Did the notochord evolve from an ancient axial muscle? The axochord hypothesis. (14th July 2015)

• Record Type: Journal Article
• Authors: Brunet, Thibaut; Lauri, Antonella; Arendt, Detlev
• Is Part Of: BioEssays. Volume 37:Number 8(2015:Aug.)
• Page Start: 836
• Page End: 850
• Publication Date: 2015-07-14
• Subjects: Molecular biology -- Periodicals; Cytology -- Periodicals; Developmental biology -- Periodicals; 572.8
• DOI: 10.1002/bies.201500027
• Languages: English
• ISSNs: 0265-9247

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="bies201500027-sec-0001" sec-type="section"> <p>The origin of the notochord is one of the key remaining mysteries of our evolutionary ancestry. Here, we present a multi‐level comparison of the chordate notochord to the axochord, a paired axial muscle spanning the ventral midline of annelid worms and other invertebrates. At the cellular level, comparative molecular profiling in the marine annelids <italic>P. dumerilii</italic> and <italic>C. teleta</italic> reveals expression of similar, specific gene sets in presumptive axochordal and notochordal cells. These cells also occupy corresponding positions in a conserved anatomical topology and undergo similar morphogenetic movements. At the organ level, a detailed comparison of bilaterian musculatures reveals that most phyla form axochord‐like muscles, suggesting that such a muscle was already present in urbilaterian ancestors. Integrating comparative evidence at the cell and organ level, we propose that the notochord evolved by modification of a ventromedian muscle followed by the assembly of an axial complex supporting swimming in vertebrate ancestors.</p> </sec> </abstract>