Official Seminar
How to make tadpole larvae during ascidian embryogenesis: germ layer separation, germ cells, and left-right asymmetry
海鞘胚胎形成過程中蝌蚪幼蟲的形成：胚層的分離，生殖細胞，和左右不對稱
Hiroki Nishida 西田宏記
Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
It is of interest to know how embryonic axes are established and how embryos are regionalized along the axes. Pattern formation involves determination of orientation and polarity of the axis as the first step, then regionalization along the axial polarity takes place. Ascidian embryos provide nice system to analyze these processes.There are three perpendicular axes, animal-vegetal axis, anterior-posterior axis, and left-right axis. In this seminar, I am going talk about three topics. First, Endoderm and mesoderm segregation along the animal-vegetal axis will be discussed. The process involves mRNA localization mediated by nuclear migration. Second topic is germ cell formation. The primordial germ cells locate at the posterior pole. Maternally localized mRNA, Pem, mediates transcription quiescence to keep totipotency of the germ cell lineage. Last one concerns left-right asymmetry. Rotation of neurula embryo driven by monocilia is crucial for left-sided gene expression and eventual morphological L-R asymmetry. These topics are also discussed along evolutionary points of view.
Another seminar
A new chordate model animal with short life cycle of five days: The Appendicularian, Oikopleura dioica.
新的只有五天生活週期的脊索模式動物：尾海鞘綱動物，異體住囊蟲
Hiroki Nishida 西田宏記
Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
Appendicularians are planktonic tunicates (urochordates), and retain a swimming tadpole shape throughout their life. Together with ascidians, they are the closest relatives of the vertebrates. Oikopleura dioica is characterized by its simplified life habit and anatomical organization. It has a tiny genome, the smallest ever found in a chordate. The genome sequence is now available. Its life cycle is extremely short – about 5 days – and it can be maintained in the laboratory over generations. Embryos and adults are transparent and consist of a small number of cells. The anatomy of adults has been described in detail. Cleavage pattern, cell lineages, and morphogenetic movements during embryogenesis have also been comprehensively documented. These features make this organism a suitable experimental model animal in which genetic manipulations would be feasible, as in Drosophila and Caenorhabditis elegans. Oikopleura is an attractive organism for developmental and evolutionary studies of chordates. It offers considerable promise for future genetic approaches.