Toxoplasma gondii infection reduces predator aversion in rats through epigenetic modulation in the host medial amygdala

Male rats (Rattus novergicus) infected with protozoan Toxoplasma gondii relinquish their innate aversion to the cat odours. This behavioural change is postulated to increase transmission of the parasite to its definitive felid hosts. Here, we show that the Toxoplasma gondii infection institutes an epigenetic change in the DNA methylation of the arginine vasopressin promoter in the medial amygdala of male rats. Infected animals exhibit hypomethylation of arginine vasopressin promoter, leading to greater expression of this nonapeptide. The infection also results in the greater activation of the vasopressinergic neurons after exposure to the cat odour. Furthermore, we show that loss of fear in the infected animals can be rescued by the systemic hypermethylation and recapitulated by directed hypomethylation in the medial amygdala. These results demonstrate an epigenetic proximate mechanism underlying the extended phenotype in the Rattus novergicus–Toxoplasma gondii association.     

The hitchhiker's guide to parasite dissemination

Toxoplasma gondii (T. gondii) is a parasitic protist that can infect nearly all nucleated cell types and tissues of warm‐blooded vertebrate hosts. T. gondii utilises a unique form of gliding motility to cross cellular barriers, enter tissues, and penetrate host cells, thus enhancing spread within an infected host. However, T. gondii also disseminates by hijacking the migratory abilities of infected leukocytes. Traditionally, this process has been viewed as a route to cross biological barriers such as the blood–brain barrier. Here, we review recent findings that challenge this view by showing that infection of monocytes downregulates the program of transendothelial migration. Instead, infection by T. gondii enhances Rho‐dependent interstitial migration of monocytes and macrophages, which enhances dissemination within tissues. Collectively, the available evidence indicates that T. gondii parasites use multiple means to disseminate within the host, including enhanced motility in tissues and translocation across biological barriers.     

Masterpiece of epigenetic engineering – how Toxoplasma gondii reprogrammes host brains to change fear to sexual attraction

The protozoan parasite Toxoplasma gondii is known to induce specific behavioural changes in its intermediate hosts, including humans, that are believed to increase the chance of its successful transmission to the definitive host, the cat. The most conspicuous change is the so‐called fatal attraction phenomenon, the switch from the mice's and rats’ natural fear of the smell of cats toward an attraction to this smell. The mechanism of this manipulation activity is unknown; however, many indices suggest that changes in the concentrations of dopamine and testosterone are involved. In this issue of Molecular Ecology, Hari Dass & Vyas ( 2014 ) present results of a study showing that, by hypomethylation of certain regulatory elements of key gene, Toxoplasma is able to reprogramme the brain's genetic machinery in such a way that cat odour activates and changes the wiring of the medial amygdala circuits responsible for sexual behaviour. This study delivers the first clear evidence of a parasite's ability to use sophisticated epigenetic engineering techniques for the manipulation of the phenotype of its infected host.     

Protozoan parasite Toxoplasma gondii manipulates mate choice in rats by enhancing attractiveness of males

Females in various species typically avoid males infected with parasites, while parasite-free males advertise their status through conspicuous phenotypic traits. This process selects for heritable resistance and reduces direct exposure of the female to parasites. Coevolving parasites are likely to attempt to circumvent this obstacle. In this paper, we demonstrate a case of parasitic manipulation of host mate choice. We report that Toxoplasma gondii, a sexually transmitted infection of brown rats, enhances sexual attractiveness of infected males. Thus under some evolutionary niches, parasites can indeed manipulate host sexual signaling to their own advantage.     

A Double‐Edged Sword: Complement Component 3 in Toxoplasma gondii Infection

Sprague Dawley rats and Kunming (KM) mice are artificially infected with type II Toxoplasma gondii strain Prugniaud (Pru) to generate toxoplasmosis, which is a fatal disease mediated by T. gondii invasion of the central nervous system (CNS) by unknown mechanisms. The aim is to explore the mechanism of differential susceptibility of mice and rats to T. gondii infection. Therefore, a strategy of isobaric tags for relative and absolute quantitation (iTRAQ) is established to identify differentially expressed proteins (DEPs) in the rats’ and the mice's brains compared to the healthy groups. In KM mice, which is susceptible to T. gondii infection, complement component 3 (C3) is upregulated and the tight junction (TJ) pathway shows a disorder. It is presumed that T. gondii‐stimulated C3 disrupts the TJ of the blood–brain barrier in the CNS. This effect allows more T. gondii passing to the brain through the intercellular space.     

New Antiparasitic Bis‐Naphthoquinone Derivatives

A series of bis‐naphthoquinone derivatives prepared by condensation of aryl aldehydes with lawsone were tested for antiparasitic activities against Toxoplasma gondii and Trypanosoma brucei parasites. Monofluorophenyl derivative 1a , 3,4‐difluorophenyl analog 1c and furyl compound 1l exhibited significant activity against T. gondii cells and appear to be new promising drug candidates against this parasite. The 3,4,5‐trifluorophenyl derivative 1g and the isovanillyl derivative 1j displayed selective activity against Leishmania major amastigotes.     

Leishmania infantum and Toxoplasma gondii: Mixed infection of macrophages in vitro and in vivo

Although macrophages have a microbicidal role in the immune system they themselves can be infected by pathogens. Often a simultaneous infection by more than one microbe may occur in a single cell. This is the first report of coinfection of macrophages with Toxoplasma gondii and Leishmania infantum, in vitro and in vivo. L. infantum does not cause severe disease in mice but T. gondii, RH strain, is lethal. Cell culture studies using THP-1 macrophages dually infected in vitro revealed that 4.3% harbored both parasites 24 h after infection. When mice were infected with both parasites on the same day 7.3% of the infected cells carried both parasites 7 days later. Yet, if mice were first infected with L. infantum and then with Toxoplasma (5 days post-infection) 18.7% of the macrophages hosted either parasite but concomitant infection could not be found and mice, already harboring L. infantum, survived Toxoplasma’s lethal effect.     

α2u-globulins mediate manipulation of host attractiveness in Toxoplasma gondii–Rattus novergicus association

Uninfected female rats (Rattus novergicus) exhibit greater attraction to the males infected with protozoan parasite Toxoplasma gondii. This phenomenon is contrary to the aversion towards infected males observed in multitude of other host–parasite associations. In this report, we describe a proximate mechanism for this anomaly. We demonstrate that T. gondii infection enhances hepatic production and urinary excretion of α2u-globulins in rats. We further demonstrate that α2u-globulins are sufficient to recapitulate male sexual attractiveness akin to effects of the infection. This manipulation possibly results in greater horizontal transmission of this parasite between the infected male and the uninfected female. It supports the notion that in some evolutionary niches parasites can alter host sexual signaling, likely leading to an increased rate of sexual transmission.Upon infection, Toxoplasma gondii invades immune-privileged organs of male rats like brain and testes. Ensuing chronic infection causes change in the behavior of the infected rats, namely: (a) loss of aversion to cat odors (Berdoy et al., 2000; Vyas and Sapolsky, 2010) and (b) gain of enhanced sexual attractiveness (Dass et al., 2011; Vyas, 2013). These changes plausibly lead to greater transmission of the parasite by trophic route to the cat intestine and by sexual route to female rats, although incontrovertible evidence of greater transmission in field conditions is not yet available (Worth et al., 2013). Correlative suggestions have also been made about increased attractiveness of infected human males and sexual transmission in humans (Hodkova et al., 2007; Flegr et al., 2014), although definitive evidence is presently unavailable. The gain in attractiveness post infection is particularly interesting because parasitism is generally observed to reduce sexual attractiveness of the host across varied phylogenies (Hamilton and Zuk, 1982; Folstad and Karter, 1992; Kavaliers et al., 2005). In this report, we investigate the proximate mechanism of this paradoxical effect.We first determined preference of uninfected estrus females for urine marks from control and infected males in an approach–approach conflict assay (detailed methods are described in Supplementary Information). Females spent greater time in bisect containing urine from the infected males (8/11 females, control < infected). For each second spent in the vicinity of urine from control males, receptive females spent 2.12 s with the infected male urine (paired t-test: |t₁₀|=2.78, P=0.019). Subsequently, female preference for low- and high-molecular weight fractions of the urine was separately quantified (LMW and HMW, respectively; cutoff=3 kDa). Volatiles bound to HMW fraction were displaced by a competitive molecule, menadione (Papes et al., 2010). Volatiles in HMW fractions before and after menadione displacement were compared with vehicle using direct analysis in real-time mass spectrometry (DART-MS). This analysis indicated the absence of any bound volatiles in displaced samples used for behavioral measurements. Analysis of variance (ANOVA) revealed significant interaction between infection status and the fractions (F_(1,30)=8.23, P=0.007). Females exhibited comparable preference to the LMW fraction of control and infected males (Figure 1a; control: 387±47 s, infected: 398±35 s; paired t-test: |t₁₅|=0.22, P>0.8; statistical power=0.054). In contrast, HMW fraction of the infected male was significantly preferred over that of control males (Figure 1a; control: 282±20 s, infected: 457±26 s; |t₁₅|=4.84, P<0.001). HMW fraction of infected animals exhibited greater attractiveness even when grafted on control LMW fraction (Figure 1b; control: 317±25 s, infected: 493±34 s; |t₁₁|=3.09, P=0.01). The majority of urinary proteins in the HMW fraction were determined to be α2u-globulins through mass spectrometric analysis (LOC259246 and LOC298109). Proteins homologous to rat α2u-globulins are also involved in chemical communication in mice (Hurst, 2009; Papes et al., 2010; Vasudevan and Vyas, 2013), including sexual signaling (Roberts et al., 2010).Open in a separate windowFigure 1The greater attractiveness of T. gondii-infected males was communicated by HMW, and not LMW, fraction of the male urine. Estrus females exhibited greater attraction to HMW fraction of the urine obtained from the infected males (a, black dots). N=16 females. ANOVA: P=0.514 for fractions; P=0.018 for infection status; P=0.007 for interaction. Abscissa and ordinate depict time spent in bisect containing urine from infected or control animals, respectively (in second, trial duration=1200 s). Solid circles depict data obtained from individual females. Gray diagonal line depicts chance (abscissa=ordinate). The attraction was not recapitulated by LMW fraction (<3 kDa) of the urine (a, gray dots). HMW obtained from infected animals was attractive to females even when combined with LMW of control urine (b). N=12 females. Mass spectroscopic analysis revealed major component of HMW fraction to be α2u-globulins.Infected animals contained greater amounts of α2u-globulin mRNA and protein in liver (Figures 2a and b). Congruently, urine from infected animals contained greater amounts of α2u-globulins (Figure 2b, 138% increase; P=0.011). In both liver and urine, the 25th percentile of α2u-globulin quantity in infected animals surpassed the 75th percentile of respective controls. α2u-globulins levels in preputial glands did not significantly differ between control and infected males (P=0.37).Open in a separate windowFigure 2Toxoplasma gondii infection increased α2u-globulins production in liver and excretion in urine. Infection enhanced α2u-globulins mRNA abundance in the liver (a). Ordinate depicts PCR cycles needed to reach a threshold when using α2u-globulins primers minus when using GAPDH primers (a housekeeping gene). Box plot depicts median, 25th percentile and 75th percentile. *P<0.05; exact Mann–Whitney test. N =7. Liver and urine from infected animals contained greater amounts of α2u-globulin protein. N=6 control, 8 infected (liver); N=7 (urine) (b). Ordinate depicts densitometric intensity, normalized to intensity of a pooled sample run in the same gel. Same pooled samples were used in all gels of the experiment. Creatinine-adjusted urine samples were used. Both groups exhibited comparable filtration rates of urine from the kidney (creatinine content; P>0.9) and a comparable tendency to place urine marks in a novel arena (P>0.9). *P<0.05 and **P<0.01; exact Mann–Whitney test. N=7. Renatured α2u-globulins postdialysis were sufficient to recapitulate greater attractiveness (c). Females exhibited attraction to FPLC-purified HMW fraction containing α2u-globulins, even after its denaturation in 3 m guanidinium chloride, subsequent dialysis and then renaturation in buffered physiological saline to remove all bound volatiles. N=12 females.Volatile substances in urine are known to bind α2u-globulins. The observation that HMW fraction from urine of infected animals was able to retain greater attractiveness even after menadione displacement supports the notion that α2u-globulins rather than volatiles bound to it were the active ingredients. We conducted a further experiment to test the possibility of residual volatiles still being bound to α2u-globulins in amounts undetectable by DART-MS. The fast protein liquid chromatography (FPLC)-purified α2u-globulins fraction was denatured, dialyzed and transferred to physiological buffer for renaturation. Dialysis with excess buffer was used in an intervening part of the cycle to remove any residual volatiles. Renaturation was confirmed by circular dichroism and tryptophan imaging. This procedure failed to rescue female attractiveness. Females exhibited robust preference to dialyzed α2u-globulins (Figure 2c; 10/12 females; |t₁₁|=4.09, P=0.002). Moreover, females exhibited clear preference for a greater concentration of FPLC-purified α2u-globulins in two-choice preference task comparing low and high doses (5 μg μl⁻¹: 334±41 s, 1.66 μg μl⁻¹: 208±24 s; paired t-test: |t₁₀|=2.78, P=0.014). These observations suggest that α2u-globulins can signal attractiveness without necessity of volatiles and in a dose-dependent manner. This is consistent with ability of HMW urinary fraction from the infected animals to evoke greater attraction, coupled with greater production of α2u-globulins postinfection. In other words, T. gondii infection increases urinary excretion of α2u-globulins, and greater α2u-globulins in the infected urine is sufficient to signal greater attractiveness. Greater α2u-globulins production in the infected rats is congruent with the observations that these proteins require testosterone for synthesis and that T. gondii infection increases testosterone production in male rats (Kulkarni et al., 1985; Lim et al., 2013).Many models of sexual selection posit that male sexual advertisement is an ‘honest'' proxy of an ability to fight infections. This honesty is thought to arrive because resources used for sexual advertising produce a handicap in ability to fight parasites or pathogens (Hamilton and Zuk, 1982; Wingfield et al., 1997). In other words, sexual signals are expensive to produce or maintain, thus allowing only fit males to engage in the advertisement. Many parasites do exploit host sexual signals. More frequently, this exploitation takes the form of either eavesdropping on sexual signals to find a new host or to inter-species mimicry of sexual signals by parasites to attract a potential host (Zuk and Kolluru, 1998; Haynes and Yeargan, 1999; Zuk et al., 2006). Parasites in these cases do not influence host advertisement per se. In this backdrop, rat–T. gondii association provides additional plausibility of the parasites changing magnitude of host sexual advertisement.Parasites are known to affect the behavior of their hosts (Hughes et al., 2012). This observation is frequently employed to argue that natural selection acts on genes and not necessarily individuals. In this narrative, the body of the host becomes an extended phenotype of the parasite (Dawkins, 1999; Hunter, 2009) and the behavioral changes correlate with increased transmission of the parasite. T. gondii has earlier been shown to increase sexual attractiveness of the infected males, resulting in greater sexual transmission of the parasite (Dass et al., 2011). Current observations present a molecular mechanism for T. gondii-induced extended phenotype.     

Testing the interactive effects of testosterone and parasites on carotenoid‐based ornamentation in a wild bird

Abstract Testosterone underlies the expression of most secondary sexual traits, playing a key role in sexual selection. However, high levels might be associated with physiological costs, such as immunosuppression. Immunostimulant carotenoids underpin the expression of many red‐yellow ornaments, but are regulated by testosterone and constrained by parasites. We manipulated testosterone and nematode burdens in red grouse (Lagopus lagopus scoticus) in two populations to tease apart their effects on carotenoid levels, ornament size and colouration in three time‐step periods. We found no evidence for interactive effects of testosterone and parasites on ornament size and colouration. We showed that ornament colouration was testosterone‐driven. However, parasites decreased comb size with a time delay and testosterone increased carotenoid levels in one of the populations. This suggests that environmental context plays a key role in determining how individuals resolve the trade‐off between allocating carotenoids for ornamental coloration or for self‐maintenance needs. Our study advocates that adequately testing the mechanisms behind the production or maintenance of secondary sexual characters has to take into account the dynamics of sexual trait expression and their environmental context.     

<Emphasis Type="Italic">Toxoplasma gondii</Emphasis> glycosylphosphatidylinositols are not involved in <Emphasis Type="Italic">T. gondii</Emphasis>-induced host cell survival

Toxoplasma gondii is an intracellular parasite able to both promote and inhibit apoptosis. T. gondii renders infected cells resistant to programmed cell death induced by multiple apoptotic triggers. On the other hand, increased apoptosis of immune cells after in vivo infection with T. gondii may suppress the immune response to the parasite. Glycosylphosphatidylinositol (GPI)-anchored proteins dominate the surface of T. gondii tachyzoites and GPIs are involved in the pathogenicity of protozoan parasites. In this report, we determine if GPIs are responsible for inhibition or induction of host cell apoptosis. We show here that T. gondii GPIs fail to block apoptosis that was triggered in human-derived cells via extrinsic or intrinsic apoptotic pathways. Furthermore, characteristics of apoptosis, e.g. caspase-3/7 activity, phosphatidylserine exposition at the cell surface or DNA strand breaks, were not observed in the presence of T. gondii GPIs. These results indicate that T. gondii GPIs are not involved in survival or in apoptosis of host cells. This absence of effect on apoptosis could be a feature common to GPIs of other parasites.     

Sexual selection shapes development and maturation rates in Drosophila

Explanations for the evolution of delayed maturity usually invoke trade‐offs mediated by growth, but processes of reproductive maturation continue long after growth has ceased. Here, we tested whether sexual selection shapes the rate of posteclosion maturation in the fruit fly Drosophila melanogaster. We found that populations maintained for more than 100 generations under a short generation time and polygamous mating system evolved faster posteclosion maturation and faster egg‐to‐adult development of males, when compared to populations kept under short generations and randomized monogamy that eliminated sexual selection. An independent assay demonstrated that more mature males have higher fitness under polygamy, but this advantage disappears under monogamy. In contrast, for females greater maturity was equally advantageous under polygamy and monogamy. Furthermore, monogamous populations evolved faster development and maturation of females relative to polygamous populations, with no detectable trade‐offs with adult size or egg‐to‐adult survival. These results suggest that a major aspect of male maturation involves developing traits that increase success in sexual competition, whereas female maturation is not limited by investment in traits involved in mate choice or defense against male antagonism. Moreover, rates of juvenile development and adult maturation can readily evolve in opposite directions in the two sexes, possibly implicating polymorphisms with sexually antagonistic pleiotropy.     

Evolution of Plant-Like Crystalline Storage Polysaccharide in the Protozoan Parasite Toxoplasma gondii Argues for a Red Alga Ancestry

Single-celled apicomplexan parasites are known to cause major diseases in humans and animals including malaria, toxoplasmosis, and coccidiosis. The presence of apicoplasts with the remnant of a plastid-like DNA argues that these parasites evolved from photosynthetic ancestors possibly related to the dinoflagellates. Toxoplasma gondii displays amylopectin-like polymers within the cytoplasm of the dormant brain cysts. Here we report a detailed structural and comparative analysis of the Toxoplasma gondii, green alga Chlamydomonas reinhardtii, and dinoflagellate Crypthecodinium cohnii storage polysaccharides. We show Toxoplasma gondii amylopectin to be similar to the semicrystalline floridean starch accumulated by red algae. Unlike green plants or algae, the nuclear DNA sequences as well as biochemical and phylogenetic analysis argue that the Toxoplasma gondii amylopectin pathway has evolved from a totally different UDP-glucose-based metabolism similar to that of the floridean starch accumulating red alga Cyanidioschyzon merolae and, to a lesser extent, to those of glycogen storing animals or fungi. In both red algae and apicomplexan parasites, isoamylase and glucan–water dikinase sequences are proposed to explain the appearance of semicrystalline starch-like polymers. Our results have built a case for the separate evolution of semicrystalline storage polysaccharides upon acquisition of photosynthesis in eukaryotes.This article contains online-only supplementary material.Reviewing Editor:Dr. Patrick Keeling     

A comparative study on the heparin‐binding proteomes of Toxoplasma gondii and Plasmodium falciparum

Toxoplasma gondii is an obligatory intracellular apicomplexan parasite which exploits host cell surface components in cell invasion and intracellular parasitization. Sulfated glycans such as heparin and heparan sulfate have been reported to inhibit cell invasion by T. gondii and other apicomplexan parasites such as Plasmodium falciparum. The aim of this study was to investigate the heparin‐binding proteome of T. gondii. The parasite‐derived components were affinity‐purified on the heparin moiety followed by MS fingerprinting of the proteins. The heparin‐binding proteins of T. gondii and P. falciparum were compared based on functionality and affinity to heparin. Among the proteins identified, the invasion‐related parasite ligands derived from tachyzoite/merozoite surface and the secretory organelles were prominent. However, the profiles of the proteins were different in terms of affinity to heparin. In T. gondii, the proteins with highest affinity to heparin were the intracellular components with functions of parasite development contrasted to that of P. falciparum, of which the rhoptry‐derived proteins were prominently identified. The profiling of the heparin‐binding proteins of the two apicomplexan parasites not only explained the mechanism of heparin‐mediated host cell invasion inhibition, but also, to a certain extent, revealed that the action of heparin on the parasite extended after endocytosis.     

Toxoplasma,testosterone, and behavior manipulation: the role of parasite strain,host variations,and intensity of infection

Toxoplasma gondii is an intracellular parasite involved in the etiology of various behavioral and hormonal alterations in humans and rodents. Various mechanisms, including induction changes of testosterone production, have been proposed in the etiology of behavioral alterations during T. gondii infection. However, controversy remains about the effects of T. gondii infection on testosterone production; in some studies, increased levels of testosterone were reported, whereas other studies reported decreased levels. This is a significant point, because testosterone has been shown to play important roles in various processes, from reproduction to fear and behavior. This contradiction seems to indicate that different factors--primarily parasite strains and host variations--have diverse effects on the intensity of T. gondii infection, which consequently has diverse effects on testosterone production and behavioral alterations. This paper reviews the role of parasite strains, host variations, and intensity of T. gondii infection on behavioral alterations and testosterone production, as well as the role of testosterone in the etiology of these alterations during toxoplasmosis.     

Antigenic Similarity Between the Coccidian Parasites Toxoplasma gondii and Hammondia hammondi1

The antigens that are present in the coccidian parasites Toxoplasma gondii and Hammondia hammondi were demonstrated and defined by using SDS-PAGE and immunoenzymatic techniques with ¹²⁵I-labeled and unlabeled antigens of T. gondii and sera of mice infected orally or intraperitoneally with H. hammondi. All cell surface antigens of T. gondii that were labeled with ¹²⁵I were recognized by antibodies in the sera of the mice infected with H. hammondi except the antigen of approximate molecular weight of 21.5 Kd. This suggests that this antigen is specific for T. gondii. Various antigens in the T. gondii-lysed antigen preparations were recognized by antibodies to H. hammondi. The number of recognized antigens increased as the infection of the mice with H. hammondi progressed. Oral infection with H. hammondi appeared to induce the formation of antibodies that recognized more T. gondii antigens than infection by intraperitoneal inoculation.     

The aspartyl protease TgASP5 mediates the export of the Toxoplasma GRA16 and GRA24 effectors into host cells

Toxoplasma gondii and Plasmodium species are obligatory intracellular parasites that export proteins into the infected cells in order to interfere with host‐signalling pathways, acquire nutrients or evade host defense mechanisms. With regard to export mechanism, a wealth of information in Plasmodium spp. is available, while the mechanisms operating in T. gondii remain uncertain. The recent discovery of exported proteins in T. gondii, mainly represented by dense granule resident proteins, might explain this discrepancy and offers a unique opportunity to study the export mechanism in T. gondii. Here, we report that GRA16 export is mediated by two protein elements present in its N‐terminal region. Because the first element contains a putative Plasmodium export element linear motif (RRLAE), we hypothesized that GRA16 export depended on a maturation process involving protein cleavage. Using both N‐ and C‐terminal epitope tags, we provide evidence for protein proteolysis occurring in the N‐terminus of GRA16. We show that TgASP5, the T. gondii homolog of Plasmodium plasmepsin V, is essential for GRA16 export and is directly responsible for its maturation in a Plasmodium export element‐dependent manner. Interestingly, TgASP5 is also involved in GRA24 export, although the GRA24 maturation mechanism is TgASP5‐independent. Our data reveal different modus operandi for protein export, in which TgASP5 should play multiple functions.     

The Toxoplasma gondii calcium‐dependent protein kinase 7 is involved in early steps of parasite division and is crucial for parasite survival

Apicomplexan parasites express various calcium‐dependent protein kinases (CDPKs), and some of them play essential roles in invasion and egress. Five of the six CDPKs conserved in most Apicomplexa have been studied at the molecular and cellular levels in Plasmodium species and/or in Toxoplasma gondii parasites, but the function of CDPK7 was so far uncharacterized. In T. gondii, during intracellular replication, two parasites are formed within a mother cell through a unique process called endodyogeny. Here we demonstrate that the knock‐down of CDPK7 protein in T. gondii results in pronounced defects in parasite division and a major growth deficiency, while it is dispensable for motility, egress and microneme exocytosis. In cdpk7‐depleted parasites, the overall DNA content was not impaired, but the polarity of daughter cells budding and the fate of several subcellular structures or proteins involved in cell division were affected, such as the centrosomes and the kinetochore. Overall, our data suggest that CDPK7 is crucial for proper maintenance of centrosome integrity required for the initiation of endodyogeny. Our findings provide a first insight into the probable role of calcium‐dependent signalling in parasite multiplication, in addition to its more widely explored role in invasion and egress.     

Isolation and characterization of microsatellite markers from Sarcocystis neurona,a causative agent of equine protozoal myeloencephalitis

The population genetics and systematics of coccidian parasites of the genus Sarcocystis remain poorly defined, notwithstanding their relevency to veterinary and human health. Despite opportunities for sexual recombination, nonrecombinant parasite clones characterized by distinct transmission and pathogenesis traits persist in related parasites (i.e. Toxoplasma gondii). In order to determine whether this may be generally true for parasitic coccidia, and to address evolutionary and taxonomic problems within the genus Sarcocystis, we isolated 12 polymorphic microsatellite markers (four to 14 alleles) for Sarcocystis neurona, the major causative agent of equine protozoal myeloencephalitis (EPM).     

HORMESIS RESULTS IN TRADE‐OFFS WITH IMMUNITY

Many have argued that we may be able to extend life and improve human health through hormesis, the beneficial effects of low‐level toxins and other stressors. But, studies of hormesis in model systems have not yet established whether stress‐induced benefits are cost free, artifacts of inbreeding, or come with deleterious side effects. Here, we provide evidence that hormesis results in trade‐offs with immunity. We find that a single topical dose of dead spores of the entomopathogenic fungus, Metarhizium robertsii, increases the longevity of the fruit fly, Drosophila melanogaster, without significant decreases in fecundity. We find that hormetic benefits of pathogen challenge are greater in lines that lack key components of antifungal immunity (Dif and Turandot M). And, in outbred fly lines, we find that topical pathogen challenge enhances both survival and fecundity, but reduces ability to fight off live infections. The results provide evidence that hormesis is manifested by stress‐induced trade‐offs with immunity, not cost‐free benefits or artifacts of inbreeding. Our findings illuminate mechanisms underlying pathogen‐induced life‐history trade‐offs, and indicate that reduced immune function may be an ironic side effect of the “elixirs of life.”