Neural Cell Type Diversity in Cnidaria

Neurons are the fundamental building blocks of nervous systems. It appears intuitive that the human brain is made up of hundreds, if not thousands different types of neurons. Conversely, the seemingly diffuse nerve net of Cnidaria is often assumed to be simple. However, evidence that the Cnidaria nervous system is indeed simple is sparse. Recent technical advances make it possible to assess the diversity and function of neurons with unprecedented resolution. Transgenic animals expressing genetically encoded Calcium sensors allow direct physiological assessments of neural responses within the nerve net and provide insight into the spatial organization of the nervous system. Moreover, response and activity patterns allow the characterization of cell types on a functional level. Molecular and genetic identities on the other hand can be assessed combining single-cell transcriptomic analysis with correlations of gene expression in defined neurons. Here I review recent advances on these two experimental strategies focusing on Hydra, Nematostella, and Clytia.

Automated summary

Neurons are the basic building blocks of nervous systems, and the human brain is composed of various types of neurons. In contrast, the nervous system of Cnidaria is commonly believed to be simple, but there is limited evidence to support this notion. Recent technological advances have allowed for the assessment of neuron diversity and function with unprecedented resolution, revealing the spatial organization of the nervous system. Additionally, single-cell transcriptomic analysis and correlations of gene expression have provided insights into the molecular and genetic identities of neurons.