2005/09/01(木)

JT生命誌研究館

柊　卓志　博士（マックスプランク研究所、フライブルグ、ドイツ）

2005年9月1日（木）午後16時00分～17時00分

場所

JT生命誌研究館

講演者

柊　卓志　博士（マックスプランク研究所、フライブルグ、ドイツ）

内容

Polarity formation in mammalian preimplantation embryos has long been a subject of controversy. Mammalian embryos are highly regulative, which has led to the conclusion that polarity specification does not exist until the blastocyst stage; however some recent reports have suggested polarity predetermination in the egg. Our recent time-lapse recordings have demonstrated that the first cleavage plane is not predetermined in the mouse egg. Morphologically, the mouse blastocyst possesses an obvious asymmetry, with the inner cell mass (ICM) at one end of the long axis of the ellipsoidal embryo and the blastocoel surrounded by the trophectoderm (TE) at the other. Thus, the intriguing question remains as to whether this asymmetry in the embryonic axis, the embryonic-abembryonic (Em-Ab) axis, is anticipated at an earlier point in development, as previously suggested. Here we show that, in contrast to previous notions, 2-cell blastomeres do not differ and that their precise future contribution to the ICM and/or the TE cannot be anticipated. Thus, all evidence so far strongly suggests the absence of predetermined axes in the mouse egg. We observe that the ellipsoidal zona pellucida exerts mechanical pressure and space constraints as the coalescing multiple blastocoel cavities are restricted to one end of the long axis of the blastocyst. We propose a novel model wherein these mechanical cues, in conjunction with the epithelial seal in the outer cell layer, lead to specification of the Em-Ab axis, thus establishing polarity for the first time in mouse embryonic development.

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