Deep homologies in chordate caudal central nervous systems.

TitleDeep homologies in chordate caudal central nervous systems.
Publication TypeJournal Article
Year of Publication2024
AuthorsKourakis MJ, Ryan K, Newman-Smith ED, Meinertzhagen IA, Smith WC
JournalbioRxiv
Date Published2024 Jun 04
ISSN2692-8205
Abstract

Invertebrate chordates, such as the tunicate , can offer insight into the evolution of the chordate phylum. Anatomical features that are shared between invertebrate chordates and vertebrates may be taken as evidence of their presence in a common chordate ancestor. The central nervous systems of larvae and vertebrates share a similar anatomy despite the CNS having ~180 neurons. However, the depth of conservation between the CNS and those in vertebrates is not resolved. The caudal CNS, while appearing spinal cord-like, has hitherto been thought to lack motor neurons, bringing into question its homology with the vertebrate spinal cord. We show here that the larval caudal CNS does, in fact, have functional motor neurons along its length, pointing to the presence of a spinal cord-like structure at the base of the chordates. We extend our analysis of shared CNS anatomy further to explore the "motor ganglion", which has been proposed to be a homolog of the vertebrate hindbrain, spinal cord, or both. We find that a cluster of neurons in the dorsal motor ganglion shares anatomical location, developmental pathway, neural circuit architecture, and gene expression with the vertebrate cerebellum. However, functionally, the cluster appears to have more in common with vertebrate cerebellum-like structures, insofar as it receives and processes direct sensory input. These findings are consistent with earlier speculation that the cerebellum evolved from a cerebellum-like structure, and suggest that the latter structure was present in the dorsal hindbrain of a common chordate ancestor.

DOI10.1101/2024.06.03.597227
Alternate JournalbioRxiv
PubMed ID38895365
PubMed Central IDPMC11185728
Grant ListR34 NS127106 / NS / NINDS NIH HHS / United States