Abstract
Ultrastructure of the fibrous strands and crystalloids in the mouse blastocysts developed from the 2-cell stage in vitro was observed in a medium containing bovine serum albumin (BSA) and in a medium containing polyvinylpyrrolidone (PVP).
Many fibrous strands composed of a bundle of fibrils, 150 Å in diameter, were distributed evenly in the cytoplasm of the 2-cell embryos. A few crystalloids composed of densely packed fibrous strands, in a loosely shaped lattice structure, were also observed in the cytoplasm of the 2-cell embryos.
Similar number of fibrous strands was observed in the cytoplasm of trophoblast cells and inner-cell-mass cells of the blastocysts developed in either medium. However, the number of fibrous strands greatly decreased as compared with the 2-cell embryos. The crystalloids showing clear lattice structure were observed in the cytoplasm of tropho-blast cells and inner-cell-mass cells of blastocysts developed in either medium. The number of crystalloids greatly increased as compared with the 2-cell embryos. The in-creasing ratio in the number of crystalloids observed in the blastocysts developed in a medium containing BSA was greater than in the blastocysts developed in a medium containing PVP.
