New insights into the cell biology of insect axonemes

Broad phosphorylation mediated by testis-specific serine/threonine kinases contributes to spermiogenesis and male fertility

Genetic studies elucidate a link between testis-specific serine/threonine kinases (TSSKs) and male infertility in mammals, but the underlying mechanisms are unclear. Here, we identify a TSSK homolog in Drosophila, CG14305 (termed dTSSK), whose mutation impairs the histone-to-protamine transition during spermiogenesis and causes multiple phenotypic defects in nuclear shaping, DNA condensation, and flagellar organization in spermatids. Genetic analysis demonstrates that kinase catalytic activity of dTSSK, which is functionally conserved with human TSSKs, is essential for male fertility. Phosphoproteomics identify 828 phosphopeptides/449 proteins as potential substrates of dTSSK enriched primarily in microtubule-based processes, flagellar organization and mobility, and spermatid differentiation and development, suggesting that dTSSK phosphorylates various proteins to orchestrate postmeiotic spermiogenesis. Among them, the two substrates, protamine-like protein Mst77F/Ser⁹ and transition protein Mst33A/Ser²³⁷, are biochemically validated to be phosphorylated by dTSSK in vitro, and are genetically demonstrated to be involved in spermiogenesis in vivo. Collectively, our findings demonstrate that broad phosphorylation mediated by TSSKs plays an indispensable role in spermiogenesis.

Three-dimensional flagella structures from animals' closest unicellular relatives, the Choanoflagellates

In most eukaryotic organisms, cilia and flagella perform a variety of life-sustaining roles related to environmental sensing and motility. Cryo-electron microscopy has provided considerable insight into the morphology and function of flagellar structures, but studies have been limited to less than a dozen of the millions of known eukaryotic species. Ultrastructural information is particularly lacking for unicellular organisms in the Opisthokonta clade, leaving a sizeable gap in our understanding of flagella evolution between unicellular species and multicellular metazoans (animals). Choanoflagellates are important aquatic heterotrophs, uniquely positioned within the opisthokonts as the metazoans' closest living unicellular relatives. We performed cryo-focused ion beam milling and cryo-electron tomography on flagella from the choanoflagellate species Salpingoeca rosetta. We show that the axonemal dyneins, radial spokes, and central pair complex in S. rosetta more closely resemble metazoan structures than those of unicellular organisms from other suprakingdoms. In addition, we describe unique features of S. rosetta flagella, including microtubule holes, microtubule inner proteins, and the flagellar vane: a fine, net-like extension that has been notoriously difficult to visualize using other methods. Furthermore, we report barb-like structures of unknown function on the extracellular surface of the flagellar membrane. Together, our findings provide new insights into choanoflagellate biology and flagella evolution between unicellular and multicellular opisthokonts.

A global [Formula: see text] gene co-expression network constructed from hundreds of experimental conditions with missing values

BACKGROUND

Gene co-expression networks (GCNs) can be used to determine gene regulation and attribute gene function to biological processes. Different high throughput technologies, including one and two-channel microarrays and RNA-sequencing, allow evaluating thousands of gene expression data simultaneously, but these methodologies provide results that cannot be directly compared. Thus, it is complex to analyze co-expression relations between genes, especially when there are missing values arising for experimental reasons. Networks are a helpful tool for studying gene co-expression, where nodes represent genes and edges represent co-expression of pairs of genes.

RESULTS

In this paper, we establish a method for constructing a gene co-expression network for the Anopheles gambiae transcriptome from 257 unique studies obtained with different methodologies and experimental designs. We introduce the sliding threshold approach to select node pairs with high Pearson correlation coefficients. The resulting network, which we name AgGCN1.0, is robust to random removal of conditions and has similar characteristics to small-world and scale-free networks. Analysis of network sub-graphs revealed that the core is largely comprised of genes that encode components of the mitochondrial respiratory chain and the ribosome, while different communities are enriched for genes involved in distinct biological processes.

CONCLUSION

Analysis of the network reveals that both the architecture of the core sub-network and the network communities are based on gene function, supporting the power of the proposed method for GCN construction. Application of network science methodology reveals that the overall network structure is driven to maximize the integration of essential cellular functions, possibly allowing the flexibility to add novel functions.

Tubulin glycylation controls axonemal dynein activity, flagellar beat, and male fertility

Posttranslational modifications of the microtubule cytoskeleton have emerged as key regulators of cellular functions, and their perturbations have been linked to a growing number of human pathologies. Tubulin glycylation modifies microtubules specifically in cilia and flagella, but its functional and mechanistic roles remain unclear. In this study, we generated a mouse model entirely lacking tubulin glycylation. Male mice were subfertile owing to aberrant beat patterns of their sperm flagella, which impeded the straight swimming of sperm cells. Using cryo-electron tomography, we showed that lack of glycylation caused abnormal conformations of the dynein arms within sperm axonemes, providing the structural basis for the observed dysfunction. Our findings reveal the importance of microtubule glycylation for controlled flagellar beating, directional sperm swimming, and male fertility.

Ciliary and cytoskeletal functions of an ancient monooxygenase essential for bioactive amidated peptide synthesis

Many secreted peptides used for cell-cell communication require conversion of a C-terminal glycine to an amide for bioactivity. This reaction is catalyzed only by the integral membrane protein peptidylglycine α-amidating monooxygenase (PAM). PAM has been highly conserved and is found throughout the metazoa; PAM-like sequences are also present in choanoflagellates, filastereans, unicellular and colonial chlorophyte green algae, dinoflagellates and haptophytes. Recent studies have revealed that in addition to playing a key role in peptidergic signaling, PAM also regulates ciliogenesis in vertebrates, planaria and chlorophyte algae, and is required for the stability of actin-based microvilli. Here we briefly introduce the basic principles involved in ciliogenesis, the sequential reactions catalyzed by PAM and the trafficking of PAM through the secretory and endocytic pathways. We then discuss the multi-faceted roles this enzyme plays in the formation and maintenance of cytoskeleton-based cellular protrusions and propose models for how PAM protein and amidating activity might contribute to ciliogenesis. Finally, we consider why some ciliated organisms lack PAM, and discuss the potential ramifications of ciliary localized PAM for the endocrine features commonly observed in patients with ciliopathies.

Honey bee predisposition of resistance to ubiquitous mite infestations

Host-parasite co-evolution history is lacking when parasites switch to novel hosts. This was the case for Western honey bees (Apis mellifera) when the ectoparasitic mite, Varroa destructor, switched hosts from Eastern honey bees (Apis cerana). This mite has since become the most severe biological threat to A. mellifera worldwide. However, some A. mellifera populations are known to survive infestations, largely by suppressing mite population growth. One known mechanism is suppressed mite reproduction (SMR), but the underlying genetics are poorly understood. Here, we take advantage of haploid drones, originating from one queen from the Netherlands that developed Varroa-resistance, whole exome sequencing and elastic-net regression to identify genetic variants associated with SMR in resistant honeybees. An eight variants model predicted 88% of the phenotypes correctly and identified six risk and two protective variants. Reproducing and non-reproducing mites could not be distinguished using DNA microsatellites, which is in agreement with the hypothesis that it is not the parasite but the host that adapted itself. Our results suggest that the brood pheromone-dependent mite oogenesis is disrupted in resistant hosts. The identified genetic markers have a considerable potential to contribute to a sustainable global apiculture.

Insights into Ciliary Genes and Evolution from Multi-Level Phylogenetic Profiling

Cilia (flagella) are important eukaryotic organelles, present in the Last Eukaryotic Common Ancestor, and are involved in cell motility and integration of extracellular signals. Ciliary dysfunction causes a class of genetic diseases, known as ciliopathies, however current knowledge of the underlying mechanisms is still limited and a better characterization of genes is needed. As cilia have been lost independently several times during evolution and they are subject to important functional variation between species, ciliary genes can be investigated through comparative genomics. We performed phylogenetic profiling by predicting orthologs of human protein-coding genes in 100 eukaryotic species. The analysis integrated three independent methods to predict a consensus set of 274 ciliary genes, including 87 new promising candidates. A fine-grained analysis of the phylogenetic profiles allowed a partitioning of ciliary genes into modules with distinct evolutionary histories and ciliary functions (assembly, movement, centriole, etc.) and thus propagation of potential annotations to previously undocumented genes. The cilia/basal body localization was experimentally confirmed for five of these previously unannotated proteins (LRRC23, LRRC34, TEX9, WDR27, and BIVM), validating the relevance of our approach. Furthermore, our multi-level analysis sheds light on the core gene sets retained in gamete-only flagellates or Ecdysozoa for instance. By combining gene-centric and species-oriented analyses, this work reveals new ciliary and ciliopathy gene candidates and provides clues about the evolution of ciliary processes in the eukaryotic domain. Additionally, the positive and negative reference gene sets and the phylogenetic profile of human genes constructed during this study can be exploited in future work.

Cilia - The sensory antennae in the eye

Cilia are hair-like projections found on almost all cells in the human body. Originally believed to function merely in motility, the function of solitary non-motile (primary) cilia was long overlooked. Recent research has demonstrated that primary cilia function as signalling hubs that sense environmental cues and are pivotal for organ development and function, tissue hoemoestasis, and maintenance of human health. Cilia share a common anatomy and their diverse functional features are achieved by evolutionarily conserved functional modules, organized into sub-compartments. Defects in these functional modules are responsible for a rapidly growing list of human diseases collectively termed ciliopathies. Ocular pathogenesis is common in virtually all classes of syndromic ciliopathies, and disruptions in cilia genes have been found to be causative in a growing number of non-syndromic retinal dystrophies. This review will address what is currently known about cilia contribution to visual function. We will focus on the molecular and cellular functions of ciliary proteins and their role in the photoreceptor sensory cilia and their visual phenotypes. We also highlight other ciliated cell types in tissues of the eye (e.g. lens, RPE and Müller glia cells) discussing their possible contribution to disease progression. Progress in basic research on the cilia function in the eye is paving the way for therapeutic options for retinal ciliopathies. In the final section we describe the latest advancements in gene therapy, read-through of non-sense mutations and stem cell therapy, all being adopted to treat cilia dysfunction in the retina.

Exploring the evolutionary history of centrosomes

The centrosome is the main organizer of the microtubule cytoskeleton in animals, higher fungi and several other eukaryotic lineages. Centrosomes are usually located at the centre of cell in tight association with the nuclear envelope and duplicate at each cell cycle. Despite a great structural diversity between the different types of centrosomes, they are functionally equivalent and share at least some of their molecular components. In this paper, we explore the evolutionary origin of the different centrosomes, in an attempt to understand whether they are derived from an ancestral centrosome or evolved independently from the motile apparatus of distinct flagellated ancestors. We then discuss the evolution of centrosome structure and function within the animal lineage.

Overview on spermatogenesis and sperm structure of Hexapoda

The main characteristics of the sperm structure of Hexapoda are reported in the review. Data are dealing with the process of spermatogenesis, including the aberrant models giving rise to a reduced number of sperm cells. The sperm heteromorphism and the giant sperm exceeding the usual sperm size for length and width are considered. The characteristics of several components of a typical insect sperm are described: the plasma membrane and its glycocalyx, the nucleus, the centriole region and the centriole adjunct, the accessory bodies, the mitochondrial derivatives and the flagellar axoneme. Finally, a detailed description of the main sperm features of each hexapodan group is given with emphasis on the flagellar components considered to have great importance in phylogenetic considerations. This study may be also useful to those requiring an introduction to hexapod reproduction.

Ultrastructure of the sperm axoneme and molecular analysis of axonemal dynein in Ephemeroptera (Insecta)

The Ephemeroptera sperm axoneme is devoid of outer dynein arms (ODA) and exhibits a pronounced modification of the central pair complex (CPC), which is substituted by the central sheath (CS): a tubular element of unknown molecular composition. We performed a detailed ultrastructural analysis of sperm axonemes in the genera Cloeon and Ecdyonurus using quick-freeze, deep-etch electron microscopy, showing that the loss of the conventional CPC is not only concomitant with the loss of ODA, but also with a substantial modification in the longitudinal distribution of both radial spokes (RS) and inner dynein arms (IDA). Such structures are no longer distributed following the alternation of different repeats as in the 9 + 2 axoneme, but instead share a 32 nm longitudinal repeat: a multiple of the 8 nm repeat observed along the CS wall. Differently from the conventional CPC, the CS and the surrounding RS possess a ninefold symmetry, coherently with the three-dimensional pattern of motility observed in Cloeon free spermatozoa. Biochemical analyses revealed that ultrastructural modifications are concomitant with a reduced complexity of the IDA heavy chain complement. We propose that these structural and molecular modifications might be related to the relief from the evolutionary constraints imposed by the CPC on the basal 9 + 9 + 2 axoneme and could also represent the minimal set compatible with flagellar beating and progressive motility mechanically regulated as suggested by the geometric clutch hypothesis. © 2014 Wiley Periodicals, Inc.

Gene duplication, tissue-specific gene expression and sexual conflict in stalk-eyed flies (Diopsidae)

Gene duplication provides an essential source of novel genetic material to facilitate rapid morphological evolution. Traits involved in reproduction and sexual dimorphism represent some of the fastest evolving traits in nature, and gene duplication is intricately involved in the origin and evolution of these traits. Here, we review genomic research on stalk-eyed flies (Diopsidae) that has been used to examine the extent of gene duplication and its role in the genetic architecture of sexual dimorphism. Stalk-eyed flies are remarkable because of the elongation of the head into long stalks, with the eyes and antenna laterally displaced at the ends of these stalks. Many species are strongly sexually dimorphic for eyespan, and these flies have become a model system for studying sexual selection. Using both expressed sequence tag and next-generation sequencing, we have established an extensive database of gene expression in the developing eye-antennal imaginal disc, the adult head and testes. Duplicated genes exhibit narrower expression patterns than non-duplicated genes, and the testes, in particular, provide an abundant source of gene duplication. Within somatic tissue, duplicated genes are more likely to be differentially expressed between the sexes, suggesting gene duplication may provide a mechanism for resolving sexual conflict.

Drosophila spermiogenesis: Big things come from little packages

Drosophila melanogaster spermatids undergo dramatic morphological changes as they differentiate from small round cells approximately 12 μm in diameter into highly polarized, 1.8 mm long, motile sperm capable of participating in fertilization. During spermiogenesis, syncytial cysts of 64 haploid spermatids undergo synchronous differentiation. Numerous changes occur at a subcellular level, including remodeling of existing organelles (mitochondria, nuclei), formation of new organelles (flagellar axonemes, acrosomes), polarization of elongating cysts and plasma membrane addition. At the end of spermatid morphogenesis, organelles, mitochondrial DNA and cytoplasmic components not needed in mature sperm are stripped away in a caspase-dependent process called individualization that results in formation of individual sperm. Here, we review the stages of Drosophila spermiogenesis and examine our current understanding of the cellular and molecular mechanisms involved in shaping male germ cell-specific organelles and forming mature, fertile sperm.

X-ray diffraction recording from single axonemes of eukaryotic flagella

We report the first X-ray diffraction patterns recorded from single axonemes of eukaryotic flagella with a diameter of only <0.2 μm, by using the technique of cryomicrodiffraction. A spermatozoon isolated from the testis of a fruit fly, Drosophila melanogaster, either intact or demembranated, was mounted straight in a glass capillary, quickly frozen and its 800-μm segment was irradiated end-on with intense synchrotron radiation X-ray microbeams (diameter, ~2 μm) at 74 K. Well-defined diffraction patterns were recorded, consisting of a large number of isolated reflection spots, extending up to 1/5 nm(-1). These reflections showed a tendency to peak every 20°, i.e., the patterns had features of an 18-fold rotational symmetry as expected from the 9-fold rotational symmetry of axonemal structure. This means that the axonemes remain untwisted, even after the manual mounting procedure. The diffraction patterns were compared with the results of model calculations based on a published electron micrograph of the Drosophila axoneme. The comparison provided information about the native state of axoneme, including estimates of axonemal diameter, interdoublet spacing, and masses of axonemal components relative to those of microtubules (e.g., radial spokes, dynein arms, and proteins associated with accessory singlet microtubules). When combined with the genetic resource of Drosophila, the technique presented here will serve as a powerful tool for studying the structure-function relationship of eukaryotic flagella in general.

[The rebirth of the ultrastructure of cilia and flagella]

The sensory and motility functions of eukaryotic cilia and flagella are essential for cell survival in protozoans and for cell differentiation and homoeostasis in metazoans. Ciliary biology has benefited early on from the input of electron microscopy. Over the last decade, the visualization of cellular structures has greatly progressed, thus it becomes timely to review the ultrastructure of cilia and flagella. Briefly touching upon the typical features of a 9+2 axoneme, we dwell extensively on the transition zone, the singlet zone, the ciliary necklace, cap and crown. The relation of the singlet zone to sensory and/or motile function, the link of the ciliary cap to microtubule dynamics and to ciliary beat, the involvement of the ciliary crown in ovocyte and mucosal propulsion, and the role of the transition zone/the ciliary necklace in axonemal stabilization, autotomy and as a diffusion barrier will all be discussed.

Drosophila Dynein intermediate chain gene, Dic61B, is required for spermatogenesis

This study reports the identification and characterization of a novel gene, Dic61B, required for male fertility in Drosophila. Complementation mapping of a novel male sterile mutation, ms21, isolated in our lab revealed it to be allelic to CG7051 at 61B1 cytogenetic region, since two piggyBac insertion alleles, CG7051(c05439) and CG7051(f07138) failed to complement. CG7051 putatively encodes a Dynein intermediate chain. All three mutants, ms21, CG7051(c05439) and CG7051(f07138), exhibited absolute recessive male sterility with abnormally coiled sperm axonemes causing faulty sperm individualization as revealed by Phalloidin staining in Don Juan-GFP background. Sequencing of PCR amplicons uncovered two point mutations in ms21 allele and confirmed the piggyBac insertions in CG7051(c05439) and CG7051(f07138) alleles to be in 5'UTR and 4(th) exon of CG7051 respectively, excision of which reverted the male sterility. In situ hybridization to polytene chromosomes demonstrated CG7051 to be a single copy gene. RT-PCR of testis RNA revealed defective splicing of the CG7051 transcripts in mutants. Interestingly, expression of cytoplasmic dynein intermediate chain, α, β, γ tubulins and α-spectrin was normal in mutants while ultra structural studies revealed defects in the assembly of sperm axonemes. Bioinformatics further highlighted the homology of CG7051 to axonemal dynein intermediate chain of various organisms, including DNAI1 of humans, mutations in which lead to male sterility due to immotile sperms. Based on these observations we conclude that CG7051 encodes a novel axonemal dynein intermediate chain essential for male fertility in Drosophila and rename it as Dic61B. This is the first axonemal Dic gene of Drosophila to be characterized at molecular level and shown to be required for spermatogenesis.

The male reproductive system of Zorotypus caudelli Karny (Zoraptera): Sperm structure and spermiogenesis

Considering the overall uniformity of the morphology of Zoraptera, the structural diversity of the male genital system is remarkable. Structures related to the male reproductive system of Zorotypus caudelli differ profoundly from those of Zorotypus hubbardi. The testes are elongated rather than spherical, the seminal vesicle is apparently absent, and the deferent ducts are very long. A feature shared by these two species and other zorapterans examined is that the two accessory glands are closely adherent to each other and form a single large structure, from which the ejaculatory duct originates. This is a potential zorapteran autapomorphy. Another feature possibly present in the groundplan of the order is the strong elongation of the sperm cells. This may be connected with a reproductive strategy of males trying to avoid re-mating of females with other males after the first copulation. The extremely long and coiled spermathecal duct of Z. caudelli and other zorapteran species is possibly correlated with the sperm elongation, and both features combined may result in a sexual isolating mechanism. The short duration of mating of Zorotypus barberi and Zorotypus gurneyi suggests that the male introduces sperm into the female tract up to the opening of the spermathecal duct using their long coiled aedeagus. A thick glycocalyx around the sperm in the distal part of the deferent ducts probably protects the sperm cells during their forward progression towards the long spermathecal duct, and is removed when they reach the apical receptacle. The spermatogenesis of Z. caudelli follows a pattern commonly found in insects, but differs distinctly from that of Z. hubbardi in the number of spermatids in each sperm cyst. An unusual and possibly autapomorphic feature of Z. caudelli is a disconnection of sub-tubules A and B at the level of microtubule doublets 1 and 6 of the mature sperm cells. It is conceivable that this results in a shorter period of sperm motility. The character combination found in different zorapteran species supports the view that the sperm, a very compact functional unit, does not evolve as a unit, but like in other more complex body regions, sperm components can also be modified independently from each other. This results in different mosaic patterns of plesiomorphic and derived features in a very compact entity in different species of the very small and otherwise uniform order Zoraptera. In Z. caudelli, for instance, the bi-layered acrosome and small accessory bodies are plesiomorphic states among several others, whereas the mitochondrial derivatives and the elongate nucleus are apparently derived conditions. Other combinations likely occur in other zorapteran species. Only few but noteworthy sperm characters indicate possible phylogenetic affinities of Zoraptera. A possible synapomorphic feature, the presence of dense laminae radiating in a cartwheel array between neighbouring centriolar triplets, is shared with Phasmatodea and Embioptera. Another potential synapomorphy shared with Phasmatodea is the presence of 17 protofilaments in the tubular wall of the outer accessory microtubules.

Ultrastructure of cilia and flagella - back to the future!

Eukaryotic cilia and flagella perform motility and sensory functions which are essential for cell survival in protozoans, and to organism development and homoeostasis in metazoans. Their ultrastructure has been studied from the early beginnings of electron microscopy, and these studies continue to contribute to much of our understanding about ciliary biology. In the light of the progress made in the visualization of cellular structures over the last decade, we revisit the ultrastructure of cilia and flagella. We briefly describe the typical features of a 9+2 axoneme before focusing extensively on the transition zone, the ciliary necklace, the singlet zone, the ciliary cap and the ciliary crown. We discuss how the singlet zone is linked to sensory and/or motile function, the contribution of the ciliary crown to ovocyte and mucosal propulsion, and the relationship between the ciliary cap and microtubule growth and shortening, and its relation to ciliary beat. We further examine the involvement of the transition zone/the ciliary necklace in axonemal stabilization, autotomy and as a diffusion barrier.

Flagellar kinesins in protists

Cilia and flagella are organelles of the cell body present in many eukaryotic cells. Although their basic structure is well conserved from unicellular organisms to mammals, they show amazing diversity in number, structure, molecular composition, disposition and function. These complex organelles are generally assembled by the action of intraflagellar transport, which is powered by kinesin and dynein motor proteins. Several types of kinesins can function in flagella. They all have a well-conserved motor domain with characteristic signatures, but display exhaustive diversification of some domains. This diversity can be explained by the multitude of functions fulfilled by these proteins (transport of cargoes along microtubules, polymerization and depolymerization of microtubules). Functional and phylogenetic analyses reveal that at least seven kinesin families are involved in flagellum assembly and function. In protists, where cilia and flagella fulfill many essential roles, this diversity of function is also observed.

Ultrastructure of spermatozoa of Onthophagus taurus (Coleoptera, Scarabaeidae) exhibits heritable variation

Sperm competition is thought to be an important selective pressure shaping sperm form and function. However, few studies have moved beyond gross examinations of sperm morphology. Sperm length is subject to sexual selection via sperm competition in the scarab beetle Onthophagus taurus. Here, the structure and ultrastructure of spermatozoa in this species were investigated using light and electron microscopy. Spermatozoa were found to be filiform, measuring about 1,200 mm in length. The sperm head consists of a three-layered acrosome and a nuclear region bearing the anterior extension of the centriole adjunct. Acrosome and nuclear regions are bilaterally symmetric, with their axes of symmetry being orthogonal to each other. Head and flagellar structures are connected by a well-developed centriole adjunct. The sperm heads are asymmetrically surrounded by accessory material and embedded into the cytoplasm of the spermatocyst cell. The accessory material is produced inside the spermatids and then transferred to the outside due to a new membrane formed around the sperm's organelles. The old spermatid membrane separates the accessory material from the cyst cell. The flagellum contains a 9+9+2 axoneme, two accessory bodies, and two mitochondrial derivatives of unequal size. The major mitochondrial derivative is significantly larger than the minor one. The axoneme is arranged in a sinusoidal manner parallel along the major mitochondrial derivative. The spermatozoa show no progressive motility when released in buffer solution which is likely to be the result of the flagellar arrangement and the structure of the major mitochondrial derivative. The cross-sectional area of the minor and the major mitochondrial derivatives show different patterns of genetic variation. The data provide the first estimates of genetic variation in sperm ultrastructure for any species, and give evidence for the persistence of genetic variation in ultrastructure required for the rapid and divergent evolution that characterizes spermatozoa generally.

Transcriptional control of genes involved in ciliogenesis: a first step in making cilia

Cilia and flagella have essential functions in a wide range of organisms. Cilia assembly is dynamic during development and different types of cilia are found in multicellular organisms. How this dynamic and specific assembly is regulated remains an important question in cilia biology. In metazoans, the regulation of the overall expression level of key components necessary for cilia assembly or function is an important way to achieve ciliogenesis control. The FOXJ1 (forkhead box J1) and RFX (regulatory factor X) family of transcription factors have been shown to be important players in controlling ciliary gene expression. They fulfill a complementary and synergistic function by regulating specific and common target genes. FOXJ1 is essential to allow for the assembly of motile cilia in vertebrates through the regulation of genes specific to motile cilia or necessary for basal body apical transport, whereas RFX proteins are necessary to assemble both primary and motile cilia in metazoans, in particular, by regulating genes involved in intraflagellar transport. Recently, different transcription factors playing specific roles in cilia biogenesis and physiology have also been discovered. All these factors are subject to complex regulation to allow for the dynamic and specific regulation of ciliogenesis in metazoans.

Centrioles: active players or passengers during mitosis?

Centrioles are cylinders made of nine microtubule (MT) triplets present in many eukaryotes. Early studies, where centrosomes were seen at the poles of the mitotic spindle led to their coining as "the organ for cell division". However, a variety of subsequent observational and functional studies showed that centrosomes might not always be essential for mitosis. Here we review the arguments in this debate. We describe the centriole structure and its distribution in the eukaryotic tree of life and clarify its role in the organization of the centrosome and cilia, with an historical perspective. An important aspect of the debate addressed in this review is how centrioles are inherited and the role of the spindle in this process. In particular, germline inheritance of centrosomes, such as their de novo formation in parthenogenetic species, poses many interesting questions. We finish by discussing the most likely functions of centrioles and laying out new research avenues.

Sperm ultrastructure and spermiogenesis of Coniopterygidae (Neuroptera, Insecta)

The spermiogenesis and the sperm ultrastructure of several species of Coniopterygidae have been examined. The spermatozoa consist of a three-layered acrosome, an elongated elliptical nucleus, a long flagellum provided with a 9+9+3 axoneme and two mitochondrial derivatives. No accessory bodies were observed. The axoneme exhibits accessory microtubules provided with 13, rather than 16, protofilaments in their tubular wall; the intertubular material is reduced and distributed differently from that observed in other Neuropterida. Sperm axoneme organization supports the isolated position of the family previously proposed on the basis of morphological data.