The structural organization of the pathogenic protozoan Tritrichomonas foetus as seen in replicas of quick frozen,freeze-fractured and deep etched cells

Summary— The quick-freezing and freeze-etching technique was used to analyse the cytoskeleton of Tritrichomonas foetus, a pathogenic protozoan of the urogenital tract of cattle. The cytoplasm presented a network of filamentous structures interacting with each other, with the surface of the hydrogenosomes and the nuclear membrane. Two nm wide filamentous structures were found in the luminal space of the Golgi complex, connecting the two faces of each cisterna. The microtubules of the pelta-axostyle system were connected by bridges 30–40 nm long and 10 nm wide, regularly spaced with an interval of 25 nm. The costa is a structure formed by a complex array of filaments and globous structures. It seems to be connected to the recurrent flagellum through a complex network formed by 15 and 10 nm wide filaments which emerge from the peripheral region of the costa and penetrate into the surface projections of the protozoan body to which the recurrent flagellum is attached. Other filaments were seen connecting the surface of these projections with the surface of the flagellum.     

Myosin IIIB uses an actin-binding motif in its espin-1 cargo to reach the tips of actin protrusions

Myosin IIIA (MYO3A) targets actin protrusion tips using a motility mechanism dependent on both motor and tail actin-binding activity [1]. We show that myosin IIIB (MYO3B) lacks tail actin-binding activity and is unable to target COS7 cell filopodia tips, yet is somehow able to target stereocilia tips. Strikingly, when MYO3B is coexpressed with espin-1 (ESPN1), a MYO3A cargo protein endogenously expressed in stereocilia [2], MYO3B targets and carries ESPN1 to COS7 filopodia tips. We show that this tip localization is lost when we remove the ESPN1 C terminus actin-binding site. We also demonstrate that, like MYO3A [2], MYO3B can elongate filopodia by transporting ESPN1 to the polymerizing end of actin filaments. The mutual dependence of MYO3B and ESPN1 for tip localization reveals a novel mechanism for the cell to regulate myosin tip localization via a reciprocal relationship with cargo that directly participates in actin binding for motility. Our results are consistent with a novel form of motility for class III myosins that requires both motor and tail domain actin-binding activity and show that the actin-binding tail can be replaced by actin-binding cargo. This study also provides a framework to better understand the late-onset hearing loss phenotype in patients with MYO3A mutations.     

Phylogenetic relationships in genus <Emphasis Type="Italic">Arachis</Emphasis> based on ITS and 5.8S rDNA sequences

Background  

The genus Arachis comprises 80 species and it is subdivided into nine taxonomic sections (Arachis, Caulorrhizae, Erectoides, Extranervosae, Heteranthae, Procumbentes, Rhizomatosae, Trierectoides, and Triseminatae). This genus is naturally confined to South America and most of its species are native to Brazil. In order to provide a better understanding of the evolution of the genus, we reconstructed the phylogeny of 45 species using the variation observed on nucleotide sequences in internal transcribed spacer regions (ITS1 and ITS2) and 5.8 S of nuclear ribosomal DNA.     

Salivary glands of <Emphasis Type="Italic">Amblyomma cajennense</Emphasis> (Acari: Ixodidae): a histological and an ultrastructural overview

The present study on the salivary glands of semi-engorged Amblyomma cajennense females has identified the various cell types present in this tissue and allowed its morphohistochemical characterization. Marking techniques were applied to detect polysaccharides (PAS), proteins (bromophenol blue), lipids (Nile blue) and calcium (von Kossa), as well as those of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results obtained by TEM showed and confirmed that these individuals’ glands are also formed by round acini that are connected to the common excretory duct through acinar and intermediate ducts. Histological data as well as ultrastructural ones showed that the glands are formed by types I, II and III acini. In this study with salivary glands polysaccharides, proteins, lipids and calcium were observed in the cytoplasm and/or cell secretion granules—both free or forming complexes, as the intensity of the marking varied according to the cell as well as the type of acini analyzed, showing the structural and functional complexity of the tick salivary glands, characteristics that give the multifunctional character to this organ.     

Regulation of stereocilia length by myosin XVa and whirlin depends on the actin-regulatory protein Eps8

Myosin XVa (MyoXVa) and its cargo whirlin are implicated in deafness and vestibular dysfunction and have been shown to localize at stereocilia tips and to be essential for the elongation of these actin protrusions [1-4]. Given that whirlin has no known actin-regulatory activity, it remains unclear how these proteins work together to influence stereocilia length. Here we show that the actin-regulatory protein Eps8 [5] interacts with MyoXVa and that mice lacking Eps8 show short stereocilia compared to MyoXVa- and whirlin-deficient mice. We show that Eps8 fails to accumulate at the tips of stereocilia in the absence of MyoXVa, that overexpression of MyoXVa results in both elongation of stereocilia and increased accumulation of Eps8 at stereocilia tips, and that the exogenous expression of MyoXVa in MyoXVa-deficient hair cells rescues Eps8 tip localization. We find that Eps8 also interacts with whirlin and that the expression of both Eps8 and MyoXVa at stereocilia tips is reduced in whirlin-deficient mice. We conclude that MyoXVa, whirlin, and Eps8 are integral components of the stereocilia tip complex, where Eps8 is a central actin-regulatory element for elongation of the stereocilia actin core.     

Membrane vesicles in magnetotactic bacteria

Magnetotactic bacteria are microorganisms that respond to magnetic fields. We have studied the surface ultrastructure of Magnetospirillum magnetotacticum and uncultured magnetotactic bacteria from a marine environment using transmission electron microscopy and freeze-etching. Numerous membrane vesicles were observed on the surface of Magnetospirillum magnetotacticum bacteria. All uncultured magnetotactic bacteria presented membrane vesicles on their surface in addition to an extensive capsular material and an S-layer formed by particles arranged in a hexagonal symmetry. We did not observe any indication of electron-dense precipitation on the surface of these microorganisms. Our results indicate that membrane vesicles are a common characteristic of magneto-tactic bacteria in natural sediments.     

Calcium-dependent mitochondrial oxidative damage promoted by 5-aminolevulinic acid

Swelling of isolated rat liver mitochondria is shown to be induced by metal-catalyzed 5-aminolevulinic acid (ALA) aerobic oxidation, a putative endogenous source of reactive species (ROS), at concentrations as low as 50–100 μM. In this concentration range, ALA is estimated to occur in the liver of acute intermittent porhyria patients. Removal of Ca²⁺ (10 μM) from the suspension of isolated rat liver mitochondria by added EGTA abolishes both the ALA-induced transmembrane-potential collapse and mitochondrial swelling. Prevention of the ALA-induced swellling by addition of ruthenium red prior to mitochondrial energization by succinate demonstrates the deleterious involvement of internal Ca²⁺. Addition of MgCl₂ at concentrations higher than 2.5 mM, prevents the ALA-induced mitochondrial swelling, transmembrane potential collapse and Ca²⁺ efflux. This indicates that Mg²⁺ protects against the mitochondrial damage promoted by ALA-generated ROS. The ALA-induced mitochondrial damage might be a key event in the liver mitochondrial damage of acute intermittent porphyria patients reported elsewhere.     

Cytotoxic effects of permethrin in oocytes of <Emphasis Type="Italic">Rhipicephalus sanguineus</Emphasis> (Acari: Ixodidae) fully engorged females: I. Direct or indirect action of the acaricide in germ cells?

Given the wide use of synthetic chemicals to control ticks, this study evaluated the effects of the permethrin pyrethroid on oocytes of Rhipicephalus sanguineus fully engorged females in order to examine whether this compound, in addition to the proven neurotoxic effect, also acts directly on germ cells. The results revealed that permethrin effectively inhibits and/or interrupts the reproductive process of R. sanguineus. Exposed oocytes exhibited prominent structural changes such as altered shape of cells and germ vesicle (oocyte nucleus), cytoplasmic vacuolation, and decrease of yolk granules. The composition of the latter, however, was not altered. These findings confirm those already reported by Roma et al. (Food Chem Toxicol 48:825–830, 2010) demonstrating that permethrin acts on germ cells of R. sanguineus via direct absorption from the hemolymph by pedicel cells, or by the oocyte plasmic membrane. On the other hand, these results contradict studies reporting that acaricides act exclusively on the nervous systems of ticks and that all the changes in other organs are a result from the indirect action of these chemical compounds, because blocking of the nervous system would compromise the normal metabolism of other organs (dependent on sensory information).     

Neotropical rainforest restoration: comparing passive,plantation and nucleation approaches

Neotropical rainforests are global biodiversity hotspots and are challenging to restore. A core part of this challenge is the very long recovery trajectory of the system: recovery of structure can take 20–190 years, species composition 60–500 years, and reestablishment of rare/endemic species thousands of years. Passive recovery may be fraught with instances of arrested succession, disclimax or emergence of novel ecosystems. In these cases, active restoration methods are essential to speed recovery and set a desired restoration trajectory. Tree plantation is the most common active approach to reestablish a high density of native tree species and facilitate understory regeneration. While this approach may speed the successional trajectory, it may not achieve, and possibly inhibit, a long-term restoration trajectory towards the high species diversity characteristic of these forests. A range of nucleation techniques (e.g., tree island planting) are important restoration options: although they may not speed recovery of structure as quickly as plantations, their emphasis on natural regeneration processes may enable greater and more natural patterns of diversity to develop. While more work needs to be done to compare forest restoration techniques in different environmental contexts, it appears that nucleation and, at times, passive restoration may best preserve the diverse legacy of these forested systems (both with lower costs). An integrated approach using both plantation productivity but also the natural functions associated with nucleation may develop composition and diversity trajectory desired in Neotropical conservation efforts.