Molecular requirements for C. elegans transgenerational epigenetic inheritance of pathogen avoidance

Area of Science:

• Neuroscience
• Genetics
• Microbiology

Background:

• * Caenorhabditis elegans* naturally prefer many bacteria, including pathogenic *Pseudomonas aeruginosa* (PA14), over lab strains like *Escherichia coli* (OP50).
• * Prior exposure to PA14 induces a rapid behavioral switch from attraction to avoidance in *C. elegans* within a single assay.
• * This rapid switch complicates assessing the worm's initial, unlearned preference.

Purpose of the Study:

• * To accurately determine the initial, unlearned preference of *C. elegans* for PA14.
• * To investigate the mechanism and extent of transgenerational epigenetic inheritance (TEI) of PA14 avoidance.
• * To identify factors influencing the expression of TEI in *C. elegans*.

Main Methods:

• * Utilized azide, a paralytic agent, to immobilize worms at their first choice, preventing behavioral switching during assays.
• * Exposed *C. elegans* to PA14 under specific conditions (25°C plate-grown PA14 at 20°C for 24 hr).
• * Analyzed the avoidance behavior of naive progeny across multiple generations (P0-F4).
• * Investigated the role of the small RNA P11 in mediating TEI.
• * Screened approximately 35 genes for involvement in TEI of learned pathogen avoidance.

Main Results:

• * Azide treatment revealed the true initial attraction of *C. elegans* to PA14, unaffected by rapid learned avoidance.
• * Specific PA14 exposure conditions induced avoidance in *C. elegans* and their progeny up to four generations later (P0-F4).
• * The small RNA P11, produced by PA14, was identified as both necessary and sufficient for this TEI of learned avoidance.
• * P11 expression is condition-dependent, being high in standard growth conditions (25°C on surfaces) but absent in others, explaining previous failures to observe F2-F4 avoidance.
• * Conservation of the P11-mediated TEI mechanism across *C. elegans* strains and *Pseudomonas* species suggests its ecological relevance.

Conclusions:

• * Accurate assessment of *C. elegans* initial bacterial preference requires methods that prevent rapid behavioral modification.
• * *C. elegans* can exhibit transgenerational epigenetic inheritance of learned PA14 avoidance, extending up to four generations.
• * The small RNA P11 is a key mediator of this TEI, with its expression influenced by environmental conditions.
• * The findings highlight the potential ecological significance of RNA-mediated epigenetic inheritance in host-pathogen interactions.