Rong Xuan Zang: Our paper is a bit more unconventional: using a non-model organism like sponges. The major question we're trying to answer is how, as animals first developed as multicellular organisms compared to unicellular organisms, they started to develop a system for the different cells to communicate with each other.

In a lot of the well-studied model systems (mice, fly, worm) we know the nervous system plays a key role in cell-cell communication, and they use neurotransmitters that often are metabolites of food. For example, serotonin is a metabolite derivative of amino acids. What we found is that these sponges use a more primitive version of that signaling system, where they use simple monoamines derived from amino acids. They don't use the enzyme that neurons use, but they actually use these other classes of enzymes that we discovered are functional.

This may resemble an ancestral state of how animal cells were talking to each other—using these simple monoamines as food derivatives for coordinating body behaviors. We also looked at how these sponges behave in response to these monoamines. We showed that they do some contraction that's not using the typical machinery we find in muscles, but is actually similar to chemotaxis machinery.

It seems to suggest a hypothetical scenario where, during early animal evolution, there was a division of labor and you created two different cell types: a cell type that interconverted environmental cues (food resources like amino acids) into these processed monoamines, and then those monoamines were sent as an intercellular signal within the multicellular organism. That activated specialized contractile networks of cells, a chemotaxis network that was previously autonomous in the unicellular organism, which has been incorporated with cell junction machinery to perform more coordinated and complex behaviors.

Jacob M. Musser: One of the cool things, too, is that the system of diffusing these modified metabolites is still present in us. Serotonin and dopamine are just modified a little bit further, and we still see them modulating peristalsis in our gut. We see them modulating the opening and closing of the capillary system. That's very similar to what's happening when sponges are opening and closing the feeding canals they have—they're built around a series of tubes.

So that ancient modulation system—being able to respond to your environment and regulate your feeding and fluid flow—is really the ancient system that the cells were talking about in early animals: What are we eating? What's going on in our environment? And how does our body respond to that?