ABSTRACT
Invertebrate chordates, such as the tunicate Ciona, can offer insight into the evolution of the chordate phylum. Anatomical features shared between invertebrate chordates and vertebrates may be taken as evidence of their presence in a common chordate ancestor. The central nervous systems (CNSs) of Ciona larvae and vertebrates share a similar anatomy despite the Ciona CNS having only ∼180 neurons. However, the depth of conservation between the Ciona CNS and those of vertebrates is not resolved. The Ciona 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 Ciona larval caudal CNS does, in fact, have functional motor neurons along its length, pointing to the presence of a functional spinal cord-like structure at the base of the chordates.
Footnotes
Author contributions
Conceptualization: W.C.S., K.R., I.A.M.; Data curation: K.R.; Formal analysis: K.R.; Funding acquisition: W.C.S.; Investigation: M.J.K., K.R., E.D.N.-S.; Project administration: W.C.S., K.R.; Supervision: W.C.S., M.J.K., I.A.M.; Writing – original draft: M.J.K., K.R., E.D.N.-S., I.A.M.; Writing – review & editing: M.J.K., K.R., E.D.N.-S., I.A.M.
Funding
R34 NS127106 from National Institute of Neurological Disorders and Stroke to W.C.S.; DE-SC0021978 from Department of Energy Office of Science to W.C.S.; DIS-0000065 from the Natural Sciences and Engineering Council of Canada to I.A.M. Deposited in PMC for release after 12 months.
Data availability
All relevant data can be found within the article and its supplementary information.
The people behind the papers
This article has an associated ‘The people behind the papers’ interview with some of the authors.
