Studies On Polarity Of Early Embryo And Related Issues In Mouse

The mechanisms of early mammalian development remain controversial. Blastocyst morphogenesis of mammals is unique, the extraembryonic structures is involved in the blastocyst. Mammalian blastocyst displays an obvious asymmetry, with the inner cell mass (ICM) at one end and the blastocyst cavity surrounded by the trophectoderm (TE) at the other. The position of the ICM in the blastocyst, i.e. the embryonic pole provides a basis for further embryonic patterning in the embryonic-abembryonic (Em-Ab) axis. It decides the dorsoventral axis of the mammalian embryo. Recently central questions is how this apparently initial asymmetry is established in early embryo, and whether the underlying mechanisms in this process decisive, or if it is operating as non-mammalian'model'organisms, in which location information play an essential role. In the present research we use KM (Kunming strain) mouse as an animal model. Nontoxic dextran conjugated with TMR(tetramethylrhodamine)and FITC(fluorecein isothiocyante)is microinjected to two of the 2-cell blastomere as molecular probe to trace the development fate of the blastomere ,in order to figure out the mechanisms of the formation of Em-Ab axis. Incision of zona pellucida, embryo bisection, chimera making are on purpose to study the relation among the sperm entry position, the second cleavage order and the blastocyst polarization.The results are as follows:1. There was no certain regulation in the distributing of the progeny of 2-cell embryo blastomere in blastocyst. Cells random distributed in the embryonic and abembryonic parts of the blastocyst.2. Most of the first polar bodies on 1-cell embryos were closed to the fertilization cone 13 hours to 15 hours after hCG injection.3. There was no relationship between the cleavage order of the 2-cell embryos and the sperm entry position (SP). Blastomeres with sperm entry position have no advantage in cleavage first.4. In 2-cell embryo Blastomere with SP and the one without SP produced similar results in capability of cleavage and develop to blastocyst. The numbers of cells in the blastocyst were similar in the two groups too.Developmental capability of chimera embryo of two SP blastomeres had no significant difference with the chimera embryo composed of two NSP blastomeres.5. The big blastomere and the two small blatomeres in 3-cell embryo had no significant difference in cleavage rates, blastocyst rates, and the numbers of cells in the two groups were similar after in vitro culture. Chimera embryo made of two big blastomeres in 3-cell and that made of four small blastomeres had not significant difference in cleavage rates, blastocyst rates, and the numbers of cells in the two groups were similar after in vitro culture.6. Pression influenced the positon of blastocoel. However, the embryo without ZP formed Em-Ab axes normally too.These results indicate that embryo polarization did not establish before blastocyst formation. It had no relationship with sperm entry position, borderline of 2-cell embryo's blastomeres and cleavage order of 2-cell embryo. Pression from zona pellucida affected blastocyst polarization. But the ultimate reason of the blastocyst polarit wasn't compression.