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Stay tuned! It is an Exciting Era for the Biology of Cilia and Flagella
No full textCilia and flagella are ubiquitous organelles in eukaryotic cells where they perform both sensory and motile functions. Many scientific papers published recently start with this sentence or have it in their introduction: Are scientists losing their creativity? There is another explanation: the plethora of new and exciting data published recently on the biology of cilia and flagella including results on the pivotal role of the primary cilium in development, and their involvement in many diseases, are focusing the attention of an increasing
number of laboratories.
This status of this research area has been fully confirmed by the success of the recent FASEB summer research conference on the Biology of Cilia and Flagella organized by Joel Rosenbaum (Yale University, USA), George Witman (University of Massachusetts Medical School, USA) and Romano Dallai (University of Siena. Italy) (Fig. 1A,B)and held atVermont Academy (USA) on August 4–9, 2007. This venue saw the active participation of more than 170 scientists from USA, Japan, Europe and Canada (Fig. 1A). The program had 12 sessions with more than 80 speakers, and 2 poster sections with
about 60 presentations.
Because of his outstanding historical contribution to the field with his studies on male sterility and Kartagener’s Syndrome, the meeting was dedicated to Dr. Bjorn Afzelius (Fig. 1C) (University of Stockholm) who, unfortunately, was unable to attend for health problems. During the opening ceremony Romano Dallai profiled the contributions of Dr. Afzelius based on more than 20 years of their scientific collaboration and friendship.
The keynote talk by George Witman also highlighted the contributions made by Bjorn Afzelius towards the identification of axonemal dynein arms as the molecular motors responsible for the microtubular sliding necessary for ciliary and flagellar beating (Afzelius, 1959). Witman emphasized the importance of Afzelius’ discovery of ultrastructural defects in cilia and flagella of patients affected by Kartagener’s Syndrome (Afzelius, 1976). His observations that patients with Situs inversus (Kartagener’s Syndrome) also were sterile were the first to pinpoint the cilium as the cause of sterility, and also to show that normal cilia were required for the development of proper body symmetry; but it was unknown at that time why the ciliary axoneme defects caused these defects in the body symmetry. Witman then reviewed the most important discoveries made recently on cilia and flagella starting with the first description of Intraflagellar Transport made in Rosembaum’s lab (Kozminski et al., 1993), and the observations made at Tokyo in Hirokawa’s lab showing that the cilia in the embryonic node are motile and are necessary for the development
of normal left/right asymmetry during embryonic development (Nonaka et al., 1998). Caspary et al. identified in 2007 some 9 + 2 cilia in the embryonic node and, 20 years after the observations by Afzelius, a definitive link was made between ciliary motility and the cellular bases of situs inversus in Kartagener’s syndrome. In the last section of his talk Witman reviewed the studies relating polycystic kidney disease (PKD) in mammals to defects in primary cilia. After this first evidence relating primary cilia with a specific disease, many other papers were published demonstrating a connection between ciliary functions and several other cystic, developmental and metabolic diseases for which the term ciliopathy has been established. It is therefore not surprising that several sessions of the meeting were dedicated to cilia and disease
Cryotechniques for electron microscopy: A minireview
No full textAim of this paper is to present a short overview about the state of the art of the
so called cryotechniques for electron microscopy. These protocols have been
developed and implemented starting in the 1980’s as alternatives, or better to
say valid complements, to the standard protocols of chemical fixation
routinely used for structural studies of biological samples by electron
microscopy. The currently available and more commonly used protocols for
rapid freezing such as: plunging, slamming, jet freezing, and high pressure
freezing are illustrated and discussed shortly in the first section of this paper.
The second section deals with processing of frozen samples summarizing the
standard protocols of cryofracture, it then proceeds with the quick-freeze,
deep-etch protocol, and ends mentioning briefly the technique for
visualization of macromolecular structures after adsorption on mica, rapid
freezing, freeze drying, and rotary shadowing.
This paper ends with a section dedicated to cryo-electron microscopy: the
most recent and high resolution protocol for observation of cell organelles and
macromolecular assemblies in frozen hydrated conditions
The ultrastructure and biochemical characterization of axonemal dynein from Asphondylia ruebsaameni Kertesz (Diptera: Cecidomyiidae).
No full textSperm ultrastructure in Chironomoidea (Insecta, Diptera)
No full textThe fine structure of spermatozoa from several species of chironomids, of Culicoides sp. (Ceratopogonidae) and of Odagmia pontina (Simulidae) was studied. A synapomorphic feature, consisting of nine kidney-shaped structures forming the centriole adjunct, was found in the chironomid species. All members of Chironomoidea share a mono-layered acrosome and a flagellar axoneme, provided with accessory tubules with 15 protofilaments in their tubular wall. The axoneme has a 9+9+2 pattern, but in an unidentified species of chironomid, a 9+9+0 model was observed where the central complex and the spokes are missing. Sperm motility is, however, maintained in all the examined species. The spermatozoa of this taxon have the tendency to complete maturation during their progression along the deferent ducts. Thus, in the proximal region of these ducts, they often show remnants of the spermatid cytoplasm. © 2007 Elsevier Ltd. All rights reserved
The ultrastructure of the spermatheca of Mordellistena brevicauda (Coleoptera, Tenebrionoidea) and the associated bacterial cells
Full text linkThe ultrastructural study on the female reproductive system of the beetle M. brevicauda (Mordellidae) confirmed the positive correlation between the length of the sperm and the size of the female seminal receptacle (Spermatheca). The spermatheca of the species is characterized by an apical bulb-like structure where the spermathecal duct forms numerous folds filled with sperm. At this level many bacterial cells are present intermingled with the duct folds. Some are organized in large structures, such as bacteriomes, while other are single bacteriocytes. The latter are often found near the basal lamina of duct epithelium. In addition, some bacteria are visible in the cytoplasm of the duct epithelial cells. Interestingly, bacterial cells have never been observed in the duct lumen. The possible function of the bacterial cells is discussed
The giant sperm axoneme of the gall-midge fly Asphondylia ruebsaameni Kertesz: fine structure and development
No full textThe centriole adjunct of insects: Need to update the definition
No full textThe ancestral eukaryotes presumably had an MTOC (microtubule organizing center) which late gave origin to the centriole and the flagellar axoneme.The centrosome of insect early spermatids is in general composed of two components: a single centriole and a cloud of electron-dense pericentriolar material (PCM). During spermiogenesis, the centriole changes its structure and gives rise to a flagellar axoneme, while the proteins of PCM, gamma tubulin in particular, are involved in the production of microtubules for the elongation and shaping of spermatid components. At the end of spermiogenesis, in many insects, additional material is deposited beneath the nucleus to form the centriole adjunct (ca). This material can also extend along the flagellum in two accessory bodies (ab) flanking the axoneme.Among Homoptera Sternorrhyncha, a progressive modification of their sperm flagella until complete disappearance has been verified. In the Archaeococcidae Matsucoccus feytaudi, however, a motile sperm flagellum-like structure is formed by an MTOC activity. This finding gives support to the hypothesis that an evolutionary reversal has occurred in the group and that the cell, when a non-functional centriole is present, activates an ancestral structure, an MTOC, to form a polarized motile bundle of microtubules restoring sperm motility.The presence and extension of the centriole adjunct in the different insect orders is also enlisted
Sperm ultrastructure of Mantophasma zephyra (Insecta, Mantophasmatodea)
No full textThe ultrastructure of Mantophasma zephyra spermatozoa is described. Sperm cells have a trilayered acrosome with conspicuous extra-acrosomal material which expands along the nucleus. The nucleus is crossed anteriorly by a canal and its posterior end is embedded in the centriole adjunct material. A centriole with microtubular triplets is present. The flagellum has a 9+9+2 axonernal pattern, two partially crystallised mitochondrial derivatives, two membranous sacs and three connecting bands. The accessory microtubules are filled with dense material and have 16 protofilaments in their tubular wall. The intertubular material is not very expanded. In the seminal vesicles spermatozoa are stuck together to form spermatodesms, and their heads are also joined by adherens junctions. A cladistic analysis based on sperm features indicates a close relationship of Mantophasmatodea with Mantodea
Structure and biochemical properties of outer arm dynein from sperm axonemes of two insect species.
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