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	International Workshop [Evolving shapes and development - viewed from changes in gene regulations]
Conference Type	Nationwide Conferences
Invitation	Invitation
Presentation Type	Speech
Lecture Type	Panelist at Symposium/Workshop (Other)
Publisher and common publisher	◎Masaki Takeuchi
Date	2010/08/04
Venue (city and name of the country)	Tokyo, Japan
Summary	Germ layer patterning and body axis formation are central issues in vertebrate embryology. Our intriguing question is how the mechanisms of embryogenesis that existed in ancestors have been modified during vertebrate evolution. Vertebrate ancestors would have increased their egg size to store yolk, and the increase is considered to account for change of cleavage pattern and germ layer formation. Because the holoblastic cleavage in which all blastomeres contribute to a part of the primary germ layers is conserved in amphibian and protochordates, it has been widely thought to be a developmental pattern in the stem lineage of vertebrates. Embryogenesis of bichir, the most basal ray-finned fish, is quite similar to that of amphibian rather than teleost, not only in its holoblastic cleavage but also in many aspects. However, in holoblastic development of not only bichir but also agnathan lamprey, meso-endoderm develop only in the equatorial marginal zone, and the vegetal cell mass consists of extraembryonic yolk cells. The study raises the viewpoint that the lamprey/bichir holoblastic development would have been ancestral to extant vertebrates and retained in their stem lineage; amphibian holoblastic development would have been acquired secondarily, accompanied by the exploitation of new molecular machinery such as maternal VegT.