A comparative analysis of the evolution of the egg envelopes and the origin of the yolk

Abstract

In this paper, the evolution of egg envelope is examined from a structural point of view. The structurally simplest eggs are found in Sponges and Cnidarians where reproduction is ensured by external fertilization. In these instances, the oocyte plasma membrane is protected by only a thin glycocalyx. A more structurally complex envelope is present in triblastic hletazoa where the vitelline membrane makes its first appearance. With the emergence of internal fertilization, the egg envelope is modified as to face the constraints imposed by the terrestrial environment. However the pursuit of such defensive strategy would have made eggs practically impermeable to spermatozoa. Eggs with a thick chorion are thus endowed with a proper micropyle to allow fertilization. With the acquisition of viviparity egg envelopes have undergone marked reduction. In this paper particular attention has also been paid to the relationship of the oocyte with accessory cells and to the nature and function of the reserve material stored in the oocyte. The role of cortical granules and of gamete interaction during fertilization is also discussed.

A Monoclonal Antibody against Chorion Proteins of the Sea Bass Dicentrarchus labrax (Linnaeus, 1758): Studies of Chorion Precursors and Applicability in Immunoassays

“…The vitelline envelope of the teleost egg, called the chorion, consists of an acellular multilayered structure that surrounds the mature egg and has specific features ranging from protection of the developing embryo to prevention of polyspermy (for a review see [1]). A distinctive feature of the teleost egg is a micropylar opening; the only other animals with this feature are insects and cephalopods [2]. The morphological structure and macromolecular composition of the chorion have been studied in various freshwater and marine fish [3][4][5][6][7][8].…”

Characterization of the main egg envelope proteins of the sea bass Dicentrarchus labrax L. (teleostea, serranidae)

“…Mature eggs of most teleost fishes are enclosed in a complex acellular envelope characterized by a micropyle that permits the entry of the sperm. Interestingly, apart from teleost fishes, the presence of a micropyle is restricted to insects and cephalopods (Mazzini et al, 1984). Egg envelope products released in the water after egg deposition have been shown to interact with homologous spermatozoa and trigger certain cell activities.…”

Reproductive biology and growth of two Vallonia species in laboratory conditions (Gastropoda: Eupulmonata: Valloniidae)

“…Some of the smallest eggs are calcified and others are not, while it appears that the larger ones are all heavily calcified which may have to do with providing the half-liquid egg contents with mechanical support once a certain size is exceeded (toMPa 1976). Various theories also suggest prevention of desiccation, protection from predators and physiological buffering (Mazzini et al 1984). In land snails the smallest hard-shelled eggs known so far belong to Truncatellina cylindrica (Vertiginidae) (0.52-0.58 mm, MyzyK 2005) and to Vallonia (Vallonidae) (not exceeding 0.9 mm, Table 2).…”