Onodera, A. | Search bioRxiv

bioRxiv2024

Glutamate, GABA, and dense-core vesicle secretion regulate predatory feeding in the nematode Pristionchus pacificus

Nematodes are one of the most diverse groups of organisms, found in various environments, and exhibit various feeding behaviours. Pristionchus pacificus displays two types of feeding behaviours: predatory and bacterial feeding. Previously, we showed that the neurotransmitter serotonin plays important roles in regulating predatory feeding in P. pacificus. However, the role of other neurotransmitters in predatory feeding remains unclear. Using the CRISPR/Cas9 system, we generated mutants of the dense-core vesicle (DCV)-based neuropeptide secretion system and genes related to seven neurotransmitters. Predatory assays revealed that the vesicular glutamate transporter Ppa-EAT-4, glutamic acid decarboxylase Ppa-UNC-25 which is involved in GABA synthesis, and the calcium-dependent activator protein for DCV secretion Ppa-UNC-31, play roles in predatory feeding behaviour. We assessed the pharyngeal movement necessary for predation as well as locomotion rate in these mutants. While the Ppa-eat-4 and Ppa-unc-31 mutants decreased predation movement, the Ppa-unc-25 mutant showed a reduction only in bacterial events compared to wild type animals. Additionally, Ppa-unc-25 and Ppa-unc-31 decreased in motor movement, potentially reducing predation efficiency. Together, these results suggest that glutamate, GABA and DCV secretion modulate feeding behaviours in P. pacificus. Our mutant collection of neurotransmitter-related genes will be useful for future analysis of neurobiology and behavioural evolution.

animal behavior and cognition↗

bioRxiv2024

Stimulatory and inhibitory G-protein signaling relays drive cAMP accumulation for timely metamorphosis in the chordate Ciona

Larvae of the ascidian Ciona initiate metamorphosis tens of minutes after adhesion to a substratum via their adhesive organ. The gap between adhesion and metamorphosis initiation is suggested to ensure the rigidity of adhesion, allowing Ciona to maintain settlement after losing locomotive activity through metamorphosis. The mechanism producing the gap is unknown. Here, by combining gene functional analyses, pharmacological analyses, and live imaging, we propose that the gap represents the time required for sufficient cAMP accumulation to trigger metamorphosis. Not only the Gs pathway but also the Gi and Gq pathways are involved in the initiation of metamorphosis in the downstream signaling cascade of the neurotransmitter GABA, the known initiator of Ciona metamorphosis. The mutual crosstalk of stimulatory and inhibitory G-proteins functions as the accelerator and brake for cAMP production, ensuring the faithful initiation of metamorphosis at an appropriate time and in the right situation.

developmental biology↗