牛受精卵

We have studied morphological features of fresh and frozen-thawed bovine embryos using light and electron microscopes, focusing on the effect of glycerol on the ultrastructures of the embryos. Special attention was paid to the effect on fine structures of glycerol removal from the embryos after freezing and thawing, comparing with the embryos from which the cryoprotectant was not removed. In the case of fresh blastocysts, many cytoplasmic projections were observed in the trophoblasts and inner cell masses, and the latter also contained lysosome-like complexes therein. Junctional complexes formed between the trophoblasts were seen. In the early blastocysts, numbers of cytoplasmic projections were also found in the blastomeres, and mitochondria concentrated near the nucleus were characteristic of the cells. Based on the electron microscopic observations, in the embryos from which the glycerol was not removed after thawing, the mitochondria were spherical in shape, with low electron density, and contained peripherally arranged cristae. On the contrary, the embryos with removed glycerol had spherical, oval-shaped or "hooded" mitochondria, with high electron density, being very similar in the ultrastructures to fresh embryos, and no arrangement of the mitochondrial cristae in peripheral was observed. Entire or partial damages to plasma membranes were observed in the blastomeres of some of the frozen-thawed and glycerol-removed embryos, resulting in the breakdown of the cell organelles through the damaged membranes. The results obtained from this experiment indicate that freeze-thaw of the bovine embryos may partly bring about the damage to plasma membranes of the blastomeres, following by the denaturation of the cell organelles.