Impact of demographics and comorbid conditions on plasma biomarkers concentrations and their diagnostic accuracy in a memory clinic cohort

Plasma biomarkers have emerged as promising tools for identifying amyloid beta (Aβ) pathology. Before implementation in routine clinical practice, confounding factors modifying their concentration beyond neurodegenerative diseases should be identified. We studied the association of a comprehensive list of demographics, comorbidities, medication and laboratory parameters with plasma p-tau181, glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) on a prospective memory clinic cohort and studied their impact on diagnostic accuracy for discriminating CSF/amyloid PET-defined Aβ status. Three hundred sixty patients (mean age 66.5 years, 55% females, 53% Aβ positive) were included. Sex, age and Aβ status-adjusted models showed that only estimated glomerular filtration rate (eGFR, standardized β -0.115 [-0.192 to -0.035], p = 0.005) was associated with p-tau181 levels, although with a much smaller effect than Aβ status (0.685 [0.607-0.763], p < 0.001). Age, sex, body mass index (BMI), Charlson comorbidity index (CCI) and eGFR significantly modified GFAP concentration. Age, blood volume (BV) and eGFR were associated with NfL levels. p-tau181 predicted Aβ status with 87% sensitivity and specificity with no relevant increase in diagnostic performance by adding any of the confounding factors. Using two cut-offs, plasma p-tau181 could have spared 62% of amyloid-PET/CSF testing. Excluding patients with chronic kidney disease did not change the proposed cut-offs nor the diagnostic performance. In conclusion, in a memory clinic cohort, age, sex, eGFR, BMI, BV and CCI slightly modified plasma p-tau181, GFAP and NfL concentrations but their impact on the diagnostic accuracy of plasma biomarkers for Aβ status discrimination was minimal.

Agreement of cerebrospinal fluid biomarkers and amyloid-PET in a multicenter study

Core Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarkers have shown incomplete agreement with amyloid-positron emission tomography (PET). Our goal was to analyze the agreement between AD CSF biomarkers and amyloid-PET in a multicenter study. Retrospective multicenter study (5 centers). Participants who underwent both CSF biomarkers and amyloid-PET scan within 18 months were included. Clinical diagnoses were made according to latest diagnostic criteria by the attending clinicians. CSF Amyloid Beta1-42 (Aβ1-42, A), phosphorliated tau 181 (pTau181, T) and total tau (tTau, N) biomarkers were considered normal (-) or abnormal ( +) according to cutoffs of each center. Amyloid-PET was visually classified as positive/negative. Agreement between CSF biomarkers and amyloid-PET was analyzed by overall percent agreement (OPA). 236 participants were included (mean age 67.9 years (SD 9.1), MMSE score 24.5 (SD 4.1)). Diagnoses were mild cognitive impairment or dementia due to AD (49%), Lewy body dementia (22%), frontotemporal dementia (10%) and others (19%). Mean time between tests was 5.1 months (SD 4.1). OPA between single CSF biomarkers and amyloid-PET was 74% for Aβ1-42, 75% for pTau181, 73% for tTau. The use of biomarker ratios improved OPA: 87% for Aβ1-42/Aβ1-40 (n = 155), 88% for pTau181/Aβ1-42 (n = 94) and 82% for tTau/Aβ1-42 (n = 160). A + T + N + cases showed the highest agreement between CSF biomarkers and amyloid-PET (96%), followed by A-T-N- cases (89%). Aβ1-42/Aβ1-40 was a better marker of cerebral amyloid deposition, as identified by amyloid tracers, than Aβ1-42 alone. Combined biomarkers in CSF predicted amyloid-PET result better than single biomarkers.

Diagnostic Performance and Clinical Applicability of Blood-Based Biomarkers in a Prospective Memory Clinic Cohort

BACKGROUND AND OBJECTIVES

Blood-based biomarkers have emerged as minimally invasive options for evaluating cognitive impairment. Most studies to date have assessed them in research cohorts, limiting their generalization to everyday clinical practice. We evaluated their diagnostic performance and clinical applicability in a prospective, real-world, memory clinic cohort.

METHODS

All patients referred with suspected cognitive impairment between July 2019 and June 2021 were prospectively invited to participate. Five plasma biomarkers (tau phosphorylated at threonine 181 [p-tau181], glial fibrillary acidic protein [GFAP], neurofilament light chain [NfL], total tau [t-tau], and ubiquitin C-terminal hydrolase L1 [UCH-L1]) were determined with single-molecule array. Performance was assessed in comparison to clinical diagnosis (blinded to plasma results) and amyloid status (CSF/PET). A group of cognitively unimpaired (CU) controls was also included.

RESULTS

Three hundred forty-nine participants (mean age 68, SD 8.3 years) and 36 CU controls (mean age 61.7, SD 8.2 years) were included. In the subcohort with available Alzheimer disease (AD) biomarkers (n = 268), plasma p-tau181 and GFAP had a high diagnostic accuracy to differentiate AD from non-neurodegenerative causes (area under the receiver operating characteristic curve 0.94 and 0.92, respectively), with p-tau181 systematically outperforming GFAP. Plasma p-tau181 levels predicted amyloid status (85% sensitivity and specificity) with accurate individual prediction in approximately 60% of the patients. Plasma NfL differentiated frontotemporal dementia (FTD) syndromes from CU (0.90) and non-neurodegenerative causes (0.93), whereas the discriminative capacity with AD and between all neurodegenerative and non-neurodegenerative causes was less accurate. A combination of p-tau181 and NfL identified FTD with 82% sensitivity and 85% specificity and had a negative predictive value for neurodegenerative diagnosis of 86%, ruling out half of the non-neurodegenerative diagnoses. In the subcohort without AD biomarkers, similar results were obtained. T-tau and UCH-L1 did not offer added diagnostic value.

DISCUSSION

Plasma p-tau181 predicted amyloid status with high accuracy and could have potentially avoided CSF/amyloid PET testing in approximately 60% of subjects in a memory clinic setting. NfL was useful for identifying FTD from non-neurodegenerative causes but behaved worse than p-tau181 in all other comparisons. Combining p-tau181 and NfL improved diagnostic performance for FTD and non-neurodegenerative diagnoses. However, the 14% false-negative results suggest that further improvement is needed before implementation outside memory clinics.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that plasma p-tau181 correlates with the presence or absence of AD and a combination of plasma p-tau181 and NfL correlates moderately well with a diagnosis of FTD.

Early-onset Alzheimer's disease shows a distinct neuropsychological profile and more aggressive trajectories of cognitive decline than late-onset

OBJECTIVES

Early- and late-onset Alzheimer's disease (EOAD and LOAD) share the same neuropathological traits but show distinct cognitive features. We aimed to explore baseline and longitudinal outcomes of global and domain-specific cognitive function in a well characterized cohort of patients with a biomarker-based diagnosis.

METHODS

In this retrospective cohort study, 195 participants were included and classified according to their age, clinical status, and CSF AD biomarker profile: 89 EOAD, 37 LOAD, 46 young healthy controls (age ≤ 65 years), and 23 old healthy controls (>65 years). All subjects underwent clinical and neuropsychological assessment, neuroimaging, APOE genotyping and lumbar puncture.

RESULTS

We found distinct neuropsychological profiles between EOAD and LOAD at the time of diagnosis. Both groups showed similar performances on memory and language domains, but the EOAD patients displayed worsened deficits in visual perception, praxis, and executive tasks (p < 0.05). Longitudinally, cognitive decline in EOAD was more pronounced than LOAD in the global outcomes at the expense of these non-amnestic domains. We found that years of education significantly influenced the decline in most of the neuropsychological tests. Besides, the APOE ε4 status showed a significant effect on the decline of memory-related tasks within the EOAD cohort (p < 0.05).

INTERPRETATION

Age of onset is a main factor shaping the cognitive trajectories in AD patients, with younger age driving to a steeper decline of the non-memory domains. Years of education are related to a transversal decline in all cognitive domains and APOE ε4 status to a specific decline in memory performance in EOAD.

Structure and content of the Entamoeba histolytica genome

The intestinal parasite Entamoeba histolytica is one of the first protists for which a draft genome sequence has been published. Although the genome is still incomplete, it is unlikely that many genes are missing from the list of those already identified. In this chapter we summarise the features of the genome as they are currently understood and provide previously unpublished analyses of many of the genes.

Signaling through the phosphatidylinositol 3-kinase regulates mechanotaxis induced by local low magnetic forces in Entamoeba histolytica

In micro-organisms, as well as in metazoan cells, cellular polarization and directed migration are finely regulated by external stimuli, including mechanical stresses. The mechanisms sustaining the transduction of such external stresses into intracellular biochemical signals remain mainly unknown. Using an external magnetic tip, we generated a magnetic field gradient that allows migration analysis of cells submitted to local low-intensity magnetic forces (50 pN). We applied our system to the amoeba Entamoeba histolytica. Indeed, motility and chemotaxis are key activities that allow this parasite to invade and destroy the human tissues during amoebiasis. The magnetic force was applied either inside the cytoplasm or externally at the rear pole of the amoeba. We observed that the application of an intracellular force did not affect cell polarization and migration, whereas the application of the force at the rear pole of the cell induced a persistent polarization and strongly directional motion, almost directly opposed to the magnetic force. This phenomenon was completely abolished when phosphatidylinositol 3-kinase activity was inhibited by wortmanin. This result demonstrated that the applied mechanical stimulus was transduced and amplified into an intracellular biochemical signal, a process that allows such low-intensity force to strongly modify the migration behavior of the cell.

[Assessment of the acceptance of set meals served at the "Sant Joan de Reus" University Hospital]

Despite the fact that, in most of the series published, cancer is the most frequent base pathology for the indication of home parenteral nutrition (HPN), the use of this technique in terminally-ill patients is still a controversial issue. Our goal has been to review the evolution of cancer patients with HPN treatment from "La Paz" Hospital with a view to studying the indication, evolution and complications. We review a total of 9 terminal oncological patients who had been treated with HPN between January 2000 and December 2002, with a mean age of 60.4 (44-81) years, the most common base cancer was gastric adenocarcinoma (44%). Intestinal obstruction in the context of peritoneal carcinomatosis was the reason for indicating HPN in 89% of cases and the median survival time was 71 (23-131) days. Catheter infection was the most frequent complication with 1.4 episodes/patient. The existence of a Home Support Team meant follow-up of patients was easier, with HPN being estimated as the treatment provided in 67% of cases. 56% of the patients were not sufficiently informed as to their underlying illness. Although HPN is one more therapeutic resource, which may or may not be used in some terminal oncological patients, we must refine the indication as much as possible to take into account a series of "systematic guarantees" including fulfilment of pertinent clinical criteria, informed consent and the adoption of a collective decision with the involvement of all the professionals monitoring the patient. We propose an action algorithm to help in improving the decision-taking process in these patients.

[Food intake, dietary habits and nutritional status of the population of Reus (X): Evolution of the diet and the contribution of macronutrients to energy intake (1983-1999) by age and sex]

BACKGROUND

To study the evolution of the diet and the nutritional intake between 1983 and 1999, by age and sex.

SUBJECTS AND METHODS

We performed a series of analysis of the food intake on a representative sample of the population of Reus (aged 10-69 years). Dietary intake was estimated using the 24-hours recall method. In 1999 the sample size was 839 individuals, 41% of them having taken part in the studies since 1983. Results are shown as mean (standard deviation).

RESULTS

In 1999, the energy intake was 2524 (582) kcal in men aged 35-44 years (n = 57), and 1827 (490) kcal in women (n = 95) (p < 0.001 between sexes). The energy intake decreases with age (significant trend [p < 0.001] between 15-69 years) and it is higher in men than in women in all the age groups studied. When comparing similar age groups, we observe that this energy intake has not changed significantly since 1983. Between 1983 and 1999 the contribution of the macronutrients to the total energy intake has become more similar between ages and sexes. In 1999, in men aged 35-44 years a 15.6% of the energy came from proteins, 42% from fat and 42.5% from carbohydrates; in women of the same age: a 17.3% of the energy came from proteins, 42.4% from fat and 40.3% from carbohydrates). During this period we observed, however, remarkable changes in the diet which imply the increasing participation of the dairy products, vegetables and meat in the energy intake, or the significant decrease of the role of tubers, eggs and visible fat.

CONCLUSIONS

Our population maintains an energy intake without significant changes, and it presents a trend towards a progressive uniformity of the nutritional balance between the different ages and sexes, although there are significant changes in some components of the diet.

Cell polarization and adhesion in a motile pathogenic protozoan: role and fate of the Entamoeba histolytica Gal/GalNAc lectin

The human pathogenic protozoan Entamoeba histolytica is a motile cell polarized into a front pseudopod and a rear uroid. The amoebic Gal/GalNAc surface lectin is a major adhesion molecule composed of an immunodominant 170-kDa heavy subunit, mostly extracellular except for a short cytoplasmic tail, and of an extracellular light subunit. The binding of multivalent ligands triggers lectin capping and recruitment to the uroid. The properties of the Gal/GalNAc lectin and its role in amoeba adhesion and uroid polarization are reviewed in the context of the molecular mechanisms underlying cell polarization and locomotion.

New insights into the role of the cytoskeleton in phagocytosis of Entamoeba histolytica

Entamoeba histolytica, a human parasite, crosses the natural barriers of the intestine and, in turn, spreads into the deeper organs, resulting in amoebiasis. The motility of the parasite and its ability to lyse or phagocytose human cells facilitates passage of the amoeba through the intestinal epithelium. Little is known about the uptake of material by this parasite; nevertheless, the cytoskeleton is believed to play a role in phagocytosis. Myosin IB, an actin-binding protein, localizes to the phagocytic cup and, with time, surrounds the internalized phagosome itself. The role of unconventional myosins in phagocytosis has also been demonstrated in other cell types, suggesting that this molecular mechanism is a common denominator in phagocytic events. Here, we summarize the emerging view of the role of unconventional myosins as well as other cytoskeleton-associated proteins in pseudopod formation at early stages of phagocytosis and during the late step of this process in E. histolytica.

Myosin IB from Entamoeba histolytica is involved in phagocytosis of human erythrocytes

Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery in humans. The disease is prevalent worldwide. Infection with E. histolytica results in invasion of the intestine by the parasite, followed by tissue damage and inflammation. During this invasive process, parasites kill and phagocytose human epithelial cells, immune cells and erythrocytes. Expression of amoebic pathogenicity requires a dynamic cytoskeleton that allows movement, tissue penetration and changes in parasite morphology. Myosin IB is a member of the myosin I family of motor proteins. Studies conducted both with Dictyostelium discoideum, a non-pathogenic amoeba, and with the yeast Saccharomyces cerevisiae indicate the involvement of myosin IB in cellular processes including movement, phagocytosis and endocytosis. Recently, we isolated the gene encoding myosin IB from E. histolytica. Thus, we decided to analyze the role of myosin IB in pathogenesis of amoeba. Using a specific anti-myosin IB antibody, this protein was localized in cell regions including the pseudopod, vesicles and underneath the plasma membrane. When E. histolytica was activated for erythrophagocytosis, myosin IB was markedly recruited to both the phagocytic cup and around internalized phagosomes. To analyze the role of myosin IB in phagocytosis, a strain overexpressing the myosin IB gene was constructed. This strain synthesizes threefold more myosin IB than the wild-type strain. Challenge of the transfected cell line with erythrocytes showed that these amoebae were deficient in erythrophagocytosis mainly in the uptake step, suggesting a role for myosin IB in the pathogenic activity of a human parasite.

The small GTP-binding protein RacG regulates uroid formation in the protozoan parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite that invades human intestine leading to ulceration and destruction of tissue. Amoebic movement and phagocytosis of human cells is accompanied by characteristic changes in cell morphology. Amoebae become polarized, developing a frontal pseudopod and a well-defined rear zone of membrane accumulation designated the uroid. In motile eukaryotic cells, a phenomenon that contributes to movement is the capping of receptors at the cell surface. During the capping process, E. histolytica concentrates ligand-receptor complexes in the uroid. Interestingly, some of these surface receptors are involved in the survival of the parasite. While looking for regulators of capping and uroid formation, we identified RacG, an E. histolytica protein that is homologous to human Rac1. This protein belongs to the Rac subfamily of small GTPases implicated in interactions between the actin cytoskeleton and the membrane of mammalian cells. Cloning of the EhracG gene and analysis of the protein activity either in murine fibroblasts or in E. histolytica revealed that EhRacG induces a characteristic Rac phenotype. When expressed in amoebae, an EhRacG-V12 mutant protein not only deregulated cell polarity, but also caused a defect in cytokinesis. Analysis of the cytoskeleton in amoebae bearing this mutant revealed that F-actin concentrated at the periphery of the cell. In addition, the number and localization of uroids were modified. These results suggest a role for EhRacG in amoebic morphogenesis and cytokinesis.

[Cytoskeletal actin and its associated proteins. Some examples in Protista]

Many processes, cell motility being an example, require cells to remodel the actin cytoskeleton in response to both intracellular and extracellular signals. Reorganization of the actin cytoskeleton involves the rapid disassembly and reassembly of actin filaments, a phenomenon regulated by the action of particular actin-binding proteins. In recent years, an interest in studying actin regulation in unicellular organisms has arisen. Parasitic protozoan are among these organisms and studies of the cytoskeleton functions of these protozoan are relevant related to either cell biology or pathogenicity. To discuss recent data in this field, a symposium concerning "Actin and actin-binding proteins in protists" was held on May 8-11 in Paris, France, during the XXXV meeting of the French Society of Protistology. As a brief summary of the symposium we report here findings concerning the in vitro actin dynamic assembly, as well as the characterization of several actin-binding proteins from the parasitic protozoan Entamoeba histolytica, Trichomonas vaginalis and Plasmodium knowlesi. In addition, localization of actin in non-pathogen protists such as Prorocentrum micans and Crypthecodinium cohnii is also presented. The data show that some actin-binding proteins facilitate organization of filaments into higher order structures as pseudopods, while others have regulatory functions, indicating very particular roles for actin-binding proteins. One of the proteins discussed during the symposium, the actin depolymerizing factor ADF, was shown to enhance the treadmilling rate of actin filaments. In vitro, ADF binds to the ADP-bound forms of G-actin and F-actin, thereby participating in and changing the rate of actin assembly. Biochemical approaches allowed the identification of a protein complex formed by HSP/C70-cap32-34 which might also be involved in depolymerization of F-actin in P. knowlesi. Molecular and cellular approaches were used to identify proteins such as ABP-120 and myosin IB at the leading edge of E. histolytica. ABP-120 organizes F-actin in a network and myosin IB participates in the pseudopod formation. Similar approaches using T. vaginalis resulted in the discovery of an actin-binding protein that participate in the F-actin reorganization during adhesion of parasites to target cells. This protein is homologous to alpha-actinin from other eukaryotic cells. Finally, by using cell biology approaches, F-actin was observed in the cytoplasm as well as in the nucleus of Dinoflagellates. The recent developments in the molecular genetics of protozoa will provide new insights to understand the roles of actin-binding proteins during cytoskeleton activities.

Virulence and functions of myosin II are inhibited by overexpression of light meromyosin in Entamoeba histolytica

Several changes in cell morphology take place during the capping of surface receptors in Entamoeba histolytica. The amoebae develop the uroid, an appendage formed by membrane invaginations, which accumulates ligand-receptor complexes resulting from the capping process. Membrane shedding is particularly active in the uroid region and leads to the elimination of accumulated ligands. This appendage has been postulated to participate in parasitic defense mechanisms against the host immune response, because it eliminates complement and specific antibodies bound to the amoeba surface. The involvement of myosin II in the capping process of surface receptors has been suggested by experiments showing that drugs that affect myosin II heavy-chain phosphorylation prevent this activity. To understand the role of this mechanoenzyme in surface receptor capping, a myosin II dominant negative strain was constructed. This mutant is the first genetically engineered cytoskeleton-deficient strain of E. histolytica. It was obtained by overexpressing the light meromyosin domain, which is essential for myosin II filament formation. E. histolytica overexpressing light meromyosin domain displayed a myosin II null phenotype characterized by abnormal movement, failure to form the uroid, and failure to undergo the capping process after treatment with concanavalin A. In addition, the amoebic cytotoxic capacities of the transfectants on human colon cells was dramatically reduced, indicating a role for cytoskeleton in parasite pathogenicity.

Protection against invasive amebiasis by a single monoclonal antibody directed against a lipophosphoglycan antigen localized on the surface of Entamoeba histolytica

A panel of monoclonal antibodies was raised from mice immunized with a membrane preparation from Entamoeba histolytica, the pathogenic species causing invasive amebiasis in humans. Antibody EH5 gave a polydisperse band in immunoblots from membrane preparations from different E. histolytica strains, and a much weaker signal from two strains of the nonpathogenic species Entamoeba dispar. Although the exact chemical structure of the EH5 antigen is not yet known, the ability of the antigen to be metabolically radiolabeled with [32P]phosphate or [3H]glucose, its sensitivity to digestion by mild acid and phosphatidylinositol-specific phospholipase C, and its specific extraction from E. histolytica trophozoites by a method used to prepare lipophosphoglycans from Leishmania showed that it could be classified as an amebal lipophosphoglycan. Confocal immunofluorescence and immunogold labeling of trophozoites localized the antigen on the outer face of the plasma membrane and on the inner face of internal vesicle membranes. Antibody EH5 strongly agglutinated amebas in a similar way to concanavalin A (Con A), and Con A bound to immunoaffinity-purified EH5 antigen. Therefore, surface lipophosphoglycans may play an important role in the preferential agglutination of pathogenic amebas by Con A. The protective ability of antibody EH5 was tested in a passive immunization experiment in a severe combined immunodeficient (SCID) mouse model. Intrahepatic challenge of animals after administration of an isotype-matched control antibody or without treatment led to the development of a liver abscess in all cases, whereas 11 out of 12 animals immunized with the EH5 antibody developed no liver abscess. Our results demonstrate the importance and, for the first time, the protective capacity of glycan antigens on the surface of the amebas.

Interaction between Entamoeba histolytica and intestinal epithelial cells involves a CD44 cross-reactive protein expressed on the parasite surface

This study shows that Entamoeba histolytica binds hyaluronic acid. The binding molecule was identified as an 80-kDa membrane protein and was recognized by anti-CD44 monoclonal antibodies. These data indicate that a CD44 cross-reacting adherence molecule is expressed on E. histolytica.

Identification and cellular localization of the actin-binding protein ABP-120 from Entamoeba histolytica

Several actin-binding proteins participate in the morphological changes that occur during amoeboid movement. The gene encoding one of these proteins, the gelation factor ABP-120, was identified and characterized from trophozoites of Entamoeba histolytica. The sequence contains 2574 nucleotides, with an open reading frame of 858 amino acids, giving a protein of 93 kDa belonging to the spectrin family. The N-terminal domain of ABP-120 from E. histolytica revealed a consensus site for actin binding homologous to the actin-binding sites of ABP-120 of Dictyostelium discoideum, alpha-actinin and spectrin. Analysis of the central domain revealed the presence of four repeats of a 73-amino-acid motif constituting 31% of the protein. In addition, a stretch of 105 amino acids was highly divergent when compared with the C-terminal domain of D. discoideum ABP-120. This sequence showed short motifs that are homologous to microtubule-binding domains. We found that ABP-120 from E. histolytica binds to F-actin. In addition, upon motility of the parasite, this protein localized in the pseudopod and the uroid region, implying a role for ABP-120 in movement and capping of surface receptors in E. histolytica.

Role of signalling and cytoskeletal rearrangements in the pathogenesis of Entamoeba histolytica

Virulence of Entamoeba histolytica is characterized by intestinal tissue invasion, engulfment of host cells and the formation of liver abscesses. The actin-rich cytoskeleton of the amoeba allows rapid changes in morphology in response to signals from external stimuli. Cellular and molecular studies have described some of the proteins that participate in signalling and in cytoskeletal changes.

Myosin II is involved in capping and uroid formation in the human pathogen Entamoeba histolytica

The redistribution and capping of surface receptors on the human pathogen Entamoeba histolytica was observed in the presence of concanavalin A (ConA). Capping was correlated with plasma membrane folding towards the rear of the amoeba and with uroid formation. The uroid is thought to play a role in the escape of amoebae from the host immune response. To localize myosin II during capping, amoebae were incubated in the presence of ConA and then analyzed by microscopy. Myosin II was three times more concentrated within the uroid compared with the rest of the cell, suggesting that the release of caps may depend upon mechanical contraction driven by myosin II activity. The use of drugs that disrupt cytoskeletal structure or that inhibit myosin heavy chain phosphorylation demonstrated that inhibition of capping prevents uroid formation. Biochemical analysis allowed the identification of two ConA receptors which have been previously described as major pathogenic antigens of this parasite: the 96-kDa antigen, which carries alcohol dehydrogenase 2 activity and binds extracellular matrix proteins, and the Gal-GalNAc-inhibitable surface lectin, which is involved in amoeba-cell interactions and in the degradation of complement particles attached to the parasite.

Cell signalling and motility in Entamoeba histolytica

Entamoeba histolytica crawls as a polarized cell following external stimuli, with the translocation of signals modifying extracellular matrix interactions and the amoeba cytoskeleton. Nancy Guillén here describes how the gliding of E. histolytica cells requires the activity of the actomyosin complex, and how actomyosin functions related to motility are necessary for pathogenesis and for amoebal escape from the host immune response.

Identification and characterization of a myosin heavy chain gene (mhcA) from the human parasitic pathogen Entamoeba histolytica

The mhcA gene from the human pathogen Entamoeba histolytica was identified using the polymerase chain reaction. It is a single copy gene expressed as a 6.4-kb mRNA. The deduced MhcA protein sequence is highly similar to myosin II from both Dictyostelium discoideum and Acanthamoeba castellanii. The globular head domain of MhcA contains the specific regions involved in ATP binding, actin binding, and interaction with myosin light chain. The tail domain is organized in an alpha-helical coiled coil structure, which suggests that MhcA is an alpha-fibrous protein. The coiled coil is interrupted by two prolines indicating that like other myosins, either from smooth muscle or from non-muscle cells, the tail of MhcA folds twice on itself. In addition, MhcA presents sequence similarities with the heavy chain phosphorylation sites of smooth and non-muscle vertebrate myosins.

The spo0A gene is implicated in the maintenance of non-complementing diploids in Bacillus subtilis

Bacillus subtilis can exist in a diploid state in which two genetically distinct chromosomes co-exist in the same cell and yet only one of them is expressed, thereby determining the phenotype. Such cells are called non-complementing diploids (Ncds). In this study, two types of experiments are reported which indicate that a previously known pleiotropic gene, spo0A, plays a role in the maintaining the diploid state, as follows. (i) When protoplasts of two Spo0A mutant strains were fused, the resulting products continued to segregate cells of both parental phenotypes for many more divisions than had been reported previously. (ii) When a stable Ncd (an Ncd in which the unexpressed markers are not spontaneously activated at a detectable level) harbouring a chloramphenicol acetyltransferase gene on the silent chromosome was transformed with spo0A null alleles the transformants often expressed chloramphenicol acetyltransferase activity. Together these results indicate that the spo0A gene is involved in maintenance of the diploid state in both unstable and stable Ncds.

Genetic analysis of fusion recombinants in Bacillus subtilis: function of the recE gene

Bacillus subtilis protoplast fusion allows the study of the genetic recombination of an entire procaryotic genome. Protoplasts from bacterial strains marked genetically by chromosomal mutations were fused using polyethylene glycol and the regenerated cells analyzed. Recombinants represent 19.3% of heterozygotic cells; they are haploids. Individual characterization of clones show a unique particular phenotype in each colony suggesting that recombination takes place immediately after fusion, probably before the first cellular division. Recombination occurs in the whole chromosome; in one-third of the cases both reciprocal recombinants could be shown in the colony. The genetic interval that includes the chromosome replication origin shows the highest recombination level. Our results suggest that the RecE protein accounts for most of the fused protoplast recombination; however, some "replication origin-specific" recombination events were independent of the recE gene product.

RecE-dependent lysogenic induction in the absence of repressor in Bacillus subtilis non-complementing diploids

The RecE protein of Bacillus subtilis, known to be required for induction of the SOS response and of phi 105 prophage, was shown to be involved in mitomycin C induction of B. subtilis diploid lysogens carrying a silent phi 105 prophage in their unexpressed chromosome. These stable non-complementing diploid lysogens, formed by protoplast fusion and regeneration, did not synthesize repressor, so that the induction observed must have resulted from RecE-dependent activation of the prophage rather than from RecE-dependent inactivation of repressor. Mitomycin C treatment does not induce permanent expression of the silent chromosome, so the activation seems to be temporary, perhaps reflecting the action of an SOS function under RecE control.

Stabilized non-complementing diploids (Ncd) from fused protoplast products of B. subtilis

Non-complementing diploids (Ncd) displaying the parental phenotype can be selected from polyethylene glycol (PEG)-treated fused polyauxotrophic protoplasts of Bacillus subtilis. These bacteria carry the two parental genomes, but only one of them is phenotypically expressed, the other being replicated but not expressed. Cellular cloning and DNA-DNA in situ hybridization led to the discovery of non-complementing diploid cells which at first sight could have been considered as parental haploids. The new class of stabilized Ncd (10(-7) segregants) can be obtained either directly after the primary fusion event or from segregating Ncd after further growth. The totally inactive chromosome of a stable Ncd can be activated after PEG-induced self fusion. DNA-mediated transformation studies using crude stable Ncd lysates as DNA donors show low frequencies for the genetic markers from the 'silent' chromosome. Contrary to the unstable Ncd situation, however, these frequencies remain low even with purified donor DNA. The differences in the transformation properties of the non-expressed markers are correlated to Ncd clone stability. These facts suggest that chromosome inactivation in PEG-induced fusion involves at least a two-stage process. The first would be reversible and the second irreversible, thus preserving the inactive chromosome state.