Jellyfish and flies use the same hormone when they’ve had enough to eat

Here, there, and everywhere?

But relatives of GLWa aren't limited to Cnidarians. More distantly related versions are found widely in animals. That's no guarantee, however, that the peptides are used for the same processes. So, to find out what GLWa might be doing elsewhere, the researchers turned to a convenient research animal, the fruit fly Drosophila, which has a GLWa relative called MIP.

Flies treated with the hormone also show a suppression of feeding behavior. And those that lack the gene that encodes the hormone continue to feed even if they've already had a lot to eat. So, the fly equivalent seems to be doing the same things.

But the striking thing is that the jellyfish version of the hormone worked in flies. You could replace the gene encoding the fly version of the hormone with the jellyfish gene, and the flies would show normal regulation of feeding. Or you can just treat the flies with the jellyfish hormone and suppress their feeding.

Fruit flies belong to the group Bilateria, which includes all animals with a defined left and right side. We know that Bilaterians and Cnidarians branched off from a common ancestor very early in the history of animal life and that this must have happened prior to the origin of most present animal groups, which happened in the Cambrian—there's clear evidence of Bilaterian animals prior to the Cambrian.

The fact that the hormone works in such widely separated species suggests that it may have originated very early in the history of animal life. The researchers also note that there appear to be relatives of this hormone in animals that branched off even earlier, such as sponges, which don't appear to have feeding behavior at all. There are even hints of a similar gene in the cells that are most closely related to animals, called choanoflagellates.

One possible explanation is that this system was regulating feeding behavior at the very start of the history of animal life on Earth. One argument against this, however, is that organisms like sponges don't seem to have any feeding behavior, so it's not clear what a hormone like this would do in these animals. The second caution is that we don't know how this hormone acts. Typically, they bind to some sort of receptor, but this research team hasn't identified the receptor for GLWa, so it's impossible to tell if the same signaling system is used in both flies and jellyfish, or the species' respective hormones happen to produce the same response through completely different mechanisms.

There are many potential ways to get a better picture of what's happening with the origin of appetite control. So, the research team here will have no shortage of experiments to do to follow up on this work.

PNAS, 2023. DOI: 10.1073/pnas.2221493120  (About DOIs).