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A wild C. elegans strain has enhanced epithelial immunity to a natural microsporidian parasite.

Balla KM, Andersen EC, Kruglyak L, Troemel ER - PLoS Pathog. (2015)

Bottom Line: We show that enhanced immunity is dominant to susceptibility, and we use quantitative trait locus mapping to identify four genomic loci associated with resistance.Furthermore, we generate near-isogenic strains to directly demonstrate that two of these loci influence resistance.Thus, our findings show that early-life immunity of C. elegans against microsporidia is a complex trait that enables the host to produce more progeny later in life, likely improving its evolutionary success.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America.

ABSTRACT
Microbial pathogens impose selective pressures on their hosts, and combatting these pathogens is fundamental to the propagation of a species. Innate immunity is an ancient system that provides the foundation for pathogen resistance, with epithelial cells in humans increasingly appreciated to play key roles in innate defense. Here, we show that the nematode C. elegans displays genetic variation in epithelial immunity against intestinal infection by its natural pathogen, Nematocida parisii. This pathogen belongs to the microsporidia phylum, which comprises a large phylum of over 1400 species of fungal-related parasites that can infect all animals, including humans, but are poorly understood. Strikingly, we find that a wild C. elegans strain from Hawaii is able to clear intracellular infection by N. parisii, with this ability restricted to young larval animals. Notably, infection of older larvae does not impair progeny production, while infection of younger larvae does. The early-life immunity of Hawaiian larvae enables them to produce more progeny later in life, providing a selective advantage in a laboratory setting--in the presence of parasite it is able to out-compete a susceptible strain in just a few generations. We show that enhanced immunity is dominant to susceptibility, and we use quantitative trait locus mapping to identify four genomic loci associated with resistance. Furthermore, we generate near-isogenic strains to directly demonstrate that two of these loci influence resistance. Thus, our findings show that early-life immunity of C. elegans against microsporidia is a complex trait that enables the host to produce more progeny later in life, likely improving its evolutionary success.

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Age- and strain-dependent variation in clearance of N. parisii infection.(A) Early N. parisii sporoplasms in an N2 animal 3 hpi, fixed, and stained for DNA with DAPI (blue) and for N. parisii rRNA with FISH (red). (B) N. parisii multi-nucleate meronts in an N2 animal 20 hpi. (A, B) Arrows indicate individual parasite cells, dotted white line indicates the intestine. (C) Percentage of animals that are infected at 3 hpi and 20 hpi. Solid lines show percentages when animals are inoculated at the L1 stage, and dashed lines show percentages when animals are inoculated at the L4 stage. The mean percentage of each condition from three independent experiments is shown with error bars as SD. Each experiment had at least 100 animals per condition. (D) Mean number of parasite cells measured by FISH 3 hpi in infected L1 and L4 stage animals from three independent experiments with error bars as SD. Asterisks indicate significance (P<0.001) by t-test. Each experiment had at least 100 animals per condition.
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ppat.1004583.g003: Age- and strain-dependent variation in clearance of N. parisii infection.(A) Early N. parisii sporoplasms in an N2 animal 3 hpi, fixed, and stained for DNA with DAPI (blue) and for N. parisii rRNA with FISH (red). (B) N. parisii multi-nucleate meronts in an N2 animal 20 hpi. (A, B) Arrows indicate individual parasite cells, dotted white line indicates the intestine. (C) Percentage of animals that are infected at 3 hpi and 20 hpi. Solid lines show percentages when animals are inoculated at the L1 stage, and dashed lines show percentages when animals are inoculated at the L4 stage. The mean percentage of each condition from three independent experiments is shown with error bars as SD. Each experiment had at least 100 animals per condition. (D) Mean number of parasite cells measured by FISH 3 hpi in infected L1 and L4 stage animals from three independent experiments with error bars as SD. Asterisks indicate significance (P<0.001) by t-test. Each experiment had at least 100 animals per condition.

Mentions: The pathogen resistance of HW animals could be caused by an inability of N. parisii to invade and establish an infection in these animals, or by the ability to limit or clear an infection once it has been established. The results from our feeding experiments with fluorescent E. coli indicated that HW animals receive a similar initial inoculum of pathogen in their intestinal lumens (S5 Fig.), but it remained possible that the pathogen may be less able to invade and establish an infection inside intestinal cells of HW animals. To investigate this possibility, we analyzed intracellular infection at a very early stage. Previously, we had identified the earliest signs of N. parisii invasion and intracellular growth at 8 hpi [25] (and see life cycle in S1 Fig.), and here we show that intracellular N. parisii parasite cells can be identified even earlier at 3 hpi, by visualization of small, mono-nucleate N. parisii ‘sporoplasms’ inside C. elegans intestinal cells (Fig. 3A). These sporoplasms then develop into larger, multi-nucleate meronts by 20 hpi (Fig. 3B). We quantified this infection and found that approximately 90% of animals in a population of either N2 or HW animals had at least one intracellular pathogen cell in their intestines (Fig. 3C). To further quantify this initial invasion and infection, we counted the number of parasite cells per animal at 3 hpi and found that this number was slightly lower in HW animals (Fig. 3D). The fact that a similar percentage of N2 or HW animals is infected at 3 hpi lends further support to the hypothesis that the variation in resistance is not caused by differences in the rate of pathogen exposure or invasion but rather by an enhanced resistance in HW animals that acts post-invasion to mediate clearance of infection.


A wild C. elegans strain has enhanced epithelial immunity to a natural microsporidian parasite.

Balla KM, Andersen EC, Kruglyak L, Troemel ER - PLoS Pathog. (2015)

Age- and strain-dependent variation in clearance of N. parisii infection.(A) Early N. parisii sporoplasms in an N2 animal 3 hpi, fixed, and stained for DNA with DAPI (blue) and for N. parisii rRNA with FISH (red). (B) N. parisii multi-nucleate meronts in an N2 animal 20 hpi. (A, B) Arrows indicate individual parasite cells, dotted white line indicates the intestine. (C) Percentage of animals that are infected at 3 hpi and 20 hpi. Solid lines show percentages when animals are inoculated at the L1 stage, and dashed lines show percentages when animals are inoculated at the L4 stage. The mean percentage of each condition from three independent experiments is shown with error bars as SD. Each experiment had at least 100 animals per condition. (D) Mean number of parasite cells measured by FISH 3 hpi in infected L1 and L4 stage animals from three independent experiments with error bars as SD. Asterisks indicate significance (P<0.001) by t-test. Each experiment had at least 100 animals per condition.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4334554&req=5

ppat.1004583.g003: Age- and strain-dependent variation in clearance of N. parisii infection.(A) Early N. parisii sporoplasms in an N2 animal 3 hpi, fixed, and stained for DNA with DAPI (blue) and for N. parisii rRNA with FISH (red). (B) N. parisii multi-nucleate meronts in an N2 animal 20 hpi. (A, B) Arrows indicate individual parasite cells, dotted white line indicates the intestine. (C) Percentage of animals that are infected at 3 hpi and 20 hpi. Solid lines show percentages when animals are inoculated at the L1 stage, and dashed lines show percentages when animals are inoculated at the L4 stage. The mean percentage of each condition from three independent experiments is shown with error bars as SD. Each experiment had at least 100 animals per condition. (D) Mean number of parasite cells measured by FISH 3 hpi in infected L1 and L4 stage animals from three independent experiments with error bars as SD. Asterisks indicate significance (P<0.001) by t-test. Each experiment had at least 100 animals per condition.
Mentions: The pathogen resistance of HW animals could be caused by an inability of N. parisii to invade and establish an infection in these animals, or by the ability to limit or clear an infection once it has been established. The results from our feeding experiments with fluorescent E. coli indicated that HW animals receive a similar initial inoculum of pathogen in their intestinal lumens (S5 Fig.), but it remained possible that the pathogen may be less able to invade and establish an infection inside intestinal cells of HW animals. To investigate this possibility, we analyzed intracellular infection at a very early stage. Previously, we had identified the earliest signs of N. parisii invasion and intracellular growth at 8 hpi [25] (and see life cycle in S1 Fig.), and here we show that intracellular N. parisii parasite cells can be identified even earlier at 3 hpi, by visualization of small, mono-nucleate N. parisii ‘sporoplasms’ inside C. elegans intestinal cells (Fig. 3A). These sporoplasms then develop into larger, multi-nucleate meronts by 20 hpi (Fig. 3B). We quantified this infection and found that approximately 90% of animals in a population of either N2 or HW animals had at least one intracellular pathogen cell in their intestines (Fig. 3C). To further quantify this initial invasion and infection, we counted the number of parasite cells per animal at 3 hpi and found that this number was slightly lower in HW animals (Fig. 3D). The fact that a similar percentage of N2 or HW animals is infected at 3 hpi lends further support to the hypothesis that the variation in resistance is not caused by differences in the rate of pathogen exposure or invasion but rather by an enhanced resistance in HW animals that acts post-invasion to mediate clearance of infection.

Bottom Line: We show that enhanced immunity is dominant to susceptibility, and we use quantitative trait locus mapping to identify four genomic loci associated with resistance.Furthermore, we generate near-isogenic strains to directly demonstrate that two of these loci influence resistance.Thus, our findings show that early-life immunity of C. elegans against microsporidia is a complex trait that enables the host to produce more progeny later in life, likely improving its evolutionary success.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America.

ABSTRACT
Microbial pathogens impose selective pressures on their hosts, and combatting these pathogens is fundamental to the propagation of a species. Innate immunity is an ancient system that provides the foundation for pathogen resistance, with epithelial cells in humans increasingly appreciated to play key roles in innate defense. Here, we show that the nematode C. elegans displays genetic variation in epithelial immunity against intestinal infection by its natural pathogen, Nematocida parisii. This pathogen belongs to the microsporidia phylum, which comprises a large phylum of over 1400 species of fungal-related parasites that can infect all animals, including humans, but are poorly understood. Strikingly, we find that a wild C. elegans strain from Hawaii is able to clear intracellular infection by N. parisii, with this ability restricted to young larval animals. Notably, infection of older larvae does not impair progeny production, while infection of younger larvae does. The early-life immunity of Hawaiian larvae enables them to produce more progeny later in life, providing a selective advantage in a laboratory setting--in the presence of parasite it is able to out-compete a susceptible strain in just a few generations. We show that enhanced immunity is dominant to susceptibility, and we use quantitative trait locus mapping to identify four genomic loci associated with resistance. Furthermore, we generate near-isogenic strains to directly demonstrate that two of these loci influence resistance. Thus, our findings show that early-life immunity of C. elegans against microsporidia is a complex trait that enables the host to produce more progeny later in life, likely improving its evolutionary success.

Show MeSH
Related in: MedlinePlus