|Activities in Academic Societies||
Japanese Society of Developmental Biologists; International Society of Developmental Biologist; The Zoology Society of Japan.
Advanced Lecture on Marine Biology, Advanced Lecture on Developmental Biology
Cells in the germline are totipotent and immortal across generations, distinguishing their existence from other cell types such as somatic cells. Interestingly, germline cells are often segregated from somatic cells during early embryogenesis in many animals. We are investigating mechanisms by which germline cells are segregated from somatic cells and acquire their characteristic features during early embryogenesis using marine invertebrates such as ascidian and larvacean embryos. We are specifically focusing on localized maternal factors that are successively inherited by the germline cells in the cleaving embryo, and on their functions in germline development. We have found that one such maternal factor PEM, which is present only in the ascidian genome, represses germline gene expression. The germline silencing is observed in many animals and is generally thought to prevent germline development from getting compromised by somatic programs that are initiated by gene expression. We are currently investigating how it was possible that essential developmental events such as germline silencing are controlled by evolutionary new genes like PEM, and how other localized maternal factors in ascidian contribute to germline segregation.
In the ascidian neurula embryo, as the first morphological sign of the tail formation, the boundary between the trunk and tail regions can be recognized morphologically as a bending of the epithelial layer, which we call “KUBIRE” (a Japanese word for “small waist”). After “KUBIRE” formation, the posterior tail section elongates significantly and eventually reaches lengths four to five fold that of the trunk. Although ascidians belong to the phylum Chordata as we humans do, the methods of making the tail in ascidians is quite different from that occurring in other chordates such as vertebrates and amphioxus in that they produce cell populations called the tailbud at the tip of the neurula embryo and which grows posteriorly. Therefore, we reasoned that there might be new principles for tissue shaping involved in unusual ways of making a tail such as that observed in the ascidian embryo. We are currently investigating how and under what molecular basis individual cells behave, how such cell behavior contributes to “KUBIRE” formation, and how the position of “KUBIRE” is determined along the anterior-posterior axis of the embryo.