An ancient monoaminergic signaling system coordinates contractility in a nerveless sponge

Area of Science:

• Animal Physiology
• Evolutionary Biology
• Cellular Signaling

Background:

• Sponges, early-diverging animals, lack neurons and muscles but coordinate canal contractions.
• Chemical neurotransmission enabled multicellular coordination and locomotion in animals.
• Understanding early animal communication is crucial for evolutionary insights.

Purpose of the Study:

• To investigate the molecular mechanisms underlying canal coordination in sponges.
• To identify the signaling molecules and pathways involved in sponge canal behavior.
• To explore the evolutionary origins of monoaminergic systems in animals.

Main Methods:

• Biochemical analysis of monoamine synthesis in *Spongilla lacustris*.
• Identification of decarboxylases and vesicular transporters.
• Phosphoproteomics and label-free 3D imaging to study signaling pathways.
• Functional assays to observe canal behavior in response to monoamines.

Main Results:

• Sponges synthesize tryptamine, phenethylamine, and tyramine, which elicit distinct canal behaviors.
• Novel decarboxylases and vesicular transporters are coexpressed in secretory neuroid and metabolic cells.
• Tryptamine activates GPCR signaling and Rho GTPases, remodeling cell adhesion and actomyosin networks.
• These molecular events drive localized constrictions and whole-body deflations in sponge canals.

Conclusions:

• An ancestral monoaminergic system predates neurons, linking secretory and contractile cell types.
• This system was likely elaborated for neuromodulation of synaptic transmission in later animal evolution.
• The findings reveal a primitive form of chemical signaling crucial for early animal multicellularity.