[Amphibian jelly envelopes (proteins secreted by the oviduct) and their role in fertilization].

The jelly envelopes, surrounding amphibian eggs and playing a major part in the initial steps of fertilization, are deposited around the eggs as they traverse the different parts of the oviduct. These envelopes form 5 to 8 morphologically distinct layers according to the species, i.e. in Anura and Caudata they are organized differently, and are composed of about ten different macromolecular components (glycoproteins). The innermost layer is rich in sulfate and poor in fucose, a carbohydrate abundant in the other layers. This is due to a fucosyltransferase deficit in the cranial part of the oviduct secreting this layer. The cranial and the medial oviduct secretory products show a lectin carbohydrate-like reaction which is pH-dependent and can be inhibited by carbohydrates like glucuronolactone. This reaction has made it possible to isolate, by affinity chromatography, the main secretory component of the cranial oviduct (Spop). This paper discusses the main functions of the jelly layers of the egg, with particular reference to fertilization. The role of their macromolecular components in sperm capacitation is clear in Anura; experimental investigation in Urodeles is more difficult. We propose several hypotheses to explain the molecular interactions leading to capacitation. Block to polyspermy in amphibians is discussed.