Wolenski J S, Hart N H
Department of Biological Sciences, Rutgers University, New Brunswick, New Jersey 08903.
J Exp Zool. 1987 Aug;243(2):259-73. doi: 10.1002/jez.1402430211.
Morphological studies on the gametes and entry of the spermatozoan into the egg of the zebra danio, Brachydanio rerio, were conducted primarily with scanning electron microscopy. The spermatozoan showed a spherical head, which lacked an acrosome, a midpiece containing several mitochondria, and a flagellum. Observations of the unfertilized egg confirmed and extended prior studies showing a distinct cluster of microvilli on the plasma membrane, identified as the sperm entry site, beneath the inner micropylar aperture (Hart and Donovan, '83). The fertilizing spermatozoan attached to the sperm entry site within 5 seconds of the mixing of a gamete suspension. Binding to the egg microvilli appeared restricted to the equatorial surface of the spermatozoan. Fusion between the plasma membranes of the interacting gametes was followed by the formation of a distinct, nipple-shaped fertilization cone. The sperm head was partially incorporated into the fertilization cone cytoplasm by 60 seconds postinsemination. The incorporation of the entire sperm head, midpiece, and a portion of the flagellum occurred between 1 and 2 minutes. During this time, the fertilization cone shortened and was transformed into a massive, blister-like cytoplasmic swelling. Concurrently, upward movements of the ooplasm resulted in the gradual disappearance of the original depression in the egg surface containing the sperm entry site. The second polar body, fully developed by 10 minutes postinsemination, formed approximately 10-15 microns from the site of sperm penetration. Development of the fertilization cone, formation of the second polar body and exocytosis of cortical granules at the sperm entry site readily occurred in parthenogenetically activated eggs, indicating that these surface rearrangements do not require sperm binding and/or fusion.
主要利用扫描电子显微镜对斑马鱼（短担尼鱼）配子的形态以及精子进入卵子的过程进行了研究。精子呈球形头部，无顶体，中部含有多个线粒体，还有一条鞭毛。对未受精卵的观察证实并拓展了之前的研究，显示在卵膜孔内口下方的质膜上有一簇明显的微绒毛，被确定为精子进入位点（哈特和多诺万，1983年）。在配子悬液混合后的5秒内，受精精子附着于精子进入位点。精子与卵微绒毛的结合似乎仅限于精子的赤道面。相互作用的配子质膜融合后，形成了一个明显的乳头状受精锥。授精后60秒，精子头部部分融入受精锥细胞质。整个精子头部、中部和部分鞭毛在1至2分钟内融入。在此期间，受精锥缩短并转变为一个巨大的、水泡状的细胞质肿胀。同时，卵质的向上运动导致卵表面含有精子进入位点的原始凹陷逐渐消失。第二极体在授精后10分钟完全发育形成，位于距精子穿透位点约10 - 15微米处。在孤雌激活的卵子中，受精锥的发育、第二极体的形成以及精子进入位点处皮质颗粒的胞吐作用很容易发生，这表明这些表面重排不需要精子结合和/或融合。
