Anuran and pig egg zona pellucida glycoproteins in fertilization and early development

The envelope surrounding the eggs of all animals has many biological functions in fertilization and development. This review focuses on the anuran egg envelope in terms of its biochemistry, biophysics, structural biology and function in sperm-egg interactions and early development (embryo hatching). Egg envelopes from Xenopus laevis are among the most studied of the anurans, and are the central theme of this review. Comparisons of Xenopus laevis envelopes with those of other anurans and with pig egg envelopes are also included. This article presents historical as well as contemporary comparative perspectives on molecular and cellular mechanisms of sperm-egg envelope binding, block to polyspermy, envelope hardening, and hatching.