It notes that the sponge genome includes tens of thousands of genes, many of which are also found among complex organisms. But, it says, what the role of some of these genes were in an animal that lacked, for instance, a nervous system or musculature was unclear. But through a whole-body single-cell RNA sequencing study of sponges, researchers from the European Molecular Biology Laboratory and elsewhere began to tease out more than a dozen cell types within sponges.
As they reported recently in Science, the EMBL-led team uncovered a handful of cell types, including pinacocytes that respond to nitric oxide, which leads to muscle relaxation in vertebrates, and choanocytes and neuroid cells within sponges' digestive chambers that express genes often involved in neurotransmission, hinting at type of communication system.
"Our data are very consistent with this notion that a large number of important functional pieces of machinery existed early in animal evolution," first author Jacob Musser, a postdoc at EMBL, tells Wired. "And a lot of early animal evolution was about starting to subdivide this out to different cells. But likely these very first cell types were very multifunctional, and they had to do multiple things."