On the structural organization of the bacillary band of Trichuris muris under cryopreparation protocols and three-dimensional electron microscopy

Whipworms of the genus Trichuris are nematode parasites that infect mammals and can lead to various intestinal diseases of human and veterinary interest. The most intimate interaction between the parasite and the host intestine occurs through the anterior region of the nematode body, inserted into the intestinal mucosa during infection. One of the most prominent structures of the nematode surface found at the infection site is the bacillary band, a surface domain formed by a number of cells, mostly stichocytes and bacillary glands, whose structure and function are still under debate. Here, we used confocal microscopy, field emission scanning electron microscopy, helium ion microscopy, transmission electron microscopy and FIB-SEM tomography to unveil the functional role of the bacillary gland cell. We analyzed the surface organization as well as the intracellular milieu of the bacillary glands of Trichuris muris in high pressure frozen/freeze-substituted samples. Results showed that the secretory content is preserved in all gland openings, presenting a projected pattern. FIB-SEM analysis showed that the lamellar zone within the bacillary gland chamber is formed by a set of lacunar structures that may exhibit secretory or absorptive functions. In addition, incubation of parasites with the fluid phase endocytosis marker sulforhodamine B showed a time-dependent uptake by the parasite mouth, followed by perfusion through different tissues with ultimate secretion through the bacillary gland. Taken together, the results show that the bacillary gland possess structural characteristics of secretory and absorptive cells and unequivocally demonstrate that the bacillary gland cell functions as a secretory structure.

Taxonomy of Physaloptera mirandai (Nematoda: Physalopteroidea) based in three-dimensional microscopy and phylogenetic positioning

Gastrointestinal nematodes are important ecological assets for the maintenance of the biodiversity in the Atlantic Forest in Brazil. They parasitize a number of animals of the local fauna, in which some species can promote serious injuries in the stomach wall of their hosts, which may lead to death. Among these nematodes, parasites of the genus Physaloptera are known to parasitize mammals (particularly carnivores and small rodents), birds and reptiles, being important for the local biodiversity. In this work, three hundred and sixty-two nematodes were recovered from the stomach of twenty-one Metachirus nudicaudatus (Didelphimorphia: Didelphidae) collected in Duas Bocas Biological Reserve, State of Espírito Santo, one of the largest Atlantic Forest remnants and important wildlife refuge of the Atlantic Forest in Brazil. Analysis using fluorescence and scanning electron microscopy as well as phylogenetic assessment using the mitochondrial cytochrome c oxidase subunit I gene showed that the parasites belong to the Physaloptera. Our results show details of the nematode morphology including the cloacal papillae distribution, cuticular topography details, 2D and 3D measurements of the structures with taxonomic importance. Molecular data confirmed the validity of P. mirandai and the phylogeny supported the monophyly of the assemblage formed by Physaloptera and Turgida. The use of a combination of quantitative and multidimensional microscopy tools, such as 3D reconstruction and modeling, allied to phylogenetic analysis may provide grounds for a new approach on helminth taxonomy and structural characterization.

New insights into the in situ microscopic visualization and quantification of inorganic polyphosphate stores by 4',6-diamidino-2-phenylindole (DAPI)-staining

Inorganic polyphosphate (PolyP) is a biological polymer that plays important roles in the cell physiology of both prokaryotic and eukaryotic organisms. Among the available methods for PolyP localization and quantification, a 4',6-diamidino-2-phenylindole(DAPI)-based assay has been used for visualization of PolyP-rich organelles. Due to differences in DAPI permeability to different compartments and/or PolyP retention after fixation, a general protocol for DAPI-PolyP staining has not yet been established. Here, we tested different protocols for DAPI-PolyP detection in a range of samples with different levels of DAPI permeability, including subcellular fractions, free-living cells and cryosections of fixed tissues. Subcellular fractions of PolyP-rich organelles yielded DAPI-PolyP fluorescence, although those with a complex external layer usually required longer incubation times, previous aldehyde fixation and/or detergent permeabilization. DAPI-PolyP was also detected in cryosections of OCT-embedded tissues analyzed by multi-photon microscopy. In addition, a semi-quantitative fluorimetric analysis of DAPI-stained fractions showed PolyP mobilization in a similar fashion to what has been demonstrated with the use of enzyme-based quantitative protocols. Taken together, our results support the use of DAPI for both PolyP visualization and quantification, although specific steps are suggested as a general guideline for DAPI-PolyP staining in biological samples with different degrees of DAPI and PolyP permeability.