Taggart D A, O'Brien H P, Moore H D
Institute of Zoology, Zoological Society of London, United Kingdom.
Anat Rec. 1993 Sep;237(1):21-37. doi: 10.1002/ar.1092370104.
To establish the mode of fertilization in a marsupial, a morphological investigation was made of the gametes of the South American grey short-tailed opossum. Monodelphis domestica, at the time of fertilization in vivo and in vitro. Oestrus was induced in females by the introduction of an unfamiliar male. To obtain oocytes recently fertilized in vivo, females were killed 18-24 hours after the first mating and the region of the oviduct containing eggs excised and fixed. Unfertilized mature oocytes were recovered from ovarian follicles 15-18 hours after first mating and fertilized in vitro with cauda epididymal spermatozoa in a modified MEM medium supplemented with bovine serum albumin at 37 degrees C in 5% CO2 in air. Following sperm-egg binding and fertilization, oocytes were fixed and prepared for light and electron microscopy. Spermatozoa unpaired prior to fertilization in vivo and in vitro and single spermatozoa bound to the zona surface by their plasmalemma overlying the acrosome on the dorsal face of the sperm head. The acrosome reaction was only observed at the zona surface (suggesting that it may be induced by zona components) and involved a vesiculation of sperm plasma and acrosomal membranes over the main body of the acrosome but not over the narrow, marginal region which persisted after the acrosome reaction was complete. Sperm penetration of the zona pellucida caused a large breach in the zona and the dispersal of perivitelline material. The fusion of the spermatozoon with the oolemma occurred first over the marginal acrosomal region and was accompanied by a fertilization cone which protruded through the zona penetration hole. Activation of the egg was characterized by the release of material from vesicles in the peripheral cytoplasm and extrusion of the second polar body. The mode of fertilization in Monodelphis was compared with what is known in other marsupials (New World and Australian) and eutherian (placental) mammals. It was concluded that the general features of the acrosome reaction and sperm-egg fusion may be essentially similar in both groups and that an evolutionary schism did not occur following the development of the eutherian mode of fertilization.
为确定有袋类动物的受精模式，对南美灰短尾负鼠（Monodelphis domestica）在体内和体外受精时的配子进行了形态学研究。通过引入陌生雄性诱导雌性发情。为获取近期在体内受精的卵母细胞，在首次交配后18 - 24小时处死雌性，切除含有卵子的输卵管区域并固定。首次交配后15 - 18小时从卵巢卵泡中回收未受精的成熟卵母细胞，在添加牛血清白蛋白的改良MEM培养基中，于37℃、5%二氧化碳的空气中与附睾尾精子进行体外受精。精子与卵子结合并受精后，固定卵母细胞，制备用于光镜和电镜观察的样本。在体内和体外受精前精子都是单个的，单个精子通过其位于精子头部背面顶体上方的质膜与透明带表面结合。顶体反应仅在透明带表面观察到（表明它可能由透明带成分诱导），涉及顶体主体上方精子质膜和顶体膜的囊泡化，但在顶体反应完成后仍存在的狭窄边缘区域未发生囊泡化。精子穿透透明带导致透明带出现大的破裂和卵周物质的扩散。精子与卵膜的融合首先发生在顶体边缘区域，同时伴有一个受精锥穿过透明带穿透孔突出。卵子激活的特征是外周细胞质中的囊泡释放物质以及第二极体的排出。将Monodelphis的受精模式与其他有袋类动物（新大陆和澳大利亚的）以及真兽类（胎盘）哺乳动物的已知情况进行了比较。得出的结论是，两组动物顶体反应和精卵融合的一般特征可能基本相似，并且在真兽类受精模式发展后并未发生进化分裂。
