Nagai Seiichiro, Mabuchi Tadashi, Hirata Shuji, Shoda Tomoko, Kasai Tsuyoshi, Yokota Sadaki, Shitara Hiroshi, Yonekawa Hiromichi, Hoshi Kazuhiko
Department of Obstetrics and Gynecology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Japan.
Tohoku J Exp Med. 2006 Oct;210(2):137-44. doi: 10.1620/tjem.210.137.
Selection of good quality oocytes is important for improvement of assisted reproductive technology. Here, we studied the relationship of the mitochondrial distribution in metaphase II stage (MII) oocytes with fertility, since mitochondria in ooplasm are essential for energy production required for fertilization and embryo development. To observe mitochondria non-invasively, we used oocytes from a transgenic mouse, in which enhanced green fluorescent protein is targeted to the mitochondrial matrix and thus fluorescence is observed exclusively in the mitochondria. Control oocytes with mitochondria distributed around the nucleus showed normal embryo developmental competence, whereas oocytes with abnormal diffuse and fragmented mitochondria showed a significantly lower rate of embryo development after activation by intracytoplasmic sperm injection or strontium, which is a very effective agent for activation of mouse oocytes. Also, we showed that the reduced developmental competence of oocytes with diffuse and fragmented mitochondria caused by vitrification and thawing is similar to that of oocytes with abnormal mitochondrial foci obtained naturally. These findings suggest that abnormal mitochondrial distribution in oocytes at MII is a cause of developmental retardation and therefore normal mitochondrial distribution could be used as a criterion for selection of good oocytes.
选择优质卵母细胞对于辅助生殖技术的改进至关重要。在此，我们研究了中期II期（MII）卵母细胞中线粒体分布与生育力的关系，因为卵质中的线粒体对于受精和胚胎发育所需的能量产生至关重要。为了无创观察线粒体，我们使用了来自转基因小鼠的卵母细胞，其中增强型绿色荧光蛋白靶向线粒体基质，因此仅在线粒体中观察到荧光。线粒体分布在细胞核周围的对照卵母细胞显示出正常的胚胎发育能力，而线粒体呈异常弥散和碎片化的卵母细胞在通过胞浆内精子注射或锶激活后，胚胎发育率显著降低，锶是一种非常有效的小鼠卵母细胞激活剂。此外，我们表明，玻璃化冷冻和解冻导致的线粒体弥散和碎片化的卵母细胞发育能力降低与自然获得的线粒体病灶异常的卵母细胞相似。这些发现表明，MII期卵母细胞中线粒体分布异常是发育迟缓的一个原因，因此正常的线粒体分布可作为选择优质卵母细胞的标准。
