ALBERT

Notes: One third of a collection of cloned Stylonychia pustulata micronuclear DNA PstI fragments were found to be of a similar size, consistent with their being members of a repetitious sequence family with a repeat size of about 160 base pairs. Cross-hybridization experiments confirmed that these small cloned fragments are related by sequence homology. Hybridization of the cloned repetitious sequences to PstI digested micronuclear DNA revealed a “ladder” of bands (step size = 160 base pairs), indicating that the repeats are found in tandem arrays. This is the first demonstration of highly repetitious, tandemly repeated sequences in a ciliated protozoan.

Notes: The erythrocytic developmental cycle of Plasmodium falciparum can be conveniently divided into the ring, trophozoite, and schizont stages based on morphology and metabolism. Using highly synchronous cultures of P. falciparum, considerable variation was demonstrated among these stages in sensitivity to chloroquine. The effects of timed, sequential exposure to several clinically relevant concentrations of chloroquine were monitored by three techniques: morphological analysis, changes in the rate of glucose consumption, and changes in the incorporation of 3H-hypoxanthine into parasite nucleic acids. All three techniques gave essentially identical results. The trophozoite and schizont stages were considerably more sensitive to the drug than ring-stage parasites. Chloroquine sensitivity decreased as nuclear division neared completion. The increase in chloroquine sensitivity was coincident with a marked rise in the rate of glucose consumption and nucleic acid synthesis. The rate of nucleic acid synthesis decreased as schizogony progressed while glucose consumption continued at high rates during this process. The degree of chloroquine sensitivity was not highly correlated with either metabolic activity.

Notes: Bloodstream trypomastigote and culture procyclic (insect midgut) forms of a cloned T. rhodesiense variant (WRATat 1) were tested for agglutination with the lectins concanavalin A (Con A), phytohemagglutinin P (PP), soybean agglutinin (SBA), fucose binding protein (FBP), wheat germ agglutinin (WGA), and castor bean lectin (RCA). Fluorescence-microscopic localization of lectin binding to both formalin-fixed trypomastigotes and red cells was determined with fluorescein isothiocyanate (FITC)-conjugated Con A, SBA, FBP, WGA, RCA, PNA (peanut agglutinin), DBA (Dolichos bifloris), and UEA (Ulex europaeus) lectins. Electron microscopic localization of lectin binding sites on bloodstream trypomastigotes was accomplished by the Con A-horseradish peroxidase-diaminobenzidine (HRP-DAB) technique, and by a Con A-biotin/avidin-ferritin method. Trypomastigotes, isolated by centrifugation or filtration through DEAE-cellulose or thawed after cryopreservation, were agglutinated by the lectins Con A and PP with agglutination strength scored as Con A 〈 PP. No agglutination was observed in control preparations or with the lectins WGA, FBA or SBA. Red cells were agglutinated by all the lectins tested. Formalin-fixed bloodstream trypomastigotes bound FITC-Con A and FITC-RCA but not FITC-WGA, -SBA, -PNA, -UEA or -DBA lectins. All FITC-labeled lectins bound to red cells. Con A receptors, visualized by Con A-HRP-DAB and Con A-biotin/avidin-ferritin techniques, were distributed uniformly on T. rhodesiense bloodstream forms. No lectin receptors were visualized on control preparations. Culture procyclics lacked a cell surface coat and were agglutinated by Con A and WGA but not RCA, SBA, PP and FBP. Procyclics were not agglutinated by lectins in the presence of competing sugar at 0.25 M. The expression of lectin binding cell surface saccharides of T. rhodesiense WRATat 1 is related to the parasite stage. Sugars resembling α-D-mannose are on the surface of bloodstream trypomastigotes and culture procyclics; n-acetyl-D-galactosamine and D-galactose residues are on bloodstream forms; and n-acetyl-D-glucosamine-like sugars are on procyclic stages.

Notes: The cationic permeant fluorescent dye rhodamine 123 (R123) was used to stain Plasmodium yoelii-infected mouse erythrocytes. Fluorescence microscopic observations demonstrated that the parasite, but not the matrix of the infected erythrocyte, accumulated the dye. Differences in fluorescence intensity could not be found at the various developmental stages of the parasite; however, quantitation of the cell-associated dye revealed an increase in R123 uptake with parasite development. The retention of the parasite-associated dye, as measured by fluorescence microscopy and spectrophotometry after extraction of R123 with butanol, was markedly reduced by treatment of the infected erythrocytes with a proton ionophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and an inhibitor of proton ATPase, dicyclohexylcarbodiimide (DCCD). These results indicate that the accumulation and retention of R123 in P. yoelii reflect the parasite membrane potential and suggest that the parasite plasma membrane has a membrane potential-generating proton pump.

Notes: Distinctive organic-walled resting cysts of at least three different types with a highly conservative morphology appear to characterize specific orders or groups of genera within the Class Polyhymenophorea (Protozoa, Ciliophora), contrasting markedly with the great diversity of form seen in trophic stages. Polyhymenophorean ciliates have been considered in the past to form a cohesive class within the Phylum Ciliophora and, possibly, to represent the pinnacle of ciliate evolution. Evidence from cysts challenges the cohesive nature of the class, suggesting that the hypotrichs should be subdivided and that they have a different phylogenetic origin from the heterotrichs, tintinnids, and oligotrichs.

Notes: Yellow-brown, algal symbionts varying in diameter from approximately 5 μ m to 20 μ m, associated with solitary Radiolaria with spongiose skeletons (i.e. Spongodrymus sp.), exhibit fine structural features resembling the Prymnesiida (botanical class, Prymnesiophyceae). A large central vacuole is surrounded by a thin layer of cytoplasm containing plastids with lamellae composed of three thylakoids and granular pyrenoids with internal tubules immersed between the thylakoids. The pyrenoids lack internal thylakoid membranes. The nucleus is surrounded by a dilated cisterna of the nuclear envelope that also encloses the plastids and gives rise to saccules of the endoplasmic reticulum. The algal symbionts appear coccoid; hence no flagella nor surface scales were observed. The symbiont fine structure is compared to similar yellow-brown symbionts associated with Acantharia. Thus far, three kinds of algal symbionts have been observed to be associated with solitary Radiolaria: dinoflagellate, prasinomonad, and this apparent prymnesiomonad.

Notes: Ultrastructural observations of the cortically-located mitochondria of Tetrahymena thermophila revealed associations not only between the mitochondria and certain of the cortical microtubule bands, but also between the mitochondria and the epiplasm of the cortex. Most of the distal mitochondrial surface is close and parallel to the epiplasm; favorable views show bridge-like structures spanning the 20–10 nm gap between the mitochondrion and the epiplasm.Previous studies have shown that the placement of mitochondria in the cortex appears to be determined by certain of the cortical microtubule bands. This study, however, shows that mitochondrion-microtubule interactions account for only a small proportion of the total mitochondrial area associated with the cortex; the rest is accounted for by the epiplasm. A possible analogue of the spectrin layer of erythrocyte membranes, the epiplasm may be important in helping to arrange the intricately organized components of the ciliate cortex. Its involvement in apparently helping to “moor” mitochondria to their cortical sites is the first suggestion of any role in cell patterning played by the epiplasm.

Notes: Ce Tetradimorpha, rencontre en eau douce se présente soit sous forme sphérique pourvue de quatre flagelles et d'axopodes rayonnants, soit sous forme allongée avec a l'avant quatre flagelles associes a quatre axopodes et a l'arriére six a huit axopodes divergents. L'etude ultrastructurale révèle un cytosquelette axopodial de type centroplastidie comprenant un centroplaste lenticulaire homogéne, centre organisateur des quatre axopodes anterieurs et des six a huit axopodes posterieurs, auquel s'ajoutent les quatre cinetosomes des flagelles anterieurs. En outre, un deuxiéme éleément cytosquelettique incluant un microtubule associe chacun des quatre cinetosomes a l'axopode antérieur correspondant. Des cordons microfibrillaires réunissent axopodes et cinetosomes au niveau du centroplaste, puis a quelque distance du centroplaste les axopodes posterieurs. Les axonémes des axopodes comprenant de 5 a 30 microtubules sont constitues de triades, lorsqu'on peut détecter une organisation. Le noyau, a nucléole central est coince dans le cone axopodial posterieur, lui-méme entouré des dictyosomes. Par l'organisation du cytosquelette, par la structure des kinétocystes, par la structure des flagelles dépourvus de mastigonémes tubulaires, Tetradimorpha différe nettement de Ciliophrys marina. Comme le prévoyait Davidson (1975), il represönte bien un des chainons dans la série évolutive des Héliozoaires centrohélidiens. Mais il ne présente guère d'affinites avec les Chrysomonadines considerees comme la souche des Héliozoaires. L'intéret de ce Protiste dans l'étude de la differentiation et de l'evolution du cytosquelette est également présente.〈section xml:id="abs1-2"〉〈title type="main"〉ABSTRACTThis freshwater species of Tetradimorpha has a spherical body with four flagella and radiating axopods; it transforms into a pear-shaped cell that anteriorly has four flagella intercalated between four axopods and posteriorly has six to eight divergent axopods. Ultrastructural study reveals an axopodial cytoskeleton of the centrohelidan type comprising an homogeneous lenticular centroplast which acts as MTOC for axopodial microtubules. A second skeletal element is a microtubular linkage between the kinetosomes and the axonemes of anterior axopods. A microtubule embedded in dense material diverges from near the base of each kinetosomes and parallels the distal portion of the axoneme of each anterior axopod. A microfibrillar envelope around the centroplast links the axopodial bases to the kinetosomes situated just above. Close to the centroplast, microfibrillar strands link the axopodial axonemes to the kinetosomes. Axopodial axonemes are composed of 5 to 30 microtubules irregularly arranged except for some that form equilateral triangles. The nucleus containing a central nucleolus is constrained within a cone formed by the axonemes of the posterior axopods and surrounded by dictyosomes. By the cytoskeletal organization, the structure of kinetocysts, and flagella wthout tubular mastigonemes, Tetradimorpha differs obviously from Ciliophrys marina. As Davidson (1975) predicted, Tetradimorpha is an intermediate link in the centrohelidan lineage: however, it lacks the characteristics of chrysomonads, the supposed ancestors of Heliozoa. The contribution of this genus to the study of the differentiation and the evolution of the cytoskeleton is also presented and discussed.