Vitelline coat

No spermatozoa are seen on the egg surface or on the vitelline coat. After 5 h of treatment with 10 M TBTCl, a few spermatozoa, with very anomalous heads, have been detected. The absence of spermatozoa on the egg surface or on the vitelline coat could be explained by the absence of the follicle cells, which, in S. plicata, primarily play an attracting function. It was previously shown that TBTCl solution, either 10 or 10 M, induces anomalies in spermatozoa, unfertilized, and fertilized eggs of Ascidia malaca. In particular, the follicle cells detach from eggs and the test cells show anomalies in their nucleus and granules. Moreover, damaged spermatozoa are observed in the vitelline coat, but never in... 

Haino-Fukushima, K. and Usui, N. (1986). Purification and immunocytochemical localization of the vitelline coat lysin of abalone spermatozoa. Dev. Biol. 115 27-34. 

Usui, N. and Haino-Fukushima, K. (1991). Two major acrosomal proteins act on different parts of the oocyte vitelline coat in the abalone Haliolis discus. Mol. Reprod. and Dev. 28 189-198. 

Sperm penetrate the zona pellucida only after completion of the acrosome reaction. A similar process occurs in nonmammalian species, where sperm must penetrate the vitelline coat. In abalone this is accomplished by release of lysin, an acrosomal protein that disperses the vitelline coat by a noncatalytic mechanism (Lewis et al., 1982 Shaw et al., 1993). In contrast, the generally accepted model for mammalian sperm penetration of the zona pellucida is the acrosin hypothesis in which proteolysis of zona pellucida matrix glycoproteins by acrosin, the acrosomal serine esterase, plays a trailblazing role in the sperm penetration process (Yanag-... 

Capone A, Rosati F, Focarelli R (1999) A 140-kDa glycopeptide from the sperm ligand of the vitelline coat of the freshwater bivalve Unio elongatidus, only contains o-linked oligosaccharide chains and mediates sperm-egg interaction. Mol Reprod Dev 54 203-207... 

Focarelli R, Rosati F (1995) The 220-kDa vitelline coat glycoprotein mediates sperm binding in the polarized egg of Unio elongatulus through O-linked oligosaccharides. Dev Biol 171 606-614... 

Ascidian sperm glycosylphosphatidylinositol-anchored CRISP-like protein as a binding partner for an allorecognizable sperm receptor on the vitelline coat. J Biol Chem 283(31) 21725-21733. 

Figure 3. Sperm-vitelline coat (VC) binding in the ascidian. Binding of sperm was localized in the vicinity of hexagonal structures on the surface of the VC in the ascidian, Halocynthia roretzi. These structures stained with several lectins, suggesting that they consist of glycosylated proteins.

During fertilization, sperm must first bind in a species-specific manner to the eggs thick extracellular coat, the zona peUucida or vitelline envelope and then undergo a form of... 

The Xenopus egg is 1.2-1.4 mm in diameter, and consists of a darkly pigmented animal hemisphere and a lighter yolky vegetal hemisphere. When laid, the eggs are oriented randomly with respect to gravity, and held in position by a transparent vitelline membrane inside a jelly coat (Fig. 1), but after fertilization, granules located just below the surface of the egg fuse with the plasma membrane and release their contents into the space between the vitelline membrane and the egg. This material provides some lubrication, allowing the egg to rotate such that the less dense animal hemisphere is uppermost. This rotation usually occurs within 20 min of fertilization. 

Figure. 6.1 Disattisca cf. tenuis, early developmental stages. (A) Embryonic stage ca. 20 h postinsemination. The embryo is (still) completely enclosed by the vitelline membrane. Larval setae (Is) stick out of the egg-shell (B) lecithotrophic hatching stage ca. 27 h post-insemination. Larval morphology resembles that of late wedge-shaped stages of articulate brachiopods. Notice the ciliary coat and the larval setae (Is), three of which form a setal bundle on either side of the larva. Scale bars A, B=20 j,m.

Younger Embryos (<16 Hours AEL). As described in Protocol 15.2, embryos are removed from the vitelline membrane and transferred to poly-L-lysine-coated coverslips with the dorsal side up under saline. An incision is made along the dorsal midline with a glass electrode or sharpened tungsten needle. The embryo is blown flat to the coverslip surface with a gentle stream of saline from a glass pipette controlled by mouth (Bate 1990 Broadie and Bate 1993a). 

---