Fine structure of the chorion and site of sperm entry in the egg of Brachydanio

作者：Nathan H. Hart, Michael Jared Donovan · 发表于：Journal of Experimental Zoology · 年份：1983 · DOI：10.1002/jez.1402270212 · 被引用次数：130 · 研究领域：Sperm and Testicular Function、Reproductive biology and impacts on aquatic species、Reproductive Biology and Fertility

Abstract The fine structure of the chorion and the region of the unfertilized egg immediately beneath the micropylar apparatus of the zebra danio, Brachydanio rerio , were studied using Nomarski differential interference optics, and scanning and transmission electron microscopy. The chorion consisted of three distinct zones: an outer, electron‐dense zone containing pore canal plugs (zona radiata externa), a middle fibrillar zone (superficial zona radiata interna), and an inner zone of 16 horizontal electrondense lamellae alternating with 15 interlamellae of lower electron density (deep zona radiata interna). The zona radiata interna was pierced by open pore canals. The single micropylar apparatus was regionalized into a cone‐shaped vestibule and a tapered micropylar canal traversing the entire chorion. The outer diameter of the micropylar canal was 7.5–8.5 μn and the inner diameter about 2.3 μn. Since the diameter of the inner micropylar aperture was slightly larger than the size of the sperm head, the block to polyspermy in eggs of the zebra danio appears to be mechanical and guaranteed by the morphological design of the micropyle. The egg plasmalemma beneath the inner micropylar aperture was differentiated as a circular cluster of 15–20 microvilli‐like projections. The cluster of surface projections, approximately 2.1–2.5 μn in diameter under scanning, electron microscopy, was distinguishable from the microplicae covering the rest of the egg surface and identified as the sp...