A novel motility pattern in quail spermatozoa with implications for the mechanism of flagellar beating

Background information. The spermatozoon of the quail (Coturnix coturnix L., var japonica) has a ‘9+2’ flagellum that is unusually long. When it moves in a viscous medium, near to the coverslip, it develops a meander waveform. Because of the high viscosity, the meander bends are static in relation to the field of view; bend propagation is therefore manifest as the forward movement of the flagellum through the meander shape. At the same time, the origin of the oscillation typically shifts proximally in a stepwise fashion. These movements have been analysed in the hope of contributing to the resolution of problems in flagellar mechanics. Results. (1) Meander waves originate from spontaneous sigmoid bend complexes. (2) On a given flagellum, fully developed meander bends are uniform in their large angle, curvature and propagation speed; interbends can vary in length and shape. (3) No intra‐axonemal sliding is transmitted through formed bends; sliding related to new bends is accommodated proximally. (4) Sliding reversal is initiated at a threshold shear angle of approx. 1 rad. (5) The arc wavespeed is the product of the arc wavelength and the beat frequency. (6) Physical obstruction to bend development causes a pause in the oscillation. (7) New bend initiation can thus be dissociated from bend propagation on the distal flagellum. (8) The steps in the forward advance of the oscillation site occur during the early phase of bend growth. Conclusions. (1) The main conclusion is that, in meander waves, the mechanical basis of the oscillation appears to be that the propulsive thrust arising from bend propagation acts as a bending stress to trigger sliding reversal, thus perpetuating the rhythmic beating. (2) Oscillations can originate at any position, provided the position is distal to a location where doublet sliding is restrained. (3) Meander waves are an example of new bend development without ‘paradoxical’ classes of sliding.     

The ciliary pocket: a once-forgotten membrane domain at the base of cilia

The PC (primary cilium) is present on most cell types in both developing and adult tissues in vertebrates. Despite multiple reports in the 1960s, the PC was almost forgotten for decades by most of the cell biology community, mainly because its function appeared enigmatic. This situation changed 10 years ago with the key discovery that this fascinating structure is the missing link between complex genetic diseases and key signalling pathways during development and tissue homoeostasis. A similar misfortune might have happened to an original membrane domain found at the base of PC in most cell types and recently termed the ‘ciliary pocket’. A morphologically related structure has also been described at the connecting cilium of photoreceptors and at the flagellum in spermatids. Its organization is also reminiscent of the flagellar pocket, a plasma membrane invagination specialized in uptake and secretion encountered in kinetoplastid protozoa. The exact function of the ciliary pocket remains to be established, but the recent observation of endocytic activity coupled to the fact that vesicular trafficking plays important roles during ciliogenesis brought excitement in the ciliary community. Here, we have tried to decipher what this highly conserved membrane domain could tell us about the function and/or biogenesis of the associated cilium.     

Tektin5, a new Tektin family member, is a component of the middle piece of flagella in rat spermatozoa

Tektins are composed of a family of filament-forming proteins localized in cilia and flagella. Four types of mammalian Tektins have been reported, and at least two types of Tektins, Tektin2 and Tektin4, have been verified to be present in sperm flagella. A new member of the TEKTIN gene family, which was designated as rat Tektin5, was obtained by PCR technique. Rat Tektin5 cDNA consists of 1,674 bp encoding a 62.8 kDa protein of 558 amino acids. Tektin5 protein contains a Tektin domain as well as a nonapeptide signature sequence that is a prominent feature of Tektin proteins. RT-PCR analysis indicated that Tektin5 was predominantly expressed in testis and that its expression was up-regulated during testis development. Immunoblot analyses revealed that Tektin5 is present in sperm flagella but not in heads and that it is completely released from rat spermatozoa by 6 M urea treatment, but not extracted by 1% Triton X-100 and 0.6 M potassium thiocyanate. Confocal laser scanning microscopy revealed that Tektin5 was located in the middle piece of flagella in rat spermatozoa with no immunolabeling in the heads and the principal piece. Immunogold electron microscopy adopting pre-embedding method discovered that Tektin5 is predominantly associated with the inner side of the mitochondrial sheath. Tektin5 might work as a middle piece component requisite for flagellar stability and sperm motility.     

Spetex-1: a new component in the middle piece of flagellum in rodent spermatozoa

Spetex-1 has recently been isolated by differential display and screening of cDNA library. It encodes a protein of 556 amino acid residues possessing coiled-coil motifs. In the rat seminiferous tubules (ST), Spetex-1 was expressed in the cytoplasm of elongating spermatids. To examine the subcellular distribution of Spetex-1 in mature spermatozoa, we performed biochemical and immunocytochemical approaches. We found that Spetex-1 that was synthesized in the cytoplasm of elongating spermatids was subsequently integrated as a middle piece component into spermatozoa during spermiogenesis. After integration, the majority of Spetex-1 in spermatozoa could be extracted by 6M urea under reduced condition but not released by the treatment of 1% Triton X-100. Immunoelectron microscopy demonstrated that Spetex-1 seemed to locate at the inner side of outer dense fibers (ODFs) in the middle piece or the narrow space between ODFs and axoneme. Spetex-1 might be involved in the stability of the structural complexity comprising axoneme and ODFs in the middle piece of sperm flagellum.     

Inside and outside of the trypanosome flagellum:a multifunctional organelle

Amongst the earliest eukaryotes, trypanosomes have developed conventional organelles but sometimes with extreme features rarely seen in other organisms. This is the case of the flagellum, containing conventional and unique structures whose role in infectivity is still enigmatic.     

THE DINOFLAGELLATE TRANSVERSE FLAGELLUM: THREE-DIMENSIONAL RECONSTRUCTIONS FROM SERIAL SECTIONS1

Serial sections through in situ transverse flagella of the dinoflagellate Peridinium cinctum f. irregulatum (Lindem.) Lefévre are presented. Three-dimensional reconstructions based upon tangential and radial series show a helically coiled axoneme lying external to and distinct from an accessory strand. Hitherto undescribed vesicles within the expanded flagellar sheath are suggested to provide a decoupling effect between axoneme and strand. The flagellar axis bears two types of hair but anchoring threads between cingulum and flagellum have not been found. Functional and taxonomic implications of these observations are briefly discussed.     

Gamma神经振荡产生机制及其功能研究进展

Gamma神经振荡的频率在30～100 Hz之间,存在于动物和人类大脑的多个区域,如丘脑、体感皮层以及海马等部位,在各个尺度水平上都可被检测到.抑制性中间神经元组成的神经网络是产生此高频节律性活动的主要条件之一.皮层的gamma神经振荡与丘脑-皮层系统有关.Gamma神经振荡具有易化突触可塑性和调节神经网络的作用,主要参与感觉特征绑定、选择性注意以及记忆等高级功能.     

Tektin 4 is located on outer dense fibers, not associated with axonemal tubulins of flagella in rodent spermatozoa

Tektins, which are thought to be the constitutive proteins of microtubules in cilia, flagella, basal bodies, and centrioles, have been reported to be involved in the stability and structural complexity of axonemal microtubules. Four types of mammalian Tektins have been reported, and at least two types of Tektins, Tektin 2 and Tektin 4, have been verified to be present in sperm flagella. To elucidate the molecular localization of Tektin 4 in flagella of rodent spermatozoa, we performed immunocytochemistry, fractionation study followed by immunoblot analysis, and immunogold electron microscopy. Confocal laser scanning microscopy and immunogold electron microscopy indicated that Tektin 4 was associated with outer dense fibers (ODFs) in both the middle and principal piece of flagella in rat and mouse spermatozoa. Tektin 4 in rat spermatozoa is completely released by 6 M urea treatment, but not extracted by 1% Triton X-100 and 0.6 M potassium thiocyanate. Pre-embedding immunoelectron microscopy demonstrated that Tektin 4 located on the abaxial (convex) surface of ODFs in flagella, not associate with axonemal microtubules. Our data strongly suggested that Tektin 4 is not associated with axonemal tubulins but an ODFs-affiliated molecule in rodent spermatozoa.     

Analysis of anisotropic diamagnetic susceptibility of a bull sperm

Bull sperm and paramecium cilium were exposed to uniform static magnetic fields to observe their magnetic orientations and measure their anisotropic diamagnetic susceptibility (deltachi) for each. The prepared samples were whole bull sperm, bull sperm flat heads, and paramecium cilia, because bull sperm tails in a perfect condition could not be prepared. The whole bull sperm and the bull sperm heads became oriented perpendicular to the magnetic fields (1.7 Tesla maximum), while the paramecium cilia became parallel to the magnetic fields (8 Tesla maximum). A whole bull sperm, a bull sperm head, and a paramecium cilium were photometrically studied to obtain deltachi for each, which were estimated to be 1 x 10(-19), 3 x 10(-19), and 2 x 10(-20) J/T(2), respectively. deltachi of a sperm flagellum was estimated from the measured value of deltachi of the paramecium cilium, which agrees well with the difference between deltachi of the whole sperm and the sperm head. Additionally, this difference of deltachi almost coincides with the deltachi values calculated from deltachi of tubulin, as well. If the magnetic effect on biological systems is solved and the magnetic orientation correlates with it, deltachi will become the quantitative index of the effect.     

The covalent oscillator: A paradigm accounting for the sliding/bending mechanism and wave propagation in cilia and flagella

Summary— In most models of wave propagation in eucaryotic flagella and cilia, a clear distinction is made between the dynein dependent microtubule sliding which represents the oscillatory motor and the bending mechanism which regulates wave propagation. Little is known about the physical elements regulating the latter: in the present model, the bending propagation is postulated to be supported by an open/close cyclic mechanism protease/ligase dependent, which involves transient covalent links between adjacent microtubular doublets; this open/close cycle propagates in register with the powering action of the dynein motor along the exoneme. The implications of the model are discussed in relation to previous data which involve protease/ligase in the axonemal function as well as other data which can be integrated by the proposed model.     

From obesity to cancer: a review on proposed mechanisms

Nowadays, obesity is considered as a serious and growing global health problem. It is documented that the overweight and obesity are major risk factors for a series of noncommunicable diseases, and in recent years, the obesity‐cancer link has received much attention. Numerous epidemiological studies have shown that obesity is associated with increased risk of several cancer types, including colon, breast, endometrium, liver, kidney, esophagus, gastric, pancreatic, gallbladder, and leukemia, and can also lead to poorer treatment. We review here the epidemiological and experimental evidences for the association between obesity and cancer. Specifically, we discuss potential mechanisms focusing how dysfunctional angiogenesis, chronic inflammation, interaction of proinflammatory cytokines, endocrine hormones, and adipokines including leptin, adiponectin insulin, growth factors, estrogen, and progesterone and strikingly, cell metabolism alteration in obesity participate in tumor development and progression, resistance to chemotherapy, and targeted therapies such as antiangiogenic and immune therapies.     

Purification and crystal structure of human ODA16: Implications for ciliary import of outer dynein arms by the intraflagellar transport machinery

Motile cilia protrude from cell surfaces and are necessary to create movement of cells and fluids in the body. At the molecular level, cilia contain several dynein molecular motor complexes including outer dynein arms (ODAs) that are attached periodically to the ciliary axoneme, where they hydrolyse ATP to create the force required for bending and motility of the cilium. ODAs are preassembled in the cytoplasm and subsequently trafficked into the cilium by the intraflagellar transport (IFT) system. In the case of the green alga Chlamydomonas reinhardtii, the adaptor protein ODA16 binds to ODAs and directly to the IFT complex component IFT46 to facilitate the ciliary import of ODAs. Here, we purified recombinant human IFT46 and ODA16, determined the high‐resolution crystal structure of the ODA16 protein, and carried out direct interaction studies of IFT46 and ODA16. The human ODA16 C‐terminal 320 residues adopt the fold of an eight‐bladed β‐propeller with high overall structural similarity to the Chlamydomonas ODA16. However, the small 80 residue N‐terminal domain, which in Chlamydomonas ODA16 is located on top of the β‐propeller and is required to form the binding cleft for IFT46, has no visible electron density in case of the human ODA16 structure. Furthermore, size exclusion chromatography and pull‐down experiments failed to detect a direct interaction between human ODA16 and IFT46. These data suggest that additional factors may be required for the ciliary import of ODAs in human cells with motile cilia.     

Sperm axoneme: a tale of tubulin posttranslation diversity

Two microtubule-containing structures are assembled during spermiogenesis: a transient manchette and a stable axoneme. Both structures contain microtubules enriched in posttranslationally modified tubulins. Despite the existence of a spectrum of tubulin isotypes postulated by the multi-tubulin hypothesis, further extended by an elaborated array of posttranslational modifications, it is unknown how this diversity influences microtubule function. There is increasing evidence that different alpha beta-tubulin isotypes can affect the structure and function of microtubules. It is also becoming increasingly clear that eukaryotic cells encode other tubulin proteins expressed by the tubulin superfamily: gamma, delta epsilon, zeta eta, and FtsZ have been identified so far. Although the role of gamma-tubulin in the nucleation of microtubule assembly is well established, the function of delta-, epsilon-, zeta-, eta-, and FtsZ-tubulins is less understood. The members of the tubulin superfamilies found in spermatids include the alpha beta-tubulin dimer, in addition to gamma-tubulin in the centrosome, and delta-tubulin in the perinuclear ring region of the mouse spermatid manchette, the centrosome region, and flagellum. Posttranslational modifications in tubulin isotypes are predominant in the C-terminus exposed on the outside surface of the microtubule. This target site may influence the interaction of microtubule-associated proteins, including motor proteins, and therefore determine the functional specificity of tubulin isotypes. It remains to be determined whether other newcomers to the superfamily of tubulins contain sites prone to posttranslational modification.     

Internal noise enhanced oscillation in a delayed circadian pacemaker

The effect of internal noise in a delayed circadian oscillator is studied by using both chemical Langevin equations and stochastic normal form theory. It is found that internal noise can induce circadian oscillation even if the delay time τ is below the deterministic Hopf bifurcation τ_h. We use signal-to-noise ratio (SNR) to quantitatively characterize the performance of such noise induced oscillations and a threshold value of SNR is introduced to define the so-called effective oscillation. Interestingly, the τ-range for effective stochastic oscillation, denoted as Δτ_EO, shows a bell-shaped dependence on the intensity of internal noise which is inversely proportional to the system size. We have also investigated how the rates of synthesis and degradation of the clock protein influence the SNR and thus Δτ_EO. The decay rate K_d could significantly affect Δτ_EO, while varying the gene expression rate K_e has no obvious effect if K_e is not too small. Stochastic normal form analysis and numerical simulations are in good consistency with each other. This work provides us comprehensive understandings of how internal noise and time delay work cooperatively to influence the dynamics of circadian oscillations.     

Synchronized oscillation in a modular neural network composed of columns

The columnar organization is a ubiquitous feature in the cerebral cortex. In this study, a neural network model simulating the cortical columns has been constructed. When fed with random pulse input with constant rate, a column generates synchronized oscillations, with a frequency varying from 3 to 43 Hz depending on parameter values. The behavior of the model under periodic stimulation was studied and the input-output relationship was non-linear. When identical columns were sparsely interconnected, the column oscillator could be locked in synchrony. In a network composed of heterogeneous columns, the columns were organized by intrinsic properties and formed partially synchronized assemblies.     

Synchronized oscillation in a modular neural network composed of columns

The columnar organization is a ubiquitous feature in the cerebral cortex. In this study, a neural network model simulating the cortical columns has been constructed. When fed with random pulse input with constant rate, a column generates synchronized oscillations, with a frequency varying from 3 to 43 Hz depending on parameter values. The behavior of the model under periodic stimulation was studied and the input-output relationship was non-linear. When identical columns were sparsely interconnected, the column oscillator could be locked in synchrony. In a network composed of heterogeneous columns, the columns were organized by intrinsic properties and formed partially synchronized assemblies.     

Ciliary motility: the components and cytoplasmic preassembly mechanisms of the axonemal dyneins

Motile cilia and flagella are organelles, which function in cell motility and in the transport of fluids over the surface of cells. Motility defects often result in a rare human disease, primary ciliary dyskinesia (PCD). Cell motility depends on axonemal dynein, a molecular motor that drives the beating of cilia and flagella. The dyneins are composed of multiple subunits, which are thought to be preassembled in the cytoplasm before they are transported into cilia and flagella. Axonemal dyneins have been extensively studied in Chlamydomonas. In addition, analyses of human PCDs over the past decade, together with studies in other model animals, have identified the conserved components required for dynein assembly. Recently also, the first cytoplasmic component of dynein assembly, kintoun (ktu), was elucidated through the analysis of a medaka mutant in combination with human genetics and cell biology and biochemical studies of Chlamydomonas. The components of dynein and the proteins involved in its cytoplasmic assembly process are discussed.     

Gadolinium-based contrast agent toxicity: a review of known and proposed mechanisms

Gadolinium chelates are widely used as contrast media for magnetic resonance imaging. The approved gadolinium-based contrast agents (GBCAs) have historically been considered safe and well tolerated when used at recommended dosing levels. However, for nearly a decade, an association between GBCA administration and the development of nephrogenic systemic fibrosis (NSF) has been recognized in patients with severe renal impairment. This has led to modifications in clinical practices aimed at reducing the potential and incidence of NSF development. Newer reports have emerged regarding the accumulation of gadolinium in various tissues of patients who do not have renal impairment, including bone, brain, and kidneys. Despite the observations of gadolinium accumulation in tissues regardless of renal function, very limited clinical data regarding the potential for and mechanisms of toxicity is available. This significant gap in knowledge warrants retrospective cohort study efforts, as well as prospective studies that involve gadolinium ion (Gd³⁺) testing in patients exposed to GBCA. This review examines the potential biochemical and molecular basis of gadolinium toxicity, possible clinical significance of gadolinium tissue retention and accumulation, and methods that can limit gadolinium body burden.