CEP20 promotes invasion and metastasis of non-small cell lung cancer cells by depolymerizing microtubules

Worldwide, Lung cancer is the leading cause of cancer-related death and poses a direct health threat, non-small cell lung cancer (NSCLC) is the most common type. In this study, we demonstrated that centrosomal protein 20 (CEP20) is upregulated in NSCLC tissues and associated with cancer invasion metastasis. Notably, CEP20 depletion inhibited NSCLC cell proliferation, migration, and microtubule polymerization. Mechanistically, we discovered that CEP20 is critical in the development of NSCLC by regulating microtubule dynamics and cell adhesion-related signaling pathways. Furthermore, the knockdown or overexpression of CEP20 affects microtubule polymerization in A549 cell lines. Our research provides a promising therapeutic target for the diagnosis and treatment of lung cancer, as well as a theoretical and experimental basis for clinical application.

The evolutionary conserved proteins CEP90, FOPNL, and OFD1 recruit centriolar distal appendage proteins to initiate their assembly

In metazoa, cilia assembly is a cellular process that starts with centriole to basal body maturation, migration to the cell surface, and docking to the plasma membrane. Basal body docking involves the interaction of both the distal end of the basal body and the transition fibers/distal appendages, with the plasma membrane. Mutations in numerous genes involved in basal body docking and transition zone assembly are associated with the most severe ciliopathies, highlighting the importance of these events in cilium biogenesis. In this context, the ciliate Paramecium has been widely used as a model system to study basal body and cilia assembly. However, despite the evolutionary conservation of cilia assembly events across phyla, whether the same molecular players are functionally conserved, is not fully known. Here, we demonstrated that CEP90, FOPNL, and OFD1 are evolutionary conserved proteins crucial for ciliogenesis. Using ultrastructure expansion microscopy, we unveiled that these proteins localize at the distal end of both centrioles/basal bodies in Paramecium and mammalian cells. Moreover, we found that these proteins are recruited early during centriole duplication on the external surface of the procentriole. Functional analysis performed both in Paramecium and mammalian cells demonstrate the requirement of these proteins for distal appendage assembly and basal body docking. Finally, we show that mammalian centrioles require another component, Moonraker (MNR), to recruit OFD1, FOPNL, and CEP90, which will then recruit the distal appendage proteins CEP83, CEP89, and CEP164. Altogether, we propose that this OFD1, FOPNL, and CEP90 functional module is required to determine in mammalian cells the future position of distal appendage proteins.

CEP90, FOPNL and OFD1 form an evolutionary conserved module which promotes the assembly of centriolar distal appendages. This study uses ultrastructure expansion microscopy to reveal the recruitment of this module on early-born procentrioles to in turn recruit centriolar distal appendage proteins, proposing that this dictates the future location of distal appendages.

Investigation of sub-chromosomal changes in males with idiopathic azoospermia by chromosomal microarray analysis

Azoospermia consists of a significant proportion of infertility aetiology in males. Although known genetic abnormalities may explain roughly the third of infertility cases, the exact aetiology is still unclear. Chromosomal microarrays are widely used to detect sub chromosomal abnormalities (e.g., microdeletions and microduplications). This study aimed to investigate aetiology in patients with idiopathic azoospermia by using the chromosomal microarray method to detect possible sub chromosomal changes. Twenty-eight patients (with a mean age of 30.4 ± 9 years) that had been diagnosed with idiopathic azoospermia between January 2019 and December 2020 were included in the study. Genomic DNA isolated from the blood of patients were amplified using polymerase chain reaction and was subjected to chromosomal microarray analysis. A total of six microdeletions were identified as clinically significant: one pathogenic copy number variation (CNV), four likely pathogenic CNVs, and one CNV of unknown clinical significance. However, clinical findings indicated that these microdeletions, with variable expression levels, may affect the spermatogenesis process and induce azoospermia. Future investigations regarding the functional effect of these deletions may contribute to our understanding of azoospermia aetiology.

Regulators of tubulin polyglutamylation control nuclear shape and cilium disassembly by balancing microtubule and actin assembly

Cytoskeletal networks play an important role in regulating nuclear morphology and ciliogenesis. However, the role of microtubule (MT) post-translational modifications in nuclear shape regulation and cilium disassembly has not been explored. Here we identified a novel regulator of the tubulin polyglutamylase complex (TPGC), C11ORF49/CSTPP1, that regulates cytoskeletal organization, nuclear shape, and cilium disassembly. Mechanistically, loss of C11ORF49/CSTPP1 impacts the assembly and stability of the TPGC, which modulates long-chain polyglutamylation levels on microtubules (MTs) and thereby balances the binding of MT-associated proteins and actin nucleators. As a result, loss of TPGC leads to aberrant, enhanced assembly of MTs that penetrate the nucleus, which in turn leads to defects in nuclear shape, and disorganization of cytoplasmic actin that disrupts the YAP/TAZ pathway and cilium disassembly. Further, we showed that C11ORF49/CSTPP1-TPGC plays mechanistically distinct roles in the regulation of nuclear shape and cilium disassembly. Remarkably, disruption of C11ORF49/CSTPP1-TPGC also leads to developmental defects in vivo. Our findings point to an unanticipated nexus that links tubulin polyglutamylation with nuclear shape and ciliogenesis.

Using Paramecium as a Model for Ciliopathies

Paramecium has served as a model organism for the studies of many aspects of genetics and cell biology: non-Mendelian inheritance, genome duplication, genome rearrangements, and exocytosis, to name a few. However, the large number and patterning of cilia that cover its surface have inspired extraordinary ultrastructural work. Its swimming patterns inspired exquisite electrophysiological studies that led to a description of the bioelectric control of ciliary motion. A genetic dissection of swimming behavior moved the field toward the genes and gene products underlying ciliary function. With the advent of molecular technologies, it became clear that there was not only great conservation of ciliary structure but also of the genes coding for ciliary structure and function. It is this conservation and the legacy of past research that allow us to use Paramecium as a model for cilia and ciliary diseases called ciliopathies. However, there would be no compelling reason to study Paramecium as this model if there were no new insights into cilia and ciliopathies to be gained. In this review, we present studies that we believe will do this. For example, while the literature continues to state that immotile cilia are sensory and motile cilia are not, we will provide evidence that Paramecium cilia are clearly sensory. Other examples show that while a Paramecium protein is highly conserved it takes a different interacting partner or conducts a different ion than expected. Perhaps these exceptions will provoke new ideas about mammalian systems.

Centrosomal protein FOR20 knockout mice display embryonic lethality and left-right patterning defects

Centrosomal protein FOR20 has been reported to be crucial for essential cellular processes, including ciliogenesis, cell migration, and cell cycle in vertebrates. However, the function of FOR20 during mammalian embryonic development remains unknown. To investigate the in vivo function of the For20 gene in mammals, we generated For20 homozygous knockout mice by gene targeting. Our data reveal that homozygous knockout of For20 results in significant embryonic growth arrest and lethality during gestation, while the heterozygotes show no obvious defects. The absence of For20 leads to impaired left-right patterning of embryos and reduced cilia in the embryonic node. Deletion of For20 also disrupts angiogenesis in yolk sacs and embryos. These results highlight a critical role of For20 in early mammalian embryogenesis.

A non-canonical function for Centromere-associated protein-E controls centrosome integrity and orientation of cell division

Centromere-associated protein-E (CENP-E) is a kinesin motor localizing at kinetochores. Although its mitotic functions have been well studied, it has been challenging to investigate direct consequences of CENP-E removal using conventional methods because CENP-E depletion resulted in mitotic arrest. In this study, we harnessed an auxin-inducible degron system to achieve acute degradation of CENP-E. We revealed a kinetochore-independent role for CENP-E that removes pericentriolar material 1 (PCM1) from centrosomes in late S/early G2 phase. After acute loss of CENP-E, centrosomal Polo-like kinase 1 (Plk1) localization is abrogated through accumulation of PCM1, resulting in aberrant phosphorylation and destabilization of centrosomes, which triggers shortened astral microtubules and oblique cell divisions. Furthermore, we also observed centrosome and cell division defects in cells from a microcephaly patient with mutations in CENPE. Orientation of cell division is deregulated in some microcephalic patients, and our unanticipated findings provide additional insights into how microcephaly can result from centrosomal defects.

ANKRD26 recruits PIDD1 to centriolar distal appendages to activate the PIDDosome following centrosome amplification

Centriole copy number is tightly maintained by the once-per-cycle duplication of these organelles. Centrioles constitute the core of centrosomes, which organize the microtubule cytoskeleton and form the poles of the mitotic spindle. Centrosome amplification is frequently observed in tumors, where it promotes aneuploidy and contributes to invasive phenotypes. In non-transformed cells, centrosome amplification triggers PIDDosome activation as a protective response to inhibit cell proliferation, but how extra centrosomes activate the PIDDosome remains unclear. Using a genome-wide screen, we identify centriole distal appendages as critical for PIDDosome activation in cells with extra centrosomes. The distal appendage protein ANKRD26 is found to interact with and recruit the PIDDosome component PIDD1 to centriole distal appendages, and this interaction is required for PIDDosome activation following centrosome amplification. Furthermore, a recurrent ANKRD26 mutation found in human tumors disrupts PIDD1 localization and PIDDosome activation in cells with extra centrosomes. Our data support a model in which ANKRD26 initiates a centriole-derived signal to limit cell proliferation in response to centrosome amplification.

FOP Negatively Regulates Ciliogenesis and Promotes Cell Cycle Re-entry by Facilitating Primary Cilia Disassembly

Primary cilia are microtubule-based, antenna-like organelles, which are formed in G0 phase and resorbed as cells re-enter the cell cycle. It has been reported that primary cilia can influence the timing of cell cycle progression. However, the molecular links between ciliogenesis and cell cycle progression are not well understood. The Fibroblast Growth Factor Receptor 1 Oncogene Partner (FOP) has been implicated in ciliogenesis, but its function in ciliogenesis is not clear. Here, we show that FOP plays a negative role in ciliogenesis. Knockdown of FOP promotes cilia elongation and suppresses cilia disassembly. In contrast, ectopic expression of FOP induces defects in primary cilia formation, which can be rescued by either pharmacological or genetic inhibition of Aurora kinase A which promotes cilia disassembly. Moreover, knockdown of FOP delays cell cycle re-entry of quiescent cells following serum re-stimulation, and this can be reversed by silencing Intraflagellar Transport 20 (IFT20), an intraflagellar transport member essential for ciliogenesis. Collectively, these results suggest that FOP negatively regulates ciliogenesis and can promote cell cycle re-entry by facilitating cilia disassembly.

Principal Postulates of Centrosomal Biology. Version 2020

The centrosome, which consists of two centrioles surrounded by pericentriolar material, is a unique structure that has retained its main features in organisms of various taxonomic groups from unicellular algae to mammals over one billion years of evolution. In addition to the most noticeable function of organizing the microtubule system in mitosis and interphase, the centrosome performs many other cell functions. In particular, centrioles are the basis for the formation of sensitive primary cilia and motile cilia and flagella. Another principal function of centrosomes is the concentration in one place of regulatory proteins responsible for the cell's progression along the cell cycle. Despite the existing exceptions, the functioning of the centrosome is subject to general principles, which are discussed in this review.

Trichoplein binds PCM1 and controls endothelial cell function by regulating autophagy

Autophagy is an essential cellular quality control process that has emerged as a critical one for vascular homeostasis. Here, we show that trichoplein (TCHP) links autophagy with endothelial cell (EC) function. TCHP localizes to centriolar satellites, where it binds and stabilizes PCM1. Loss of TCHP leads to delocalization and proteasome-dependent degradation of PCM1, further resulting in degradation of PCM1's binding partner GABARAP. Autophagic flux under basal conditions is impaired in THCP-depleted ECs, and SQSTM1/p62 (p62) accumulates. We further show that TCHP promotes autophagosome maturation and efficient clearance of p62 within lysosomes, without affecting their degradative capacity. Reduced TCHP and high p62 levels are detected in primary ECs from patients with coronary artery disease. This phenotype correlates with impaired EC function and can be ameliorated by NF-κB inhibition. Moreover, Tchp knock-out mice accumulate of p62 in the heart and cardiac vessels correlating with reduced cardiac vascularization. Taken together, our data reveal that TCHP regulates endothelial cell function via an autophagy-mediated mechanism.

Centriolar satellite biogenesis and function in vertebrate cells

Centriolar satellites are non-membranous cytoplasmic granules that concentrate in the vicinity of the centrosome, the major microtubule-organizing centre (MTOC) in animal cells. Originally assigned as conduits for the transport of proteins towards the centrosome and primary cilium, the complexity of satellites is starting to become apparent. Recent studies defined the satellite proteome and interactomes, placing hundreds of proteins from diverse pathways in association with satellites. In addition, studies on cells lacking satellites have revealed that the centrosome can assemble in their absence, whereas studies on acentriolar cells have demonstrated that satellite assembly is independent from an intact MTOC. A role for satellites in ciliogenesis is well established; however, their contribution to other cellular functions is poorly understood. In this Review, we discuss the developments in our understanding of centriolar satellite assembly and function, and why satellites are rapidly becoming established as governors of multiple cellular processes. We highlight the composition and biogenesis of satellites and what is known about the regulation of these aspects. Furthermore, we discuss the evolution from thinking of satellites as mere facilitators of protein trafficking to the centrosome to thinking of them being key regulators of protein localization and cellular proteostasis for a diverse set of pathways, making them of broader interest to fields beyond those focused on centrosomes and ciliogenesis.

Mutation of FOP/FGFR1OP in mice recapitulates human short rib-polydactyly ciliopathy

Skeletal dysplasias are a clinically and genetically heterogeneous group of bone and cartilage disorders. A total of 436 skeletal dysplasias are listed in the 2015 revised version of the nosology and classification of genetic skeletal disorders, of which nearly 20% are still genetically and molecularly uncharacterized. We report the clinical and molecular characterization of a lethal skeletal dysplasia of the short-rib group caused by mutation of the mouse Fop gene. Fop encodes a centrosomal and centriolar satellite (CS) protein. We show that Fop mutation perturbs ciliogenesis in vivo and that this leads to the alteration of the Hedgehog signaling pathway. Fop mutation reduces CSs movements and affects pericentriolar material composition, which probably participates to the ciliogenesis defect. This study highlights the role of a centrosome and CSs protein producing phenotypes in mice that recapitulate a short rib-polydactyly syndrome when mutated.

A centriolar FGR1 oncogene partner-like protein required for paraflagellar rod assembly, but not axoneme assembly in African trypanosomes

Proteins of the FGR1 oncogene partner (or FOP) family are found at microtubule organizing centres (MTOCs) including, in flagellate eukaryotes, the centriole or flagellar basal body from which the axoneme extends. We report conservation of FOP family proteins, TbFOPL and TbOFD1, in the evolutionarily divergent sleeping sickness parasite Trypanosoma brucei, showing (in contrast with mammalian cells, where FOP is essential for flagellum assembly) depletion of a trypanosome FOP homologue, TbFOPL, affects neither axoneme nor flagellum elongation. Instead, TbFOPL depletion causes catastrophic failure in assembly of a lineage-specific, extra-axonemal structure, the paraflagellar rod (PFR). That depletion of centriolar TbFOPL causes failure in PFR assembly is surprising because PFR nucleation commences approximately 2 µm distal from the basal body. When over-expressed with a C-terminal myc-epitope, TbFOPL was also observed at mitotic spindle poles. Little is known about bi-polar spindle assembly during closed trypanosome mitosis, but indication of a possible additional MTOC function for TbFOPL parallels MTOC localization of FOP-like protein TONNEAU1 in acentriolar plants. More generally, our functional analysis of TbFOPL emphasizes significant differences in evolutionary cell biology trajectories of FOP-family proteins. We discuss how at the molecular level FOP homologues may contribute to flagellum assembly and function in diverse flagellates.

Centrosomal protein FOR20 is essential for cilia-dependent development in zebrafish embryos

Centrosomal proteins play critical roles in ciliogenesis. Mutations in many centrosomal proteins have been documented to contribute to developmental defects and cilium-related diseases. Centrosomal protein fibroblast growth factor receptor 1 oncogene partner-related protein of 20 kDa (FOR20) is crucial for ciliogenesis in mammalian cells and the unicellular eukaryote Paramecium; however, the biologic significance of FOR20 in vertebrate development remains unclear. We cloned the zebrafish homolog of the for20 gene and found that for20 mRNA is enriched in ciliated tissues during early zebrafish development. Knockdown of for20 by morpholino oligonucleotides in zebrafish results in multiple ciliary phenotypes, including curved body, hydrocephaly, pericardial edema, kidney cysts, and left-right asymmetry defects. for20 morphants show reduced number and length of cilia in Kupffer's vesicle and pronephric ducts. High-speed video microscopy reveals that cilia in most for20 morphants are consistently paralyzed or beat arrhythmically. To confirm the ciliary phenotypes of for20 morphants, we used the CRISPR/Cas9 system to disrupt for20 gene in zebrafish. for20 mutants exhibit multiple ciliary phenotypes resembling the defects in for20 morphants. All of these phenotypes in for20 morphants and mutants are significantly reversed by exogenous expression of for20 mRNA. Taken together, these data suggest that FOR20 is required for cilium-mediated processes during zebrafish embryogenesis.-Xie, S., Jin, J., Xu, Z., Huang, Y., Zhang, W., Zhao, L., Lo, L. J., Peng, J., Liu, W., Wang, F., Shu, Q., Zhou, T. Centrosomal protein FOR20 is essential for cilia-dependent development in zebrafish embryos.

Microtubule-binding protein FOR20 promotes microtubule depolymerization and cell migration

Microtubules are highly dynamic filaments assembled from αβ-tubulin heterodimers and play important roles in many cellular processes, including cell division and migration. Microtubule dynamics is tightly regulated by microtubule-associated proteins (MAPs) that function by binding to microtubules or free tubulin dimers. Here, we report that FOR20 (FOP-related protein of 20 kDa), a conserved protein critical for ciliogenesis and cell cycle progression, is a previously uncharacterized MAP that facilitates microtubule depolymerization and promotes cell migration. FOR20 not only directly binds to microtubules but also regulates microtubule dynamics in vitro by decreasing the microtubule growth rate and increasing the depolymerization rate and catastrophe frequency. In the in vitro microtubule dynamics assays, FOR20 appears to preferentially interact with free tubulin dimers over microtubules. Depletion of FOR20 inhibits microtubule depolymerization and promotes microtubule regrowth after the nocodazole treatment in HeLa cells. In addition, FOR20 knockdown significantly inhibits both individual and collective migration of mammalian cells. Taken together, these data suggest that FOR20 functions as a MAP to promote microtubule depolymerization and cell migration.

Variation in Basal Body Localisation and Targeting of Trypanosome RP2 and FOR20 Proteins

TOF-LisH-PLL motifs define FOP family proteins; some members are involved in flagellum assembly. The critical role of FOP family protein FOR20 is poorly understood. Here, we report relative localisations of the four FOP family proteins in parasitic Trypanosoma brucei: TbRP2, TbOFD1 and TbFOP/FOP1-like are mature basal body proteins whereas TbFOR20 is present on pro- and mature basal bodies - on the latter it localises distal to TbRP2. We discuss how the data, together with published work for another protist Giardia intestinalis, informs on likely FOR20 function. Moreover, our localisation study provides convincing evidence that the antigen recognised by monoclonal antibody YL1/2 at trypanosome mature basal bodies is FOP family protein TbRP2, not tyrosinated α-tubulin as widely stated in the literature. Curiously, FOR20 proteins from T. brucei and closely related African trypanosomes possess short, negatively-charged N-terminal extensions absent from FOR20 in other trypanosomatids and other eukaryotes. The extension is necessary for protein targeting, but insufficient to re-direct TbRP2 to probasal bodies. Yet, FOR20 from the American trypanosome T. cruzi, which lacks any extension, localises to pro- and mature basal bodies when expressed in T. brucei. This identifies unexpected variation in FOR20 architecture that is presently unique to one clade of trypanosomatids.

A centrosomal protein FOR20 regulates microtubule assembly dynamics and plays a role in cell migration

Here, we report that a centrosomal protein FOR20 [FOP (FGFR1 (fibroblast growth factor receptor 1) oncogene protein)-like protein of molecular mass of 20 kDa; also named as C16orf63, FLJ31153 or PHSECRG2] can regulate the assembly and stability of microtubules. Both FOR20 IgG antibody and GST (glutathione S-transferase)-tagged FOR20 could precipitate tubulin from the HeLa cell extract, indicating a possible interaction between FOR20 and tubulin. FOR20 was also detected in goat brain tissue extract and it cycled with microtubule-associated proteins. Furthermore, FOR20 bound to purified tubulin and inhibited the assembly of tubulin in vitro. The overexpression of FOR20 depolymerized interphase microtubules and the depletion of FOR20 prevented nocodazole-induced depolymerization of microtubules in HeLa cells. In addition, the depletion of FOR20 suppressed the dynamics of individual microtubules in live HeLa cells. FOR20-depleted MDA-MB-231 cells displayed zigzag motion and migrated at a slower rate than the control cells, indicating that FOR20 plays a role in directed cell migration. The results suggested that the centrosomal protein FOR20 is a new member of the microtubule-associated protein family and that it regulates the assembly and dynamics of microtubules.

Identification and characterization of a centrosomal protein, FOR20 as a novel S100A6 target

S100A6 is a Ca²⁺-signal transducer that interacts with numerous proteins and regulates their biochemical functions. Here we identified a centrosomal protein, FOR20 (FOP-related protein of 20 kDa) as a novel S100A6 target by screening protein microarrays carrying 19,676 recombinant GST-fused human proteins. Binding experiments revealed that S100A6 interacts with the N-terminal region (residues 1-30) of FOR20 in a Ca²⁺-dependent manner in vitro and in living cells. Several S100 proteins including S100A1, A2, A4, A11, B also exhibited Ca²⁺-dependent interactions with FOR20 as well as S100A6. We found that two distantly related centrosomal proteins, FOP and OFD1, also possess N-terminal regions with a significant sequence similarity to the putative S100A6-binding site (residues 1-30) in FOR20 and are capable of binding to S100A6 in a Ca²⁺-dependent manner. Taken together, these results may indicate that S100A6 interacts with FOR20 and related centrosomal proteins through a conserved N-terminal domain, suggesting a novel Ca²⁺-dependent regulation of centrosomal function.

The adverse effect of FOPNL genomic variant is reversed by bortezomib-based treatment protocols in multiple myeloma

Fibroblast growth factor receptor 1 oncogene partner N-terminal like gene (FOPNL) rs72773978 polymorphism was identified as an adverse prognostic factor in multiple myeloma (MM). We aimed to investigate the associations of rs72773978 with clinical characteristics and treatment outcome in 373 Hungarian MM patients. In our cohort, FOPNL polymorphism showed differential prognostic effect that depended on the treatment applied. Among patients treated with non-proteasome inhibitor (PI)-based therapy, carriership of the minor allele was significantly associated with adverse overall survival (p=.022). In contrast, the adverse effect was overcome by the application of PI-containing treatment (p=.048). Multivariate analyses revealed the independent adverse effect of rs72773978 on survival in the non-PI-treated group (p=.045), but not in PI treatment (OS: p=.093). We confirmed the adverse prognostic effect of rs72773978 associated with non-PI-based treatment regimens. Our results point to the importance of genotypic prognostic information associated with complex clinical background MM.

DISCOVERY OF FUNCTIONAL AND DISEASE PATHWAYS BY COMMUNITY DETECTION IN PROTEIN-PROTEIN INTERACTION NETWORKS

Advances in cellular, molecular, and disease biology depend on the comprehensive characterization of gene interactions and pathways. Traditionally, these pathways are curated manually, limiting their efficient annotation and, potentially, reinforcing field-specific bias. Here, in order to test objective and automated identification of functionally cooperative genes, we compared a novel algorithm with three established methods to search for communities within gene interaction networks. Communities identified by the novel approach and by one of the established method overlapped significantly (q < 0.1) with control pathways. With respect to disease, these communities were biased to genes with pathogenic variants in ClinVar (p ≪ 0.01), and often genes from the same community were co-expressed, including in breast cancers. The interesting subset of novel communities, defined by poor overlap to control pathways also contained co-expressed genes, consistent with a possible functional role. This work shows that community detection based on topological features of networks suggests new, biologically meaningful groupings of genes that, in turn, point to health and disease relevant hypotheses.

RABL2 interacts with the intraflagellar transport-B complex and CEP19 and participates in ciliary assembly

RABL2 interacts with the intraflagellar transport-B (IFT-B) complex and CEP19 in a mutually exclusive manner. A point mutation of RABL2 found in sperm motility–defective mice abolishes its binding to IFT-B but not to CEP19. A RABL2-defective Chlamydomonas strain exhibits a nonflagellated phenotype, suggesting a crucial role of RABL2 in ciliary assembly.

Proteins localized to the basal body and the centrosome play crucial roles in ciliary assembly and function. Although RABL2 and CEP19 are conserved in ciliated organisms and have been implicated in ciliary/flagellar functions, their roles are poorly understood. Here we show that RABL2 interacts with CEP19 and is recruited to the mother centriole and basal body in a CEP19-dependent manner and that CEP19 is recruited to the centriole probably via its binding to the centrosomal protein FGFR1OP. Disruption of the RABL2 gene in Chlamydomonas reinhardtii results in the nonflagellated phenotype, suggesting a crucial role of RABL2 in ciliary/flagellar assembly. We also show that RABL2 interacts, in its GTP-bound state, with the intraflagellar transport (IFT)-B complex via the IFT74–IFT81 heterodimer and that the interaction is disrupted by a mutation found in male infertile mice (Mot mice) with a sperm flagella motility defect. Intriguingly, RABL2 binds to CEP19 and the IFT74–IFT81 heterodimer in a mutually exclusive manner. Furthermore, exogenous expression of the GDP-locked or Mot-type RABL2 mutant in human cells results in mild defects in ciliary assembly. These results indicate that RABL2 localized to the basal body plays crucial roles in ciliary/flagellar assembly via its interaction with the IFT-B complex.

Basal body positioning and anchoring in the multiciliated cell Paramecium tetraurelia: roles of OFD1 and VFL3

Background

The development of a ciliary axoneme requires the correct docking of the basal body at cytoplasmic vesicles or plasma membrane. In the multiciliated cell Paramecium, three conserved proteins, FOR20, Centrin 2, and Centrin 3 participate in this process, FOR20 and Centrin 2 being involved in the assembly of the transition zone. We investigated the function of two other evolutionary conserved proteins, OFD1 and VFL3, likely involved in this process.

Results

In Paramecium tetraurelia, a single gene encodes OFD1, while four genes encode four isoforms of VFL3, grouped into two families, VFL3-A and VFL3-B. Depletion of OFD1 and the sole VFL3-A family impairs basal body docking. Loss of OFD1 yields a defective assembly of the basal body distal part. Like FOR20, OFD1 is recruited early during basal body assembly and localizes at the transition zone between axoneme and membrane at the level of the microtubule doublets. While the recruitment of OFD1 and Centrin 2 proceed independently, the localizations of OFD1 and FOR20 at the basal body are interdependent. In contrast, in VFL3-A depleted cells, the unanchored basal bodies harbor a fully organized distal part but display an abnormal distribution of their associated rootlets which mark their rotational asymmetry. VFL3-A, which is required for the recruitment of Centrin 3, is transiently present near the basal bodies at an early step of their duplication. VFL3-A localizes at the junction between the striated rootlet and the basal body.

Conclusion

Our results demonstrate the conserved role of OFD1 in the anchoring mechanisms of motile cilia and establish its relations with FOR20 and Centrin 2. They support the hypothesis of its association with microtubule doublets. They suggest that the primary defect of VFL3 depletion is a loss of the rotational asymmetry of the basal body which specifies the sites of assembly of the appendages which guide the movement of basal bodies toward the cell surface. The localization of VFL3 outside of the basal body suggests that extrinsic factors could control this asymmetry.

Electronic supplementary material

The online version of this article (doi:10.1186/s13630-017-0050-z) contains supplementary material, which is available to authorized users.

A chromosome 16p13.11 microduplication causes hyperactivity through dysregulation of miR-484/protocadherin-19 signaling

Chromosome 16p13.11 microduplication is a risk factor associated with various neurodevelopmental disorders such as attention-deficit/hyperactivity disorder, intellectual disabilities, developmental delay and autistic spectrum disorder. The underlying molecular mechanism of this genetic variation remained unknown, but its core genetic locus-conserved across mice and humans-contains seven genes. Here, we generated bacterial artificial chromosome-transgenic mice carrying a human 16p13.11 locus, and these mice showed the behavioral hyperactivity phenotype. We identified miR-484 as the responsible gene using a combination of expression and functional analyses. Mature miR-484 was expressed during active cortical neurogenesis, and overexpression of miR-484 decreased proliferation and increased neural progenitor differentiation in vivo. Luciferase screening identified the 3'-untranslated region of protocadherin-19 (Pcdh19) as a target of miR-484. The effect of miR-484 on neurogenesis was rescued by ectopic PCDH19 expression. These results demonstrate that miR-484 promotes neurogenesis by inhibiting PCDH19. Dysregulation of neurogenesis by imbalanced miR-484/PCDH19 expression contributes to the pathogenesis of 16p13.11 microduplication syndrome.

PCM1 Depletion Inhibits Glioblastoma Cell Ciliogenesis and Increases Cell Death and Sensitivity to Temozolomide

A better understanding of the molecules implicated in the growth and survival of glioblastoma (GBM) cells and their response to temozolomide (TMZ), the standard-of-care chemotherapeutic agent, is necessary for the development of new therapies that would improve the outcome of current GBM treatments. In this study, we characterize the role of pericentriolar material 1 (PCM1), a component of centriolar satellites surrounding centrosomes, in GBM cell proliferation and sensitivity to genotoxic agents such as TMZ. We show that PCM1 is expressed around centrioles and ciliary basal bodies in patient GBM biopsies and derived cell lines and that its localization is dynamic throughout the cell cycle. To test whether PCM1 mediates GBM cell proliferation and/or response to TMZ, we used CRISPR/Cas9 genome editing to generate primary GBM cell lines depleted of PCM1. These PCM1-depleted cells displayed reduced AZI1 satellite protein localization and significantly decreased proliferation, which was attributable to increased apoptotic cell death. Furthermore, PCM1-depleted lines were more sensitive to TMZ toxicity than control lines. The increase in TMZ sensitivity may be partly due to the reduced ability of PCM1-depleted cells to form primary cilia, as depletion of KIF3A also ablated GBM cells' ciliogenesis and increased their sensitivity to TMZ while preserving PCM1 localization. In addition, the co-depletion of KIF3A and PCM1 did not have any additive effect on TMZ sensitivity. Together, our data suggest that PCM1 plays multiple roles in GBM pathogenesis and that associated pathways could be targeted to augment current or future anti-GBM therapies.

Regulation of centriolar satellite integrity and its physiology

Centriolar satellites comprise cytoplasmic granules that are located around the centrosome. Their molecular identification was first reported more than a quarter of a century ago. These particles are not static in the cell but instead constantly move around the centrosome. Over the last decade, significant advances in their molecular compositions and biological functions have been achieved due to comprehensive proteomics and genomics, super-resolution microscopy analyses and elegant genetic manipulations. Centriolar satellites play pivotal roles in centrosome assembly and primary cilium formation through the delivery of centriolar/centrosomal components from the cytoplasm to the centrosome. Their importance is further underscored by the fact that mutations in genes encoding satellite components and regulators lead to various human disorders such as ciliopathies. Moreover, the most recent findings highlight dynamic structural remodelling in response to internal and external cues and unexpected positive feedback control that is exerted from the centrosome for centriolar satellite integrity.

Tethering of an E3 ligase by PCM1 regulates the abundance of centrosomal KIAA0586/Talpid3 and promotes ciliogenesis

To elucidate the role of centriolar satellites in ciliogenesis, we deleted the gene encoding the PCM1 protein, an integral component of satellites. PCM1 null human cells show marked defects in ciliogenesis, precipitated by the loss of specific proteins from satellites and their relocation to centrioles. We find that an amino-terminal domain of PCM1 can restore ciliogenesis and satellite localization of certain proteins, but not others, pinpointing unique roles for PCM1 and a group of satellite proteins in cilium assembly. Remarkably, we find that PCM1 is essential for tethering the E3 ligase, Mindbomb1 (Mib1), to satellites. In the absence of PCM1, Mib1 destabilizes Talpid3 through poly-ubiquitylation and suppresses cilium assembly. Loss of PCM1 blocks ciliogenesis by abrogating recruitment of ciliary vesicles associated with the Talpid3-binding protein, Rab8, which can be reversed by inactivating Mib1. Thus, PCM1 promotes ciliogenesis by tethering a key E3 ligase to satellites and restricting it from centrioles.

DOI:http://dx.doi.org/10.7554/eLife.12950.001

OFIP/KIAA0753 forms a complex with OFD1 and FOR20 at pericentriolar satellites and centrosomes and is mutated in one individual with oral-facial-digital syndrome

Oral-facial-digital (OFD) syndromes are rare heterogeneous disorders characterized by the association of abnormalities of the face, the oral cavity and the extremities, some due to mutations in proteins of the transition zone of the primary cilia or the closely associated distal end of centrioles. These two structures are essential for the formation of functional cilia, and for signaling events during development. We report here causal compound heterozygous mutations of KIAA0753/OFIP in a patient with an OFD VI syndrome. We show that the KIAA0753/OFIP protein, whose sequence is conserved in ciliated species, associates with centrosome/centriole and pericentriolar satellites in human cells and forms a complex with FOR20 and OFD1. The decreased expression of any component of this ternary complex in RPE1 cells causes a defective recruitment onto centrosomes and satellites. The OFD KIAA0753/OFIP mutant loses its capacity to interact with FOR20 and OFD1, which may be the molecular basis of the defect. We also show that KIAA0753/OFIP has microtubule-stabilizing activity. OFD1 and FOR20 are known to regulate the integrity of the centriole distal end, confirming that this structural element is a target of importance for pathogenic mutations in ciliopathies.

Centriolar satellites assemble centrosomal microcephaly proteins to recruit CDK2 and promote centriole duplication

Primary microcephaly (MCPH) associated proteins CDK5RAP2, CEP152, WDR62 and CEP63 colocalize at the centrosome. We found that they interact to promote centriole duplication and form a hierarchy in which each is required to localize another to the centrosome, with CDK5RAP2 at the apex, and CEP152, WDR62 and CEP63 at sequentially lower positions. MCPH proteins interact with distinct centriolar satellite proteins; CDK5RAP2 interacts with SPAG5 and CEP72, CEP152 with CEP131, WDR62 with MOONRAKER, and CEP63 with CEP90 and CCDC14. These satellite proteins localize their cognate MCPH interactors to centrosomes and also promote centriole duplication. Consistent with a role for satellites in microcephaly, homozygous mutations in one satellite gene, CEP90, may cause MCPH. The satellite proteins, with the exception of CCDC14, and MCPH proteins promote centriole duplication by recruiting CDK2 to the centrosome. Thus, centriolar satellites build a MCPH complex critical for human neurodevelopment that promotes CDK2 centrosomal localization and centriole duplication.

Genome-wide association study identifies variants at 16p13 associated with survival in multiple myeloma patients

Here we perform the first genome-wide association study (GWAS) of multiple myeloma (MM) survival. In a meta-analysis of 306 MM patients treated at UCSF and 239 patients treated at the Mayo clinic, we find a significant association between SNPs near the gene FOPNL on chromosome 16p13 and survival (rs72773978; P=6 × 10(-10)). Patients with the minor allele are at increased risk for mortality (HR: 2.65; 95% CI: 1.94-3.58) relative to patients homozygous for the major allele. We replicate the association in the IMMEnSE cohort including 772 patients, and a University of Utah cohort including 318 patients (rs72773978 P=0.044). Using publicly available data, we find that the minor allele was associated with increased expression of FOPNL and increased expression of FOPNL was associated with higher expression of centrosomal genes and with shorter survival. Polymorphisms at the FOPNL locus are associated with survival among MM patients.

Centriolar satellites: key mediators of centrosome functions

Centriolar satellites are small, microscopically visible granules that cluster around centrosomes. These structures, which contain numerous proteins directly involved in centrosome maintenance, ciliogenesis, and neurogenesis, have traditionally been viewed as vehicles for protein trafficking towards the centrosome. However, the recent identification of several new centriolar satellite components suggests that this model offers only an incomplete picture of their cellular functions. While the mechanisms controlling centriolar satellite status and function are not yet understood in detail, emerging evidence points to these structures as important hubs for dynamic, multi-faceted regulation in response to a variety of cues. In this review, we summarize the current knowledge of the roles of centriolar satellites in regulating centrosome functions, ciliogenesis, and neurogenesis. We also highlight newly discovered regulatory mechanisms targeting centriolar satellites and their functional status, and we discuss how defects in centriolar satellite components are intimately linked to a wide spectrum of human diseases.

Cep126 is required for pericentriolar satellite localisation to the centrosome and for primary cilium formation

Background Information

The centrosome is the primary microtubule-organising centre of animal cells and it has crucial roles in several fundamental cellular functions, including cell division, cell polarity, and intracellular transport. The mechanisms responsible for this are not completely understood.

Results

The poorly characterised protein CEP126 localises to the centrosome, pericentriolar satellites and the base of the primary cilium. Suppression of CEP126 expression results in dispersion of the pericentriolar satellites and disruption of the radial organisation of the microtubules, and induces disorganisation of the mitotic spindle. Moreover, CEP126 depletion or the transfection of a CEP126 truncation mutant in hTERT-RPE-1 and IMCD3 cells impairs the formation of the primary cilium.

Conclusions

We propose that CEP126 is a regulator of microtubule organisation at the centrosome that acts through modulation of the transport of pericentriolar satellites, and consequently, of the organisation of cell structure.

An alternative model for the role of RP2 protein in flagellum assembly in the African trypanosome

The tubulin cofactor C domain-containing protein TbRP2 is a basal body (centriolar) protein essential for axoneme formation in the flagellate protist Trypanosoma brucei, the causal agent of African sleeping sickness. Here, we show how TbRP2 is targeted and tethered at mature basal bodies and provide novel insight into TbRP2 function. Regarding targeting, understanding how several hundred proteins combine to build a microtubule axoneme is a fundamental challenge in eukaryotic cell biology. We show that basal body localization of TbRP2 is mediated by twinned, N-terminal TOF (TON1, OFD1, and FOP) and LisH motifs, motifs that otherwise facilitate localization of only a few conserved proteins at microtubule-organizing centers in animals, plants, and flagellate protists. Regarding TbRP2 function, there is a debate as to whether the flagellar assembly function of specialized, centriolar tubulin cofactor C domain-containing proteins is processing tubulin, the major component of axonemes, or general vesicular trafficking in a flagellum assembly context. Here we report that TbRP2 is required for the recruitment of T. brucei orthologs of MKS1 and MKS6, proteins that, in animal cells, are part of a complex that assembles at the base of the flagellum to regulate protein composition and cilium function. We also identify that TbRP2 is detected by YL1/2, an antibody classically used to detect α-tubulin. Together, these data suggest a general processing role for TbRP2 in trypanosome flagellum assembly and challenge the notion that TbRP2 functions solely in assessing tubulin “quality” prior to tubulin incorporation into the elongating axoneme.

The ciliary cytoskeleton

Cilia and flagella are surface-exposed, finger-like organelles whose core consists of a microtubule (MT)-based axoneme that grows from a modified centriole, the basal body. Cilia are found on the surface of many eukaryotic cells and play important roles in cell motility and in coordinating a variety of signaling pathways during growth, development, and tissue homeostasis. Defective cilia have been linked to a number of developmental disorders and diseases, collectively called ciliopathies. Cilia are dynamic organelles that assemble and disassemble in tight coordination with the cell cycle. In most cells, cilia are assembled during growth arrest in a multistep process involving interaction of vesicles with appendages present on the distal end of mature centrioles, and addition of tubulin and other building blocks to the distal tip of the basal body and growing axoneme; these building blocks are sorted through a region at the cilium base known as the ciliary necklace, and then transported via intraflagellar transport (IFT) along the axoneme toward the tip for assembly. After assembly, the cilium frequently continues to turn over and incorporate tubulin at its distal end in an IFT-dependent manner. Prior to cell division, the cilia are usually resorbed to liberate centrosomes for mitotic spindle pole formation. Here, we present an overview of the main cytoskeletal structures associated with cilia and centrioles with emphasis on the MT-associated appendages, fibers, and filaments at the cilium base and tip. The composition and possible functions of these structures are discussed in relation to cilia assembly, disassembly, and length regulation.

Centrosomal protein FOR20 is essential for S-phase progression by recruiting Plk1 to centrosomes

Centrosomes are required for efficient cell cycle progression mainly by orchestrating microtubule dynamics and facilitating G1/S and G2/M transitions. However, the role of centrosomes in S-phase progression is largely unknown. Here, we report that depletion of FOR20 (FOP-related protein of 20 kDa), a conserved centrosomal protein, inhibits S-phase progression and prevents targeting of Plk1 (polo-like kinase 1) to centrosomes, where FOR20 interacts with Plk1. Ablation of Plk1 also significantly induces S-phase defects, which are reversed by ectopic expression of Plk1, even a kinase-dead mutant, but not a mutant that fails to localize to centrosomes. Exogenous expression of centrosome-tethered Plk1, but not wild-type Plk1, overrides FOR20 depletion-induced S-phase defects independently of its kinase activity. Thus, these data indicate that recruitment of Plk1 to centrosomes by FOR20 may act as a signal to license efficient progression of S-phase. This represents a hitherto uncharacterized role of centrosomes in cell cycle regulation.

Plk1: unexpected roles in DNA replication

FOR20, a conserved centrosomal protein, is essential for Plk1 to localize to the centrosome during the S phase and regulate DNA replication. The absence of either Plk1 or FOR20 can stall the cell cycle by a previously unknown intra-S phase centrosomal checkpoint.

Primary ciliogenesis requires the distal appendage component Cep123

Primary cilium formation is initiated at the distal end of the mother centriole in a highly co-ordinated manner. This requires the capping of the distal end of the mother centriole with a ciliary vesicle and the anchoring of the basal body (mother centriole) to the cell cortex, both of which are mediated by the distal appendages. Here, we show that the distal appendage protein Cep123 (Cep89/CCDC123) is required for the assembly, but not the maintenance, of a primary cilium. In the absence of Cep123 ciliary vesicle formation fails, suggesting that it functions in the early stages of primary ciliogenesis. Consistent with such a role, Cep123 interacts with the centriolar satellite proteins PCM-1, Cep290 and OFD1, all of which play a role in primary ciliogenesis. These interactions are mediated by a domain in the C-terminus of Cep123 (400-783) that overlaps the distal appendage-targeting domain (500-600). Together, the data implicate Cep123 as a new player in the primary ciliogenesis pathway and expand upon the role of the distal appendages in this process.

FOP is a centriolar satellite protein involved in ciliogenesis

Centriolar satellites are proteinaceous granules that are often clustered around the centrosome. Although centriolar satellites have been implicated in protein trafficking in relation to the centrosome and cilium, the details of their function and composition remain unknown. FOP (FGFR1 Oncogene Partner) is a known centrosome protein with homology to the centriolar satellite proteins FOR20 and OFD1. We find that FOP partially co-localizes with the satellite component PCM1 in a cell cycle-dependent manner, similarly to the satellite and cilium component BBS4. As for BBS4, FOP localization to satellites is cell cycle dependent, with few satellites labeled in G1, when FOP protein levels are lowest, and most labeled in G2. FOP-FGFR1, an oncogenic fusion that causes a form of leukemia called myeloproliferative neoplasm, also localizes to centriolar satellites where it increases tyrosine phosphorylation. Depletion of FOP strongly inhibits primary cilium formation in human RPE-1 cells. These results suggest that FOP is a centriolar satellite cargo protein and, as for several other satellite-associated proteins, is involved in ciliogenesis. Localization of the FOP-FGFR1 fusion kinase to centriolar satellites may be relevant to myeloproliferative neoplasm disease progression.

CEP90 is required for the assembly and centrosomal accumulation of centriolar satellites, which is essential for primary cilia formation

Centriolar satellites are PCM-1-positive granules surrounding centrosomes. Proposed functions of the centriolar satellites include protein targeting to the centrosome, as well as communication between the centrosome and surrounding cytoplasm. CEP90 is a centriolar satellite protein that is critical for spindle pole integrity in mitotic cells. In this study, we examined the biological functions of CEP90 in interphase cells. CEP90 physically interacts with PCM-1 at centriolar satellites, and this interaction is essential for centrosomal accumulation of the centriolar satellites and eventually for primary cilia formation. CEP90 is also required for BBS4 loading on centriolar satellites and its localization in primary cilia. Our results imply that the assembly and transport of centriolar satellites are critical steps for primary cilia formation and ciliary protein recruitment.

FOR20, a conserved centrosomal protein, is required for assembly of the transition zone and basal body docking at the cell surface

Within the FOP family of centrosomal proteins, the conserved FOR20 protein has been implicated in the control of primary cilium assembly in human cells. To ascertain its role in ciliogenesis, we have investigated the function of its ortholog, PtFOR20p, in a multiciliated unicellular organism, Paramecium. By a combined functional and cytological analysis, we found that PtFOR20p specifically localizes at basal bodies and is required to build the transition zone, a prerequisite to their maturation and docking at the cell surface, hence to ciliogenesis. We also found that PtCen2p (one of the two basal body specific centrins, ortholog of HsCen2) is required to recruit PtFOR20p at the developing basal body and to control its length. In contrast, the other basal body specific centrin, PtCen3p, is not needed for assembly of the transition zone, but is required downstream, for basal body docking. Comparison of the structural defects induced by depletion of PtFOR20p, PtCen2p or PtCen3p respectively illustrates the dual role of the transition zone in the biogenesis of the basal body and in cilium assembly. The multiple potential roles of the transition zone during basal body biogenesis and the evolutionary conserved function of the FOP proteins in microtubule membrane interactions are discussed.

Centriolar satellites: busy orbits around the centrosome

Since its first description by Theodor Boveri in 1888, the centrosome has been studied intensely, and it revealed detailed information about its structure, molecular composition and its various functions. The centrosome consists of two centrioles, which generally appear in electron microscopy as barrel-shaped structures usually composed of nine microtubule triplets. An amorphous mass of pericentriolar material surrounds the centrioles and accumulates many proteins important for the integrity and function of centrosomes, such as the γ-tubulin ring complex (γ-TuRC) that mediates microtubule nucleation and capping. In animal somatic cells, the centrosome generally accounts for the major microtubule organizing center, and the duplicated pair of centrosomes determines the poles of the microtubule-based mitotic spindle. Despite detailed insights into the centrosome's structure and function, it has been a complete mystery until a few years ago how centrosomes duplicate and assemble. Moreover, it is still largely unclear if and how centrosomal proteins or protein complexes are exchanged, replaced or qualitatively altered. Previously identified cytoplasmic granules, named "pericentriolar" or "centriolar satellites", might fulfil such functions in protein targeting and exchange, and communication between the centrosomes and the cytoplasm. In this review, we summarize current knowledge about the structure, molecular composition and possible roles of the satellites that seem to surround the core of the centrosome in most animal cells.

Mining the Giardia genome and proteome for conserved and unique basal body proteins

Giardia lamblia is a flagellated protozoan parasite and a major cause of diarrhoea in humans. Its microtubular cytoskeleton mediates trophozoite motility, attachment and cytokinesis, and is characterised by an attachment disk and eight flagella that are each nucleated in a basal body. To date, only 10 giardial basal body proteins have been identified, including universal signalling proteins that are important for regulating mitosis or differentiation. In this study, we have exploited bioinformatics and proteomic approaches to identify new Giardia basal body proteins and confocal microscopy to confirm their localisation in interphase trophozoites. This approach identified 75 homologs of conserved basal body proteins in the genome including 65 not previously known to be associated with Giardia basal bodies. Thirteen proteins were confirmed to co-localise with centrin to the Giardia basal bodies. We also demonstrate that most basal body proteins localise to additional cytoskeletal structures in interphase trophozoites. This might help to explain the roles of the four pairs of flagella and Giardia-specific organelles in motility and differentiation. A deeper understanding of the composition of the Giardia basal bodies will contribute insights into the complex signalling pathways that regulate its unique cytoskeleton and the biological divergence of these conserved organelles.

Centriolar satellites are assembly points for proteins implicated in human ciliopathies, including oral-facial-digital syndrome 1

Ciliopathies are caused by mutations in genes encoding proteins required for cilia organization or function. We show through colocalization with PCM-1, that OFD1 (the product of the gene mutated in oral-facial-digital syndrome 1) as well as BBS4 and CEP290 (proteins encoded by other ciliopathy genes) are primarily components of centriolar satellites, the particles surrounding centrosomes and basal bodies. RNA interference experiments reveal that satellite integrity is mutually dependent upon each of these proteins. Upon satellite dispersal, through mitosis or forced microtubule depolymerization, OFD1 and CEP290 remain centrosomal, whereas BBS4 and PCM-1 do not. OFD1 interacts via its fifth coiled-coil motif with the N-terminal coiled-coil domain of PCM-1, which itself interacts via its C-terminal non-coiled-coil region with BBS4. OFD1 localization to satellites requires its N-terminal region, encompassing the LisH motif, whereas expression of OFD1 C-terminal constructs causes PCM-1 and CEP290 mislocalization. Moreover, in embryonic zebrafish, OFD1 and BBS4 functionally synergize, determining morphogenesis. Our observation that satellites are assembly points for several mutually dependent ciliopathy proteins provides a further possible explanation as to why the clinical spectrum of OFD1, Bardet-Biedl and Joubert syndromes overlap. Furthermore, definition of how OFD1 and PCM-1 interact helps explain why different OFD1 mutations lead to clinically variable phenotypes.

The pericentriolar satellite protein CEP90 is crucial for integrity of the mitotic spindle pole

Pericentriolar satellites are electron-dense granules that are concentrated around the centrosome. They are involved in the recruitment of centrosomal proteins and microtubule organization in interphase cells, but their mitotic functions are largely unknown. In this study, we characterize CEP90 as a component of pericentriolar satellites. CEP90 is present both in the centrosome and in the cytoplasm, but is transiently concentrated at the centrosome once cells enter mitosis. Depletion of CEP90 caused mitotic arrest with misaligned chromosomes. Spindle pole fragmentation was the most characteristic phenotype in CEP90-depleted cells. Spindle poles were fragmented as soon as the spindles attached, suggesting that the mechanical forces of spindle microtubules physically stress the structure of CEP90-depleted spindle poles. Based on these results, we propose that CEP90 is crucial for maintaining the integrity of spindle poles during mitosis.

Ancestral centriole and flagella proteins identified by analysis of Naegleria differentiation

Naegleria gruberi is a single-celled eukaryote best known for its remarkable ability to form an entire microtubule cytoskeleton de novo during its metamorphosis from an amoeba into a flagellate, including basal bodies (equivalent to centrioles), flagella and a cytoplasmic microtubule array. Our publicly available full-genome transcriptional analysis, performed at 20-minute intervals throughout Naegleria differentiation, reveals vast transcriptional changes, including the differential expression of genes involved in metabolism, signaling and the stress response. Cluster analysis of the transcriptional profiles of predicted cytoskeletal genes reveals a set of 55 genes enriched in centriole components (induced early) and a set of 82 genes enriched in flagella proteins (induced late). The early set includes genes encoding nearly every known conserved centriole component, as well as eight previously uncharacterized, highly conserved genes. The human orthologs of at least five genes localize to the centrosomes of human cells, one of which (here named Friggin) localizes specifically to mother centrioles.