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

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 external, a middle fibrillar zone (superficial zona radiata interna), and an inner zone of 16 horizontal electron-dense 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 pm and the inner diameter about 2.3 pm. 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

Gamete interactions in teleost fish: the egg envelope. Basic studies and perspectives as environmental biomonitor

“…There are numerous channels cross the entire width of the chorion in a regular pattern, each occupied by oocyte and follicle cell microvilli in close apposition (Fig. 1D,E) (Dumont and Brummett, 1980;Hart and Donovan, 1983;Guraya, 1986;Cotelli et al, 1988;Arezo et al, 2007;Berois et al, 2007;Modig et al, 2008). In mature and ovulated pelagic oocytes (Fig.…”

“…As teleost sperm lacks acrosome, during fertilization there is no acrosome reaction (Guraya, 1986;Hart, 1990). The sperm fuses to the oocyte cell membrane underlying the micropyle and special structures there, such as microvilli or folds, have been reported in some fi sh (Brummett and Dumont, 1979;Dumont and Brummett, 1980;Hart and Donovan, 1983). In the surface of both gametes lies the key to species-specifi city.…”

Identification of recessive maternal‐effect mutations in the zebrafish using a gynogenesis‐based method

“…3d,e). The animal pole of the zebrafish egg is where the sperm enters the egg (Hart and Donovan, 1983;Hart et al, 1992) and is also the site where the female pronucleus is located (Selman et al, 1993;Dekens et al, 2003;our unpublished data). These observations are consistent Dekens et al (2003).…”

Structural analysis of fertilization in the fish Brycon orbignyanus

“…The first spermatozoon that reaches the micropyle and penetrates it will interact with the microvilli found on the oocyte plasmatic membrane (Hart & Donovan, 1983;Iwamatsu, 2000).…”