Deuterostome Genomics: Lineage-Specific Protein Expansions That Enabled Chordate Muscle Evolution

Abstract

Fish-like larvae were foundational to the chordate body plan, given the basal placement of free-living lancelets. That body plan probably made it possible for chordate ancestors to swim by beating a tail formed of notochord and bilateral paraxial muscles. In order to investigate the molecular genetic basis of the origin and evolution of paraxial muscle, we deduced the evolutionary histories of 16 contractile protein genes from paraxial muscle, based on genomic data from all five deuterostome lineages, using a newly developed orthology identification pipeline and a species tree. As a result, we found that more than twice as many orthologs of paraxial muscle genes are present in chordates, as in nonchordate deuterostomes (ambulacrarians). Orthologs of paraxial-type actin and troponin C genes are absent in ambulacrarians and most paraxial muscle protein isoforms diversified via gene duplications that occurred in each chordate lineage. Analyses of genes with known expression sites indicated that some isoforms were reutilized in specific muscles of nonvertebrate chordates via gene duplications. As orthologs of most paraxial muscle genes were present in ambulacrarians, in addition to expression patterns of related genes and functions of the two protein isoforms, regulatory mechanisms of muscle genes should also be considered in future studies of the origin of paraxial muscle.

ORTHOSCOPE: An Automatic Web Tool for Phylogenetically Inferring Bilaterian Orthogroups with User-Selected Taxa

“…2015), but it also identified those that contributed to formation of chordate characteristics (Inoue et al. 2017; Inoue and Satoh 2018).…”

Expression of smooth muscle-like effectors and core cardiomyocyte regulators in the contractile papillae of Ciona

“…Third, smooth muscles are also thought to be absent from tunicates [ 14 , 97 ], the sister group to the vertebrates within the phylum Chordata [ 24 ]. Although tunicate adult body wall muscles are structurally non-striated, they use conventional striated muscle contractility effectors and are specified by MRF, suggesting they have secondarily lost their striations [ 51 , 80 ]. Recent studies have revealed that tunicates possess homologs of various structures, cell types, and tissues that were previously presented as vertebrate novelties [ 1 , 2 , 27 , 98 , 100 ].…”

Enhancer activities of amphioxus Brachyury genes in embryos of the ascidian, Ciona intestinalis

“…The mid‐dorsal fold gives rise to notochord, and the left and right folds form somites in neurulae. In addition, cephalochordate notochord is composed of myofibrils, like the somites on both sides (Inoue & Satoh, ; Ruppert, ; Suzuki & Satoh, ). On the other hand, urochordate and vertebrate embryos form the notochord by convergent extension of its presumptive cells, which occur on both sides of early‐stage embryos (Satoh, ).…”