Takeuchi Masaki    Department   Kawasaki University of Medical Welfare  ,    Position   Associate Professor
Language	English
Title	The early embryogenesis of Polypterus (bichirs): Insights into the origin and evolution of vertebrate body plans
Conference	The 34th Annual Meeting of the Molecular Biology Society of Japan
Conference Type	Nationwide Conferences
Presentation Type	Poster notice
Lecture Type	General
Publisher and common publisher	◎Masaki Takeuchi, Maiko Takahashi, Shinichi Aizawa
Date	2011/12/14
Venue (city and name of the country)	Yokohama, Japan
Summary	Germ layer patterning and body axis formation are central issues in vertebra te embryology. Our intriguing question is how the mechanisms that existed in an ancestral vertebrate have been modified during vertebrate evolution. Polypterus (bichirs, a basalmost ray-finned fishes) is a suitable model representing the nonteleost ray-finned fishes because of its phylogenic posi tion and morphological features. Importantly, bichir embryogenesis is quite similar to that of amphibians rather than teleosts. However, the yolky veget al cell mass generated by the holoblastic cleavage in bichir and agnathan la mprey embryos, differently from Xenopus embryos, is not endodermal bu t extraembryonic. Therefore, we propose the idea that bichir/lamprey-type ho loblastic development is ancestral to that of the extant vertebrates and tha t their pattern has been responsible for the frequent transitions from holob lastic to meroblastic cleavage as a pre-pattern in the vertebrate lineage. M eanwhile, germ layer patterning in the extant amphibian lineage might have b een acquired secondarily by the exploitation of lineage-specific molecular m achinery, such as the maternal VegT.<BR>As an additional topic, we re port about the existence and significance of a siamois-related gene i n bichir. Xenopus siamois is a homeobox gene coding for a transcripti onal mediator of the dorsal Wnt signaling pathway and is necessary for forma tion of the Spemann's organizer. However, its homologous genes had been neve r found in other taxa. This bichir gene and Xenopus siamois have iden tical protein activity, but each gene plays different roles for bichir or <I Xenopus embryogenesis.