[The behaviour of rabbit ICM in culture system in vitro]

The behaviour of ICMs isolated from early blastocysts of rabbit by microsurgery and incubated in cultural system in vitro, are varied according to the growing state of ICM. The band type growing extends from the proximal to the distal end, while the differentiation of cells in this kind initiates from the distal toward the proximal and gradually. The band type ICM possesses obvious polarity. The differentiation of different kind of cells appear one after another in order and the arrangement of differentiated germinal layer are clearcut. Therefore, the band type ICM is a good model for the investigation of differentiation cell and cell lineage. Whereas the ball type of growing ICM possesses no polarity. The cell in this type of ICM appears to differentiate from the outer surface of the ball toward the center gradually. The cellular differentiation starts later and the rate of proliferation of differentiated cells are lower than those of the band type ICM. After 7 days of incubation in vitro most of the ICM remain undifferentiation. The ball type ICM is a good model for the isolation of the embryonic stem cell line. There are two steps that the extraembryonic endoderm of rabbit are differentiated from ICM. The first kind of extraembryonic endoderm formed from ICM after 3 days of incubation in vitro. It is the parietal extraembryonic endoderm which migrate so far from the primitive ectoderm. The second kind of extraembryonic endoderm differentiates from ICM after 4 days of incubation in vitro. It is the visceral endoderm, most of which followed the migration of the first endoderm and the rest of them invade into the trophectoderm near the primitive ectoderm.