Multiple Origins of Neurons From Secretory Cells

Development of the nervous system in the early hatching larvae of the ctenophore Mnemiopsis leidyi

“…Together with existing morphological data on the appearance of neural cells with short non-overlapping processes, this suggests that integration of multiple effectors occurs non-synaptically using either paracrine secretions (Moroz, 2021) or alternative integrative systems such as electrical coupling using pannexins/innexins (Moroz et al, 2014; or both. This mode of intercellular communication might be ancestral and present in the nerveless ancestors of all Metazoa (Moroz, 2021;Moroz et al, 2021) Second, a gradual increase in the complexity of neuronal architecture includes the rise in the number of neural cells and their connectivity, eventually forming the subepithelial neural nets as elementary circuits.…”

Divergent Ca2+/calmodulin feedback regulation of CaV1 and CaV2 voltage-gated calcium channels evolved in the common ancestor of Placozoa and Bilateria

“…Placozoans lack a nervous system and synapses, although they possess most genes required for electrochemical neural signaling ( 19 ). The two most early diverging animal phyla are the poriferans (sponges) and ctenophores (comb jellies), the former lacking a nervous system ( 26 ) and the latter bearing the most divergent nervous systems, proposed by some to have evolved independently ( 27 ). Both ctenophores and sponges lack Ca V 1 and Ca V 3 channels ( 4 ), making placozoans the most early diverging group to possess a complete set of Ca V 1 to Ca V 3 channels, as well as one ancillary Ca V β and two Ca V α 2 δ orthologues ( 20 ).…”

Selective Advantages of Synapses in Evolution

“…Over 60 years, scientists put forward the idea that neurons evolved from secretory cells (reviewed Moroz, 2014 , 2021 ). But what kind of preadaptations in secretory cells (apart from exocytosis itself) might facilitate synaptogenesis?…”

“…Emerging evidence suggests that neurons evolved more than once from secretory cells (reviewed by Moroz, 2014 , 2021 ). Such events might independently occur about 550–540 million years ago in ancestors of three basal metazoan lineages: ctenophores, cnidarians, and bilaterians (Moroz et al, 2021b ).…”

“…This opinion piece was initiated by one of the reviewers' comments to our recent paper (Moroz, 2021 ): “ While it seems perfectly plausible that neurons have originated, several times, from secretory cells, some questions arise about the origination process: There must be selective advantages of synaptic versus secretory communication ? ” We would like to thank the reviewer for excellent suggestions and provocative questions.…”