Encystation of Entamoeba histolytica in Axenic Culture

Entamoeba histolytica is a parasitic protozoan that causes amoebic dysentery, which affects approximately 90 million people each year worldwide. E. histolytica is transmitted through ingestion of food and water contaminated with the cyst form, which undergoes excystation in the small intestine to the trophozoite form that colonizes the large intestine. The reptile pathogen Entamoeba invadens has served as a model for studying stage conversion between the trophozoite and cyst form due to lack of reproducible encystation of E. histolytica in the laboratory. Although much has been learned about encystation and excystation using E. invadens, the findings do not fully translate to E. histolytica due to the extensive genetic and host differences between these species. Here, we present the first reproducible encystation of E. histolytica in vitro. The cysts produced were viable and displayed the four characteristic hallmarks: round shape, chitinous cell wall, tetranucleation, and detergent resistance. Using flow cytometry analysis, glucose limitation and high cell density were key for encystation, as for E. invadens. Entry into encystation was enhanced by the short-chain fatty acids acetate and propionate, unlike for E. invadens. This new model will now allow the further study of E. histolytica stage conversion, transmission, and treatment.

Globodera rostochiensis (yellow potato cyst nematode).

G. rostochiensis is a world wide pest of temperate areas, including both temperate countries and temperate regions of tropical countries, for example India's Nigrilis region. Distribution is linked to that of the potato crop. Potato cyst nematode is considered to have originated from the Andes region of South America, from where it spread to Europe with potatoes. The ease with which it has been transported across continents proves what a resilient pest it is. The cyst form which adheres to host roots, stolons and tubers and to soil particles during transportation gives rise to new infestations where climate and food source are both available and favourable. Secondary means of dispersal is through the movement of contaminated farm machinery, farming implements and contaminated footwear. Cysts are also successfully spread by wind dispersal, during winter storms or sand storms where top soil is redistributed. Rain which causes flooding and water to run off fields into trenches or irrigation channels also redistributes cysts into adjoining areas.

Long-Term Relationships: the Complicated Interplay between the Host and the Developmental Stages of Toxoplasma gondii during Acute and Chronic Infections

SUMMARYToxoplasma gondiirepresents one of the most common parasitic infections in the world. The asexual cycle can occur within any warm-blooded animal, but the sexual cycle is restricted to the feline intestinal epithelium.T. gondiiis acquired through consumption of tissue cysts in undercooked meat as well as food and water contaminated with oocysts. Once ingested, it differentiates into a rapidly replicating asexual form and disseminates throughout the body during acute infection. After stimulation of the host immune response,T. gondiidifferentiates into a slow-growing, asexual cyst form that is the hallmark of chronic infection. One-third of the human population is chronically infected withT. gondiicysts, which can reactivate and are especially dangerous to individuals with reduced immune surveillance. Serious complications can also occur in healthy individuals if infected with certainT. gondiistrains or if infection is acquired congenitally. No drugs are available to clear the cyst form during the chronic stages of infection. This therapeutic gap is due in part to an incomplete understanding of both host and pathogen responses during the progression ofT. gondiiinfection. While many individual aspects ofT. gondiiinfection are well understood, viewing the interconnections between host and parasite during acute and chronic infection may lead to better approaches for future treatment. The aim of this review is to provide an overview of what is known and unknown about the complex relationship between the host and parasite during the progression ofT. gondiiinfection, with the ultimate goal of bridging these events.

Stress Management in Cyst-Forming Free-Living Protists: Programmed Cell Death and/or Encystment

In the face of harsh conditions and given a choice, a cell may (i) undergo programmed cell death, (ii) transform into a cancer cell, or (iii) enclose itself into a cyst form. In metazoans, the available evidence suggests that cellular machinery exists only to execute or avoid programmed cell death, while the ability to form a cyst was either lost or never developed. For cyst-forming free-living protists, here we pose the question whether the ability to encyst was gained at the expense of the programmed cell death or both functions coexist to counter unfavorable environmental conditions with mutually exclusive phenotypes.

Acanthamoebadifferentiation: a two-faced drama ofDr Jekyll and Mr Hyde

SUMMARYThe ability of cyst-forming protists such asAcanthamoebato escape death by transforming into a cyst form, that is resistant to harsh physiological, environmental and pharmacological conditions, has continued to pose a serious challenge to human and animal health. A complete understanding of the fundamental principles of genome evolution and biochemical pathways of cellular differentiation offers unprecedented opportunities to counter detrimental outcomes.Acanthamoebacan elude inhospitable conditions by forming cysts. Here we unravel the processes involved in the phenotypic switching ofAcanthamoeba, which are critical in our efforts to find potential targets for chemotherapy.

The Secretory Apparatus of an Ancient Eukaryote: Protein Sorting to Separate Export Pathways Occurs Before Formation of Transient Golgi-like Compartments

Transmission of the protozoan parasite Giardia intestinalis to vertebrate hosts presupposes the encapsulation of trophozoites into an environmentally resistant and infectious cyst form. We have previously shown that cyst wall proteins were faithfully sorted to large encystation-specific vesicles (ESVs), despite the absence of a recognizable Golgi apparatus. Here, we demonstrate that sorting to a second constitutively active pathway transporting variant-specific surface proteins (VSPs) to the surface depended on the cytoplasmic VSP tail. Moreover, pulsed endoplasmic reticulum (ER) export of chimeric reporters containing functional signals for both pathways showed that protein sorting was done at or very soon after export from the ER. Correspondingly, we found that a limited number of novel transitional ER-like structures together with small transport intermediates were generated during encystation. Colocalization of transitional ER regions and early ESVs with coat protein (COP) II and of maturing ESVs with COPI and clathrin strongly suggested that ESVs form by fusion of ER-derived vesicles and subsequently undergo maturation by retrograde transport. Together, the data supported the hypothesis that in Giardia, a primordial secretory apparatus is in operation by which proteins are sorted in the early secretory pathway, and the developmentally induced ESVs carry out at least some Golgi functions.