Biology subjects

de Souza, W.

Publications and source records attributed to de Souza, W..

5 recordsLinked to original sources

bioRxiv2022

Antibodies to protozoan variable surface antigens induce antigenic variation

The genomes of most protozoa encode families of variant surface antigens, whose mutually exclusive changes in expression allow parasitic microorganisms to evade the host immune response1,2. It is widely assumed that antigenic variation in protozoan parasites is accomplished by the spontaneous appearance within the population of cells expressing antigenic variants that escape antibody-mediated cytotoxicity1,2. Here we show, both in vitro and in animal infections, that antibodies to Variant-specific Surface Proteins (VSPs) of the intestinal parasite Giardia lamblia are not cytotoxic, inducing instead VSP clustering into liquid-ordered phase membrane microdomains that trigger a massive release of microvesicles carrying the original VSP and switch in expression to different VSPs by a calcium-dependent mechanism. Surface microvesiculization and antigenic switching are also stimulated when Trypanosoma brucei and Tetrahymena thermophila are confronted to antibodies directed to their GPI-anchored variable surface glycoproteins. This novel mechanism of surface antigen clearance throughout its release into microvesicles coupled to the stochastic induction of new phenotypic variants not only changes the current paradigm of spontaneous antigenic switching but also provides a new framework for understanding the course of protozoan infections as a host/parasite adaptive process.

microbiology↗

bioRxiv2020

Morphological and biochemical repercussions of Toxoplasma gondii infection in a 3D human brain neurospheres model

BackgroundToxoplasmosis is caused by the parasite Toxoplasma gondii that can infect the central nervous system (CNS), promoting neuroinflammation, neuronal loss, neurotransmitter imbalance and behavioral alterations. T. gondii infection is also related to neuropsychiatric disorders such as schizophrenia. The pathogenicity and inflammatory response in rodents are different to the case of humans, compromising the correlation between the behavioral alterations and physiological modifications observed in the disease. In the present work we used BrainSpheres, a 3D CNS model derived from human pluripotent stem cells (iPSC), to investigate the morphological and biochemical repercussions of T. gondii infection in human neural cells. MethodsWe evaluated T. gondii ME49 strain proliferation and cyst formation in both 2D cultured human neural cells and BrainSpheres. Aspects of cell morphology, ultrastructure, viability, gene expression of neural phenotype markers, as well as secretion of inflammatory mediators were evaluated for 2 and 4 weeks post infection in BrainSpheres. ResultsT. gondii can infect BrainSpheres, proliferating and inducing cysts formation, neural cell death, alteration in neural gene expression and triggering the release of several inflammatory mediator. ConclusionsBrainSpheres reproduce many aspects of T. gondii infection in human CNS, constituting a useful model to study the neurotoxicity and neuroinflammation mediated by the parasite. In addition, BrainSpheres can be an important tool for better understanding the possible correlation between psychiatric disorders and human CNS infection with T. gondii

neuroscience↗

bioRxiv2020

Ultrastructural analysis of SARS-CoV-2 interactions with the host cell via high resolution scanning electron microscopy

SARS-CoV-2 is the cause of the ongoing COVID-19 pandemic. Here, we investigated the interaction of this new coronavirus with Vero cells using high resolution scanning electron microscopy. Surface morphology, the interior of infected cells and the distribution of viral particles in both environments were observed 2 and 48 hours after infection. We showed areas of viral processing, details of vacuole contents, and viral interactions with the cell surface. Intercellular connections were also approached, and viral particles were adhered to these extensions suggesting direct cell-to-cell transmission of SARS-CoV-2. HighlightsWe used high resolution scanning electron microscopy to investigate Vero cells infected with SARS-CoV-2 at 2 and 48 hours post-infection. The central conclusions of this work include: O_LIInfected cells display polarization of their cytosol forming a restricted viroplasm-like zone dedicated to virus production and morphogenesis. C_LIO_LIThis is the first demonstration of SARS-CoV-2 attachment by scanning electron microscopy. C_LIO_LIThis is the first scanning electron microscopy images of the interior of SARS-CoV-2 infected cells and exploration of their vacuole contents. C_LIO_LIPerspective-viewing of bordering vesicles in close association with vacuoles. C_LIO_LIObservation of membrane ruffles and structures suggestive of exocytosis on the surface of infected cells. C_LIO_LIThe first demonstration of viral surfing in cell-to-cell communication on SARS-CoV-2 infection. C_LI

microbiology↗

bioRxiv2020

Let it bud: an ultrastructural study of Cryptococcus neoformans surface during budding events

Cryptococcus neoformans is a fungal pathogen that causes life-threatening infections in immunocompromised individuals. It is surrounded by three concentric structures that separate the cell from the extracellular space: the plasma membrane, the cell wall and the polysaccharide capsule. Although several studies have revealed the chemical composition of these structures, little is known about their ultrastructural organization and remodeling during C. neoformans budding event. Here, by combining the state-of-the-art in light and electron microscopy techniques we describe the morphological remodeling that occurs synergistically among the capsule, cell wall and plasma membrane during budding in C. neoformans. Our results show that the cell wall deforms to generate a specialized budding region at one of the cells poles. This region subsequently begins to break into layers that are slightly separated from each other and with thick tips. We also observe a reduction in density of the capsular polysaccharide around these specialized regions. Daughter cells present a distinct spatial organization, with polysaccharide fibers aligned in the direction of budding. In addition, to control the continuous openings between mother and daughter cells, the latter developed a strategy to shield themselves by forming multilamellar membrane structures in conjunction with their capsules. Together, our findings provide compelling ultrastructural evidence for a dynamic C. neoformans surface remodeling during budding and may have important implications for future studies exploring these remodeled specialized regions as drug-targets against cryptococcosis.

microbiology↗

bioRxiv2019

Control of assembly of extra-axonemal structures: the paraflagellar rod of trypanosomes

Eukaryotic flagella are complex microtubule based organelles and in many organisms there are extra-axonemal structures present, including the outer dense fibres of mammalian sperm and the paraflagellar rod (PFR) of trypanosomes. Flagellum assembly is a complex process occurring across three main compartments, the cytoplasm, the transition fibre-transition zone, and the flagellum. It begins with translation of protein components, followed by their sorting and trafficking into the flagellum, transport to the assembly site and then incorporation. Flagella are formed from over 500 proteins; the principles governing axonemal component assembly are relatively clear. However, the coordination and sites of extra-axonemal structure assembly processes are less clear. We have discovered two cytoplasmic proteins in T. brucei that are required for PFR formation, PFR assembly factors 1 and 2. Deletion of either PFR-AF1 or PFR-AF2 dramatically disrupted PFR formation and caused a reduction in the amount of major PFR proteins. The presence of cytoplasmic factors required for PFR formation aligns with the concept of processes occurring across multiple compartments to facilitate axoneme assembly and this is likely a common theme for extra-axonemal structure assembly. Summary statementEukaryotic flagella are complex organelles. In many organisms there are extra-axonemal structures including the trypanosome paraflagellar rod. We have discovered two cytoplasmic proteins that are required for paraflagellar rod formation.

cell biology↗