A Systematic Screen to Discover and Analyze Apicoplast Proteins Identifies a Conserved and Essential Protein Import Factor

Parasites of the phylum Apicomplexa cause diseases that impact global health and economy. These unicellular eukaryotes possess a relict plastid, the apicoplast, which is an essential organelle and a validated drug target. However, much of its biology remains poorly understood, in particular its elaborate compartmentalization: four membranes defining four different spaces. Only a small number of organellar proteins have been identified in particular few proteins are known for non-luminal apicoplast compartments. We hypothesized that enlarging the catalogue of apicoplast proteins will contribute toward identifying new organellar functions and expand the realm of targets beyond a limited set of characterized pathways. We developed a bioinformatic screen based on mRNA abundance over the cell cycle and on phyletic distribution. We experimentally assessed 57 genes, and of 30 successful epitope tagged candidates eleven novel apicoplast proteins were identified. Of those, seven appear to target to the lumen of the organelle, and four localize to peripheral compartments. To address their function we then developed a robust system for the construction of conditional mutants via a promoter replacement strategy. We confirm the feasibility of this system by establishing conditional mutants for two selected genes – a luminal and a peripheral apicoplast protein. The latter is particularly intriguing as it encodes a hypothetical protein that is conserved in and unique to Apicomplexan parasites and other related organisms that maintain a red algal endosymbiont. Our studies suggest that this peripheral plastid protein, PPP1, is likely localized to the periplastid compartment. Conditional disruption of PPP1 demonstrated that it is essential for parasite survival. Phenotypic analysis of this mutant is consistent with a role of the PPP1 protein in apicoplast biogenesis, specifically in import of nuclear-encoded proteins into the organelle

Autophagy Protein Atg3 is Essential for Maintaining Mitochondrial Integrity and for Normal Intracellular Development of Toxoplasma gondii Tachyzoites

Autophagy is a cellular process that is highly conserved among eukaryotes and permits the degradation of cellular material. Autophagy is involved in multiple survival-promoting processes. It not only facilitates the maintenance of cell homeostasis by degrading long-lived proteins and damaged organelles, but it also plays a role in cell differentiation and cell development. Equally important is its function for survival in stress-related conditions such as recycling of proteins and organelles during nutrient starvation. Protozoan parasites have complex life cycles and face dramatically changing environmental conditions; whether autophagy represents a critical coping mechanism throughout these changes remains poorly documented. To investigate this in Toxoplasma gondii, we have used TgAtg8 as an autophagosome marker and showed that autophagy and the associated cellular machinery are present and functional in the parasite. In extracellular T. gondii tachyzoites, autophagosomes were induced in response to amino acid starvation, but they could also be observed in culture during the normal intracellular development of the parasites. Moreover, we generated a conditional T. gondii mutant lacking the orthologue of Atg3, a key autophagy protein. TgAtg3-depleted parasites were unable to regulate the conjugation of TgAtg8 to the autophagosomal membrane. The mutant parasites also exhibited a pronounced fragmentation of their mitochondrion and a drastic growth phenotype. Overall, our results show that TgAtg3-dependent autophagy might be regulating mitochondrial homeostasis during cell division and is essential for the normal development of T. gondii tachyzoites

Health-related stigma as a determinant of functioning in young adults with narcolepsy.

Symptoms of narcolepsy tend to arise during adolescence or young adulthood, a formative time in human development during which people are usually completing their education and launching a career. Little is known about the impact of narcolepsy on the social aspects of health-related quality of life in young adults. The purpose of this study was to examine relationships between health-related stigma, mood (anxiety and depression) and daytime functioning in young adults with narcolepsy compared to those without narcolepsy. Young adults (age 18-35) with narcolepsy (N = 122) and without narcolepsy (N = 93) were mailed a packet that included questionnaires and a self-addressed postage paid envelope. The questionnaire included demographic information and a composite of instruments including the SF 36, Functional Outcomes of Sleep Questionnaire (FOSQ), Fife Stigma Scale (FSS), Epworth Sleepiness Scale (ESS) and Hospital Anxiety and Depression Scale (HADS). Variable associations were assessed using descriptive statistics, ANOVA, Mann-Whitney U Test, correlations, stepwise multiple regression and path analysis. Young adults with narcolepsy perceived significantly more stigma and lower mood and health-related quality of life than young adults without narcolepsy (p<0.01). Health-related stigma was directly and indirectly associated with lower functioning through depressed mood. Fifty-two percent of the variance in functioning was explained by the final model in the young adults with narcolepsy. Health-related stigma in young adults with narcolepsy is at a level consistent with other chronic medical illnesses. Health-related stigma may be an important determinant of functioning in young adults with narcolepsy. Future work is indicated toward further characterizing stigma and developing interventions that address various domains of stigma in people with narcolepsy

Path model fit indices.

<p>Note. NFI = normed fit index, CFI = comparative fit index, RMSEA—root mean square error of approximation.</p><p>Path model fit indices.</p

Descriptive statistics: Key variables.

<p>Analyses are reported as mean ± SD. SSIS-Stigma and Social Impact Scale, HADS-Hospital Anxiety and Depression Scale, SF36—Short Form Health Survey, QOL- Quality of Life, FOSQ—Functional Outcomes of Sleep Questionnaire, ESS- Epworth Sleepiness Scale, PSQI-Pittsburgh Sleep Quality Index.</p><p>Descriptive statistics: Key variables.</p

Direct and indirect effects of key variables on functioning.

<p>Note. Effects are standardized,</p><p>^aFunctional Outcomes of Sleep total score,</p><p>^bEpworth Sleepiness Scale,</p><p>^c Stigma and Social Impact Scale total score,</p><p>^dHADS Depression.</p><p>Direct and indirect effects of key variables on functioning.</p

Sample characteristics.

<p>Analyses are reported as mean (+/- SD) for continuous variables and percentages for</p><p>categorical variables.</p><p>Sample characteristics.</p