Takeuchi Masaki    Department   Kawasaki University of Medical Welfare  ,    Position   Associate Professor
Language	English
Title	The Early Embryogenesis of Polypterus (bichir) ~Insights into the Origin and Evolution of Developmental Mechanisms in Vertebrates~
Conference	CDB Symposium
Conference Type	International society and overseas society
Presentation Type	Poster notice
Lecture Type	General
Publisher and common publisher	◎Takeuchi Masaki, Aizawa Shinichi
Date	2013/03/04
Venue (city and name of the country)	Kobe, Japan
Society abstract	CDB Symposium 2013. The Making of a Vertebrate 268-269
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. A major stream of vertebrates (Osteichthyes) evolved into two monophyletic lineages: Sarcopterygii, including amphibians and amniotes, and Actinopterygii (ray-finned fishes), including teleosts as the crown group. Bichir diverged from all other actinopterygians soon after this divarication. Therefore, bichir is uniquely well suited for studies assessing the ancestral state of Osteichthyes/Actinopterygii as well as understanding the divergence of embryogenesis in teleosts and amphibians. Importantly, bichir embryogenesis is quite similar to that of amphibian rather than teleost, not only in its holoblastic cleavage but also in many aspects. Amphibian holoblastic cleavage in which all blastomeres contribute to any one of the three primary germ layers has been widely thought to be a developmental pattern in the stem lineage of vertebrates. However, in holoblastic development of not only bichir but also agnathan lamprey, meso-endoderm develop in the marginal zone, and vegetal cell mass is extraembryonic yolk cells. In order to explain these results, we present the viewpoint that the lamprey/bichir holoblastic development would have been ancestral to extant vertebrates and retained in their stem lineage. Their pattern might have been responsible for the frequent transitions from holoblastic to meroblastic cleavage as a pre-pattern in the vertebrate lineage. Amphibian holoblastic development would have been acquired secondarily, accompanied by the exploitation of lineage-specific molecular machineries such as maternal VegT.