Abstract
Invertebrates can be primed to enhance their protection against pathogens they have encountered before. This enhanced immunity can be passed maternally or paternally to the offspring and is known as transgenerational immune priming. We challenged larvae of the red flour beetle Tribolium castaneum by feeding them on diets supplemented with Escherichia coli, Micrococcus luteus or Pseudomonas entomophila, thus mimicking natural exposure to pathogens. The oral uptake of bacteria induced immunity-related genes in the offspring, but did not affect the methylation status of the egg DNA. However, we observed the translocation of bacteria or bacterial fragments from the gut to the developing eggs via the female reproductive system. Such translocating microbial elicitors are postulated to trigger bacterial strain-specific immune responses in the offspring and provide an alternative mechanistic explanation for maternal transgenerational immune priming in coleopteran insects.
Highlights
Invertebrates can mount specific immune responses against previously encountered pathogens [1,2], this phenomenon varies in its specificity [3,4]
To determine whether similar transgenerational immune priming (TGIP) mechanisms may be involved in T. castaneum, an insect that is established as a model for bacterial oral infections [13] and in which both maternal and paternal TGIP have already been confirmed [14], we investigated the transfer of bacterial particles ingested by female beetles and the methylation status of DNA in the offspring
We investigated the processes underlying maternal TGIP in T. castaneum, focusing on two proposed mechanisms: the transfer of ingested bacterial particles from the larval gut to the eggs of adult female beetles and the methylation status of the maternal and offspring DNA
Summary
Invertebrates can mount specific immune responses against previously encountered pathogens [1,2], this phenomenon varies in its specificity [3,4]. This effect, known as transgenerational immune priming (TGIP), has been described for crustaceans [1], insects [5] and molluscs [6] Both males and females can deliver information about the pathogens they have encountered to their offspring, but maternal and paternal TGIP in beetles differs in terms of specificity and the investment of resources [6,7,8,9]. Eggs (50 mg, three biological replicates) from adults (5– 7 days old) raised on white flour supplemented with bacteria (see above) were collected for DNA isolation using the ZR Tissue and Insect MicroPrep kit (ZymoResearch), and the global DNA methylation status was determined using the colorimetric MethylFlash methylated DNA quantification kit (Epigentek, Farmingdale, NY) according to the manufacturer’s instructions. A cryostat microtome CM 1850 (Leica Microsystems) was used to prepare 10 mm sections at – 208C and these were mounted with Fluoromount-GTM (Southern Biotech) and observed under a DM5000 B fluorescence microscope (Leica; see the electronic supplementary material)
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