Developmental changes in the localization of calcium binding sites in Acanthamoeba castellanii

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

The 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.

Calcium pathway through a mineralizing epithelium in the crustacean Orchestia in pre-molt: ultrastructural cytochemistry and X-ray microanalysis

During the pre-exuvial period of the terrestrial crustacean Orchestia, the calcium of the old cuticle is almost entirely reabsorbed and stored as calcareous concretions in the lumen of the midgut posterior caeca. The elaboration of these concretions is due to transport by the caecal epithelium. With ultrastructural cytochemistry controlled by X-ray microanalysis, it can be demonstrated that the main sites of ionized or ionizable calcium are the apical microvilli and an extracellular (lateral and basal) network of channels. Direct precipitating cytochemical methods, using potassium pyroantimonate or pyrophosphate, potassium oxalate or oxalic acid, sodium fluoride, sodium tungstate, and indirect substitution methods, using lead acetate or nitrate and cobalt nitrate were comparatively used. The results are interpreted in favour of the hypothesis of an extracellular transport pathway for calcium through the lateral smooth septate junctions, in conjunction with a more classical apical transport through the microvilli.

Growth phase dependent alterations in the surface coat of Acanthamoeba castellanii

Application of ruthenium red, cationized ferritin and concanavalin A to exponentially growing trophozoites reveals on their plasma membrane negatively charged surface coat bearing sugar residues. In the coat of trophozoites from advanced stationary growth phase no sugar residues can be visualized. In mature cysts the external layer of their wall is negatively charged, however, on their protoplast surface no terminals reacting with the 2 polycations, or with concanavalin A can be revealed, even though the penetration of the reagents has been ensured by enzymatic impairing of the cyst wall. The results are confronted with the known facts concerning alterations of physiological properties of plasma membrane occurring during the life cycle of Acanthamoeba.