Effect of Brefeldin-A on Compaction of Preimplantation Mouse Embryos.

Abstract

Abstract. The effect of the protein transport inhibitor brefeldin A (BFA) on compaction of early mouse embryos was investigated morphologically and immunocytochemically. After placing 4-and 8-cell mouse embryos in a medium with BFA for 3 or 6 h, the features of compaction were investigated. It was found that the effects of BFA on compaction were dependent upon the cell stage when this drug was applied. Compaction was delayed when embryos were placed in BFA during the mid or late 8-cell stage (3-6 and 6-9 h post division to the 8-cell stage). In embryos treated with BFA, Roh-ConA binding was weakened and detected at the cell contact regions. The distribution of microvilli seemed to be altered. It was concluded that protein transport for compaction was initiated at the early 8-cell stage just before the development of the compacted state. Key words: Mouse embryo, Protein transport, Compaction, Cell polarity.(J. Reprod. Dev. 43: [303][304][305][306][307][308][309][310] 1997) ompaction of the 8-cell mouse embryo is an important process leading to blastocyst formaBrefeldin A (BFA) is an inhibitor of vesicular transport from the endoplasmic reticulum to the Golgi apparatus [25]. BFA inhibited compaction of mouse embryos [24]. In the present study, the effects of BFA treatment of 4-and 8-cell stage embryos on compaction were examined. The main objective of the present study is to determine the time when intracellular protein transport necessary for compaction is initiated in mouse embryos cultured in vitro. Materials and Methods Embryo collection and culture in vitroF1 (C57BL/6 × C3H/He) female mice (6-10 weeks old) were superovulated by intraperitoneal injection of 8 IU pregnant mare's serum gonadotrophin (PMSG, Sankyo, Japan) followed 48 h later by 8 IU human chorionic gonadotrophin (hCG, Teikoku Hormone Mfg., Japan). The female mice C tion. During this process, blastomeres flatten upon each other to maximize cell contact [1], and a rearrangement of many components of the cell surface [2][3][4][5][6][7], cytoplasm and cytoskeleton [8][9][10][11][12] occurs. In this stage, gap junctional communication is established between blastomeres [13][14][15][16][17].Transcription necessary for compaction is completed by the mid 4-cell stage [18][19][20]. Membrane proteins necessary for compaction, such as E-cadherin and connexin 43, are also synthesized from the late 4-cell stage onward [21][22][23][24] and are then transported to the plasma membrane. These proteins are phosphorylated and assembled into a restricted array. However, these temporally regulated steps of post-translational events are not well known.