CCTalpha and CCTdelta chaperonin subunits are essential and required for cilia assembly and maintenance in Tetrahymena

An amino acid-resolution interactome for motile cilia identifies the structure and function of ciliopathy protein complexes

Motile cilia are ancient, evolutionarily conserved organelles whose dysfunction underlies motile ciliopathies, a broad class of human diseases. Motile cilia contain a myriad of different proteins that assemble into an array of distinct machines, and understanding the interactions and functional hierarchies among them presents an important challenge. Here, we defined the protein interactome of motile axonemes using cross-linking mass spectrometry in Tetrahymena thermophila. From over 19,000 cross-links, we identified over 4,700 unique amino acid interactions among over 1,100 distinct proteins, providing both macromolecular and atomic-scale insights into diverse ciliary machines, including the intraflagellar transport system, axonemal dynein arms, radial spokes, the 96-nm ruler, and microtubule inner proteins. Guided by this dataset, we used vertebrate multiciliated cells to reveal functional interactions among several poorly defined human ciliopathy proteins. This dataset provides a resource for studying the biology of an ancient organelle and the molecular etiology of human genetic disease.

Peptide Fraction from Naja mandalayensis Snake Venom Showed Neuroprotection Against Oxidative Stress in Hippocampal mHippoE-18 Cells but Not in Neuronal PC12 Cells

Functional characterization of peptide fraction (PF) from snake venom has provided novel opportunities to investigate possible neuroprotective compounds relevant to pharmaceuticals. This study was performed to investigate the PF-mediated neuroprotection obtained from Naja mandalayensis snake venom, a member of the Elapidae family, using two neuronal cell lines, undifferentiated PC12 and differentiated mHippoE-18, in response to H2O2-induced oxidative stress. Cells were pre-treated for 4 h with PF (10, 1, 0.01, and 0.001 μg mL-1), and thereafter exposed to H2O2 (0.5 mmol L-1) for 20 h. Then, the oxidative stress markers and label-free differential proteome strategy were analyzed to understand the neuroprotective effects of PF. In PC12 cells, PF showed no neuroprotective effects against oxidative stress. In mHippoE-18 cells, PF at 0.01 and 0.001 μg mL-1 increased the viability and metabolism of cells against H2O2-induced neurotoxicity, reducing reactive oxygen species (ROS) generation. Interestingly, PF also exhibited a substantial reduction in baseline ROS levels compared to the control, indicating that PF could have compounds with antioxidant features. The comparative proteomic profiling identified 53 proteins with differential expression related to antioxidant action, catalysis, molecular function regulators, structural molecule activity, translation regulatory activity, ATP, and binding. The PF + H2O2 group indicated that protein expression is 6% upregulated, 4% downregulated, and 94% unchanged compared to the H2O2 group. Three significant proteins upregulated in the PF + H2O2 group, including elongation factor 2 (P58252), proteasome subunit alpha type (E9Q0X0), and E2 ubiquitin-conjugating enzyme (A0A338P786), suggested that PF-mediated neuroprotection happens through translational regulation and the degradation of defective proteins via the proteasome complex. Additionally, differential protein expression in PF changed the metabolism, protein synthesis, synaptic activity, and intracellular transport, suggesting that PF contains the rich mixture of bioactive peptides of interest pharmacologically. Overall, this study offers new opportunities for evaluating whether PF's neuroprotective features in specific neuronal cells are maintained and to investigate neurodegenerative disease drug development processes.

Structural diversity of axonemes across mammalian motile cilia

Reproduction, development and homeostasis depend on motile cilia, whose rhythmic beating is powered by a microtubule-based molecular machine called the axoneme. Although an atomic model of the axoneme is available for the alga Chlamydomonas reinhardtii1, structures of mammalian axonemes are incomplete1-5. Furthermore, we do not fully understand how molecular structures of axonemes vary across motile-ciliated cell types in the body. Here we use cryoelectron microscopy, cryoelectron tomography and proteomics to resolve the 96-nm modular repeat of axonemal doublet microtubules (DMTs) from both sperm flagella and epithelial cilia of the oviduct, brain ventricles and respiratory tract. We find that sperm DMTs are the most specialized, with epithelial cilia having only minor differences across tissues. We build a model of the mammalian sperm DMT, defining the positions and interactions of 181 proteins including 34 newly identified proteins. We elucidate the composition of radial spoke 3 and uncover binding sites of kinases associated with regeneration of ATP and regulation of ciliary motility. We discover a sperm-specific, axoneme-tethered T-complex protein ring complex (TRiC) chaperone that may contribute to construction or maintenance of the long flagella of mammalian sperm. We resolve axonemal dyneins in their prestroke states, illuminating conformational changes that occur during ciliary movement. Our results illustrate how elements of chemical and mechanical regulation are embedded within the axoneme, providing valuable resources for understanding the aetiology of ciliopathy and infertility, and exemplifying the discovery power of modern structural biology.

An amino acid-resolution interactome for motile cilia illuminates the structure and function of ciliopathy protein complexes

Motile cilia are ancient, evolutionarily conserved organelles whose dysfunction underlies motile ciliopathies, a broad class of human diseases. Motile cilia contain myriad different proteins that assemble into an array of distinct machines, so understanding the interactions and functional hierarchies among them presents an important challenge. Here, we defined the protein interactome of motile axonemes using cross-linking mass spectrometry (XL/MS) in Tetrahymena thermophila. From over 19,000 XLs, we identified 4,757 unique amino acid interactions among 1,143 distinct proteins, providing both macromolecular and atomic-scale insights into diverse ciliary machines, including the Intraflagellar Transport system, axonemal dynein arms, radial spokes, the 96 nm ruler, and microtubule inner proteins, among others. Guided by this dataset, we used vertebrate multiciliated cells to reveal novel functional interactions among several poorly-defined human ciliopathy proteins. The dataset therefore provides a powerful resource for studying the basic biology of an ancient organelle and the molecular etiology of human genetic disease.

Usher syndrome proteins ADGRV1 (USH2C) and CIB2 (USH1J) interact and share a common interactome containing TRiC/CCT-BBS chaperonins

The human Usher syndrome (USH) is the most common form of a sensory hereditary ciliopathy characterized by progressive vision and hearing loss. Mutations in the genes ADGRV1 and CIB2 have been associated with two distinct sub-types of USH, namely, USH2C and USH1J. The proteins encoded by the two genes belong to very distinct protein families: the adhesion G protein-coupled receptor ADGRV1 also known as the very large G protein-coupled receptor 1 (VLGR1) and the Ca²⁺- and integrin-binding protein 2 (CIB2), respectively. In the absence of tangible knowledge of the molecular function of ADGRV1 and CIB2, pathomechanisms underlying USH2C and USH1J are still unknown. Here, we aimed to enlighten the cellular functions of CIB2 and ADGRV1 by the identification of interacting proteins, a knowledge that is commonly indicative of cellular functions. Applying affinity proteomics by tandem affinity purification in combination with mass spectrometry, we identified novel potential binding partners of the CIB2 protein and compared these with the data set we previously obtained for ADGRV1. Surprisingly, the interactomes of both USH proteins showed a high degree of overlap indicating their integration in common networks, cellular pathways and functional modules which we confirmed by GO term analysis. Validation of protein interactions revealed that ADGRV1 and CIB2 mutually interact. In addition, we showed that the USH proteins also interact with the TRiC/CCT chaperonin complex and the Bardet Biedl syndrome (BBS) chaperonin-like proteins. Immunohistochemistry on retinal sections demonstrated the co-localization of the interacting partners at the photoreceptor cilia, supporting the role of USH proteins ADGRV1 and CIB2 in primary cilia function. The interconnection of protein networks involved in the pathogenesis of both syndromic retinal dystrophies BBS and USH suggest shared pathomechanisms for both syndromes on the molecular level.

Identification and subcellular localization analysis of CCTα in microsporidian Nosema bombycis

CCT is a chaperonin which is widely present in eukaryotic cells and mainly involves in the folding and assembly of cytoskeletal proteins β-tubulin and actin. The alpha subunit of CCT(CCTα) plays a pivotal role in the folding and assembly of cytoskeletal protein(s) as an individuals or complexes. In this study, we report cloning, characterization and expression of the CCTα of Nosema bombycis (NbCCTα) for the first time. The NbCCTα gene contains a complete ORF of 1629 bp in length that encodes a 542-amino acid polypeptide. The NbCCTα is 59.662 kDa molecular weight in size with an isoelectric point (pI) of 5.81, no signal peptide or transmembrane domain. The IFA results showed that the NbCCTα was co-localized with actin and β-tubulin in the cytoplasm, nucleus, nuclear membrane and plasma membrane of N. bombycis in the process of proliferation. qPCR analysis showed that the relative expression level of NbCCTα increased from 24 h to 96 h post-infection (hp.i) of N. bombycis, and reached the highest at 96 hp.i. The relative expression level of NbCCTα gene after RNAi was restrained at a low level from 48 hp.i to 96 hp.i. Knockdown of NbCCTα gene down-regulated the expression of Nbβ-tubulin and Nbactin genes. These results imply that NbCCTα may play an important role in the lifecycle of N. bombycis.

Mechanisms of triggering malaria gametocytogenesis by AP2-G

The transcription factor (TF) AP2-G is essential for gametocytogenesis in the malaria parasite; however, it remains unclear if AP2-G determines commitment to sexual stage development fate in the schizont stage, or whether AP2-G directly initiates sexual stage differentiation and development beginning in the late-trophozoite stage. In this study, we addressed this issue by investigating the expression profile of AP2-G and determining genome-wide target genes in Plasmodium berghei. Fluorescence microscopy showed that AP2-G expression was first observed in the parasite 12 h after erythrocyte invasion and peaked at 18 h when sexual features were first manifested in early gametocytes. Expression of AP2-G decreased with manifestation of sex-specific features. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) was performed at peak AP2-G expression and identified over 1000 binding sites in the genome. The main binding motif of the TF predicted from the binding sites was GTACNY. Predicted targets contained a number of genes related to protein biogenesis, suggesting that AP2-G plays a role in establishing a cellular basis required for sexual differentiation. AP2-G binding sites also existed upstream of gametocyte-specific TFs, namely AP2-G2, AP2-FG, and AP2-G itself. Furthermore, the target contained two AP2 TF-related genes. Disruption of these genes resulted in the arrest of ookinete development. These results suggest another role of AP2-G: activating a transcriptional cascade to promote conversion into early gametocytes. Taken together, AP2-G is involved not in establishing sexual commitment of schizonts, but rather in triggering the initiation of differentiation and the early development of gametocytes in the late trophozoite stage.

Spatial constraints on chromosomes are instrumental to meiotic pairing

In most eukaryotes, the meiotic chromosomal bouquet (comprising clustered chromosome ends) provides an ordered chromosome arrangement that facilitates pairing and recombination between homologous chromosomes. In the protist Tetrahymena thermophila, the meiotic prophase nucleus stretches enormously, and chromosomes assume a bouquet-like arrangement in which telomeres and centromeres are attached to opposite poles of the nucleus. We have identified and characterized three meiosis-specific genes [meiotic nuclear elongation 1-3 (MELG1-3)] that control nuclear elongation, and centromere and telomere clustering. The Melg proteins interact with cytoskeletal and telomere-associated proteins, and probably repurpose them for reorganizing the meiotic prophase nucleus. A lack of sequence similarity between the Tetrahymena proteins responsible for telomere clustering and bouquet proteins of other organisms suggests that the Tetrahymena bouquet is analogous, rather than homologous, to the conserved eukaryotic bouquet. We also report that centromere clustering is more important than telomere clustering for homologous pairing. Therefore, we speculate that centromere clustering may have been the primordial mechanism for chromosome pairing in early eukaryotes.

Cilia Distal Domain: Diversity in Evolutionarily Conserved Structures

Eukaryotic cilia are microtubule-based organelles that protrude from the cell surface to fulfill sensory and motility functions. Their basic structure consists of an axoneme templated by a centriole/basal body. Striking differences in ciliary ultra-structures can be found at the ciliary base, the axoneme and the tip, not only throughout the eukaryotic tree of life, but within a single organism. Defects in cilia biogenesis and function are at the origin of human ciliopathies. This structural/functional diversity and its relationship with the etiology of these diseases is poorly understood. Some of the important events in cilia function occur at their distal domain, including cilia assembly/disassembly, IFT (intraflagellar transport) complexes' remodeling, and signal detection/transduction. How axonemal microtubules end at this domain varies with distinct cilia types, originating different tip architectures. Additionally, they show a high degree of dynamic behavior and are able to respond to different stimuli. The existence of microtubule-capping structures (caps) in certain types of cilia contributes to this diversity. It has been proposed that caps play a role in axoneme length control and stabilization, but their roles are still poorly understood. Here, we review the current knowledge on cilia structure diversity with a focus on the cilia distal domain and caps and discuss how they affect cilia structure and function.

TRiC/CCT Chaperonin: Structure and Function

The eukaryotic group II chaperonin TRiC/CCT assists the folding of 10% of cytosolic proteins including many key structural and regulatory proteins. TRiC plays an essential role in maintaining protein homeostasis, and dysfunction of TRiC is closely related to human diseases including cancer and neurodegenerative diseases. TRiC consists of eight paralogous subunits, each of which plays a specific role in the assembly, allosteric cooperativity, and substrate recognition and folding of this complex macromolecular machine. TRiC-mediated substrate folding is regulated through its ATP-driven conformational changes. In recent years, progresses have been made on the structure, subunit arrangement, conformational cycle, and substrate folding of TRiC. Additionally, accumulating evidences also demonstrate the linkage between TRiC oligomer or monomer and diseases. In this review, we focus on the TRiC structure itself, TRiC assisted substrate folding, TRiC and disease, and the potential therapeutic application of TRiC in various diseases.

Tetrahymena Cilia Cap is Built in a Multi-step Process: A Study by Atomic Force Microscopy

Cilia are complex and dynamic organelles that have motility and sensory functions. Defects in cilia biogenesis and function are at the origin of human ciliopathies. In motile cilia, a basal body organizes the axoneme composed of nine microtubule doublets surrounding a central pair of singlet microtubules. The distal ends of axonemal microtubules are attached to the membrane by microtubule-capping structures. Little is known about the early steps of cilium assembly. Although cilia grow and resorb from their distal tips, it remains poorly understood where and when the components of the caps are first assembled. By using Atomic Force Microscopy in tapping mode, with resolution at the nanometer range and with minimum sample manipulation, we show that Tetrahymena cilia assembly requires transient assembly of structures, composed of three components that are placed asymmetrically on an early elongating axoneme. In small uncapped axonemes the microtubule central pair was never observed. Additionally, we show that cilia cap assembly is a multi-step process in which structures of different sizes and shapes are put together in close proximity before the axoneme appears capped. We propose that the cap modifies the axoneme microtubule rate of polymerization and present a model for Tetrahymena cilia cap assembly.

Bardet-Biedl Syndrome as a Chaperonopathy: Dissecting the Major Role of Chaperonin-Like BBS Proteins (BBS6-BBS10-BBS12)

Bardet-Biedl syndrome (BBS) is a rare genetic disorder that belongs to the group of ciliopathies, defined as diseases caused by defects in cilia structure and/or function. The six diagnostic features considered for this syndrome include retinal dystrophy, obesity, polydactyly, cognitive impairment and renal and urogenital anomalies. Furthermore, three of the 21 genes currently known to be involved in BBS encode chaperonin-like proteins (MKKS/BBS6, BBS10, and BBS12), so BBS can be also considered a member of the growing group of chaperonopathies. Remarkably, up to 50% of clinically-diagnosed BBS families can harbor disease-causing variants in these three genes, which highlights the importance of chaperone defects as pathogenic factors even for genetically heterogeneous syndromes such as BBS. In addition, it is interesting to note that BBS families with deleterious variants in MKKS/BBS6, BBS10 or BBS12 genes generally display more severe phenotypes than families with changes in other BBS genes. The chaperonin-like BBS proteins have structural homology to the CCT family of group II chaperonins, although they are believed to conserve neither the ATP-dependent folding activity of canonical CCT chaperonins nor the ability to form CCT-like oligomeric complexes. Thus, they play an important role in the initial steps of assembly of the BBSome, which is a multiprotein complex essential for mediating the ciliary trafficking activity. In this review, we present a comprehensive review of those genetic, functional and evolutionary aspects concerning chaperonin-like BBS proteins, trying to provide a new perspective that expands the classical conception of BBS only from a ciliary point of view.

Multigenerational effects of tris(1,3-dichloro-2-propyl) phosphate on the free-living ciliate protozoa Tetrahymena thermophila exposed to environmentally relevant concentrations and after subsequent recovery

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is considered a re-emerging environmental pollutant, and exposure to environmentally relevant concentrations has been shown to cause individual developmental toxicity in zebrafish and the water flea (Daphnia magna). However, multigenerational effects during exposure to TDCIPP and after subsequent recovery were unknown. In the present study, individuals of a model aquatic organism, the ciliated protozoan, T. thermophila were exposed to environmentally-relevant concentrations of TDCIPP (0, 300 or 3000 ng/L) for 60 days (e.g., theoretically 372 generations) followed by a 60-day period of recovery, during which T. thermophila were not exposed to TDCIPP. During exposure and after exposure, effects at the molecular, histological, individual and population levels were examined. Multigenerational exposure to 300 or 3000 ng TDCIPP/L for 60 days significantly decreased numbers of individuals, sizes of individuals, expressed as length and width of bodies, number of cilia, and depth and diameter of basal bodies of cilia, and up-regulated expressions of genes related to assembly and maintenance of cilia. Complete or partial recoveries of theoretical sizes of populations as well as sizes of individuals and expressions of genes were observed during the 60-day recovery period. Effects on number of cilia and depth and diameter of basal body of cilia were not reversible and could still be observed long after cease of TDCIPP exposure. Collectedly, and shown for the first time, multigenerational effects to T. thermophila were caused by exposure to environmentally relevant concentrations of TDCIPP. Also, there were multi-generational effects at the population level that were not caused by carry-over exposure to TDCIPP. The "permanent" alterations and their potential significance are discussed.

A Dynamic Protein Interaction Landscape of the Human Centrosome-Cilium Interface

The centrosome is the primary microtubule organizing center of the cells and templates the formation of cilia, thereby operating at a nexus of critical cellular functions. Here, we use proximity-dependent biotinylation (BioID) to map the centrosome-cilium interface; with 58 bait proteins we generate a protein topology network comprising >7,000 interactions. Analysis of interaction profiles coupled with high resolution phenotypic profiling implicates a number of protein modules in centriole duplication, ciliogenesis, and centriolar satellite biogenesis and highlights extensive interplay between these processes. By monitoring dynamic changes in the centrosome-cilium protein interaction landscape during ciliogenesis, we also identify satellite proteins that support cilia formation. Systematic profiling of proximity interactions combined with functional analysis thus provides a rich resource for better understanding human centrosome and cilia biology. Similar strategies may be applied to other complex biological structures or pathways.

The TCP1γ subunit of Leishmania donovani forms a biologically active homo-oligomeric complex

Chaperonins are a class of molecular chaperons that encapsulate nascent or stress-denatured proteins and assist their intracellular assembly and folding in an ATP-dependent manner. The ubiquitous eukaryotic chaperonin, TCP1 ring complex is a hetero-oligomeric complex comprising two rings, each formed of eight subunits that may have distinct substrate recognition and ATP hydrolysis properties. In Leishmania, only the TCP1γ subunit has been cloned and characterized. It exhibited differential expression at various growth stages of promastigotes. In the present study, we expressed the TCP1γ subunit in Escherichia coli to investigate whether it forms chaperonin-like complexes and plays a role in protein folding. LdTCP1γ formed high-molecular-weight complexes within E. coli cells as well as in Leishmania cell lysates. The recombinant protein is arranged into two back-to-back rings of seven subunits each, as predicted by homology modelling and observed by negative staining electron microscopy. This morphology is consistent with that of the oligomeric double-ring group I chaperonins found in mitochondria. The LdTCP1γ homo-oligomeric complex hydrolysed ATP, and was active as assayed by luciferase refolding. Thus, the homo-oligomer performs chaperonin reactions without partner subunit(s). Further, co-immunoprecipitation studies revealed that LdTCP1γ interacts with actin and tubulin proteins, suggesting that the complex may have a role in maintaining the structural dynamics of the cytoskeleton of parasites.

Revisiting the tubulin folding pathway: new roles in centrosomes and cilia

Centrosomes and cilia are critical eukaryotic organelles which have been in the spotlight in recent years given their implication in a myriad of cellular and developmental processes. Despite their recognized importance and intense study, there are still many open questions about their biogenesis and function. In the present article, we review the existing data concerning members of the tubulin folding pathway and related proteins, which have been identified at centrosomes and cilia and were shown to have unexpected roles in these structures.

Essential role of the chaperonin CCT in rod outer segment biogenesis

PURPOSE

While some evidence suggests an essential role for the chaperonin containing t-complex protein 1 (CCT) in ciliogenesis, this function remains poorly understood mechanistically. We used transgenic mice, previously generated in our lab, and characterized by a genetically-induced suppression of CCT in rod photoreceptors as well as a malformation of the rod sensory cilia, the outer segments, to gain new insights into this underlying molecular mechanism.

METHODS

The CCT activity in rod photoreceptors of mice was suppressed by overexpressing the chaperonin inhibitor, phosducin-like protein short, and the ensuing changes of cellular morphology were analyzed by light and electron microscopy. Protein expression levels were studied by fluorescent microscopy and Western blotting.

RESULTS

Suppressing the chaperonin made the photoreceptors incompetent to build their outer segments. Specifically, the CCT-deficient rods appeared unable to expand the outer segment plasma membrane, and accommodate growth of this compartment. Seeking the molecular mechanisms underlying such a shortcoming, we found that the affected rods could not express normal levels of Bardet-Biedl Syndrome (BBS) proteins 2, 5, and 7 and, owing to that deficiency, were unable to assemble the BBSome, a multisubunit complex responsible for ciliary trafficking. A similar effect in response to the chaperonin suppression was also observed in cultured ciliated cells.

CONCLUSIONS

Our data provide new evidence indicating the essential role of the chaperonin CCT in the biogenesis of vertebrate photoreceptor sensory cilia, and suggest that it may be due to the direct participation of the chaperonin in the posttranslational processing of selected BBS proteins and assembly of the BBSome.

The nucleotide-binding proteins Nubp1 and Nubp2 are negative regulators of ciliogenesis

Nucleotide-binding proteins Nubp1 and Nubp2 are MRP/MinD-type P-loop NTPases with sequence similarity to bacterial division site-determining proteins and are conserved, essential proteins throughout the Eukaryotes. They have been implicated, together with their interacting minus-end directed motor protein KIFC5A, in the regulation of centriole duplication in mammalian cells. Here we show that Nubp1 and Nubp2 are integral components of centrioles throughout the cell cycle, recruited independently of KIFC5A. We further demonstrate their localization at the basal body of the primary cilium in quiescent vertebrate cells or invertebrate sensory cilia, as well as in the motile cilia of mouse cells and in the flagella of Chlamydomonas. RNAi-mediated silencing of nubp-1 in C. elegans causes the formation of morphologically aberrant and additional cilia in sensory neurons. Correspondingly, downregulation of Nubp1 or Nubp2 in mouse quiescent NIH 3T3 cells markedly increases the number of ciliated cells, while knockdown of KIFC5A dramatically reduces ciliogenesis. Simultaneous double silencing of Nubp1 + KIFC5A restores the percentage of ciliated cells to control levels. We document the normal ciliary recruitment, during these silencing regimes, of basal body proteins critical for ciliogenesis, namely CP110, CEP290, cenexin, Chibby, AurA, Rab8, and BBS7. Interestingly, we uncover novel interactions of Nubp1 with several members of the CCT/TRiC molecular chaperone complex, which we find enriched at the basal body and recruited independently of the Nubps or KIFC5A. Our combined results for Nubp1, Nubp2, and KIFC5A and their striking effects on cilium formation suggest a central regulatory role for these proteins, likely involving CCT/TRiC chaperone activity, in ciliogenesis.

PHLP2 is essential and plays a role in ciliogenesis and microtubule assembly in Tetrahymena thermophila

Recent studies have implicated the phosducin-like protein-2 (PHLP2) in regulation of CCT, a chaperonin whose activity is essential for folding of tubulin and actin. However, the exact molecular function of PHLP2 is unclear. Here we investigate the significance of PHLP2 in a ciliated unicellular model, Tetrahymena thermophila, by deleting its single homolog, Phlp2p. Cells lacking Phlp2p became larger and died within 96 h. Overexpressed Phlp2p-HA localized to cilia, basal bodies, and cytosol without an obvious change in the phenotype. Despite similar localization, overexpressed GFP-Phlp2p caused a dominant-negative effect. Cells overproducing GFP-Phlp2p had decreased rates of proliferation, motility and phagocytosis, as compared to wild type cells or cells overproducing a non-tagged Phlp2p. Growing GFP-Phlp2p-overexpressing cells had fewer cilia and, when deciliated, failed to regenerate cilia, indicating defects in cilia assembly. Paclitaxel-treated GFP-Phlp2p cells failed to elongate cilia, indicating a change in the microtubules dynamics. The pattern of ciliary and cytosolic tubulin isoforms on 2D gels differed between wild type and GFP-Phlp2p-overexpressing cells. Thus, in Tetrahymena, PhLP2 is essential and under specific experimental conditions its activity affects tubulin and microtubule-dependent functions including cilia assembly.

DYX1C1 is required for axonemal dynein assembly and ciliary motility

DYX1C1 has been associated with dyslexia and neuronal migration in the developing neocortex. Unexpectedly, we found that deleting exons 2-4 of Dyx1c1 in mice caused a phenotype resembling primary ciliary dyskinesia (PCD), a disorder characterized by chronic airway disease, laterality defects and male infertility. This phenotype was confirmed independently in mice with a Dyx1c1 c.T2A start-codon mutation recovered from an N-ethyl-N-nitrosourea (ENU) mutagenesis screen. Morpholinos targeting dyx1c1 in zebrafish also caused laterality and ciliary motility defects. In humans, we identified recessive loss-of-function DYX1C1 mutations in 12 individuals with PCD. Ultrastructural and immunofluorescence analyses of DYX1C1-mutant motile cilia in mice and humans showed disruptions of outer and inner dynein arms (ODAs and IDAs, respectively). DYX1C1 localizes to the cytoplasm of respiratory epithelial cells, its interactome is enriched for molecular chaperones, and it interacts with the cytoplasmic ODA and IDA assembly factor DNAAF2 (KTU). Thus, we propose that DYX1C1 is a newly identified dynein axonemal assembly factor (DNAAF4).

Analysis of microtubule plus-end-tracking proteins in cilia

The microtubule (MT) plus-end-tracking proteins (+TIPs) belonging to the end binding (EB) protein family have been studied extensively in the context of cytoplasmic MTs and were shown to play pivotal roles in regulating MT dynamics and in recruiting other +TIPs to MT ends. Early studies in the green alga Chlamydomonas reinhardtii showed that EB1 localizes to the distal flagellum tip and the basal body, and subsequent studies using green fluorescent protein-tagged fusion proteins have demonstrated similar localization of EBs in other ciliated organisms, including mammalian cells as demonstrated here. Functional analysis of EBs in cultured mammalian cells revealed that EB1 and EB3 are required for biogenesis of primary cilia. Although mammalian EB3 localizes to the tip of some cilia and induces cilium elongation, EBs primarily seem to promote ciliogenesis via MT minus-end anchoring at the basal body, in turn facilitating vesicular trafficking to the cilium base. Moreover, mammalian EBs were shown to interact with several proteins implicated in MT minus-end anchoring and/or vesicular trafficking to cilia. Recent work suggests that apart from EBs, additional +TIPs may be present at the distal tip of cilia where they could regulate axoneme assembly, stability, or disassembly.

Proteomic analysis of apoptotic and oncotic pancreatic acinar AR42J cells treated with caerulein

This study aims to determine the differentially expressed proteins in the pancreatic acinar cells undergoing apoptosis and oncosis stimulated with caerulein to explore different cell death process of the acinar cell. AR42J cells were treated with caerulein to induce cell model of acute pancreatitis. Cells that were undergoing apoptosis and oncosis were separated by flow cytometry. Then differentially expressed proteins in the two groups of separated cells were detected by shotgun liquid chromatography-tandem mass spectrometry. The results showed that 11 proteins were detected in both apoptosis group and oncosis group, 17 proteins were detected only in apoptosis group and 29 proteins were detected only in oncosis group. KEGG analysis showed that proteins detected only in apoptosis group were significantly enriched in 10 pathways, including ECM-receptor interaction, cell adhesion molecules, and proteins detected only in oncosis group were significantly enriched in three pathways, including endocytosis, base excision repair, and RNA degradation. These proteins we detected are helpful for us to understand the process of cell death in acute pancreatitis and may be useful for changing the death mode of pancreatic acinar cells, thus attenuating the severity of pancreatitis.

Mob1: defining cell polarity for proper cell division

Mob1 is a component of both the mitotic exit network and Hippo pathway, being required for cytokinesis, control of cell proliferation and apoptosis. Cell division accuracy is crucial in maintaining cell ploidy and genomic stability and relies on the correct establishment of the cell division axis, which is under the control of the cell's environment and its intrinsic polarity. The ciliate Tetrahymena thermophila possesses a permanent anterior–posterior axis, left–right asymmetry and divides symmetrically. These unique features of Tetrahymena prompted us to investigate the role of Tetrahymena Mob1. Unexpectedly, we found that Mob1 accumulated in basal bodies at the posterior pole of the cell, and is the first molecular polarity marker so far described in Tetrahymena. In addition, Mob1 depletion caused the abnormal establishment of the cell division plane, providing clear evidence that Mob1 is important for its definition. Furthermore, cytokinesis was arrested and ciliogenesis delayed in Tetrahymena cells depleted of Mob1. This is the first evidence for an involvement of Mob1 in cilia biology. In conclusion, we show that Mob1 is an important cell polarity marker that is crucial for correct division plane placement, for cytokinesis completion and for normal cilia growth rates.