Drobnis E Z, Andrew J B, Katz D F
Department of Obstetrics and Gynecology, School of Medicine, University of California, Davis 95616.
J Exp Zool. 1988 Feb;245(2):206-19. doi: 10.1002/jez.1402450210.
Following fertilization, the zona pellucida, a glycoprotein shell investing mammalian eggs, becomes more resistant to dissolution by various agents. This decreased solubility, termed zona hardening, does not occur in hamsters. Thus, universal roles of zona hardening in the block to polyspermy and in oviductal interaction with embryos have been discounted. Although these roles probably have mechanical components, zona hardening has been assessed only as decreased solubility. In our studies, mouse and hamster ovulated oocytes were compared with 2-cell embryos by capillary suction. Step changes in pipet pressure were measured manometrically while resulting zona deformations were determined videomicrographically. Both mouse and hamster zonae were more "deformable" in oocytes than embryos. These results suggest that mechanical zona hardening may be a universal phenomenon. In addition to zona hardening following fertilization, a "spontaneous" zona hardening phenomenon has been reported for mouse oocytes (not embryos) cultured in vitro. In our system, this spontaneous decrease in zona solubility by protease was not accompanied by a mechanical change. In contrast, hamster oocyte and embryo zonae became slightly more soluble, and considerably more deformable during 4-h culture. Thus, spontaneous zona hardening is not a universal phenomenon, and, while decreased solubility has been called "hardening", it is not always accompanied by a mechanical change.
受精后，透明带（一种包裹哺乳动物卵子的糖蛋白外壳）对各种试剂溶解的抵抗力增强。这种溶解度降低，即所谓的透明带硬化，在仓鼠中不会发生。因此，透明带硬化在阻止多精入卵以及输卵管与胚胎相互作用中的普遍作用已被否定。尽管这些作用可能有机械方面的因素，但透明带硬化仅被评估为溶解度降低。在我们的研究中，通过毛细管抽吸将小鼠和仓鼠排卵后的卵母细胞与2细胞胚胎进行比较。通过压力测量法测量移液管压力的阶跃变化，同时通过视频显微镜确定由此产生的透明带变形。小鼠和仓鼠的透明带在卵母细胞中比在胚胎中更“易变形”。这些结果表明，机械性透明带硬化可能是一种普遍现象。除了受精后的透明带硬化外，已有报道称体外培养的小鼠卵母细胞（而非胚胎）存在“自发”透明带硬化现象。在我们的系统中，蛋白酶导致的透明带溶解度的这种自发降低并未伴随机械变化。相比之下，仓鼠卵母细胞和胚胎的透明带在4小时培养期间溶解度略有增加，且变形性显著增加。因此，自发透明带硬化并非普遍现象，而且，虽然溶解度降低被称为“硬化”，但它并不总是伴随着机械变化。
