Neural mechanisms of parasite-induced summiting behavior in “zombie”Drosophila

Abstract

For at least two centuries, scientists have been enthralled by the zombie behaviors induced by mind-controlling parasites. Despite this interest, the mechanistic bases of these uncanny processes have remained mostly a mystery. Here, we leverage the recently established Entomophthora muscae-Drosophila melanogaster zombie fly system to reveal the molecular and cellular underpinnings of summit disease, a manipulated behavior evoked by many fungal parasites. Using a new, high-throughput behavior assay to measure summiting, we discovered that summiting behavior is characterized by a burst of locomotion and requires the host circadian and neurosecretory systems, specifically DN1p circadian neurons, pars intercerebralis to corpora allata projecting (PI-CA) neurons and corpora allata (CA), who are solely responsible for juvenile hormone (JH) synthesis and release. Summiting is a fleeting phenomenon, posing a challenge for physiological and biochemical experiments requiring tissue from summiting flies. We addressed this with a machine learning classifier to identify summiting animals in real time. PI-CA neurons and CA appear to be intact in summiting animals, despite E. muscae cells invading the host brain, particularly in the superior medial protocerebrum (SMP), the neuropil that contains DN1p axons and PI-CA dendrites. The blood-brain barrier of flies late in their infection was significantly permeabilized, suggesting that factors in the hemolymph may have greater access to the central nervous system during summiting. Metabolomic analysis of hemolymph from summiting flies revealed differential abundance of several compounds compared to non-summiting flies. Transfusing the hemolymph of summiting flies into non-summiting recipients induced a burst of locomotion, demonstrating that factor(s) in the hemolymph likely cause summiting behavior. Altogether, our work reveals a neuro-mechanistic model for summiting wherein fungal cells perturb fly hemolymph, activating the neurohormonal pathway linking clock neurons to juvenile hormone production in the CA, ultimately inducing locomotor activity in their host.

Multiomic interpretation of fungus-infected ant metabolomes during manipulated summit disease

“…Notably, Ophiocordyceps does not appear to typically reside directly or very invasively within the brain, suggesting ergothioneine may be secreted by the fungus 13 , 21 , 27 . Similarly, infection with the very distantly related host manipulating fungus Entomophthora muscae leads to increased ergothioneine in the hemolymph of infected flies 103 .…”

“…Manipulators of vertebrate behavior are also thought to leverage serotoninergic and dopaminergic processes to alter fish and mouse behaviors related to escape responses, locomotion, and aggression 51 , 113 – 115 . Broadly implicating small molecules in parasitic host manipulation, infection of flies by the manipulating fungus E. muscae leads to permeabilization of the host blood–brain-barrier and experimental transfers of hemolymph from manipulated summiting hosts to naïve flies induces modest bouts of hyperactivity 103 . How much of the alteration of neurotransmitter metabolism may be a general response to fungal infection and how much results from specific manipulation by Ophiocordyceps is difficult to pinpoint at this time.…”

Fungi activate Toll-1 dependent immune evasion to induce cell loss in the host brain

“…Once attached, B. bassiana spores germinate and produce hyphae that degrade the cuticle by secreting various chitinases and proteases (Fan et al, 2007, Fang et al, 2009, Zhang et al, 2008). Spores in the brain and a compromised blood-brain barrier were also found following E. muscae infection in Drosophila (Elya et al, 2023, Elya et al, 2018). B. bassiana could also trigger a host response facilitating macrophage entry across the BBB and into the brain (see (Winkler et al, 2021)).…”