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Proceedings of the National Academy of... Jul 2023Cilia build distinct subdomains with variable axonemal structures to perform diverse functions in cell motility and signaling. In sensory cilia across species, an...
Cilia build distinct subdomains with variable axonemal structures to perform diverse functions in cell motility and signaling. In sensory cilia across species, an axoneme differentiates longitudinally into a middle segment with nine microtubule (MT) doublets and a distal segment with nine MT singlets that extends from the A tubules of the doublets. Here, we study axoneme differentiation in by analyzing the flagellar inner junction protein FAP20 and PCRG1 that connect A and B tubules in . The nematode CFAP-20 is restricted to the middle segment with doublets, and its loss disconnects A and B tubules. However, PCRG-1 is absent from most sensory cilia, and its deletion does not disrupt cilia. Ectopic introduction of PCRG-1 into cilia generated abnormal MT doublets in the distal segment and reduced intraflagellar transport and animal sensation. Thus, the absence of an inner junction protein prevents B-tubule extension, which contributes to axoneme differentiation and ciliary function.
Topics: Animals; Axoneme; Cilia; Chlamydomonas; Caenorhabditis elegans; Biological Transport; Microtubules; Flagella
PubMed: 37463209
DOI: 10.1073/pnas.2303955120 -
Current Opinion in Structural Biology Feb 2023The axoneme of motile cilia and eukaryotic flagella is an ordered assembly of hundreds of proteins that powers the locomotion of single cells and generates flow of... (Review)
Review
The axoneme of motile cilia and eukaryotic flagella is an ordered assembly of hundreds of proteins that powers the locomotion of single cells and generates flow of liquid and particles across certain mammalian tissues. The symmetric and organized structure of the axoneme has invited structural biologists to unravel its intricate architecture at different scales. In the last few years, single-particle cryo-electron microscopy provided high-resolution structures of axonemal complexes that comprise dozens of proteins and are key to cilia function. This review summarizes unique structural features of the axoneme and the framework they provide to understand cilia assembly, the mechanism of ciliary beating, and clinical conditions associated with impaired cilia motility.
Topics: Animals; Cilia; Axoneme; Flagella; Cryoelectron Microscopy; Proteins; Mammals
PubMed: 36586349
DOI: 10.1016/j.sbi.2022.102516 -
Experimental Animals Nov 2020Infertility is a global health issue that affects 1 in 6 couples, with male factors contributing to 50% of cases. The flagellar axoneme is a motility apparatus of... (Review)
Review
Infertility is a global health issue that affects 1 in 6 couples, with male factors contributing to 50% of cases. The flagellar axoneme is a motility apparatus of spermatozoa, and disruption of its structure or function could lead to male infertility. The axoneme consists of a "9+2" structure that contains a central pair of two singlet microtubules surrounded by nine doublet microtubules, in addition to several macromolecular complexes such as dynein arms, radial spokes, and nexin-dynein regulatory complexes. Molecular components of the flagellar axoneme are evolutionally conserved from unicellular flagellates to mammals, including mice. Although knockout (KO) mice have been generated to understand their function in the formation and motility regulation of sperm flagella, the majority of KO mice die before sexual maturation due to impaired ciliary motility, which makes it challenging to analyze mature spermatozoa. In this review, we introduce methods that have been used to overcome premature lethality, focusing on KO mouse lines of central pair components.
Topics: Animals; Axoneme; Dyneins; Infertility, Male; Male; Mice, Knockout; Microtubule-Associated Proteins; Microtubules; Sperm Motility; Sperm Tail
PubMed: 32554934
DOI: 10.1538/expanim.20-0064 -
Small (Weinheim An Der Bergstrasse,... Aug 2022Cilia and flagella are beating rod-like organelles that enable the directional movement of microorganisms in fluids and fluid transport along the surface of biological...
Cilia and flagella are beating rod-like organelles that enable the directional movement of microorganisms in fluids and fluid transport along the surface of biological organisms or inside organs. The molecular motor axonemal dynein drives their beating by interacting with microtubules. Constructing synthetic beating systems with axonemal dynein capable of mimicking ciliary beating still represents a major challenge. Here, the bottom-up engineering of a sustained beating synthoneme consisting of a pair of microtubules connected by a series of periodic arrays of approximately eight axonemal dyneins is reported. A model leads to the understanding of the motion through the cooperative, cyclic association-dissociation of the molecular motor from the microtubules. The synthoneme represents a bottom-up self-organized bio-molecular machine at the nanoscale with cilia-like properties.
Topics: Axonemal Dyneins; Axoneme; Cilia; Dyneins; Flagella; Microtubules
PubMed: 35815940
DOI: 10.1002/smll.202107854 -
Mammalian axoneme central pair complex proteins: Broader roles revealed by gene knockout phenotypes.Cytoskeleton (Hoboken, N.J.) Jan 2016The axoneme genes, their encoded proteins, their functions and the structures they form are largely conserved across species. Much of our knowledge of the function and... (Review)
Review
The axoneme genes, their encoded proteins, their functions and the structures they form are largely conserved across species. Much of our knowledge of the function and structure of axoneme proteins in cilia and flagella is derived from studies on model organisms like the green algae, Chlamydomonas reinhardtii. The core structure of cilia and flagella is the axoneme, which in most motile cilia and flagella contains a 9 + 2 configuration of microtubules. The two central microtubules are the scaffold of the central pair complex (CPC). Mutations that disrupt CPC genes in Chlamydomonas and other model organisms result in defects in assembly, stability and function of the axoneme, leading to flagellar motility defects. However, targeted mutations generated in mice in the orthologous CPC genes have revealed significant differences in phenotypes of mutants compared to Chlamydomonas. Here we review observations that support the concept of cell-type specific roles for the CPC genes in mice, and an expanded repertoire of functions for the products of these genes in cilia, including non-motile cilia, and other microtubule-associated cellular functions.
Topics: Animals; Axoneme; Cytoskeletal Proteins; Gene Knockout Techniques; Humans; Mice; Microtubule Proteins; Microtubule-Associated Proteins
PubMed: 26785425
DOI: 10.1002/cm.21271 -
Cell Jun 2023Sperm motility is crucial to reproductive success in sexually reproducing organisms. Impaired sperm movement causes male infertility, which is increasing globally. Sperm...
Sperm motility is crucial to reproductive success in sexually reproducing organisms. Impaired sperm movement causes male infertility, which is increasing globally. Sperm are powered by a microtubule-based molecular machine-the axoneme-but it is unclear how axonemal microtubules are ornamented to support motility in diverse fertilization environments. Here, we present high-resolution structures of native axonemal doublet microtubules (DMTs) from sea urchin and bovine sperm, representing external and internal fertilizers. We identify >60 proteins decorating sperm DMTs; at least 15 are sperm associated and 16 are linked to infertility. By comparing DMTs across species and cell types, we define core microtubule inner proteins (MIPs) and analyze evolution of the tektin bundle. We identify conserved axonemal microtubule-associated proteins (MAPs) with unique tubulin-binding modes. Additionally, we identify a testis-specific serine/threonine kinase that links DMTs to outer dense fibers in mammalian sperm. Our study provides structural foundations for understanding sperm evolution, motility, and dysfunction at a molecular level.
Topics: Male; Animals; Cattle; Sperm Tail; Sperm Motility; Semen; Microtubules; Axoneme; Spermatozoa; Mammals
PubMed: 37327785
DOI: 10.1016/j.cell.2023.05.026 -
Cytoskeleton (Hoboken, N.J.) Oct 2020Loss of the cilium is important for cell cycle progression and certain developmental transitions. Chytrid fungi are a group of basal fungi that have retained centrioles...
Loss of the cilium is important for cell cycle progression and certain developmental transitions. Chytrid fungi are a group of basal fungi that have retained centrioles and cilia, and they can disassemble their cilia via axoneme internalization as part of the transition from free-swimming spores to sessile sporangia. While this type of cilium disassembly has been observed in many single-celled eukaryotes, it has not been well characterized because it is not observed in common model organisms. To better characterize cilium disassembly via axoneme internalization, we focused on chytrids Rhizoclosmatium globosum and Spizellomyces punctatus to represent two lineages of chytrids with different motility characteristics. Our results show that each chytrid species can reel in its axoneme into the cell body along its cortex on the order of minutes, while S. punctatus has additional faster ciliary compartment loss and lash-around mechanisms. S. punctatus retraction can also occur away from the cell cortex and is partially actin dependent. Post-internalization, the tubulin of the axoneme is degraded in both chytrids over the course of about 2 hr. Axoneme disassembly and axonemal tubulin degradation are both partially proteasome dependent. Overall, chytrid cilium disassembly is a fast process that separates axoneme internalization and degradation.
Topics: Axoneme; Cilia; Fungi
PubMed: 33103844
DOI: 10.1002/cm.21637 -
Journal of Assisted Reproduction and... Feb 2016This review article provides a critical analysis of the structure and molecular mechanisms of the microtubule axoneme of cilia and sperm flagella and their associated... (Review)
Review
This review article provides a critical analysis of the structure and molecular mechanisms of the microtubule axoneme of cilia and sperm flagella and their associated elements required for male fertility.A broad range of genetic and molecular defects (ciliopathies) are considered in the context of human diseases involving impaired motility in cilia and sperm flagella, providing provocative thought for future research in the area of male infertility.
Topics: Axoneme; Cilia; Flagella; Humans; Infertility, Male; Male; Reproductive Techniques, Assisted; Spermatozoa
PubMed: 26825807
DOI: 10.1007/s10815-016-0652-1 -
Current Biology : CB Dec 2023Dyneins are a family of motor proteins that carry out motility and force generation functions towards the minus end of microtubule filaments. Cytoplasmic dynein...
Dyneins are a family of motor proteins that carry out motility and force generation functions towards the minus end of microtubule filaments. Cytoplasmic dynein (dynein-1) is responsible for transporting intracellular cargos in the retrograde direction in the cytoplasm, anchoring several organelles to the microtubule network, driving nuclear migration in developing neurons, and orienting the mitotic spindle in dividing cells. All other dyneins are localized to cilia. Similar to dynein-1, dynein-2 walks along microtubules and drives intraflagellar transport in the retrograde direction. Other ciliary dyneins are positioned between adjacent microtubule doublets of the axoneme and power ciliary beating by sliding microtubules relative to each other. In this primer, we first highlight the structure, mechanism, and regulation of dynein-1, which is the best-characterized member of the dynein motor family, and then describe the unique features and cellular roles of other dyneins. We also discuss accessory proteins that regulate the activation and motility of dynein motors in different cellular contexts.
Topics: Dyneins; Microtubules; Axoneme; Kinesins; Spindle Apparatus
PubMed: 38113834
DOI: 10.1016/j.cub.2023.10.064 -
Proceedings of the National Academy of... Aug 2022Cilium formation and regeneration requires new protein synthesis, but the underlying cytosolic translational reprogramming remains largely unknown. Using ribosome...
Cilium formation and regeneration requires new protein synthesis, but the underlying cytosolic translational reprogramming remains largely unknown. Using ribosome footprinting, we performed global translatome profiling during cilia regeneration in and uncovered that flagellar genes undergo an early transcriptional activation but late translational repression. This pattern guided our identification of sphingolipid metabolism enzymes, including serine palmitoyltransferase (SPT), as essential regulators for ciliogenesis. Cryo-electron tomography showed that ceramide loss abnormally increased the membrane-axoneme distance and generated bulged cilia. We found that ceramides interact with intraflagellar transport (IFT) particle proteins that IFT motors transport along axoneme microtubules (MTs), suggesting that ceramide-IFT particle-IFT motor-MT interactions connect the ciliary membrane with the axoneme to form rod-shaped cilia. SPT-deficient vertebrate cells were defective in ciliogenesis, and SPT mutations from patients with hereditary sensory neuropathy disrupted cilia, which could be restored by sphingolipid supplementation. These results reveal a conserved role of sphingolipid in cilium formation and link compromised sphingolipid production with ciliopathies.
Topics: Axoneme; Ceramides; Chlamydomonas; Cilia; Flagella; Protein Transport; Regeneration; Sphingolipids
PubMed: 35895683
DOI: 10.1073/pnas.2201096119