Axonemal localization ofChlamydomonasPACRG, a homologue of the humanParkin-coregulated gene product

Structure and dynamics of photoreceptor sensory cilia

The rod and cone photoreceptor cells of the vertebrate retina have highly specialized structures that enable them to carry out their function of light detection over a broad range of illumination intensities with optimized spatial and temporal resolution. Most prominent are their unusually large sensory cilia, consisting of outer segments packed with photosensitive disc membranes, a connecting cilium with many features reminiscent of the primary cilium transition zone, and a pair of centrioles forming a basal body which serves as the platform upon which the ciliary axoneme is assembled. These structures form a highway through which an enormous flux of material moves on a daily basis to sustain the continual turnover of outer segment discs and the energetic demands of phototransduction. After decades of study, the details of the fine structure and distribution of molecular components of these structures are still incompletely understood, but recent advances in cellular imaging techniques and animal models of inherited ciliary defects are yielding important new insights. This knowledge informs our understanding both of the mechanisms of trafficking and assembly and of the pathophysiological mechanisms of human blinding ciliopathies.

Crystal structure of human PACRG in complex with MEIG1 reveals roles in axoneme formation and tubulin binding

The Parkin co-regulated gene protein (PACRG) binds at the inner junction between doublet microtubules of the axoneme, a structure found in flagella and cilia. PACRG binds to the adaptor protein meiosis expressed gene 1 (MEIG1), but how they bind to microtubules is unknown. Here, we report the crystal structure of human PACRG in complex with MEIG1. PACRG adopts a helical repeat fold with a loop that interacts with MEIG1. Using the structure of the axonemal doublet microtubule from the protozoan Chlamydomonas reinhardtii and single-molecule fluorescence microscopy, we propose that PACRG binds to microtubules while simultaneously recruiting free tubulin to catalyze formation of the inner junction. We show that the homologous PACRG-like protein also mediates dual tubulin interactions but does not bind MEIG1. Our findings establish a framework to assess the function of the PACRG family of proteins and MEIG1 in regulating axoneme assembly.

Mechanisms of PINK1, ubiquitin and Parkin interactions in mitochondrial quality control and beyond

Parkinson's disease (PD) is a degenerative movement disorder resulting from the loss of specific neuron types in the midbrain. Early environmental and pathophysiological studies implicated mitochondrial damage and protein aggregation as the main causes of PD. These findings are now vindicated by the characterization of more than 20 genes implicated in rare familial forms of the disease. In particular, two proteins encoded by the Parkin and PINK1 genes, whose mutations cause early-onset autosomal recessive PD, function together in a mitochondrial quality control pathway. In this review, we will describe recent development in our understanding of their mechanisms of action, structure, and function. We explain how PINK1 acts as a mitochondrial damage sensor via the regulated proteolysis of its N-terminus and the phosphorylation of ubiquitin tethered to outer mitochondrial membrane proteins. In turn, phospho-ubiquitin recruits and activates Parkin via conformational changes that increase its ubiquitin ligase activity. We then describe how the formation of polyubiquitin chains on mitochondria triggers the recruitment of the autophagy machinery or the formation of mitochondria-derived vesicles. Finally, we discuss the evidence for the involvement of these mechanisms in physiological processes such as immunity and inflammation, as well as the links to other PD genes.

Structure of the Decorated Ciliary Doublet Microtubule

The axoneme of motile cilia is the largest macromolecular machine of eukaryotic cells. In humans, impaired axoneme function causes a range of ciliopathies. Axoneme assembly, structure, and motility require a radially arranged set of doublet microtubules, each decorated in repeating patterns with non-tubulin components. We use single-particle cryo-electron microscopy to visualize and build an atomic model of the repeating structure of a native axonemal doublet microtubule, which reveals the identities, positions, repeat lengths, and interactions of 38 associated proteins, including 33 microtubule inner proteins (MIPs). The structure demonstrates how these proteins establish the unique architecture of doublet microtubules, maintain coherent periodicities along the axoneme, and stabilize the microtubules against the repeated mechanical stress induced by ciliary motility. Our work elucidates the architectural principles that underpin the assembly of this large, repetitive eukaryotic structure and provides a molecular basis for understanding the etiology of human ciliopathies.

PACRG and FAP20 form the inner junction of axonemal doublet microtubules and regulate ciliary motility

We previously demonstrated that PACRG plays a role in regulating dynein-driven microtubule sliding in motile cilia. To expand our understanding of the role of PACRG in ciliary assembly and motility, we used a combination of functional and structural studies, including newly identified Chlamydomonas pacrg mutants. Using cryo-electron tomography we show that PACRG and FAP20 form the inner junction between the A- and B-tubule along the length of all nine ciliary doublet microtubules. The lack of PACRG and FAP20 also results in reduced assembly of inner-arm dynein IDA b and the beak-MIP structures. In addition, our functional studies reveal that loss of PACRG and/or FAP20 causes severe cell motility defects and reduced in vitro microtubule sliding velocities. Interestingly, the addition of exogenous PACRG and/or FAP20 protein to isolated mutant axonemes restores microtubule sliding velocities, but not ciliary beating. Taken together, these studies show that PACRG and FAP20 comprise the inner junction bridge that serves as a hub for both directly modulating dynein-driven microtubule sliding, as well as for the assembly of additional ciliary components that play essential roles in generating coordinated ciliary beating.

The evolution and patterning of male gametophyte development

The reproductive adaptations of land plants have played a key role in their terrestrial colonization and radiation. This encompasses mechanisms used for the production, dispersal and union of gametes to support sexual reproduction. The production of small motile male gametes and larger immotile female gametes (oogamy) in specialized multicellular gametangia evolved in the charophyte algae, the closest extant relatives of land plants. Reliance on water and motile male gametes for sexual reproduction was retained by bryophytes and basal vascular plants, but was overcome in seed plants by the dispersal of pollen and the guided delivery of non-motile sperm to the female gametes. Here we discuss the evolutionary history of male gametogenesis in streptophytes (green plants) and the underlying developmental biology, including recent advances in bryophyte and angiosperm models. We conclude with a perspective on research trends that promise to deliver a deeper understanding of the evolutionary and developmental mechanisms of male gametogenesis in plants.

Transcription factor DUO1 generated by neo-functionalization is associated with evolution of sperm differentiation in plants

Evolutionary mechanisms underlying innovation of cell types have remained largely unclear. In multicellular eukaryotes, the evolutionary molecular origin of sperm differentiation is unknown in most lineages. Here, we report that in algal ancestors of land plants, changes in the DNA-binding domain of the ancestor of the MYB transcription factor DUO1 enabled the recognition of a new cis-regulatory element. This event led to the differentiation of motile sperm. After neo-functionalization, DUO1 acquired sperm lineage-specific expression in the common ancestor of land plants. Subsequently the downstream network of DUO1 was rewired leading to sperm with distinct morphologies. Conjugating green algae, a sister group of land plants, accumulated mutations in the DNA-binding domain of DUO1 and lost sperm differentiation. Our findings suggest that the emergence of DUO1 was the defining event in the evolution of sperm differentiation and the varied modes of sexual reproduction in the land plant lineage.

Sequence variant analysis of RNA sequences in severe equine asthma

Background

Severe equine asthma is a chronic inflammatory disease of the lung in horses similar to low-Th2 late-onset asthma in humans. This study aimed to determine the utility of RNA-Seq to call gene sequence variants, and to identify sequence variants of potential relevance to the pathogenesis of asthma.

Methods

RNA-Seq data were generated from endobronchial biopsies collected from six asthmatic and seven non-asthmatic horses before and after challenge (26 samples total). Sequences were aligned to the equine genome with Spliced Transcripts Alignment to Reference software. Read preparation for sequence variant calling was performed with Picard tools and Genome Analysis Toolkit (GATK). Sequence variants were called and filtered using GATK and Ensembl Variant Effect Predictor (VEP) tools, and two RNA-Seq predicted sequence variants were investigated with both PCR and Sanger sequencing. Supplementary analysis of novel sequence variant selection with VEP was based on a score of <0.01 predicted with Sorting Intolerant from Tolerant software, missense nature, location within the protein coding sequence and presence in all asthmatic individuals. For select variants, effect on protein function was assessed with Polymorphism Phenotyping 2 and screening for non-acceptable polymorphism 2 software. Sequences were aligned and 3D protein structures predicted with Geneious software. Difference in allele frequency between the groups was assessed using a Pearson’s Chi-squared test with Yates’ continuity correction, and difference in genotype frequency was calculated using the Fisher’s exact test for count data.

Results

RNA-Seq variant calling and filtering correctly identified substitution variants in PACRG and RTTN. Sanger sequencing confirmed that the PACRG substitution was appropriately identified in all 26 samples while the RTTN substitution was identified correctly in 24 of 26 samples. These variants of uncertain significance had substitutions that were predicted to result in loss of function and to be non-neutral. Amino acid substitutions projected no change of hydrophobicity and isoelectric point in PACRG, and a change in both for RTTN. For PACRG, no difference in allele frequency between the two groups was detected but a higher proportion of asthmatic horses had the altered RTTN allele compared to non-asthmatic animals.

Discussion

RNA-Seq was sensitive and specific for calling gene sequence variants in this disease model. Even moderate coverage (<10–20 counts per million) yielded correct identification in 92% of samples, suggesting RNA-Seq may be suitable to detect sequence variants in low coverage samples. The impact of amino acid alterations in PACRG and RTTN proteins, and possible association of the sequence variants with asthma, is of uncertain significance, but their role in ciliary function may be of future interest.

Electrostatic interaction between polyglutamylated tubulin and the nexin-dynein regulatory complex regulates flagellar motility

The 3D localization of polyglutamylated tubulin in eukaryotic flagella is identified. Polyglutamylated tubulins are located on the interface between the microtubule and its cross-bridging structure, the N-DRC. Flagellar motility is regulated by electrostatic interaction between negatively charged tubulins and positively charged N-DRC.

Tubulins undergo various posttranslational modifications. Among them, polyglutamylation is involved in the motility of eukaryotic flagella and the stability of the axonemal microtubules. However, it remains unclear where polyglutamylated tubulin localizes precisely within the axoneme and how tubulin polyglutamylation affects flagellar motility. In this study, we identified the three-dimensional localization of the polyglutamylated tubulin in Chlamydomonas flagella using antibody labeling and cryo–electron tomography. Polyglutamylated tubulins specifically located in close proximity to a microtubule-cross-bridging structure called the nexin–dynein regulatory complex (N-DRC). Because N-DRC is positively charged, we hypothesized that there is an electrostatic interaction between the polyglutamylated tubulin and the N-DRC, and therefore we mutated the amino acid sequences of DRC4 to modify the charge of the N-DRC. We found that both augmentation and reduction of the positive charge on DRC4 resulted in reduced flagellar motility. Moreover, reduced motility in a mutant with a structurally defective N-DRC was partially restored by increasing the positive charge on DRC4. These results clearly indicate that beating motion of flagella is maintained by the electrostatic cross-bridge formed between the negatively charged polyglutamylated tubulins and the positively charged N-DRC.

Microtubule binding protein PACRG plays a role in regulating specific ciliary dyneins during microtubule sliding

The complex waveforms characteristic of motile eukaryotic cilia and flagella are produced by the temporally and spatially regulated action of multiple dynein subforms generating sliding between subsets of axonemal microtubules. Multiple protein complexes have been identified that are associated with the doublet microtubules and that mediate regulatory signals between key axonemal structures, such as the radial spokes and central apparatus, and the dynein arm motors; these complexes include the N-DRC, MIA, and CSC complexes. Previous studies have shown that PACRG (parkin co-regulated gene) forms a complex that is anchored to the axonemal doublet microtubules. Loss of PACRG causes defects in ciliary motility and cilia related diseases. Here, we use an in vitro microtubule sliding assay to demonstrate that PACRG and its interactors are part of a signaling pathway that includes the central apparatus, radial spokes and specific inner dynein arm subforms to control dynein-driven microtubule sliding. Using a biochemical approach, our studies also indicate that PACRG interacts with the radial spokes. © 2016 Wiley Periodicals, Inc.

The basal bodies of Chlamydomonas reinhardtii

The unicellular green alga, Chlamydomonas reinhardtii, is a biflagellated cell that can swim or glide. C. reinhardtii cells are amenable to genetic, biochemical, proteomic, and microscopic analysis of its basal bodies. The basal bodies contain triplet microtubules and a well-ordered transition zone. Both the mother and daughter basal bodies assemble flagella. Many of the proteins found in other basal body-containing organisms are present in the Chlamydomonas genome, and mutants in these genes affect the assembly of basal bodies. Electron microscopic analysis shows that basal body duplication is site-specific and this may be important for the proper duplication and spatial organization of these organelles. Chlamydomonas is an excellent model for the study of basal bodies as well as the transition zone.

PACRG, a protein linked to ciliary motility, mediates cellular signaling

Cilia are cellular projections that can be motile to generate fluid flow or nonmotile to enable signaling. Both forms are based on shared components, and proteins involved in ciliary motility, like PACRG, may also function in ciliary signaling. Caenorhabditis elegans PACRG acts in a subset of nonmotile cilia to influence a learning behavior and promote longevity.

Cilia are microtubule-based organelles that project from nearly all mammalian cell types. Motile cilia generate fluid flow, whereas nonmotile (primary) cilia are required for sensory physiology and modulate various signal transduction pathways. Here we investigate the nonmotile ciliary signaling roles of parkin coregulated gene (PACRG), a protein linked to ciliary motility. PACRG is associated with the protofilament ribbon, a structure believed to dictate the regular arrangement of motility-associated ciliary components. Roles for protofilament ribbon–associated proteins in nonmotile cilia and cellular signaling have not been investigated. We show that PACRG localizes to a small subset of nonmotile cilia in Caenorhabditis elegans, suggesting an evolutionary adaptation for mediating specific sensory/signaling functions. We find that it influences a learning behavior known as gustatory plasticity, in which it is functionally coupled to heterotrimeric G-protein signaling. We also demonstrate that PACRG promotes longevity in C. elegans by acting upstream of the lifespan-promoting FOXO transcription factor DAF-16 and likely upstream of insulin/IGF signaling. Our findings establish previously unrecognized sensory/signaling functions for PACRG and point to a role for this protein in promoting longevity. Furthermore, our work suggests additional ciliary motility-signaling connections, since EFHC1 (EF-hand containing 1), a potential PACRG interaction partner similarly associated with the protofilament ribbon and ciliary motility, also positively regulates lifespan.

Transcriptional Framework of Male Gametogenesis in the Liverwort Marchantia polymorpha L

In land plants, there are two types of male gametes: one is a non-motile sperm cell which is delivered to the egg cell by a pollen tube, and the other is a motile sperm cell with flagella. The molecular mechanism underlying the sexual reproduction with the egg and pollen-delivered sperm cell is well understood from studies using model plants such as Arabidopsis and rice. On the other hand, the sexual reproduction with motile sperm has remained poorly characterized, due to the lack of suitable models. Marchantia polymorpha L. is a model basal land plant with sexual reproduction involving an egg cell and bi-flagellated motile sperm. To understand the differentiation process of plant motile sperm, we analyzed the gene expression profile of developing antheridia of M. polymorpha. We performed RNA-sequencing experiments and compared transcript profiles of the male sexual organ (antheridiophore and antheridium contained therein), female sexual organ (archegoniophore) and a vegetative organ (thallus). Transcriptome analysis showed that the antheridium expresses nearly half of the protein-coding genes predicted in the genome, but it also has unique features. The antheridium transcriptome shares some common features with male gamete transcriptomes of angiosperms and animals, and homologs of genes involved in male gamete formation and function in angiosperms and animals were identified. In addition, we showed that some of them had distinct expression patterns in the spermatogenous tissue of developing antheridia. This study provides a transcriptional framework on which to study the molecular mechanism of plant motile sperm development in M. polymorpha as a model.

Sperm dysfunction and ciliopathy

Sperm motility is driven by motile cytoskeletal elements in the tail, called axonemes. The structure of axonemes consists of 9 + 2 microtubules, molecular motors (dyneins), and their regulatory structures. Axonemes are well conserved in motile cilia and flagella through eukaryotic evolution. Deficiency in the axonemal structure causes defects in sperm motility, and often leads to male infertility. It has been known since the 1970s that, in some cases, male infertility is linked with other symptoms or diseases such as Kartagener syndrome. Given that these links are mostly caused by deficiencies in the common components of cilia and flagella, they are called "immotile cilia syndrome" or "primary ciliary dyskinesia," or more recently, "ciliopathy," which includes deficiencies in primary and sensory cilia. Here, we review the structure of the sperm flagellum and epithelial cilia in the human body, and discuss how male fertility is linked to ciliopathy.

The neomuran revolution and phagotrophic origin of eukaryotes and cilia in the light of intracellular coevolution and a revised tree of life

Three kinds of cells exist with increasingly complex membrane-protein targeting: Unibacteria (Archaebacteria, Posibacteria) with one cytoplasmic membrane (CM); Negibacteria with a two-membrane envelope (inner CM; outer membrane [OM]); eukaryotes with a plasma membrane and topologically distinct endomembranes and peroxisomes. I combine evidence from multigene trees, palaeontology, and cell biology to show that eukaryotes and archaebacteria are sisters, forming the clade neomura that evolved ~1.2 Gy ago from a posibacterium, whose DNA segregation and cell division were destabilized by murein wall loss and rescued by the evolving novel neomuran endoskeleton, histones, cytokinesis, and glycoproteins. Phagotrophy then induced coevolving serial major changes making eukaryote cells, culminating in two dissimilar cilia via a novel gliding-fishing-swimming scenario. I transfer Chloroflexi to Posibacteria, root the universal tree between them and Heliobacteria, and argue that Negibacteria are a clade whose OM, evolving in a green posibacterium, was never lost.

FAP20 is an inner junction protein of doublet microtubules essential for both the planar asymmetrical waveform and stability of flagella in Chlamydomonas

The question of what proteins compose the junctions between two tubules in doublet microtubules is long-standing. Here a conserved flagellar protein, FAP20, is shown to be an inner junction component important for stabilizing the axoneme and scaffolding intra–B-tubular structures required for a planar asymmetrical waveform.

The axoneme—the conserved core of eukaryotic cilia and flagella—contains highly specialized doublet microtubules (DMTs). A long-standing question is what protein(s) compose the junctions between two tubules in DMT. Here we identify a highly conserved flagellar-associated protein (FAP), FAP20, as an inner junction (IJ) component. The flagella of Chlamydomonas FAP20 mutants have normal length but beat with an abnormal symmetrical three-dimensional pattern. In addition, the mutant axonemes are liable to disintegrate during beating, implying that interdoublet connections may be weakened. Conventional electron microscopy shows that the mutant axonemes lack the IJ, and cryo–electron tomography combined with a structural labeling method reveals that the labeled FAP20 localizes at the IJ. The mutant axonemes also lack doublet-specific beak structures, which are localized in the proximal portion of the axoneme and may be involved in planar asymmetric flagellar bending. FAP20 itself, however, may not be a beak component, because uniform localization of FAP20 along the entire length of all nine DMTs is inconsistent with the beak's localization. FAP20 is the first confirmed component of the IJ. Our data also suggest that the IJ is important for both stabilizing the axoneme and scaffolding intra–B-tubular substructures required for a planar asymmetrical waveform.

The N-DRC forms a conserved biochemical complex that maintains outer doublet alignment and limits microtubule sliding in motile axonemes

The nexin–dynein regulatory complex (N-DRC) is implicated in the control of dynein activity as a structural component of the nexin link. This study identifies several new subunits of the N-DRC and demonstrates for the first time that it forms a discrete biochemical complex that maintains outer doublet integrity and regulates microtubule sliding.

The nexin–dynein regulatory complex (N-DRC) is proposed to coordinate dynein arm activity and interconnect doublet microtubules. Here we identify a conserved region in DRC4 critical for assembly of the N-DRC into the axoneme. At least 10 subunits associate with DRC4 to form a discrete complex distinct from other axonemal substructures. Transformation of drc4 mutants with epitope-tagged DRC4 rescues the motility defects and restores assembly of missing DRC subunits and associated inner-arm dyneins. Four new DRC subunits contain calcium-signaling motifs and/or AAA domains and are nearly ubiquitous in species with motile cilia. However, drc mutants are motile and maintain the 9 + 2 organization of the axoneme. To evaluate the function of the N-DRC, we analyzed ATP-induced reactivation of isolated axonemes. Rather than the reactivated bending observed with wild-type axonemes, ATP addition to drc-mutant axonemes resulted in splaying of doublets in the distal region, followed by oscillatory bending between pairs of doublets. Thus the N-DRC provides some but not all of the resistance to microtubule sliding and helps to maintain optimal alignment of doublets for productive flagellar motility. These findings provide new insights into the mechanisms that regulate motility and further highlight the importance of the proximal region of the axoneme in generating flagellar bending.

Ciliary and non-ciliary expression and function of PACRG during vertebrate development

Background

Park2-co-regulated gene (PACRG) is evolutionarily highly conserved from green algae to mammals. In Chlamydomonas and trypanosomes, the PACRG protein associates with flagella. Loss of PACRG results in shortened or absent flagella. In mouse the PACRG protein is required for spermatogenesis. The purpose of the present study was to analyze (1) the expression patterns of PACRG during vertebrate embryogenesis, and (2) whether the PACRG protein was required for left-right (LR) axis specification through cilia-driven leftward flow in Xenopus laevis.

Methods

PACRG cDNAs were cloned and expression was analyzed during early embryonic development of Xenopus, mouse, rabbit and zebrafish. Antisense morpholino oligonucleotide (MO) mediated gene knockdown was applied in Xenopus to investigate LR development at the level of tissue morphology, leftward flow and asymmetric marker gene expression, using timelapse videography, scanning electron microscopy (SEM) and whole-mount in situ hybridization. Results were statistically evaluated using Wilcoxon paired and χ² tests.

Results

PACRG mRNA expression was found in cells and tissues harboring cilia throughout the vertebrates. Highly localized expression was also detected in the brain. During early development, PACRG was specifically localized to epithelia where leftward flow arises, that is, the gastrocoel roof plate (GRP) in Xenopus, the posterior notochord (PNC) in mammals and Kupffer’s vesicle (KV) in zebrafish. Besides its association with ciliary axonemes, subcellular localization of PACRG protein was found around the nucleus and in a spotty pattern in the cytoplasm. A green fluorescent protein (GFP) fusion construct preferentially labeled cilia, rendering PACRG a versatile marker for live imaging. Loss-of-function in the frog resulted dose dependently in LR, neural tube closure and gastrulation defects, representing ciliary and non-ciliary functions of PACRG.

Conclusions

The PACRG protein is a novel essential factor of cilia in Xenopus.

Sperm flagella: comparative and phylogenetic perspectives of protein components

Sperm motility is necessary for the transport of male DNA to eggs in species with both external and internal fertilization. Flagella comprise several proteins for generating and regulating motility. Central cytoskeletal structures called axonemes have been well conserved through evolution. In mammalian sperm flagella, two accessory structures (outer dense fiber and the fibrous sheath) surround the axoneme. The axonemal bend movement is based on the active sliding of axonemal doublet microtubules by the molecular motor dynein, which is divided into outer and inner arm dyneins according to positioning on the doublet microtubule. Outer and inner arm dyneins play different roles in the production and regulation of flagellar motility. Several regulatory mechanisms are known for both dyneins, which are important in motility activation and chemotaxis at fertilization. Although dynein itself has certain properties that contribute to the formation and propagation of flagellar bending, other axonemal structures-specifically, the radial spoke/central pair apparatus-have essential roles in the regulation of flagellar bending. Recent genetic and proteomic studies have explored several new components of axonemes and shed light on the generation and regulation of sperm motility during fertilization.

Patched1 haploinsufficiency impairs ependymal cilia function of the quaking viable mice, leading to fatal hydrocephalus

The quaking viable (qk(v)) mice harbor an autosomal recessive mutation that deletes the parkin co-regulated gene (pacrg) and parkin (park2) genes, and alters the expression of the quaking (qkI) gene. qk(v) mice have been well-studied for their dysmyelination phenotype caused by the altered expression of the qkI gene. The qk(v) mice exhibit sterility in males and develop acquired mild hydrocephalus due to the lack of PACRG expression. To identify genetic interactors of the pacrg-parkin-qkI locus, we crossbred the qk(v) mice with various mouse strains including the patched1 (ptch1)-deficient mice. The ptch1 heterozygous mice exhibit increased Sonic Hedgehog (Shh) signaling and are prone to several malignancies including tumorigenesis. In the present study, we show that the qk(v/v); ptch1⁺/⁻ mice are distinguished by a dome-shaped skull at 4 to 6weeks of age and exhibit dilation of the lateral and third ventricles leading to fatal acquired hydrocephalus by ~5months of age, unlike their littermate controls that did not develop the condition. The qk(v/v); ptch1⁺/⁻ mice contained normal ciliated ependymal cells lining the ventricles of the brain, but these cells were functionally compromised with a severe cilial mediated flow defect. Our findings suggest that the ptch1 and the pacrg-parkin-qkI loci genetically interact to regulate cilia function of the ependymal cells.

Deletion of the Parkin co-regulated gene causes defects in ependymal ciliary motility and hydrocephalus in the quakingviable mutant mouse

The quakingviable mouse (qkv) is a spontaneous recessive mouse mutant with a deletion of approximately 1.1 Mb in the proximal region of chromosome 17. The deletion affects the expression of three genes; quaking (Qk), Parkin-coregulated gene (Pacrg) and parkin (Park2). The resulting phenotype, which includes dysmyelination of the central nervous system and male sterility, is due to reduced expression of Qk and a complete lack of Pacrg expression, respectively. Pacrg is required for correct development of the spermatozoan flagella, a specialized type of motile cilia. In vertebrates, motile cilia are required for multiple functions related to cellular movement or movement of media over a stationary cell surface. To investigate the potential role of PACRG in motile cilia we analysed qkv mutant mice for evidence of cilial dysfunction. Histological and magnetic resonance imaging analyses demonstrated that qkv mutant mice were affected by acquired, communicating hydrocephalus (HC). Structural analysis of ependymal cilia demonstrated that the 9 + 2 arrangement of axonemal microtubules was intact and that both the density of ciliated cells and cilia length was similar to wild-type littermates. Cilia function studies showed a reduction in ependymal cilial beat frequency and cilial mediated flow in qkv mutant mice compared with wild-type littermate controls. Moreover, transgenic expression of Pacrg was necessary and sufficient to correct this deficit and rescue the HC phenotype in the qkv mutant. This study provides novel in vivo evidence that Pacrg is required for motile cilia function and may be involved in the pathogenesis of human ciliopathies, such as HC, asthenospermia and primary ciliary dyskinesia.

HA-tagging of putative flagellar proteins in Chlamydomonas reinhardtii identifies a novel protein of intraflagellar transport complex B

Proteomic analysis of flagella from the green alga Chlamydomonas reinhardtii has identified over 600 putative flagellar proteins. The genes encoding nine of these not previously characterized plus the previously described PACRG protein were cloned, inserted into a vector adding a triple-HA tag to the C-terminus of the gene product, and transformed into C. reinhardtii. Expression was confirmed by western blotting. Indirect immunofluorescence located all 10 fusion proteins in the flagellum; PACRG was localized to a subset of outer doublet microtubules. For some proteins, additional signal was observed in the cell body. Among the latter was FAP232-HA, which showed a spotted distribution along the flagella and an accumulation at the basal bodies. This pattern is characteristic for intraflagellar transport (IFT) proteins. FAP232-HA co-localized with the IFT protein IFT46 and co-sedimented with IFT particles in sucrose gradients. Furthermore, it co-immunoprecipitated with IFT complex B protein IFT46, but not with IFT complex A protein IFT139. We conclude that FAP232 is a novel component of IFT complex B and rename it IFT25. Homologues of IFT25 are encoded in the genomes of a subset of organisms that assemble cilia or flagella; C. reinhardtii IFT25 is 37% identical to the corresponding human protein. Genes encoding IFT25 homologues are absent from the genomes of organisms that lack cilia and flagella and, interestingly, also from those of Drosophila melanogaster and Caenorhabditis elegans, suggesting that IFT25 has a specialized role in IFT that is not required for the assembly of cilia or flagella in the worm and fly. Cell Motil. Cytoskeleton 2009. (c) 2009 Wiley-Liss, Inc.

A novel ankyrin-repeat protein interacts with the regulatory proteins of inner arm dynein f (I1) of Chlamydomonas reinhardtii

How ciliary and flagellar motility is regulated is a challenging problem. The flagellar movement in Chlamydomonas reinhardtii is in part regulated by phosphorylation of a 138 kD intermediate chain (IC138) of inner arm dynein f (also called I1). In the present study, we found that the axoneme of mutants lacking dynein f lacks a novel protein having ankyrin repeat motifs, registered as FAP120 in the flagellar proteome database. FAP120 is also missing or decreased in the axonemes of bop5, a mutant that has a mutation in the structural gene of IC138 but assembles the dynein f complex. Intriguingly, the amounts of FAP120 in the axonemes of different alleles of bop5 and several dynein f-lacking mutants roughly parallel their contents of IC138. These results suggest a weak but stoichiometric interaction between FAP120 and IC138. We propose that FAP120 functions in the regulatoryprocess as part of a protein complex involving IC138. Cell Motil. Cytoskeleton 2008. (c) 2008 Wiley-Liss, Inc.

MEIG1 is essential for spermiogenesis in mice

Spermatogenesis can be divided into three stages: spermatogonial mitosis, meiosis of spermatocytes, and spermiogenesis. During spermiogenesis, spermatids undergo dramatic morphological changes including formation of a flagellum and chromosomal packaging and condensation of the nucleus into the sperm head. The genes regulating the latter processes are largely unknown. We previously discovered that a bi-functional gene, Spag16, is essential for spermatogenesis. SPAG16S, the 35 kDa, testis-specific isoform derived from the Spag16 gene, was found to bind to meiosis expressed gene 1 product (MEIG1), a protein originally thought to play a role in meiosis. We inactivated the Meig1 gene and, unexpectedly, found that Meig1 mutant male mice had no obvious defect in meiosis, but were sterile as a result of impaired spermatogenesis at the stage of elongation and condensation. Transmission electron microscopy revealed that the manchette, a microtubular organelle essential for sperm head and flagellar formation was disrupted in spermatids of MEIG1-deficient mice. We also found that MEIG1 associates with the Parkin co-regulated gene (PACRG) protein, and that testicular PACRG protein is reduced in MEIG1-deficient mice. PACRG is thought to play a key role in assembly of the axonemes/flagella and the reproductive phenotype of Pacrg-deficient mice mirrors that of the Meig1 mutant mice. Our findings reveal a critical role for the MEIG1/PARCG partnership in manchette structure and function and the control of spermiogenesis.

Expression and localization of the Parkin co-regulated gene in mouse CNS suggests a role in ependymal cilia function

Parkin Co-Regulated Gene (PACRG) is a gene that shares a bi-directional promoter with the Parkinson's disease associated gene parkin. The functional role of PACRG is not well understood, although the gene has been associated with parkinsonian syndromes and more recently with eukaryotic cilia and flagella. We investigated the expression of Pacrg in the mouse brain by in situ hybridization and observed robust expression of Pacrg in the cells associated with the lateral, third and fourth ventricle, in addition to the aqueduct of Sylvius and choroid plexus. For all regions of Pacrg expression identified, strong expression was observed in the newborn period and this was maintained into adulthood. Immunohistochemical analysis showed that Pacrg was a component of the ependymal cells and cilia lining the ventricles. Based on our results and the previous association of PACRG homologues with cilia and flagella, we propose that Pacrg is a component of the ependymal cilia and may play an important role in motile cilia development and/or function in the CNS.

Flow on the right side of the gastrocoel roof plate is dispensable for symmetry breakage in the frog Xenopus laevis

Leftward flow of extracellular fluid breaks the bilateral symmetry of most vertebrate embryos, manifested by the ensuing asymmetric induction of Nodal signaling in the left lateral plate mesoderm (LPM). Flow is generated by rotational beating of polarized monocilia at the posterior notochord (PNC; mammals), Kupffer's vesicle (KV; teleost fish) and the gastrocoel roof plate (GRP; amphibians). To manipulate flow in a defined way we cloned dynein heavy chain genes dnah5, 9 and 11 in Xenopus. dnah9 expression was closely related to motile cilia from neurulation onwards. Morphant tadpoles showed impaired epidermal ciliary beating. Leftward flow at the GRP was absent, resulting in embryos with loss of asymmetric marker gene expression. Remarkably, unilateral knockdown on the right side of the GRP did not affect laterality, while left-sided ablation of flow abolished marker gene expression. Thus, flow was required exclusively on the left side of the GRP to break symmetry in the frog. Our data suggest that the substrate of flow is generated within the GRP and not at its margin, disqualifying Nodal as a candidate morphogen.

Molecular analysis of the PArkin co-regulated gene and association with male infertility

OBJECTIVE

To investigate the potential role of PArkin co-regulated gene (PACRG) in human male infertility.

DESIGN

Case-control study.

SETTING

Academic reproductive biology department.

PATIENT(S)

Blood samples were obtained from 610 patients and 156 normal control subjects.

INTERVENTION(S)

Genomic DNA was used as template for polymerase chain reaction amplification of the PACRG promoter and coding exons. The amplified fragments were tested for DNA sequence variations by direct sequencing and restriction enzyme analysis.

MAIN OUTCOME MEASURE(S)

Gene structure and sequence alterations of PACRG in infertile male patients.

RESULT(S)

The structure of PACRG was determined to comprise 5 coding exons, generating a single transcript in the testis which encoded a predicted protein of 257 amino acids. No pathogenic mutations were identified; however, a variant in the promoter of PACRG was shown to be significantly associated with azoospermia, but not oligospermia, in the case-control cohort.

CONCLUSION(S)

Mutation of PACRG was not identified as a cause of male infertility, but variation in the promoter was demonstrated to be a risk factor associated with azoospermia.

Molecular architecture of the centriole proteome: the conserved WD40 domain protein POC1 is required for centriole duplication and length control

Centrioles are intriguing cylindrical organelles composed of triplet microtubules. Proteomic data suggest that a large number of proteins besides tubulin are necessary for the formation and maintenance of a centriole's complex structure. Expansion of the preexisting centriole proteome from the green alga Chlamydomonas reinhardtii revealed additional human disease genes, emphasizing the significance of centrioles in normal human tissue homeostasis. We found that two classes of ciliary disease genes were highly represented among the basal body proteome: cystic kidney disease (especially nephronophthisis) syndromes, including Meckel/Joubert-like and oral-facial-digital syndrome, caused by mutations in CEP290, MKS1, OFD1, and AHI1/Jouberin proteins and cone-rod dystrophy syndrome genes, including UNC-119/HRG4, NPHP4, and RPGR1. We further characterized proteome of the centriole (POC) 1, a highly abundant WD40 domain-containing centriole protein. We found that POC1 is recruited to nascent procentrioles and localizes in a highly asymmetrical pattern in mature centrioles corresponding to sites of basal-body fiber attachment. Knockdown of POC1 in human cells caused a reduction in centriole duplication, whereas overexpression caused the appearance of elongated centriole-like structures. Together, these data suggest that POC1 is involved in early steps of centriole duplication as well as in the later steps of centriole length control.

Ciliary tubulin and its post-translational modifications

Tubulin, the most abundant axonemal protein, is extensively modified by several highly conserved post-translational mechanisms including acetylation, detyrosination, glutamylation, and glycylation. We discuss the pathways that contribute to the assembly and maintenance of axonemal microtubules, with emphasis on the potential functions of post-translational modifications that affect tubulin. The recent identification of a number of tubulin modifying enzymes and mutational studies of modification sites on tubulin have allowed for significant functional insights. Polymeric modifications of tubulin (glutamylation and glycylation) have emerged as important determinants of the 9 + 2 axoneme assembly and motility.