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 developmental mechanisms in vertebrate
Conference	44th Annual Meeting for the Japanese Society of Developmental Biologists (cosponsor: the Asia-Pacific Developmental Biology Network)
Conference Type	Nationwide Conferences
Invitation	Invitation
Presentation Type	Speech
Lecture Type	Panelist at Symposium/Workshop (Other)
Publisher and common publisher	◎Masaki Takeuchi
Date	2011/05/21
Venue (city and name of the country)	Okinawa Convention Center (Ginowan City, Okinawa, Japan)
Summary	Germ layer patterning and body axis formation are central issues in vertebrate embryology. An 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 position and morphological features. Importantly, bichir embryogenesis is quite similar to that of amphibians rather than teleosts. However, the yolky vegetal cell mass generated by holoblastic cleavage is not endodermal but extraembryonic in the bichirs and lampreys, differently from Xenopus. Therefore, we propose the idea that bichir-type holoblastic development is ancestral to that of the extant vertebrates and that their pattern has been responsible for the frequent transitions from holoblastic to meroblastic cleavage as a pre-pattern in the vertebrate lineage. Meanwhile, germ layer patterning in the extant amphibian lineage might have been acquired secondarily by the exploitation of lineage-specific molecular machinery, such as the maternal VegT. As an additional topic, we report about the existence and significance of a siamois-related gene in bichir. Xenopus siamois is a homeobox gene cording for a transcriptional mediator of the dorsal Wnt signaling pathway and is necessary for formation of the Spemann's organizer. However, its homologues had been never found in other taxa. We show that this bichir gene has the identical activity of Xsiamois and plays important but different roles for bichir embryogenesis.