these structures evolved through the diversification of a common membrane-coating ancestor, the protocoatomer. While in cilia, the descendants of this protein complex evolved into parts of the intraflagellar transport complexes and BBSome, the nucleus gained its selectivity by recruiting protocoatomer-like proteins to the nuclear envelope to form the selective nuclear pore complexes. Recent studies show a growing number of proteins shared between the proteomes of the respective organelles, and it is currently unknown how ciliary transport proteins could acquire nuclear functions and vice versa. The nuclear functions of ciliary proteins are still observable today and remain relevant for the understanding of the disease mechanisms behind ciliopathies. In this work, we review the evolutionary history of cilia and nucleus and their respective defining proteins and integrate current knowledge into theories for early eukaryotic evolution. We postulate a scenario where both compartments co-evolved and that fits current models of eukaryotic evolution, explaining how ciliary proteins and nucleoporins acquired their dual functions.

Ccrk-Mak/Ick signaling is a ciliary transport regulator essential for retinal photoreceptor survival.

Primary cilia are microtubule-based sensory organelles whose dysfunction causes ciliopathies in humans. The formation, function, and maintenance of primary cilia depend crucially on intraflagellar transport (IFT); however, the regulatory mechanisms of IFT at ciliary tips are poorly understood. Here, we identified that the ciliopathy kinase Mak is a ciliary tip-localized IFT regulator that cooperatively acts with the ciliopathy kinase Ick, an IFT regulator. Simultaneous disruption of Mak and Ick resulted in loss of photoreceptor ciliary axonemes and severe retinal degeneration. Gene delivery of Ick and pharmacological inhibition of FGF receptors, Ick negative regulators, ameliorated retinal degeneration in Mak -/- mice. We also identified that Ccrk kinase is an upstream activator of Mak and Ick in retinal photoreceptor cells. Furthermore, the overexpression of Mak, Ick, and Ccrk and pharmacological inhibition of FGF receptors suppressed ciliopathy-related phenotypes caused by cytoplasmic dynein inhibition in cultured cells. Collectively, our results show that the Ccrk-Mak/Ick axis is an IFT regulator essential for retinal photoreceptor maintenance and present activation of Ick as a potential therapeutic approach for retinitis pigmentosa caused by MAK mutations.

The role of cilia in the development, survival, and regeneration of hair cells.

Mutations impacting cilia genes lead to a class of human diseases known as ciliopathies. This is due to the role of cilia in the development, survival, and regeneration of many cell types. We investigated the extent to which disrupting cilia impacted these processes in lateral line hair cells of zebrafish. We found that mutations in two intraflagellar transport (IFT) genes, ift88 and dync2h1, which lead to the loss of kinocilia, caused increased hair cell apoptosis. IFT gene mutants also have a decreased mitochondrial membrane potential, and blocking the mitochondrial uniporter causes a loss of hair cells in wild-type zebrafish but not mutants, suggesting mitochondria dysfunction may contribute to the apoptosis seen in these mutants. These mutants also showed decreased proliferation during hair cell regeneration but did not show consistent changes in support cell number or proliferation during hair cell development. These results show that the loss of hair cells seen following disruption of cilia through either mutations in anterograde or retrograde IFT genes appears to be due to impacts on hair cell survival but not necessarily development in the zebrafish lateral line.

Architecture of RabL2-associated complexes at the ciliary base: A structural modeling perspective: Deciphering the structural organization of ciliary RabL2 complexes.

Cilia are slender, micrometer-long organelles present on the surface of eukaryotic cells. They function in signaling and locomotion and are constructed by intraflagellar transport (IFT). The assembly of IFT complexes into so-called IFT trains to initiate ciliary entry at the base of the cilium remains a matter of debate. Here, we use structural modeling to provide an architectural framework for how RabL2 is anchored at the ciliary base via CEP19 before being handed over to IFT trains for ciliary entry. Our models suggest that the N-terminal domain of CEP43 forms a homo-dimer to anchor at the subdistal appendages of cilia through a direct interaction with CEP350. A long linker region separates the N-terminal domain of CEP43 from the C-terminal domain, which captures CEP19 above the subdistal appendages and close to the distal appendages. Furthermore, we present a structural model for how RabL2-CEP19 associates with the IFT-B complex, providing insight into how RabL2 is handed over from CEP19 to the IFT complex. Interestingly, RabL2 association with the IFT-B complex appears to induce a significant conformational change in the IFT complex via a kink in the coiled-coils of the IFT81/74 proteins, which may prime the IFT machinery for entry into cilia.

Haploinsufficiency of intraflagellar transport protein 172 causes autism-like behavioral phenotypes in mice through BDNF

IntroductionPrimary cilia are hair-like solitary organelles growing on most mammalian cells that play fundamental roles in embryonic patterning and organogenesis. Defective cilia often cause a suite of inherited diseases called ciliopathies with multifaceted manifestations. Intraflagellar transport (IFT), a bidirectional protein trafficking along the cilium, actively facilitates the formation and absorption of primary cilia. IFT172 is the largest component of the IFT-B complex, and its roles in Bardet-Biedl Syndrome (BBS) have been appreciated with unclear mechanisms. ObjectivesWe performed a battery of behavioral tests with Ift172 haploinsufficiency (Ift172+/-) and WT littermates. We use RNA sequencing to identify the genes and signaling pathways that are differentially expressed and enriched in the hippocampus of Ift172+/- mice. Using AAV-mediated sparse labeling, electron microscopic examination, patch clamp and local field potential recording, western blot, luciferase reporter assay, chromatin immunoprecipitation, and neuropharmacological approach, we investigated the underlying mechanisms for the aberrant phenotypes presented by Ift172+/- mice. ResultsIft172+/- mice displayed excessive self-grooming, elevated anxiety, and impaired cognition. RNA sequencing revealed enrichment of differentially expressed genes in pathways relevant to axonogenesis and synaptic plasticity, which were further confirmed by less spine density and synaptic number. Ift172+/- mice demonstrated fewer parvalbumin-expressing neurons, decreased inhibitory synaptic transmission, augmented theta oscillation, and sharp-wave ripples in the CA1 region. Moreover, Ift172 haploinsufficiency caused less BDNF production and less activated BDNF-TrkB signaling pathway through transcription factor Gli3. Application of 7,8-Dihydroxyflavone, a potent small molecular TrkB agonist, fully restored BDNF-TrkB signaling activity and abnormal behavioral phenotypes presented by Ift172+/- mice. With luciferase and chip assays, we provided further evidence that Gli3 may physically interact with BDNF promoter I and regulate BDNF expression. ConclusionsOur data suggest that Ift172 per se drives neurotrophic effects and, when defective, could cause neurodevelopmental disorders reminiscent of autism-like disorders.

Exome Sequencing of a Blastomycosis Case–Control Cohort From Manitoba and Northwestern Ontario, Canada

ABSTRACTBackgroundBlastomycosis is a pulmonary disease caused by Blastomyces spp., a group of pathogenic dimorphic fungi endemic to a number of geographic regions, specifically Manitoba and northwestern Ontario, Canada. Immunosuppression is a major risk factor affecting disease susceptibility, yet host immunity is not well understood. Genetic immunodeficiencies can also influence disease, with variants in IL6, GATA2 and VDBP shown to influence susceptibility. Additional genetic factors in disease susceptibility and severity remain undetected. Our study seeks to identify potential genetic risk factors in a blastomycosis case–control cohort from Manitoba and northwestern Ontario, Canada.MethodsExomes from 18 blastomycosis cases and 9 controls were sequenced, variants were identified and filtered for accuracy and quality. We performed candidate gene prioritisation and variant aggregation to identify genetic associations and explored the full exome dataset.ResultsNinety‐nine genetic variants in 42 candidate genes were identified in the exome dataset. No variants associated with susceptibility were identified in a single‐variant analysis although two non‐synonymous variants in TYK2 were enriched among cases suggesting a possible role in susceptibility. Gene‐based association analysis found variants in TLR1 enriched in controls (p = 0.024) suggesting a possible protective effect. Gene cluster analysis identified genetic variants in genes of chromatin remodelling, proteasome and intraflagellar transport significantly enriched in cases (false discovery rates < 14%).ConclusionsThe findings in this study show novel associations with blastomycosis susceptibility. A better understanding of host immunity and genetic predisposition to Blastomyces infection can help to inform clinical practice for improved outcomes.

Contribution of intraflagellar transport to compartmentalization and maintenance of the photoreceptor cell.

The first steps of vision take place in the ciliary outer segment compartment of photoreceptor cells. The protein composition of outer segments is uniquely suited to perform this function. The most abundant among these proteins is the visual pigment, rhodopsin, whose outer segment trafficking involves intraflagellar transport (IFT). Here, we report three major findings from the analysis of mice in which ciliary transport was acutely impaired by conditional knockouts of IFT-B subunits. First, we demonstrate the existence of a sorting mechanism whereby mislocalized rhodopsin is recruited to and concentrated in extracellular vesicles prior to their release, presumably to protect the cell from adverse effects of protein mislocalization. Second, reducing rhodopsin expression significantly delays photoreceptor degeneration caused by IFT disruption, suggesting that controlling rhodopsin levels may be an effective therapy for some cases of retinal degenerative disease. Last, the loss of IFT-B subunits does not recapitulate a phenotype observed in mutants of the BBSome (another ciliary transport protein complex relying on IFT) in which non-ciliary proteins accumulate in the outer segment. Whereas it is widely thought that the role of the BBSome is to primarily participate in ciliary transport, our data suggest that the BBSome has another major function independent of IFT and possibly related to maintaining the diffusion barrier of the ciliary transition zone.

Distinct roles of Kif6 and Kif9 in mammalian ciliary trafficking and motility.

Ciliary beat and intraflagellar transport depend on dynein and kinesin motors. The kinesin-9 family members Kif6 and Kif9 are implicated in motile cilia motilities across protists and mammals. How they function and whether they act redundantly, however, remain unclear. Here, we show that Kif6 and Kif9 play distinct roles in mammals. Kif6 forms puncta that move bidirectionally along axonemes, whereas Kif9 appears to oscillate regionally on the ciliary central apparatus. Consistently, only Kif6 displays microtubule-based motor activity in vitro, and its ciliary localization requires its ATPase activity. Kif6 deficiency in mice disrupts coordinated ciliary beat across ependymal tissues and impairs cerebrospinal fluid flow, resulting in severe hydrocephalus and high mortality. Kif9 deficiency causes mild hydrocephalus without obviously affecting the ciliary beat or the lifespan. Kif6-/- and Kif9-/- males are infertile but exhibit oligozoospermia with poor sperm motility and defective forward motion of sperms, respectively. These results suggest Kif6 as a motor for cargo transport and Kif9 as a central apparatus regulator.

Discriminating motilities: Coordinating IFT with flagellar beating patterns.

Intraflagellar transport has traditionally been studied in immobilized flagella. In this issue, Gray et al. (https://doi.org/10.1083/jcb.202401154) introduced a novel methodology for fast imaging in free-swimming Leishmania, revealing the impacts of flagellum immobilization on intraflagellar transport and its inverse correlation with cell swimming speed.

Obesity impairs ciliary function and mucociliary clearance in the murine airway epithelium.

Obesity is a risk factor for increased morbidity and mortality in viral respiratory infection. Mucociliary clearance (MCC) in the airway is the primary host defense against viral infections. However, the impact of obesity on MCC is unclear, prompting this study. Using murine tracheal tissue culture and in vitro influenza A virus (IAV) infection models, we analyzed cilia-driven flow and ciliary beat frequency (CBF) in the airway epithelium to evaluate MCC. Short-term IAV infection increased cilia-driven flow and CBF in control mice, but not in high-fat diet-induced obese mice. Basal cilia-driven flow and CBF were also lower in obese mice than in control mice. Mechanistically, the increase of extracellular adenosine triphosphate (ATP) release during IAV infection, which was observed in the control mice, was abolished in the obese mice; however, the addition of ATP increased cilia-driven flow and CBF both in control and obese mice to a similar extent. In addition, RNA sequencing and reverse transcription-polymerase chain reaction revealed the downregulation of several cilia-related genes, including Dnah1, Dnal1, Armc4, and Ttc12 (the dynein-related genes); Ulk4 (the polychaete differentiation gene); Cep164 (the ciliogenesis and intraflagellar transport gene); Rsph4a, Cfap206, and Ppil6 (the radial spoke structure and assembly gene); and Drc3(the nexin-dynein regulatory complex genes) in obese murine tracheal tissues compared with their control levels. In conclusion, our studies demonstrate that obesity attenuates MCC under basal conditions and during IAV infection by downregulating the expression of cilia-related genes and suppressing the release of extracellular ATP, thereby increasing the susceptibility and severity of IAV infection.NEW & NOTEWORTHY Our study shows that obesity impairs airway mucociliary clearance (MCC), an essential physical innate defense mechanism for viral infection. Mechanically, this is likely due to the obesity-induced downregulation of cilia-related genes and attenuation of extracellular ATP release. This study provides novel insights into the mechanisms driving the higher susceptibility and severity of viral respiratory infections in individuals with obesity.

MI-181 Modulates Cilia Length and Restores Cilia Length in Cells with Defective Shortened Cilia.

Primary cilia are membrane-covered microtubule-based structures that protrude from the cell surface and are critical for cell signaling and homeostasis during human development and adulthood. Dysregulation of cilia formation, length, and function can lead to a spectrum of human diseases and syndromes known as ciliopathies. Although some genetic and chemical screens have been performed to define important factors that modulate cilia biogenesis and length control, there are currently no clinical treatments that restore cilia length in patients. We report that the microtubule-targeting agent MI-181(mitotic inhibitor-181) is a potent modulator of cilia length and biogenesis. Treatment of retinal pigment epithelial-1 cells with MI-181 induced an increase in the average size of cilia and in the percent ciliated cells under nonstarved conditions. Importantly, MI-181 was effective at rescuing cilia length and ciliation defects in cells that had been treated with the intraflagellar transport inhibitor Ciliobrevin D or the O-GlcNAc transferase inhibitor OSMI-1. Most importantly, MI-181 induced an increase in cilia length and restored ciliation in cells with compromised shortened cilia at low nanomolar concentrations and did not show an inhibitory response at high concentrations. Therefore, MI-181 represents a lead molecule for developing drugs targeting ciliopathies characterized by shortened cilia.

Abstract Mo078: Identifying Genetic Determinants of Phytosterol Levels: A Genome-Wide Association and Meta-Analysis Study Unveils a New Locus Influencing Campesterol Serum Concentrations

Background: Sitosterolemia, a rare inherited disorder, stems from mutations in the ABCG5/ABCG8 genes, which play a critical role in plant sterol transport. These genetic anomalies result in reduced phytosterol excretion, causing an accumulation in the body that can lead to serious health issues, such as premature coronary artery disease. Hypothesis: The study aimed to uncover the genetic determinants influencing plant sterol levels within the Middle East/North Africa (MENA) population, focusing on individuals from Qatar. It hypothesized that unique genetic variations might influence these levels, contributing to the development of sitosterolemia. Aims: To conduct the first genome-wide association study (GWAS) in the MENA region to identify genetic variants affecting plant sterol levels in the Qatari population, and to compare these findings with those from populations of European ancestry. Methods: The study utilized the Metabolon platform for analyzing serum levels of β-sitosterol and campesterol, combined with genome sequence data from the Qatar Genome Program. A trans-ancestry meta-analysis compared our findings with those from a large European cohort, while conditional analysis helped identify specific single nucleotide polymorphisms (SNPs) associated with these sterols. Results: The research identified two independent SNPs related to β-sitosterol ((rs145164937 and rs4299376) and two to campesterol (rs7598542 and rs75901165) in the Qatari population, alongside previously reported variants ( P <5.0 ×10 -8 ) .Notably, one variant (rs75901165) was located in the Intraflagellar Transport 43 (IFT43) gene, diverging from the common ABCG5/8 locus. The study also supported the association of variants in the SCARB1 and ABO genes with sitosterolemia and assessed a polygenic risk score's efficacy based on European GWAS data in the Qatari cohort. Conclusion(s): The findings underscore the significance of conducting population-specific genetic research to understand better and manage conditions like sitosterolemia. This research highlights the importance of personalized treatment approaches for hyperlipidemia and the value of establishing comprehensive multi-omics databases tailored to specific populations.

Genome-wide association study and meta-analysis of phytosterols identifies a novel locus for serum levels of campesterol

Sitosterolemia is a rare inherited disorder caused by mutations in the ABCG5/ABCG8 genes. These genes encode proteins involved in the transport of plant sterols. Mutations in these genes lead to decreased excretion of phytosterols, which can accumulate in the body and lead to a variety of health problems, including premature coronary artery disease. We conducted the first genome-wide association study (GWAS) in the Middle East/North Africa population to identify genetic determinants of plant sterol levels in Qatari people. GWAS was performed on serum levels of β-sitosterol and campesterol using the Metabolon platform from Qatar Biobank (QBB) and genome sequence data provided by Qatar Genome Program. A trans-ancestry meta-analysis of data from our Qatari cohort with summary statistics from a previously published large cohort (9758 subjects) of European ancestry was conducted. Using conditional analysis, we identified two independent single nucleotide polymorphisms associated with β-sitosterol (rs145164937 and rs4299376), and two others with campesterol (rs7598542 and rs75901165) in the Qatari population in addition to previously reported variants. All of them map to the ABCG5/8 locus except rs75901165 which is located within the Intraflagellar Transport 43 (IFT43) gene. The meta-analysis replicated most of the reported variants, and our study provided significant support for the association of variants in SCARB1 and ABO with sitosterolemia. Evaluation of a polygenic risk score devised from European GWAS data showed moderate performance when applied to QBB (adjusted-R2 = 0.082). These findings provide new insights into the genetic architecture of phytosterol metabolism while showing the importance including under-represented populations in future GWAS studies.

Extensive structural rearrangement of intraflagellar transport trains underpins bidirectional cargo transport

Bidirectional transport in cilia is carried out by polymers of the IFTA and IFTB protein complexes, called anterograde and retrograde intraflagellar transport (IFT) trains. Anterograde trains deliver cargoes from the cell tothe cilium tip, then convert into retrograde trains for cargo export. We set out to understand how the IFT complexes can perform these two directly opposing roles before and after conversion. We use cryoelectron tomography and in situ cross-linking mass spectrometry to determine the structure of retrograde IFT trains and compare it with the known structure of anterograde trains. The retrograde train is a 2-fold symmetric polymer organized around a central thread of IFTA complexes. We conclude that anterograde-to-retrograde remodeling involves global rearrangements of the IFTA/B complexes and requires complete disassembly of the anterograde train. Finally, we describe how conformational changes to cargo-binding sites facilitate unidirectional cargo transport in a bidirectional system.