EST analysis of gene expression in testis of the ascidian Ciona intestinalis

The Role of Soluble Adenylyl Cyclase in the Regulation of Flagellar Motility in Ascidian Sperm

Flagellar motility in sperm is activated and regulated by factors related to the eggs at fertilization. In the ascidian Ciona intestinalis, a sulfated steroid called the SAAF (sperm activating and attracting factor) induces both sperm motility activation and chemotaxis. Cyclic AMP (cAMP) is one of the most important intracellular factors in the sperm signaling pathway. Adenylyl cyclase (AC) is the key enzyme that synthesizes cAMP at the onset of the signaling pathway in all cellular functions. We previously reported that both transmembrane AC (tmAC) and soluble AC (sAC) play important roles in sperm motility in Ciona. The tmAC plays a major role in the SAAF-induced activation of sperm motility. On the other hand, sAC is involved in the regulation of flagellar beat frequency and the Ca2+-dependent chemotactic movement of sperm. In this study, we focused on the role of sAC in the regulation of flagellar motility in Ciona sperm chemotaxis. The immunochemical analysis revealed that several isoforms of sAC protein were expressed in Ciona sperm, as reported in mammals and sea urchins. We demonstrated that sAC inhibition caused strong and transient asymmetrization during the chemotactic turn, and then sperm failed to turn toward the SAAF. In addition, real-time Ca2+ imaging in sperm flagella revealed that sAC inhibition induced an excessive and prolonged Ca2+ influx to flagella. These results indicate that sAC plays a key role in sperm chemotaxis by regulating the clearance of [Ca2+]i and by modulating Ca2+-dependent flagellar waveform conversion.

Single-Cell RNA Sequencing of the Testis of Ciona intestinalis Reveals the Dynamic Transcriptional Profile of Spermatogenesis in Protochordates

Spermatogenesis is a complex and continuous process of germ-cell differentiation. This complex process is regulated by many factors, of which gene regulation in spermatogenic cells plays a decisive role. Spermatogenesis has been widely studied in vertebrates, but little is known about spermatogenesis in protochordates. Here, for the first time, we performed single-cell RNA sequencing (scRNA-seq) on 6832 germ cells from the testis of adult Ciona intestinalis. We identified six germ cell populations and revealed dynamic gene expression as well as transcriptional regulation during spermatogenesis. In particular, we identified four spermatocyte subtypes and key genes involved in meiosis in C. intestinalis. There were remarkable similarities and differences in gene expression during spermatogenesis between C. intestinalis and two other vertebrates (Chinese tongue sole and human). We identified many spermatogenic-cell-specific genes with functions that need to be verified. These findings will help to further improve research on spermatogenesis in chordates.

Spef1/CLAMP binds microtubules and actin-based structures and regulates cell migration and epithelia cell polarity

During migration, cells invade, repair, and create barriers leading to the formation of new cellular contacts in target tissues. Cell migration requires many proteins that collectively form the cytoskeleton. The main cytoskeletal elements are actin filaments, microtubules (MTs), and intermediate filaments. These structures work in concert with a large number of accessory proteins that contribute in a variety of ways to regulate filament assembly and turnover, to alter the configuration or arrangement of filaments by bundling or crosslinking, to link the cytoskeleton to other structures in the cell, such as membranes and junctions, and to transport cargo along the filaments. Sperm flagella protein-1 (Spef1), also designated calponin homology and microtubules-associated protein (CLAMP), is a multifunctional protein that interacts with cytoskeletal structures, including MTs, actin filaments, and focal adhesions in epithelia. In this review, we outline Spef1/CLAMP structure and expression in several cellular models. The function of Spef1/CLAMP in flagellar and ciliary motility, MT-binding and stability, regulation of planar cell polarity, and potential contribution to the maintenance of actin-based structures, such as lamellipodia and filopodia during cell migration, are also discussed.

The Roles of Two CNG Channels in the Regulation of Ascidian Sperm Chemotaxis

Spermatozoa sense and respond to their environmental signals to ensure fertilization success. Reception and transduction of signals are reflected rapidly in sperm flagellar waveforms and swimming behavior. In the ascidian Ciona intestinalis (type A; also called C. robusta), an egg-derived sulfated steroid called SAAF (sperm activating and attracting factor), induces both sperm motility activation and chemotaxis. Two types of CNG (cyclic nucleotide-gated) channels, Ci-tetra KCNG (tetrameric, cyclic nucleotide-gated, K⁺-selective) and Ci-HCN (hyperpolarization-activated and cyclic nucleotide-gated), are highly expressed in Ciona testis from the comprehensive gene expression analysis. To elucidate the sperm signaling pathway to regulate flagellar motility, we focus on the role of CNG channels. In this study, the immunochemical analysis revealed that both CNG channels are expressed in Ciona sperm and localized to sperm flagella. Sperm motility analysis and Ca²⁺ imaging during chemotaxis showed that CNG channel inhibition affected the changes in flagellar waveforms and Ca²⁺ efflux needed for the chemotactic turn. These results suggest that CNG channels in Ciona sperm play a vital role in regulating sperm motility and intracellular Ca²⁺ regulation during chemotaxis.

Branchial cilia and sperm flagella recruit distinct axonemal components

Eukaryotic cilia and flagella have highly conserved 9 + 2 structures. They are functionally diverged to play cell-type-specific roles even in a multicellular organism. Although their structural components are therefore believed to be common, few studies have investigated the molecular diversity of the protein components of the cilia and flagella in a single organism. Here we carried out a proteomic analysis and compared protein components between branchial cilia and sperm flagella in a marine invertebrate chordate, Ciona intestinalis. Distinct feature of protein recruitment in branchial cilia and sperm flagella has been clarified; (1) Isoforms of α- and β-tubulins as well as those of actins are distinctly used in branchial cilia or sperm flagella. (2) Structural components, such as dynein docking complex, tektins and an outer dense fiber protein, are used differently by the cilia and flagella. (3) Sperm flagella are specialized for the cAMP- and Ca2+-dependent regulation of outer arm dynein and for energy metabolism by glycolytic enzymes. Our present study clearly demonstrates that flagellar or ciliary proteins are properly recruited according to their function and stability, despite their apparent structural resemblance and conservation.

Reproductive protein evolution in two cryptic species of marine chordate

Background

Reproductive character displacement (RCD) is a common and taxonomically widespread pattern. In marine broadcast spawning organisms, behavioral and mechanical isolation are absent and prezygotic barriers between species often operate only during the fertilization process. Such barriers are usually a consequence of differences in the way in which sperm and egg proteins interact, so RCD can be manifest as faster evolution of these proteins between species in sympatry than allopatry. Rapid evolution of these proteins often appears to be a consequence of positive (directional) selection. Here, we identify a set of candidate gamete recognition proteins (GRPs) in the ascidian Ciona intestinalis and showed that these GRPs evolve more rapidly than control proteins (those not involved in gamete recognition). Choosing a subset of these gamete recognition proteins that show evidence of positive selection (CIPRO37.40.1, CIPRO60.5.1, CIPRO100.7.1), we then directly test the RCD hypothesis by comparing divergence (omega) and polymorphism (McDonald-Kreitman, Tajima's D, Fu and Li's D and F, Fay and Wu's H) statistics in sympatric and allopatric populations of two distinct forms of C. intestinalis (Types A and B) between which there are strong post-zygotic barriers.

Results

Candidate gamete recognition proteins from two lineages of C. intestinalis (Type A and B) are evolving more rapidly than control proteins, consistent with patterns seen in insects and mammals. However, ω (d_N/d_S) is not significantly different between the sympatric and allopatric populations, and none of the polymorphism statistics show significant differences between sympatric and allopatric populations.

Conclusions

Enhanced prezygotic isolation in sympatry has become a well-known feature of gamete recognition proteins in marine broadcast spawners. But in most cases the evolutionary process or processes responsible for this pattern have not been identified. Although gamete recognition proteins in C. intestinalis do appear to evolve more rapidly, on average, than proteins with other functions, rates of evolution are not different in allopatric and sympatric populations of the two reproductively isolated forms. That sympatry is probably human-mediated, and therefore recent, may explain the absence of RCD.

Cell type and function of neurons in the ascidian nervous system

Ascidians, or sea squirts, are primitive chordates, and their tadpole larvae share a basic body plan with vertebrates, including a notochord and a dorsal tubular central nervous system (CNS). The CNS of the ascidian larva is formed through a process similar to vertebrate neurulation, while the ascidian CNS is remarkably simple, consisting of about 100 neurons. Recent identification of genes that are specifically expressed in a particular subtype of neurons has enabled us to reveal neuronal networks at single-cell resolution. Based on the information on neuron subtype-specific genes, different populations of neurons have been visualized by whole-mount in situ hybridization, immunohistochemical staining using specific antibodies, and fluorescence labeling of cell bodies and neurites by a fluorescence protein reporter driven by neuron-specific promoters. Neuronal populations that have been successfully visualized include glutamatergic, cholinergic, gamma-aminobutyric acid/glycinergic, and dopaminergic neurons, which have allowed us to propose functional regionalization of the CNS and a neural circuit for locomotion. Thus, the simple nervous system of the ascidian larva can serve as an attractive model system for studying the development, function, and evolution of the chordate nervous system.

A novel, single, transmembrane protein CATSPERG is associated with CATSPER1 channel protein

All four CATSPER channel pore-forming subunits (CATSPER1-4) are localized in the sperm principal piece. They form an alkalization-activated Ca2+-permeable channel and are required for sperm-hyperactivated motility, egg coat penetration, and male fertility. Unlike many other ion channels, the composition of the CATSPER protein complex is poorly defined. Herein, we describe the novel protein CATSPERG associated with the CATSPER complex. CATSPERG is predicted to be a single transmembrane-spanning protein with a large extracellular domain and a short intracellular tail. Like all the CATSPERs and the previously identified CATSPER-associated protein CATSPERB, CATSPERG is only expressed in testis and is localized in the sperm principal piece. In CATSPER1-deficient sperm, the CATSPERG protein (but not the K+ channel protein KCNU1) is also lost. Together with previous findings, our data suggest that the CATSPER protein complex contains pore-forming proteins and two additional proteins (CATSPERB and CATSPERG) and that the trafficking and/or assembly of these proteins depends on CATSPER1.

Identification of guanylate cyclases and related signaling proteins in sperm tail from sea stars by mass spectrometry

Marine invertebrates employ external fertilization to take the advantages of sexual reproduction as one of excellent survival strategies. To prevent mismatching, successful fertilization can be made only after going though strictly defined steps in the fertilization. In sea stars, the fertilization process starts with the chemotaxis of sperm followed by hyperactivation of sperm upon arriving onto the egg coat, and then sperm penetrate to the egg coat before achieving the fusion. To investigate whether the initiation of chemotaxis and the following signaling has species specificity, we conducted comparative studies in the protein level among sea stars, Asterias amurensis, A. forbesi, and Asterina pectinifera. Since transcription of messenger ribonucleic acid (mRNA) has been suppressed in gamete, the roles of sperm proteins during the fertilization cannot be investigated by examining the mRNA profile. Therefore, proteomics analysis by mass spectrometry was used in this study. In sea stars, upon receiving asteroidal sperm-activating peptide (asterosap), the receptor membrane-bound guanylate cyclases in the sperm tail trigger sperm chemotaxis. We confirmed the presence of membrane-bound guanylate cyclases in the three sea star species, and they all had the same structural domains including the extracellular domain, kinase-like domain, and guanylate cyclase domain. The majority of peptides recovered were from alpha-helices distributed on the solvent side of the protein. More peptides were recovered from the intracellular domains. The transmembrane domain has not been recovered. The functions of the receptors seemed to be conserved among the species. Furthermore, we identified proteins that may be involved in the guanylate cyclase-triggered signaling pathway.

Mechanism of self-sterility in a hermaphroditic chordate

Hermaphroditic organisms avoid inbreeding by a system of self-incompatibility (SI). A primitive chordate (ascidian) Ciona intestinalis is an example of such an organism, but the molecular mechanism underlying its SI system is not known. Here, we show that the SI system is governed by two gene loci that act cooperatively. Each locus contains a tightly linked pair of polycystin 1-related receptor (s-Themis) and fibrinogen-like ligand (v-Themis) genes, the latter of which is located in the first intron of s-Themis but transcribed in the opposite direction. These genes may encode male- and female-side self-recognition molecules. The SI system of C. intestinalis has a similar framework to that of flowering plants but utilizing different molecules.

The UHRF family: Oncogenes that are drugable targets for cancer therapy in the near future?

In this paper, we review the current literature about the UHRF family that in particular includes the UHRF1 and UHRF2 genes. Its members play a fundamental role in cell proliferation through different structural domains. These domains include a ubiquitin-like domain (NIRF_N), a plant homeodomain (PHD) domain, a SRA domain and a RING domain. The SRA domain has only been observed in this family probably conferring unique properties to it. The unique enzymatic activity so far identified in this family involves the RING finger that contains a ubiquitin E3 ligase activity toward, for instance, histones. The physiological roles played by the UHRF family are most likely exerted during embryogenic development and when proliferation is required in adults. Interestingly, UHRF members are putative oncogenes regulated by tumor suppressor genes, but they exert also a feedback control on these latter. Finally, we propose some new roles for this family, including regulation and/or inheritance of the epigenetic code. Alteration of these regulatory mechanisms, such as those occurring in cancer cells, may be involved in carcinogenesis. The reasons why the UHRF family could be an interesting target for developing anticancer drugs is also developed.

CatSperbeta, a novel transmembrane protein in the CatSper channel complex

Four CatSper ion channel subunit genes (CatSpers 1-4) are required for sperm cell hyperactivation and male fertility. The four proteins assemble (presumably as a tetramer) to form a sperm-specific, alkalinization-activated Ca(2+)-selective channel. We set out to identify proteins associating with CatSper that might help explain its unique role in spermatozoa. Using a transgenic approach, a CatSper1 complex was purified from mouse testis that contained heat shock protein 70-2, a testis-specific chaperone, and CatSperbeta, a novel protein with two putative transmembrane-spanning domains. Like the CatSper ion channel subunits, CatSperbeta was restricted to testis and localized to the principal piece of the sperm tail. CatSperbeta protein is absent in CatSper1(-/-) sperm, suggesting that it is required for trafficking or formation of a stable channel complex. CatSperbeta is the first identified auxiliary protein to the CatSper channel.

Functional proteomics inCiona intestinalis: A breakthrough in the exploration of the molecular and cellular mechanism of ascidian development

Ascidians have been providing a unique experimental system for a variety of fields, including reproductive biology, developmental biology, neurobiology, immunology, and evolutional biology. Recent progress in the genome sequencing of Ciona intestinalis has led to the development of a great tool for investigating the gene functions and expressions involved in several biological events in ascidians. The disclosure of genomic information has ushered in the postgenomic era, spearheaded by extensive protein analysis. The characterization of the function, localization, and molecular interaction of cellular proteins results in a more direct description of the molecular mechanism underlying several biological processes. Proteomics in ascidians, however, has just recently appeared and is not well established yet. In this study, we give an outline of the technical processes used in proteomics and review the recent status of ascidian proteomics.

Ciona intestinalis as an emerging model organism: its regeneration under controlled conditions and methodology for egg dechorionation

The ascidian Ciona intestinalis is a model organism of developmental and evolutionary biology and may provide crucial clues concerning two fundamental matters, namely, how chordates originated from the putative deuterostome ancestor and how advanced chordates originated from the simplest chordates. In this paper, a whole-life-span culture of C. intestinalis was conducted. Fed with the diet combination of dry Spirulina, egg yolk, Dicrateria sp., edible yeast and weaning diet for shrimp, C. intestinalis grew up to average 59 mm and matured after 60 d cultivation. This culture process could be repeated using the artificially cultured mature ascidians as material. When the fertilized eggs were maintained under 10, 15, 20, 25 degrees C, they hatched within 30 h, 22 h, 16 h and 12 h 50 min respectively experiencing cleavage, blastulation, gastrulation, neurulation, tailbud stage and tadpole stage. The tadpole larvae were characterized as typical but simplified chordates because of their dorsal nerve cord, notochord and primordial brain. After 8 - 24 h freely swimming, the tadpole larvae settled on the substrates and metamorphosized within 1- 2 d into filter feeding sessile juvenile ascidians. In addition, unfertilized eggs were successfully dechorionated in filtered seawater containing 1% Tripsin, 0.25% EDTA at pH of 10.5 within 40 min. After fertilization, the dechorionated eggs developed well and hatched at normal hatching rate. In conclusion, this paper presented feasible methodology for rearing the tadpole larvae of C. intestinalis into sexual maturity under controlled conditions and detailed observations on the embryogenesis of the laboratory cultured ascidians, which will facilitate developmental and genetic research using this model system.

Molecular characterization ofCiona sperm outer arm dynein reveals multiple components related to outer arm docking complex protein 2

Using proteomic and immunochemical techniques, we have identified the light and intermediate chains (IC) of outer arm dynein from sperm axonemes of the ascidian Ciona intestinalis. Ciona outer arm dynein contains six light chains (LC) including a leucine-rich repeat protein, Tctex1- and Tctex2-related proteins, a protein similar to Drosophila roadblock and two components related to Chlamydomonas LC8. No LC with thioredoxin domains is included in Ciona outer arm dynein. Among the five ICs in Ciona, three are orthologs of those in sea urchin dynein: two are WD-repeat proteins and the third one, unique to metazoan sperm flagella, contains both thioredoxin and nucleoside diphosphate kinase modules. The remaining two Ciona ICs have extensive coiled coil structure and show sequence similarity to outer arm dynein docking complex protein 2 (DC2) that was first identified in Chlamydomonas flagella. We recently identified a third DC2-like protein with coiled coil structure, Ci-Axp66.0 that is also associated in substoichiometric amounts with Ciona outer arm dynein. In addition, Oda5p, a component of an additional complex required for assembly of outer arm dynein in Chlamydomonas flagella, also groups with this family of DC2-like proteins. Thus, the assembly of outer arm dynein onto doublet microtubules involves multiple coiled-coil proteins related to DC2.

Spef1, a conserved novel testis protein found in mouse sperm flagella

We describe the cloning and characterisation of Spef1, a novel testis-specific gene. Spef1 has evolutionary orthologues in a wide range of species including mammals, other vertebrates, Drosophila, and protozoans with motile cilia or flagella. A second homologue of the gene, Spef2, is also present in several species, suggesting that these genes form part of a novel gene family. The Spef1 protein has two conserved domains, one of which is more strongly conserved in both homologues of the gene. Expression analysis of Spef1 in mice shows that it is expressed predominantly in adult testis, suggesting a role in spermatogenesis. Using an antibody generated to recombinant Spef1, we demonstrate a specific pattern of Spef1 localisation in the seminiferous epithelium of adult mouse testis. Further immunohistochemical analysis using electron microscopy shows Spef1 to be present in the tails of developing and epididymal sperm, internal to the fibrous sheath and around the outer dense fibres of the sperm flagellum.

Calcium Channels and Ca2+ Fluctuations in Sperm Physiology

Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.

Using ascidian embryos to study the evolution of developmental gene regulatory networks

Ascidians are ideally positioned taxonomically at the base of the chordate tree to provide a point of comparison for developmental regulatory mechanisms that operate among protostomes, non-chordate deuterostomes, invertebrate chordates, and vertebrates. In this review, we propose a model for the gene regulatory network that gives rise to the ascidian notochord. The purpose of this model is not to clarify all of the interactions between molecules of this network, but to provide a working schematic of the regulatory architecture that leads to the specification of endoderm and the patterning of mesoderm in ascidian embryos. We describe a series of approaches, both computational and biological, that are currently being used, or are in development, for the study of ascidian embryo gene regulatory networks. It is our belief that the tools now available to ascidian biologists, in combination with a streamlined mode of development and small genome size, will allow for more rapid dissection of developmental gene regulatory networks than in more complex organisms such as vertebrates. It is our hope that the analysis of gene regulatory networks in ascidians can provide a basic template which will allow developmental biologists to superimpose the modifications and novelties that have arisen during deuterostome evolution.

Molecular characterization of radial spoke subcomplex containing radial spoke protein 3 and heat shock protein 40 in sperm flagella of the ascidian Ciona intestinalis

Members of the heat-shock protein (HSP)40 regulate the protein folding activity of HSP70 proteins and help the functional specialization of this molecular chaperone system in various types of cellular events. We have recently identified Hsp40 as a component of flagellar axoneme in the ascidian Ciona intestinalis, suggesting a correlation between Hsp40 related chaperone system and flagellar function. In this study, we have found that Ciona 37-kDa Hsp40 is extracted from KCl-treated axonemes with 0.5 M KI solution and comigrates with radial spoke protein (RSP)3 along with several proteins as a complex through gel filtration and ion exchange columns. Peptide mass fingerprinting with matrix-assisted laser desorption ionization/time of flight/mass spectrometry revealed that other proteins in the complex include a homolog of sea urchin spokehead protein (homolog of RSP4/6), a membrane occupation and recognition nexus repeat protein with sequence similarity with meichroacidin, and a functionally unknown 33-kDa protein. A spoke head protein, LRR37, is not included in the complex, suggesting that the complex constructs the stalk of radial spoke. Immunoelectron microscopy indicates that Hsp40 is localized in the distal portion of spoke stalk, possibly at the junction between spoke head and the stalk.

Local database and the search program for proteomic analysis of sperm proteins in the ascidian Ciona intestinalis

Separation of proteins by two-dimensional electrophoresis and following mass spectrometry (MS) is now a conventional technique for proteomic analysis. For proteomic analysis of a certain tissue with a limited information of primary structures of proteins, we have developed an analytical system for peptide mass fingerprinting in gene products in the testis of the ascidian Ciona intestinalis. Ciona sperm proteins were separated by two-dimensional gel electrophoresis and the tryptic fragments were subjected to MALDI-TOF/MS. The mass pattern was searched against on-line databases but resulted in less identification of these proteins. We have constructed a MS database from Ciona testis ESTs and the genome draft sequence, along with a newly devised, perl-based search program PerMS for peptide mass fingerprinting. This system could identify more than 80% of Ciona sperm proteins, suggesting that it could be widely applied for proteomic analysis for a limited tissue with less genomic information.

Analysis of expressed sequence tags from roots of resistant soybean infected by the soybean cyst nematode

The soybean cyst nematode (SCN) Heterodera glycines is the most devastating pest of soybean in the U.S.A. The resistance response elicited by SCN in soybean is complex, and genes involved in the response to a large extent are unknown and not well characterized. We constructed cDNA libraries made from mRNA extracted from roots of the resistant soybean Glycine max L. Merr. 'Peking' at 12 h, 2 to 4 days, and 6 to 8 days post inoculation with the soybean cyst nematode, population NL1-RHp, similar to race 3. Expressed sequence tag analysis of the libraries provides rapid discovery of genes involved in the response of soybean to the nematode. A total of 3454 cDNA clones were examined from the three libraries, of which 25 cDNAs were derived from nematode RNA. The levels of certain stress-induced genes such as SAM22 and glutathione S-transferase (GST8) were elevated in the SCN-infected roots relative to uninoculated roots. Early defense response genes, particularly ascorbate peroxidase and lipoxygenase, were abundant in the 12-h library. By 6-8 days, the expression of most of those genes was not as abundant, whereas genes coding for unknown proteins and stress-induced proteins continued to be highly expressed. These ESTs and associated information will be useful to scientists examining gene and protein interactions between nematodes and plants.

Hyperactivated sperm motility driven by CatSper2 is required for fertilization

Elevations of sperm Ca2+ seem to be responsible for an asymmetric form of motility called hyperactivation, which is first seen near the time of fertilization. The mechanism by which intracellular Ca2+ concentrations increase remains unknown despite considerable investigation. Although several prototypical voltage-gated calcium channels are present in spermatozoa, they are not essential for motility. Furthermore, the forward velocity and percentage of motility of spermatozoa are associated with infertility, but their importance relative to hyperactivation also remains unknown. We show here that disruption of the gene for a recently described sperm-specific voltage-gated cation channel, CatSper2, fails to significantly alter sperm production, protein tyrosine phosphorylation that is associated with capacitation, induction of the acrosome reaction, forward velocity, or percentage of motility, yet CatSper2-/- males are completely infertile. The defect that we identify in the null sperm cells is a failure to acquire hyperactivated motility, which seems to render spermatozoa incapable of generating the "power" needed for penetration of the extracellular matrix of the egg. A loss of power is suggested also by experiments in which the viscosity of the medium was increased after incubation of spermatozoa in normal capacitating conditions. In high-viscosity medium, CatSper2-null spermatozoa lost the ability to swim forward, whereas wild-type cells continued to move forward. Thus, CatSper2 is responsible for driving hyperactivated motility, and, even with typical sperm forward velocities, fertilization is not possible in the absence of this highly active form of motility.

Novel vanadium-binding proteins (vanabins) identified in cDNA libraries and the genome of the ascidian Ciona intestinalis

Ascidians, especially those belonging to the suborder Phlebobranchia, can accumulate high levels of vanadium. Vanadium-binding proteins (vanabins) were first isolated from a vanadium-accumulating ascidian, Ascidia sydneiensis samea, and then the vanabins were cloned, their expression was studied, and metal-binding assays were conducted. In order to unravel the mechanism of vanadium accumulation, we searched for vanabin-like genes in other animals, including other ascidians. A database search revealed five groups of cDNAs that encoded vanabin-like proteins in another ascidian, Ciona intestinalis. The genes encoding C. intestinalis vanabins, CiVanabin1 to CiVanabin5, were clustered in an 8.4-kb genomic region. The direction of transcription of each gene was identical and each gene had a single intron. All the C. intestinalis vanabins were cysteine-rich, and the repetitive pattern of cysteines closely resembled that of A. sydneiensis samea vanabins. Using immobilized metal ion affinity chromatography (IMAC), we found that a recombinant protein of at least one of the C. intestinalis vanabins (CiVanabin5) bound to vanadium(IV) ions.

Sperm motility-activating complex formed by t-complex distorters

Transmission ratio distortion is a dramatic example of non-Mendelian transmission. In mice, t-haplotype males produce dysfunctional +-sperm and normal t-sperm, leading to transmission in favor of t-sperm. Genetic studies have indicated that the t-complex responder locus, Tcr, rescues t-sperm but not +-sperm from defective products of t-complex distorter loci, Tcds. Light chain 1 (LC1) and LC3 from sea urchin sperm outer arm dynein have sequence similarities to Tctex2 and Tctex1, respectively, both of which are wild-type products of Tcds. We show here that LC1 and LC3 are able to make a 1:1 complex. Since Tcr is a member of the Smok (sperm motility kinase) family and LC1 is phosphorylated at the activation of sperm motility in a cAMP-dependent manner, this complex in a dynein motor molecule might be a direct target of Smok/Tcr kinase in a signal cascade that regulates sperm motility. Thus, we designate it as Smoac (sperm motility activating complex).

Transcript mapping and genome annotation of ascidian mtDNA using EST data

Mitochondrial transcripts of two ascidian species were reconstructed through sequence assembly of publicly available ESTs resembling mitochondrial DNA sequences (mt-ESTs). This strategy allowed us to analyze processing and mapping of the mitochondrial transcripts and to investigate the gene organization of a previously uncharacterized mitochondrial genome (mtDNA). This new strategy would greatly facilitate the sequencing and annotation of mtDNAs. In Ciona intestinalis, the assembled mt-ESTs covered 22 mitochondrial genes ( approximately 12,000 bp) and provided the partial sequence of the mtDNA and the prediction of its gene organization. Such sequences were confirmed by amplification and sequencing of the entire Ciona mtDNA. For Halocynthia roretzi, for which the mtDNA sequence was already available, the inferred mt transcripts allowed better definition of gene boundaries (16S rRNA, ND1, ATP6, and tRNA-Ser genes) and the identification of a new gene (an additional Phe-tRNA). In both species, polycistronic and immature transcripts, creation of stop codons by polyadenylation, tRNA signal processing, and rRNA transcript termination signals were identified, thus suggesting that the main features of mitochondrial transcripts are conserved in Chordata.

Characterization of a cAMP-dependent protein kinase catalytic subunit from rainbow trout spermatozoa

The cyclic AMP-dependent phosphorylation of proteins is essential for the initiation of sperm motility in salmonid fishes. This study isolated cDNA for the catalytic subunit of a cAMP-dependent protein kinase (PKA-C) from rainbow trout testis. The deduced amino acid sequence shows 75-80% identity to sequences previously reported in other organisms. However, the N-terminal regions of PKA-C from the testis as well as ovary in the trout appear slightly shorter than those from other tissues, suggesting that small PKA-C might be specific to germ cells. An immunofluorescence study using polyclonal antibody against trout testis PKA-C shows that it localizes along sperm flagellum. Furthermore, immunoelectron microscopy revealed that PKA-C is anchored to the outer arm dynein of flagellar axonemes. These results suggest that PKA-C is involved in regulating the flagellar motility of sperm via phosphorylation of a subunit of the outer arm dynein.

Sperm cells of Zea mays have a complex complement of mRNAs

Although double fertilization in angiosperm was discovered in 1898, we still know nothing about the proteins that mediate gamete recognition and fusion in plants. Because sperm are small and embedded within the large vegetative cell of the pollen grain, mRNAs from sperm are poorly represented in EST databases. We optimized fluorescence-activated cell sorting (FACS) in order to isolate Zea mays sperm free of contaminating vegetative cell cytoplasm, and constructed a cDNA library. Sequencing of over 1100 cDNAs from the unamplified library revealed that sperm have a diverse complement of mRNAs. Most transcripts were singletons; the most abundant was sequenced only 17 times. About 8% of the sequences are predicted to encode secreted or plasma membrane-localized proteins and are therefore candidates that might mediate gamete interactions. About 8% of the sequences correspond to retroposons. Plant sperm have condensed chromatin and are thought to be transcriptionally inactive. We used RT-PCR and in situ hybridization to determine when selected sperm mRNAs were transcribed. Sperm transcripts encoding proteins involved in general cell functions were present throughout pollen development and were more abundant in tricellular pollen than in sperm cells, suggesting that these transcripts were also present in the larger vegetative cell. However, several transcripts, which encode proteins that are most similar to hypothetical Arabidopsis proteins, appeared to be present exclusively in the sperm cells inside mature pollen, but were already present in unicellular microspores. This suggests that certain transcripts might be transcribed early during pollen development and later partitioned into the sperm cells.

Molecular cloning and sequence analysis of an ascidian egg beta-N-acetylhexosaminidase with a potential role in fertilization

Beta-N-acetylhexosaminidase, which is found almost ubiquitously in sperm of invertebrates and vertebrates, supposedly mediates a carbohydrate-based transient sperm-egg coat binding. In ascidians and mammals, beta-hexosaminidase released at fertilization from eggs has been proposed to modify sperm receptor glycoproteins of the egg envelope, thus setting up a block to polyspermy. Previously, it was shown that in potential sperm receptor glycoproteins of the ascidian Phallusia mammillata, N-acetylglucosamine is the prevailing glycoside residue and that the egg harbors three active molecular forms of beta-hexosaminidase. In the present study, P. mammillata beta-hexosaminidase cDNA was isolated from an ovarian cDNA library and characterized. The deduced amino acid sequence showed a high similarity with other known beta-hexosaminidases; however, P. mammillata beta-hexosaminidase had a unique potential N-glycosylation site. A phylogenetic analysis suggested that P. mammillata beta-hexosaminidase developed independently after having branched off from the common ancestor gene of the chordate enzyme before two isoforms of the mammalian enzyme appeared. In situ hybridization revealed stage-specific expression of beta-hexosaminidase mRNA during oogenesis in the oocyte and in the accessory test and follicle cells. This suggests that the three egg beta-hexosaminidase forms are specific for the oocyte, test cells and follicle cells.

Large scale EST analyses in Ciona intestinalis: its application as Northern blot analyses

We have conducted large-scale EST analyses of transcripts expressed in the basal chordate Ciona intestinalis. The cDNA libraries examined were from fertilized eggs, cleaving embryos, gastrulae/neurulae, tailbud embryos, larvae and whole young adults, and the gonad (ovary and testis), endostyle, neural complex, heart, and blood cells of the adult. Because the libraries were not normalized or amplified, the occurrence of cDNA clones or EST counts in each library may reflect the quantity of transcripts of the corresponding genes. Thus, comparison of the EST counts of a certain gene at the six developmental stages may reflect the temporal expression pattern of the gene, while the comparison of EST counts in different tissues of the adult may reflect the spatial expression pattern of the gene. Here we present evidence that this is the case, and that the EST count can therefore be used like "Northern blot analysis" of Ciona genes.

Hemocytes of Ciona intestinalis express multiple genes involved in innate immune host defense

Ascidians, which are classified as urochordata, appear to employ a primitive system of host defense that is considered to be a prototype of vertebrate innate immunity. We performed a cDNA/EST study to identify the genes expressed in the hemocytes of Ciona intestinalis. We obtained 3357 one-path reads that were then grouped into 1889 independent clusters. Although two thirds of the clusters could not be assigned to any particular gene, the remaining 530 clusters had significant homology to genes with known function. Of these, 62 clusters appeared to be related to host defense mechanisms. These include transcripts whose products are probably involved in cytotoxicity, detoxification, inflammation, and apoptosis. As expected, elements of acquired immunity were not detected. Thus, Ciona hemocytes appear to express a number of host defense-related genes involved in innate immune mechanisms.

Identification of a novel leucine-rich repeat protein as a component of flagellar radial spoke in the Ascidian Ciona intestinalis

Axonemes are highly organized microtubule-based structures conserved in many eukaryotes. In an attempt to study axonemes by a proteomics approach, we selectively cloned cDNAs of axonemal proteins by immunoscreening the testis cDNA library from the ascidian Ciona intestinalis by using an antiserum against whole axonemes. We report here a 37-kDa protein of which cDNA occurred most frequently among total positive clones. This protein, named LRR37, belongs to the class of SDS22+ leucine-rich repeat (LRR) family. LRR37 is different from the LRR outer arm dynein light chain reported in Chlamydomonas and sea urchin flagella, and thus represents a novel axonemal LRR protein. Immunoelectron microscopy by using a polyclonal antibody against LRR37 showed that it is localized on the tip of the radial spoke, most likely on the spoke head. The LRR37 protein in fact seems to form a complex together with radial spoke protein 3 in a KI extract of the axonemes. These results suggest that LRR37 is a component of the radial spoke head and is involved in the interaction with other radial spoke components or proteins in the central pair projection.