Antibodies to variable surface antigens induce antigenic variation in the intestinal parasite Giardia lamblia

The genomes of most protozoa encode families of variant surface antigens. In some parasitic microorganisms, it has been demonstrated that mutually exclusive changes in the expression of these antigens allow parasites to evade the host's immune response. It is widely assumed that antigenic variation in protozoan parasites is accomplished by the spontaneous appearance within the population of cells expressing antigenic variants that escape antibody-mediated cytotoxicity. Here we show, both in vitro and in animal infections, that antibodies to Variant-specific Surface Proteins (VSPs) of the intestinal parasite Giardia lamblia are not cytotoxic, inducing instead VSP clustering into liquid-ordered phase membrane microdomains that trigger a massive release of microvesicles carrying the original VSP and switch in expression to different VSPs by a calcium-dependent mechanism. This novel mechanism of surface antigen clearance throughout its release into microvesicles coupled to the stochastic induction of new phenotypic variants not only changes current paradigms of antigenic switching but also provides a new framework for understanding the course of protozoan infections as a host/parasite adaptive process.

Giardia intestinalis thymidine kinase is a high-affinity enzyme crucial for DNA synthesis and an exploitable target for drug discovery

Giardiasis is a diarrheal disease caused by the unicellular parasite Giardia intestinalis, for which metronidazole is the main treatment option. The parasite is dependent on exogenous deoxyribonucleosides for DNA replication and thus is also potentially vulnerable to deoxyribonucleoside analogs. Here, we characterized the G. intestinalis thymidine kinase, a divergent member of the thymidine kinase 1 family that consists of two weakly homologous parts within one polypeptide. We found that the recombinantly expressed enzyme is monomeric, with 100-fold higher catalytic efficiency for thymidine compared to its second-best substrate, deoxyuridine, and is furthermore subject to feedback inhibition by dTTP. This efficient substrate discrimination is in line with the lack of thymidylate synthase and dUTPase in the parasite, which makes deoxy-UMP a dead-end product that is potentially harmful if converted to deoxy-UTP. We also found that the antiretroviral drug azidothymidine (AZT) was an equally good substrate as thymidine and was active against WT as well as metronidazole-resistant G. intestinalis trophozoites. This drug inhibited DNA synthesis in the parasite and efficiently decreased cyst production in vitro, which suggests that it could reduce infectivity. AZT also showed a good effect in G. intestinalis–infected gerbils, reducing both the number of trophozoites in the small intestine and the number of viable cysts in the stool. Taken together, these results suggest that the absolute dependency of the parasite on thymidine kinase for its DNA synthesis can be exploited by AZT, which has promise as a future medication effective against metronidazole-refractory giardiasis.

A Thermostable Oral SARS-CoV-2 Vaccine Induces Mucosal and Protective Immunity

An ideal protective vaccine against SARS-CoV-2 should not only be effective in preventing disease, but also in preventing virus transmission. It should also be well accepted by the population and have a simple logistic chain. To fulfill these criteria, we developed a thermostable, orally administered vaccine that can induce a robust mucosal neutralizing immune response. We used our platform based on retrovirus-derived enveloped virus-like particles (eVLPs) harnessed with variable surface proteins (VSPs) from the intestinal parasite Giardia lamblia, affording them resistance to degradation and the triggering of robust mucosal cellular and antibody immune responses after oral administration. We made eVLPs expressing various forms of the SARS-CoV-2 Spike protein (S), with or without membrane protein (M) expression. We found that prime-boost administration of VSP-decorated eVLPs expressing a pre-fusion stabilized form of S and M triggers robust mucosal responses against SARS-CoV-2 in mice and hamsters, which translate into complete protection from a viral challenge. Moreover, they dramatically boosted the IgA mucosal response of intramuscularly injected vaccines. We conclude that our thermostable orally administered eVLP vaccine could be a valuable addition to the current arsenal against SARS-CoV-2, in a stand-alone prime-boost vaccination strategy or as a boost for existing vaccines.

Specific histone modifications play critical roles in the control of encystation and antigenic variation in the early-branching eukaryote Giardia lamblia

During evolution, parasitic microorganisms have faced the challenges of adapting to different environments to colonize a variety of hosts. Giardia lamblia, a common cause of intestinal disease, has developed fascinating strategies to adapt both outside and inside its host's intestine, such as trophozoite differentiation into cyst and the switching of its major surface antigens. How gene expression is regulated during these adaptive processes remains undefined. Giardia lacks some typical eukaryotic features, like canonical transcription factors, linker histone H1, and complex promoter regions; suggesting that post-transcriptional and translational control of gene expression is essential for parasite survival. However, epigenetic factors may also play critical roles at the transcriptional level. Here, we describe the most common post-translational histone modifications; characterize enzymes involved in these reactions, and analyze their association with the Giardia's differentiation processes. We present evidence that NAD⁺-dependent and NAD⁺-independent histone deacetylases regulate encystation; however, a unique NAD⁺-independent histone deacetylase modulate antigenic switching. The rates of acetylation of H4K8 and H4K16 are critical for encystation, whereas a decrease in acetylation of H4K8 and methylation of H3K9 occur preferentially during antigenic variation. These results show the complexity of the mechanisms regulating gene expression in this minimalistic protozoan parasite.

Vaccination of domestic animals with a novel oral vaccine prevents Giardia infections, alleviates signs of giardiasis and reduces transmission to humans

Giardia lamblia is a human intestinal parasite and one of the most frequent enteric pathogen of companion animals. Clinical manifestations of giardiasis, such as diarrhoea, anorexia, weight loss and lethargy, have been associated with Giardia infections in both domestic and farm animals. A few anti-parasitic drugs are routinely used to treat giardiasis, but re-infections are common and drug-resistant strains have already been reported. Unfortunately, efficient vaccines against Giardia are not available. Giardia undergoes antigenic variation; through this mechanism, parasites can avoid the host’s immune defenses, causing chronic infections and/or re-infections. Antigenic variation is characterised by a continuous switch in the expression of members of a homologous family of genes encoding surface antigens. In a previous report, we indicated that in Giardia, the mechanism responsible for the exchange of variant-specific surface proteins (VSPs) involves the RNA interference (RNAi) pathway. From a repertoire of ~200 VSP genes, only one is expressed on the surface of single trophozoites; however, RNAi machinery disruption generates trophozoites that express the complete VSP repertoire. We also demonstrated that gerbils orally immunised with VSPs isolated from these altered parasites showed high levels of protection. Here we tested this vaccine in cats and dogs, and found that it is highly efficient in preventing new infections and reducing chronic giardiasis in domestic animals both in experimental and natural infections. Remarkably, immunisation of dogs in a highly endemic area strongly decreased the percentage of infected children in the community, suggesting that this vaccine would block the zoonotic transmission of the disease.

Genetic load in northern populations of Drosophila subobscura

O-chromosomes were sampled from two natural populations in Finland, one population in Sweden and one population from Spain. Viability was assessed using the Va/Ba balanced lethal strain. The genetic load for lethals and semilethals was 0.165/0.065 in Helsinki and 0.151/0.101 in Tvärminne, Finland; 0.309/0.118 in Gävle, Sweden and 0.351/0.112 in Barcelona, Spain. With the exception of the Gävle population, the results confirm the general picture that marginal populations are characterized by light loads in comparison with the central ones. Homozygotes for normal or almost normal chromosomes from the Gävle population were less viable than corresponding homozygotes from other marginal populations. Random combinations of wild chromosomes from the Spanish and Finnish populations did not show increased viability over random Spanish heterozygotes.

Identification of variant-specific surface proteins in Giardia muris trophozoites

Giardia lamblia undergoes antigenic variation, a process that might allow the parasite to evade the host's immune response and adapt to different environments. Here we show that Giardia muris, a related species that naturally infects rodents, possesses multiple variant-specific surface proteins (VSPs) and expresses VSPs on its surface, suggesting that it undergoes antigenic variation similar to that of G. lamblia.

Does Drosophila melanogaster use ethanol as an energy source during starvation?

The influence of starvation on activities of three enzymes (ADH, ODH and alpha GPDH) was studied in Drosophila melanogaster. The changes were compared in two inbred lines which had different allelic combinations at the Odh and Aldox loci. We also studied the effect of ethanol on media which contained no sucrose ("starvation conditions"). The results show that there are large differences in the larval and adult alcohol utilization. The alcohol content of the medium, in the absence of sugar, appeared to be toxic for the larvae, while the adults appeared to utilize it as an energy source. The two strains differed little in their responses to starvation or to the ethanol treatment applied under starvation conditions. We conclude that the degree of toxicity of ethanol is highly dependent on the presence of sucrose.

The influence of the Odh-Aldox region of the third chromosome on the response of Drosophila melanogaster to environmental alcohol

Second instar larvae of Drosophila melanogaster were exposed to exogenous alcohol, which is known to influence the activities of several enzymes. In this study, the activity changes were followed in four enzymes (ADH, ODH, alpha GPDH and AOX) during ethanol exposure and compared in three inbred lines that had different allelic combinations at the Odh and Aldox loci. The results indicate that the Odh-Aldox region of the third chromosome may alter the general response to ethanol. The activity of ADH increased considerably in two strains in the larval stages in the presence of alcohol; nevertheless, strain 1, with the OdhS-AldoxF allelic combination, showed a delay in the ADH induction compared to strain 2, which had the OdhF-AldoxS combination. In strain 3 (OdhS*-AldoxS) larvae, ADH induction by environmental ethanol was not detected. Moreover, the activities of alpha GPDH and AOX in strains 2 and 3 were not affected by ethanol. In contrast, the activities of all four enzymes in strain 1 changed after exposure to ethanol.

Heritabilities and additive genetic variances of the activities of some enzymes in Drosophila melanogaster populations living in different habitats

Drosophila melanogaster samples were collected from a large population in two habitats: farmyards and distilleries. Samples were taken from two villages in each habitat. Three isofemale lines were established from all four samples and full-sib crosses were set in each isofemale line. Activities of four enzymes (ADH, alpha GPDH, IDH and 6PGDH) were measured in the offspring of each cross on starch gel after electrophoresis. Broad sense heritabilities and additive genetic variances were estimated in all four samples. Most of the activity variation was observed within the isofemale lines. The isofemale lines tended to be more different in the distilleries than in the farmyards. There was no significant difference in the average activities between the two habitats for any of the enzymes investigated. The additive genetic variance of the enzyme activities did not exhibit a consistent habitat pattern. In the farmyard habitat, we detected a higher activity variation in Tiszafüred than in the other village. Strong correlation was observed among the activities of the enzymes investigated. Correlation coefficients indicated higher level of correlation in the samples collected in Tiszafüred than in those originating from Tiszaszolos. The heritability values were rather high and they had a considerable variation both between the habitats and across the enzymes.

A unique mechanism of nuclear division in Giardia lamblia involves components of the ventral disk and the nuclear envelope

The fine structure of the binucleate, parasitic protist Giardia lamblia during interphase and divisional stages was studied by serial thin sectioning and three-dimensional reconstructions. The earlier sign of nuclear division is the development of a few peripheral areas of densely packed chromatin directly attached to the inner nuclear envelope. An intracytoplasmic sheet of ventral disk components grows from the cell periphery towards one of the nuclei, apparently constricting this nucleus, which becomes located at a ventral bulge. After the basal bodies become duplicated, a full nuclear division occurs in trophozoites, giving two pairs of parent-daughter nuclei. This full division occurs in a dorsal-ventral direction, with the resulting nuclear pairs located at the sides of the two sets of basal bodies. A new ventral disk is formed from the disk-derived sheets in the cell harboring the four nuclei. Cytokinesis is polymorphic, but at early stages is dorsal-to-dorsal. Encysting trophozoites show the development of Golgi cisternae stacks and dense, specific secretory granules. 3-D reconstructions show that cysts contain a single pair of incompletely strangled nuclei. The dividing Giardia lacks a typical, microtubular spindle either inside or outside the nuclei. The nuclear envelope seems to be the only structure involved in the final division of the parent-daughter nuclei.

Evolution of clonality and polyploidy in a weevil system

The increased interest in asexual organisms calls for in-depth studies of asexual complexes that actively give rise to new clones. We present an extensive molecular study of the Otiorhynchus scaber (Coleoptera, Curculionidae) weevil system. Three forms have traditionally been recognized: diploid sexuals, triploid, and tetraploid parthenogens. All forms coexist in a small central area, but only the polyploid parthenogens have colonized marginal areas. Analyzing the phylogenetic relationship, based on three partial mitochondrial genes, of 95 individuals from 19 populations, we find that parthenogenesis and polyploidy have originated at least three times from different diploid lineages. We observe two major mitochondrial lineages, with over 2.5% sequence divergence between the most basal groups within them, and find that current distribution and phylogenetic relationships are weakly correlated. Quite unexpectedly, we also discover diploid clones that coexist with, and are morphologically indistinguishable from, the diploid sexual females. Our results support that these diploid clones are derived directly from the diploid sexuals. We also find that it is mainly an increase in ploidy level and not the benefits of asexual reproduction that confers to polyploid parthenogens the advantage over their diploid sexual relatives.

Interaction between the Adh and Odh loci in response to ethanol in Drosophila melanogaster

Six Drosophila melanogaster strains were constructed from two isofemale lines. The strains had four allele combinations at the alcohol dehydrogenase (Adh) and octanol dehydrogenase (Odh) loci, while all alpha-glycerophosphate dehydrogenase (alpha Gpdh), malate dehydrogenase (Mdh), and aldehyde oxidase (Aldox) alleles were identical. Second-instar and early and late third-instar larvae were exposed to different concentrations of ethanol (0, 5, and 7.5%) and 3 days later fresh weights and the activities of ADH, ODH, alpha GPDH, and MDH were measured. Activity differences were observed between the two Adh genotypes: ADHF allozyme had considerably higher activity than ADHS. Exogenous ethanol resulted in the highest increase in ADH activity in the second- and early third-instar stages. This ADH induction depended on the allele combination at the Adh and Odh loci; e.g., in the strain having the AdhS-OdhS allele combination, increased ADH activity was observed only after exposure to 7.5% ethanol. ODH activities differed according to the Odh genotypes, in that the ODHS allozyme had a higher activity than ODHF. ODH activities did not appreciably respond to different ethanol treatments. All six strains had identical alleles at the Mdh and alpha Gpdh loci, but nevertheless, the responses of these enzymes to ethanol depended on the allele combinations at the Adh and Odh loci. alpha GPDH activity followed that of ADH in all experiments. MDH activities were not influenced by exogenous ethanol in the strains homozygous for the AdhS allele. In AdhF strains, however, exposure to 7.5% ethanol resulted in a considerable decrease in MDH activity in the second-instar larvae. Correlations among the response variables showed that ODH activities were strongly associated with fresh weight and the activities of all other enzymes, except for ADH. ADH activity, however, showed a significant correlation only with alpha GPDH activity throughout the larval life. Both MDH and ODH activities were found to be in strong negative correlation with ADH activity in the second-instar larvae. At this most sensitive life stage, the metabolic response to ethanol is highly correlated.

Enzymatic responses of Drosophila melanogaster to long- and short-term exposures to ethanol

The effects of environmental ethanol on larva-to-pupa survival and on the activities of four enzymes were investigated in three Drosophila melanogaster strains. The strains had different allelic combinations at the Odh and Aldox loci on their third chromosomes, but they all carried the Adh(S)-Gpdh(F) allelic combination on the second chromosome. Replicates of each of the strains were exposed to three different ethanol treatments: (i) no ethanol in the medium (control); (ii) 5% ethanol for a single generation (short-term exposure); (iii) 5% ethanol for 20 generations (long-term exposure). In all experiments, the activities of four enzymes (ADH, ODH, GPDH and AOX) were measured in larvae, pupae and adults. The results showed that (i) the larval and adult metabolic responses to environmental ethanol were different; (ii) enzyme activity changes under short-term exposure differed from those measured under long-term exposure; (iii) the activities of the allozymes common to all strains (ADH-S and GPDH-F), differed depending on the genetic background. Changes in larva-to-pupa survival were seen when the larvae of control and exposed lines of the three strains were confronted with various concentrations of ethanol. In all three strains, the exposed lines had significantly higher initial survival rate and ethanol tolerance than the control lines. Strain-specific differences were observed in the ethanol tolerance of both types of line.

Differences in environmental temperature, ethanol and sucrose associated with enzyme activity and weight changes in Drosophila melanogaster

Activity changes of three enzymes (ADH, ODH and AOX) of Drosophila melanogaster were followed under different environmental conditions. The influences of ethanol, starvation (no carbohydrates in the medium) and ethanol stress during starvation were studied at both 18 and 26 degrees C. Two strains that were monomorphic for different alleles at the Odh and Aldox loci but otherwise identical were used. The investigated environmental conditions affected ADH induction by exogenous ethanol differently in the two strains. The different allozymes of ODH and AOX also responded differently to the treatments. We observed that the sucrose content of the medium on which ethanol exposure took place and the temperature strongly affected the responses within any single strain. Correlations were estimated among the three enzymes in the larval and adult stages of each strain separately. At both temperatures, differences between strains were observed in the patterns of associations of the response variables, in the larval, but not in the adult stages.

Chloroplast DNA variation in the grass tribe Festuceae

Six grasses, Hordeum sativum, Dactylis glomerata, Festuca arundinacea, F. pratensis, F. rubra and Lolium multiflorum were subjected to chloroplast DNA analysis based on restriction endonuclease digestion fragments and end labeling with (35)S nucleotides. This method is compared with others in general use. The results indicate that Lolium multiflorum is closely affiliated with Festuca pratensis and F. arundinacea; in fact much closer than F. rubra is to any of them.

Insertion polymorphism in pea chloroplast DNA

The chloroplast DNA of higher plants is suitable for restriction endonuclease analysis due to its size and homogeneity. We have analysed 48 different cultivars of pea (Pisum sativum) with EcoRI and HindIII. Of these, only 24 show the standard genotype, the remaining 24 comprise four different classes of short insertions, three of which are found at the same site. Even though this kind of insertion polymorphism has not been detected elsewhere in the plant kingdom, it is consistent with the discovery that the chloroplast DNA of pea is destabilised through the loss of an inverted repeat.

A simple method for pharmacological separation of motivation attention and learning

A simple 2 X 2 factorial analysis provides separation of drive and learning aspects in a bar press escape learning. In addition, attentional measure is given considering the dispersion of results. This experimental design has been proved with Diazepam, a drug of rather well known effects, to assert the validity of the method.

Genetic polymorphism and evolution in parthenogenetic animals : Part 9: Absence of variation within parthenogenetic aphid clones

The enzyme gene variability within parthenogenetic clones of Acyrtosiphon pisum has been followed by gel electrophoresis. No variation was observed within any clone. One enzyme locus was found to vary between clones. No evidence was found to support gene recombination due to the alleged endomeiosis. This hypothesis is proven to be also theoretically untenable. The low average heterozygosity in aphids is explained as a result of directional selection operating upon the parthenogenetic aphid clones, as a consequence of which the heterozygosity is lowered.

Polyploidy in insect evolution

Of all living organisms insects are the group with the highest number of existing species. It is, of course, true that a fraction of the total number of insects has been cytologically studied. Polyploid forms are rare exceptions among them. Polyploidy in insects is always associated with the parthenogenetic mode of reproduction. The cytologically verified cases are described. As for the geographic distribution of polyploid insects, they have successfully colonized vast land areas. Their distributions are, in general, northern and montane. The polyploid races are in general far more widespread than their diploid bisexual ancestors. The possible models of origin of polyploid insects are covered as well as data on their gaenetic variability. There are apparent environmental correlations in the distribution of certain forms. Most polyploid insects have life cycles extending over two (or more) years. They are also in general flightless forms. Hypotheses on the relation between heterozygosity in polyploids as well as the consequences of mutations in polyploid lineages are also presented.

Enzyme polymorphism in feral, outbred and inbred rats (Rattus norvegicus)

Polymorphism at 25 loci coding for liver enzymes was studied in two feral, three outbred and three inbred rat strains by starch gel electrophoresis. No variation was found at 14 loci, and a low degree of polymorphism was detected at three. Eight loci were polymorphic in more than one population. The average degree of heterozygosity per locus per individual feral rat was 0-07. The degrees of heterozygosity observed in the outbred and inbred strains were lower, from 0-006 to 0-012. Contrary to expectation, the inbred strains were neither monomorphic nor appreciably less heterozygous than the outbred ones. The heterozygosity of the inbred strains was primarily due to two polymorphic loci, G-3-pdh and alpha-Gpdh. The reason for this polymorphism is probably the superior homeostasis of the heterozygotes.

Genetic polymorphism and evolution in parthenogenetic animals. V. Triploid Adoxus obscurus (Coleoptera: Chrysomelidae)

The genetic variability at 16 enzyme loci in 52 Scandinavian triploid parthenogenetic populations of the beetleAdoxus obscurushas been studied by starch-gel electrophoresis. The overall genotypes of different beetles have been compared with each other and with a sample from a diploid bisexual population from Canada. Eighty per cent of the parthenogenetic beetles have the same overall genotype. The remainder belong to six genotypes, three of which are found in only one population. The variability within and between parthenogenetic populations ofA. obscurusis much lower than in other comparable parthenogenetic insects studied by us. This is interpreted to be a consequence of the efficient migration of the genotypes with the highest fitness, leading to a replacement of less-adapted genotypes.A. obscurusis a flying insect, whereas the other parthenogenetic insects studied by us are sluggish flightless forms.

Genetic polymorphism and evolution in parthenogenetic animals. II. Diploid and polyploid Solenobia triquetrella (Lepidoptera: Psychidae)

Genic polymorphism at sixteen enzyme loci of four different chromosomal races of Solenobia triquetrella (bisexual, two diploid parthenogenetic races and tetraploid parthenogentiic) has been studied by starch gel electrophoresis. Isolated small diploid bisexual populations have rather uniform allele frequencies at all loci which we have studied. Diploid and tetraploid parthenogenetic individuals of this species are in general as heterozygous as bisexual ones. All parthenogenetic local populations are different from each other in the Alps. These parthenogenetic genotypes cannot be derived from a common ancestor through single mutations but rather bear evidence for a polyphyletic origin of parthenogenesis in Solenobia triquetrella. In the marginal distribution areas of the species in northern Europe single genotypes are spread over far larger areas than in the mountain regions of central Europe. This may be due to the old origin of parthenogenesis and polyploidy in northern Europe. No new parthenogenetic and polyploid strains have lately arisen in the regions outside of the Alps.

GENETIC POLYMORPHISM AND EVOLUTION IN PARTHENOGENETIC ANIMALS. I. POLYPLOID CURCULIONIDAE

The genetic variability at enzyme loci in different triploid and tetraploid parthenogenetic weevil populations has been elucidated by starch gel electrophoresis. The overall genotype of individual weevils belonging to different populations has been determined for over 25 loci. The results are compared with those obtained for diploid bisexual races of either the same or closely related species. The variation within a parthenogenetic population differs from that in diploid, sexually reproducing populations, i.e. the allele frequencies are not in a Hardy-Weinberg equilibrium. The results indicate that apomictic parthenogenetic populations can differentiate genetically. The genotypes within a population resemble each other more than genotypes belonging to different populations. It is evident that evolution still continues-even if slowed down—in parthenogenetic weevils. A comparison between the allele relationships in geographically isolated polyploid parthenogenetic populations and related diploid bisexual forms does not support the hypothetical hybrid origin of parthenogenesis and polyploidy in weevils. Parthenogenesis within a parthenogenetic weevil species is evidently monophyletic.