Molecular and electrophysiological properties underlying calcium signaling in muscle cells of ctenophores

Background Recent phylogenetic evidence placing ctenophores as a sister lineage to the rest of the animals has challenged existing views as to the origins of muscles, neurons, and nervous systems. Most of the electrophysiological and morphological data available for ctenophores predate the genomic age. An integrated cellular, genomic, and transcriptomic approach has yet to be employed in ctenophores; accordingly, little is known about how ctenophore cells detect, process, and coordinate internal and external signals. Results Here we show that excitable cells of the ctenophore Mnemiopsis neuromuscular system express a basic set of voltage-gated channels capable of generating and transmitting action potentials. Activation of those cells and generation of action potentials are accompanied by recurrent transient elevations in cytoplasmic Ca 2+ , allowing calcium imaging and evaluation of the activity of populations of sensory cells, neurons, and muscles. Despite the complex evolutionary histories of many of the channels, receptors, and specification factors involved in the operation and specification of these cell types, ctenophore excitable cells share core physiological and transcriptomic properties with those of cnidarians and bilaterians. Conclusions Together, these data support an evolutionary scenario in which the muscle and neural cells of ctenophores, cnidarians, and bilaterians descended from an excitable cell present in the last common ancestor of animals.