Protein trafficking through the endosomal system prepares intracellular parasites for a home invasion

Toxoplasma (toxoplasmosis) and Plasmodium (malaria) use unique secretory organelles for migration, cell invasion, manipulation of host cell functions, and cell egress. In particular, the apical secretory micronemes and rhoptries of apicomplexan parasites are essential for successful host infection. New findings reveal that the contents of these organelles, which are transported through the endoplasmic reticulum (ER) and Golgi, also require the parasite endosome-like system to access their respective organelles. In this review, we discuss recent findings that demonstrate that these parasites reduced their endosomal system and modified classical regulators of this pathway for the biogenesis of apical organelles

Autophagy Protein Atg3 is Essential for Maintaining Mitochondrial Integrity and for Normal Intracellular Development of Toxoplasma gondii Tachyzoites

Autophagy is a cellular process that is highly conserved among eukaryotes and permits the degradation of cellular material. Autophagy is involved in multiple survival-promoting processes. It not only facilitates the maintenance of cell homeostasis by degrading long-lived proteins and damaged organelles, but it also plays a role in cell differentiation and cell development. Equally important is its function for survival in stress-related conditions such as recycling of proteins and organelles during nutrient starvation. Protozoan parasites have complex life cycles and face dramatically changing environmental conditions; whether autophagy represents a critical coping mechanism throughout these changes remains poorly documented. To investigate this in Toxoplasma gondii, we have used TgAtg8 as an autophagosome marker and showed that autophagy and the associated cellular machinery are present and functional in the parasite. In extracellular T. gondii tachyzoites, autophagosomes were induced in response to amino acid starvation, but they could also be observed in culture during the normal intracellular development of the parasites. Moreover, we generated a conditional T. gondii mutant lacking the orthologue of Atg3, a key autophagy protein. TgAtg3-depleted parasites were unable to regulate the conjugation of TgAtg8 to the autophagosomal membrane. The mutant parasites also exhibited a pronounced fragmentation of their mitochondrion and a drastic growth phenotype. Overall, our results show that TgAtg3-dependent autophagy might be regulating mitochondrial homeostasis during cell division and is essential for the normal development of T. gondii tachyzoites

Geometric uncertainty propagation in laminar flows solved by RBF-FD meshless technique

The Non-Intrusive Polynomial Chaos method is employed to analyze incompressible and laminar fluid flows in presence of geometric uncertainties on the boundaries, which are described by stochastic variables with known probability distribution. Non-Intrusive methods allow the use of existing deterministic solvers, which are treated as black boxes. Therefore the quantification of the fluid flow uncertainties is based on a set of deterministic response evaluations. The required thermo-fluid dynamics solutions over the deterministic geometries are obtained through a Radial Basis Function-generated Finite Differences (RBF-FD) meshless method. The validation of the presented approach is carried out through analytical test cases (isothermal flow between non-parallel walls) with one geometric uncertainty. The applicability of the presented approach to practical problems is then presented through the prediction of geometric uncertainty effects on the non-isothermal flow over a heated backward-facing step

Fictitious Domain Approach for Spectral/hp Element Method

We propose a fictitious domain method combined with spectral/hp elements for the solution of second-order differential problems. This paper presents the formulation, validation and application of fictitiuos domain-spectral/hp element algorithm to one- and two-dimensional Poisson problems. Fictitious domain methods allow problems formulated on an intricate domain Ω to be solved on a simpler domain Π containing Ω. The Poisson equation, extended to the new domain Π, is expressed as an equivalent set of first-order equations by introducing the gradient as an additional indipendent variable, and spectral/hp element method is used to develop the discrete model. Convergence of relative energy norm η is verified computing smooth solutions to one- and two-dimensional Poisson equations. Thermal field calculations for heatsink profile is presented to demonstrate the predictive capability of the proposed formulation

Propagation of geometric uncertainties in heat transfer problems solved by RBF-FD meshless method

The design of engineering components must take into account the manufacturing tolerances of production processes since they lead to uncertainties in the behaviour of the products. It is therefore of valuable practical interest to quantify such uncertainties, with particular reference to problems involving geometrical uncertainties of the boundaries. This task is carried out in the present work by coupling the Non-Intrusive Polynomial Chaos (PC) method, employed for the quantification of uncertainties, with a Radial Basis Function Finite Differences (RBF-FD) meshless method, employed for the numerical simulations. The PC method with the Non-Intrusive formulation allows the use of existing deterministic solvers for the accurate prediction of the sought random response, i.e., the statistic moments of the involved variables. The RBF-FD method is therefore employed as a black box solver for the required set of problems defined over deterministic domains. The main advantage of the RBF-FD meshless method over traditional mesh-based methods is its capability of easily deal with practical problems defined over complex-shaped domains since no traditional mesh is required. The geometrical flexibility of the RBF-FD is even more advantageous in the context of geometric uncertainty quantification with the Non-Intrusive PC method since different solutions over different geometries are required. The applicability of the proposed approach to practical problems is then presented through the prediction of geometric uncertainty effects for a tube heat exchanger under natural convection where a 2D steady incompressible flow is considered