第1091回生物科学セミナー
Origin, Evolution and Development of the Chordates
Dr. Billie J. Swalla（University of Washington, Friday Harbor Laboratories）
2016年03月04日(金) 17:00-18:00 理学部2号館 201号室
Vertebrates share several distinct morphological characters with three
invertebrate groups, lancelets, tunicates and hemichordates.
Tunicates, lancelets and vertebrates are a monophyletic group, the
chordates, which share five morphological characters: a notochord, a
dorsal neural tube, an endostyle, a muscular, post-anal tail and
pharyngeal gill slits. Hemichordates share some of these chordate
features, the pharyngeal gill slits, an endostyle and a post-anal tail,
and were thought to contain a notochord homolog, the stomochord, and
a dorsal neural tube in the neck region. Developmental genetics and
genomics have allowed re-examination of the question of chordate
origins, comparing developmental gene expression in embryos of
different phyla has allowed insights into the molecular mechanisms
underlying morphological changes. Genomics has allowed insight
into the phylogenetic relationships of the chordates and their
invertebrate relatives, and comparison of the shared genetic pathways
in related embryos. Recent evidence from my lab and others has shown
that the chordate ancestor was likely a benthic worm, with a mouth
and pharyngeal gill slits, supported by cartilaginous gill bars. It is
possible that the deuterostome ancestor was actually a chordate and
that notochord was lost in the ambulacrarian ancestor, with
echinoderms losing all of the chordate features.
