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In most mammals, there is a block stage when fertilized ova(zygotes) are cultured and these zygotes can not develop to the blastocyst in vitro system except when cultured in ampulla portion of the oviduct. In mouse, this block stage is in a early 2-cell embryo. Its reason is that in vitro culture system can not mimic the in vivo system and can not satisfy all the conditions of dynamic environment and all the physiological conditions of embryos development of the in vivo system. Most basic reason of this 2-cell block is the inactivation of cdc genes of the nuclei, which is caused by unknown factor(s) of the in vitro system. In the present study, it is aimed to investigate the causing factor of mouse 2-cell block by the addition or removal of the components of the culture medium. Female mice of ICR strain (4-6 weeks old) were used. Superovulation was induced with PMSG 51U and HCG 51U at 48-hour interval. Then, immediately the female mice were mated with fertile males. Zygotes or early 2-cell embryos were collected by flushing the oviducts 18-30 hours after HCG injection. M16 was the basic medium used in the present study from which phosphate or glucose was omitted and vitamins (inositol, panthotheic acid), Fe+++, insulin, amino acids(glutamine, methionine, phenylalanine and proline) and EDTA were added depending on the experimental groups. In these different medium components, zygotes or 2-cell embryos were cultured for 24, 72 and 96 hours. Results as followings were obtained from this study. 1. Phosphate of the medium was strongly ingibitory to 2-cell embryo development, and 33-38% of 2-cell block were overcome by emission of phosphate from the cultrue medium. 2. Glucose seems to have neutral effect differenty from those of hamster. It did not show any inhibition or stimulation of 2-cell embryo development. 3. Panthotheic acid and inositol show some stimulatory effect of development of the 2-cell embryos which were already overcome by the emission of phosphate from the culture medium. 4. Fe+++ seems to be inhibitory to the compaction of 8-cell embryos by replacing CA++ of the culture medium. In the presence of Fe+++, all the embryos could not develop to 8-cell stage. 5. Overcoming effect of EDTA of 2-cell block was 67%. This seems to be caused by regulation of Ca++ function which is the major divalent lon in the culture dedium. It is further needed for the study of Ca++ function in mouse 2-cell block.
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