Seminars and Symposia
IDAC Seminar, 16 May 2011
|Secretariat, Alumni Association, IDAC|
|Date||Monday, 16 May 2011,16:00～|
|Room||Dai-kaigi-shitsu, IDAC Research Bldg.|
|Title||「Multipotent cell regulation in sea urchins」
「Science support in Brown University」
|Person-in-charge||Kouetsu Ogasawara Dept. Immunobiology (ex 8585)|
|Abstract||Cell plasticity is a key factor of a cell to be multipotent, and an essential and fundamental process for an organism to develop, regenerate and survive successfully. Echinoderms, a sister group to chordates, are known for having remarkable regenerative capabilities, the greatest among deuterostomes. Here we report our recent findings by using sea urchin multipotent cells.
Many indirect developing animals create specialized multipotent cells in early development to construct the adult body and perhaps to hold the fate of the primordial germ cells. In sea urchin embryos, small micromeres formed at the fifth division appear to be such multipotent cells: they are relatively quiescent in embryos, but contribute significantly to the coelomic sacs of the larvae, from which the major tissues of the adult rudiment are derived. These cells appear to be regulated by a conserved gene set that includes the classic germline lineage genes vasa, nanos and piwi. Although previous research has demonstrated that the germline is not specified at the fourth division, here we have deleted small micromeres at the fifth division and have raised the resultant larvae to maturity. These embryos developed normally and did not overexpress Vasa, as did embryos from a micromere deletion, implying the compensatory gene regulatory network was not activated in small micromere-deleted embryos. Adults from control and micromere-deleted embryos developed gonads and visible gametes, whereas animals derived from small micromere-deleted embryos formed small gonads that lacked gametes. These results suggest that germline specification depends on the small micromeres.
We also found a novel function of Vasa, a widely conserved ATP-dependent RNA helicase that functions in the germ line in all animals from cnidarians to mammals. In multipotent embryonic cells of sea urchins, it was found that Vasa is localized to the mitotic apparatus of every blastomere and inhibition of Vasa synthesis prevents cells from exiting mitosis. Unexpectedly, Vasa interacts with cyclinB mRNA and is required for its efficient translation. These results suggest that Vasa functions not only in the germline but also in multipotent stem cells as a mitotic cell-cycle regulator, and unique multipotency of sea urchin cells is a great advantage to study cell plasticity.