Abstract
Ascidian embryonic development is known to be phylogenetic prototype of the vertebrate embryogenesis. The cleavage-arrested large embryonic cells derived from the early 2 to 8 cell ascidian embryos revealed the multi-directional differentiation under the condition of cell-cell interaction like vertebrate stem cells. This differentiation without cell-cleavage gives us a rare chance to examine the fate selection mechanism under the condition of mixed cell-fate determinants in single cells, which will not be possible in mammalian systems. Especially either cell in an ascidian 2-cell embryo (2C cell) has multiple fates and develops into any cell-types in a tadpole. To find the condition for controlled induction of a specific cell-type, cleavage-arrested cell-triplets were prepared in various combinations, in which a 2C cell was in contact with any one of four types of cell-pairs from 8-cell embryos. The differentiation resulted from the fate selected in the 2C cell was quantitatively identified in terms of cell-type specific ion channel expressions on the cell membrane. Differentiation of the 2C cell into major cell-types, such as neural, muscular and epidermal, was reproducibly induced by selecting the type of contacting cell-pair and the developmental time difference between the cell-pair and 2C cell. Similarities between cleavage-arrested 2C cells and vertebrate embryonic stem cells will be discussed and a proposal that the ascidian 2C cell is a simple model for toti-potent stem cells will be presented. [J Physiol Sci. 2008;58 Suppl:S3]
