Profiling cellular diversity in sponges informs animal cell type and nervous system evolution

The evolutionary origin of metazoan cell types such as neurons and muscles is not known. Using whole-body single-cell RNA sequencing in a sponge, an animal without nervous system and musculature, we identified 18 distinct cell types. These include nitric oxide-sensitive contractile pinacocytes, amoeboid phagocytes, and secretory neuroid cells that reside in close contact with digestive choanocytes that express scaffolding and receptor proteins. Visualizing neuroid cells by correlative x-ray and electron microscopy revealed secretory vesicles and cellular projections enwrapping choanocyte microvilli and cilia. Our data show a communication system that is organized around sponge digestive chambers, using conserved modules that became incorporated into the pre- and postsynapse in the nervous systems of other animals.

Automated summary

Through whole-body single-cell RNA sequencing in sponges, researchers identified 18 distinct cell types, including contractile pinacocytes, amoeboid phagocytes, and secretory neuroid cells. These cells interact closely with digestive choanocytes, which express scaffolding and receptor proteins, indicating a communication system organized around sponge digestive chambers. Visualizing neuroid cells revealed secretory vesicles and cellular projections enwrapping choanocyte microvilli and cilia, suggesting the presence of conserved modules that may have evolved into synaptic structures in other animals' nervous systems.