1,721,040 research outputs found
The sperm glycocalyx of Pezotettix giornai (Rossi) (Insecta: Orthoptera) after quick-freeze, deep-etching
No full textMature spermatozoa of the catantopid orthopteran Pezotettix giornai are characterized by an elaborate external glycocalyx. This coating is removed during storage in spermatheca allowing preparation of sperm to their interaction with female gametes. We have studied this membrane coating in mature sperm by both conventional transmission electron microscopy and quick-freeze, deep-etching. The ultrastructural studies allowed visualization of three different domains in glycocalyx of testicular and deferent duct spermatozoa and only two in sperm cell isolated from seminal vesicles. These observations thus demonstrate that a remodeling of the male germ cell starts already during their storage in the seminal vesicle and is completed in the female genital tract. In this paper a three-dimensional (3D) model of sperm external coating is presented and discussed
The organization of actin in the apical region of insect midgut cells after deep-etching
No full textThe midgut of Tenebrio larvae, which reveals a strong reaction for F-actin beneath the apical microvilli after rhodamine-phalloidin treatment, was studied to examine localization of actin. Freeze-fracture replicas of the lateral midgut borders reveal that smooth septate junctions with their characteristic rows of aligned intramembranous particles (IMPs) are found on the upper third of these borders. Thin sections show that short punctate adhering junctions may also occur on this part of the border. Deep etching reveals that the rows of septate junctional IMPs are closely juxtaposed to cytoplasmic fibrils that demonstrate the structural features typical of actin as well as heavy meromyosin labeling. These actin fibrils appear to insert into the junctional membranes. Hence cytoskeletal elements have an intimate spatial association with the membrane modifications typical of intercellular septate junctions and may be involved in the positioning of their component IMPs and also possibly of their septal ribbons
Crystalloid body, refractile body and virus-like particles in Apicomplexa: what is in there?
No full textThe phylum of Apicomplexa comprises parasitic protozoa that share distinctive features such as the apical complex, the apicoplast, specialized cytoskeletal components and secretory organelles. Other unique cytoplasmic inclusions sharing similar features have been described in some representatives of Apicomplexa, although under different denominations. These are the crystalloid body, present for example in Cryptosporidium, Plasmodium and Cystoisospora; the refractile body in Eimeria and Lankesterella; and virus-like particles, also present in Eimeria and Cryptosporidium. Yet, the specific role of these cytoplasmic inclusions in the cell cycle of these protozoa is still unknown. Here, we discuss their morphology, possible inter-relatedness and speculate upon their function to bring these organelles back to the attention of the scientific community and promote new interest towards original research on these elusive structures
Fine structure of the salivary glands of Heliothrips haemorrhoidalis (Bouchè) (Thysanoptera: Thripidae)
No full textSalivary glands of Heliothrips haemorrhoidalis consist of two parts: the tubular and the ovoidal glands. The tubular glands have microvillate cells, which are rich in mitochondria, associated with sinuous plasma membrane and produce a watery secretion. The ovoid glands have cells that are rich in rough endoplasmic reticulum and Golgi complexes and produce viscous secretions of proteinaceous material. It is hypothesized that the viscous secretion contains enzymes that could be activated in appropriate ionic conditions provided by the watery secretion. This mechanism could be realized when the two products are aspirated by the cibarial pump, mixing and flowing into the mouthcone before being injected into the plant cells
Sperm structure of Mecoptera and Siphonaptera (Insecta) and the phylogenetic position of Boreus hyemalis
No full textSperm ultrastructure has been studied in three species of the taxa Mecoptera and Siphonaptera. The spermatozoon of the scorpion fly Panorpa germanica shows an apical bilayered acrosome, a helicoidal nucleus, a centriolar region and a 9+2 flagellar axoneme helicoidally arranged around a long mitochondrial derivative. A second mitochondrial derivative is very short and present only in the centriolar region. A single accessory body is present and it is clearly formed as a prolongation of the centriole adjunct material. Two lateral lamellae run parallel to the nucleus. The snow fly Boreus hyemails has a conventional sperm structure and shows a bilayered acrosome, a long nucleus, a centriolar region, two mitochondrial derivatives and two accessory bodies. The axoneme is of the 9+2 type and is flattened at the tail tip. Both P. germanica and B. hyemalis have two longitudinal extra-axonemal rods and have a glycocalyx consisting of longitudinal parallel ridges or filaments. The spermatozoon of the flea Ctenocephalides canis has a long apical bilayered acrosome, a nucleus, a centriolar region, a 9+2 axoneme wound around two unequally sized mitochondrial derivatives, and two triangular accessory bodies. In the posterior tail end the flagellar axoneme disorganises and a few microtubular doublets run helicoidally around the remnant mitochondrial derivative. The glycocalyx consists of fine transverse striations. In all three species, the posterior tail tip is characterised by a dense matrix embedding the disorganised axoneme. From this comparative analysis of the sperm structure it is concluded that Mecoptera, as traditionally defined, is monophyletic and that B. hyemalis is a member of Mecoptera rather than of Siphonaptera
Sperm ultrastructure in several species of Carabidae beetles (Insecta, Adephaga) and their organization in spermatozeugmata
No full textSperm structure of seven species from different Carabidae tribes was studied. Carabus preslii and Carabus granulatus interstitialis form sperm bundles (spermatozeugmata) in which the heads of conventional insect sperm cells are embedded in the apical cap (spermatostyle), leaving the posterior flagella free. On the contrary, Pterostichus morio, Pterostichus melas, Pterostichus melanarius and Amara aulica form complex spermatozeugmata bearing conspicuous axial spermatostyles associated with lateral groups of sperm. Individual sperm cells are contained in chambers delimited by laminar extensions of the cortical region of the spermatostyle. Demetrias atricapillus shares the general spermatozeugma structure with the above species, but the anterior spermatostyle region has a different structure and posteriorly, the lateral groups of sperm are separated from the spermatostyle but remain connected to it by peduncles consisting of extensions of the cortical region of the spermatostyle. The sperm of the species examined in the study consist of a short, flat acrosomal cap and, with the exception of the Carabus species, show long nuclei which extend parallel to the axonemes, along the flagella. Two relatively small mitochondrial derivatives and two small accessory bodies flank the axoneme. These bodies become very thick in the posterior flagellar region of D. atricapillus. The study revealed different spermatozeugma models and different sperm organization in the Carabidae family
Ultrastructure of the male accessory glands of Allacma fusca (Insecta, Collembola)
No full textThe accessory glands of Allacma fusca(L.) (Insecta, Collembola, Sminthuridae) consist of a series of
secretory units that are arranged in parallel and open into the ejaculatory duct. Each unit is composed of microvillate
cells stacked around a common cavity. Basal cells are involved in ion-control of fluids from the hemocoel to
the cavity. The intermediate and apical cells, which have a laminar appearance and contain many microtubules,
are involved in the structural integrity of the unit. Supporting cells ensheath the most apical cells. Large openings
in the cuticle allow the gland secretion to flow into the ejaculatory duct lumen. These openings are protected by a
porous cuticle different from that lining the epithelium of the ejaculatory duct. Conspicuous muscle fibers run
along the lateroventral side of the ejaculatory duct beneath the insertion of the accessory glands. The fine structure
of the accessory glands indicates that they are type I ectodermic glands as defined by Noirot & Quennedey
(1974). Their function could be to control the fluidity of the material for spermatophore formation and to ensure the
proper physiological conditions for spermatozoa stored in the ejaculatory duct lumen
Coevolution between female seminal receptacle and sperm morphology in the semiaquatic measurer bug Hydrometra stagnorum L. (Heteroptera, Hydrometridae)
No full textThe coevolution between sperm length and size of the female sperm-storage organs is described for the first time within Heteroptera. The long sperm of the measurer bug Hydrometra stagnorum is characterized by the unusually long acrosome with its anterior region helically arranged, and by a very short nucleus. The sperm flagellum has a 9 + 9+2 conventional axoneme and crystallized mitochondrial derivatives. The female spermatheca consists of an extraordinarily long spermathecal duct ending with an apical spermathecal bulb into which flows also the secretions of a relatively short spermathecal gland. Both spermathecal duct and gland have a thin epithelium lined by a cuticle, beneath which a complex of secretory and duct forming cells are present. The secretions of these two structures flow into the apical spermathecal bulb. A thick layer of muscle fibers surrounds the epithelium. These results confirm the opinion that the dimensions of the female reproductive sperm-storage organs are able to drive the sperm morphology
New details on the fine structure of the rhoptry of Toxoplasma gondii
No full textRhoptries are organelles that have important, complex roles in Apicomplexa
biology. During Toxoplasma gondii infection, these organelles take part in several essential and
complex processes that include host cell entry and parasite development. Using different electron
microscopy techniques, we characterized the fine morphology of the rhoptries of two of the most important
life stages of T. gondii: the tachyzoite and the bradyzoite forms. The observed tachyzoite
and bradyzoite rhoptries had delimited regions characterized by a dark and electron-dense neck,
an amorphous and less electron-dense bulb, and a region of intermediate electron density, which
connects the bulb to the neck. Metal replicas of frozen-fractured tachyzoites showed intramembranous
particles of different densities and sizes on the fractured faces of rhoptry membranes. Both in
tachyzoites and bradyzoites, the intramembranous particles were arranged in distinctive parallel
arrays that decorated most part of these organelles. Tubulo-vesicular subcompartments and free
particles within the rhoptry lumen were observed on freeze-fractured replicas. Cryo-fixed, deepetched
samples showed several pore-like structures localized in the bulb portion. No obvious evidence
was found of a possible connection between rhoptries and micronemes
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