Amphibian eggs

Laposata, M.M. and W.A. Dunson. 1998. Effects of boron and nitrate on hatching success of amphibian eggs. Arch. Environ. Contam. Toxicol. 35 615-619. 

L6vtrup and Hansson Mild (1981) Sharp maximum in cortical tension of amphibian eggs 16... 

Pleurodeles waltl and Ambystoma mexicanum (axolotl), bred in many laboratories, were chosen because of the abundance of mucins which surround their eggs. The first analyses led to the isolation of Lewis and Lewis antigenic determinants, which are known to be related to human tumor-associated antigens. For these reasons, the jelly coats of amphibian eggs could represent a valuable model to examine 0-linked carbohydrate structures during evolution, associated with a possible function involving specific markers for the fertilization process. 

The requirement of oviducal secretion surrounding amphibian eggs for fertilization is known since the last century. Although amphibians have been often considered as models for studying the mechanism of gamete interaction, the molecular basis for the jelly requirement has been puzzling. The important literature devoted to this subject (for general reviews, see refs. [6-19]) can be summarized as follows. 

As shown in Figs. 1-8, a species-specific structural diversity has been observed in carbohydrate chains of amphibian egg jelly. 

The starting hypothesis that amphibian egg jellies could be a good source of carbohydrates has been shown to be correct. Moreover, the tissues of the animals and in particular the oviducts could also be the source of new and specific glycosyltransferases. The structures listed in Figs. 1-8 allow us to speculate about the activity levels and specificities of transferases in the glycosylation process of oviducal mucins. In fact, referring only to the fucosyltransferase activities, a minimum of six enzymes such as Kdn (al-4)FucT, Fuc(al-4)Kdn (al-2)FucT, Fuc(al-4)Kdn (al-3)FucT, Kdn (al-... 

The first biological observations were made on preparation of the yolks of amphibian eggs and of cephalopod spermatozoa by Schmidt (33) and of molluscan eggs by Pfeiffer (29) though almost a century before Virchow (42) had described polarization crosses in fresh and preserved specimens of myelin. Nageotte (26) studied these structures and myelinic figures in... 

In amphibian eggs (fig. 10.2), the cell cycle has a simple form as it consists in the periodic alternation of mitosis and interphase. Mitosis is associated with the activation of a factor known as maturation (or mitosis) promoting factor (MPF). Activation of MPF is triggered by the building up to a threshold of cyclin, a protein whose name reflects its... 

F61ix, M.A., J.C. Labbe, M. Doree,T. Hunt E. Karsenti. 1990. Triggering of cyclin degradation in interphase extracts of amphibian eggs by cdc2 kinase. Nature 346 379 82. 

Lorca, T., D. Fesquet, F. Zindy, F. Le Bouffant, M. Cerruti, C. Brechot, G. Devauchelle M. Doree. 1991a. An okadaic acid-sensitive phosphatase negatively controls the cyclin degradation pathway in amphibian eggs. Mol. Cell. Biol. 11 1171-5. 

AvkNn. Tetrameric glycoprotein (Mr 66000), occurring in the albumen of bird and amphibian eggs and in the genital tracts of all animals. Denaturization occurs on boiling and irradiation. 

Lohka. M. J., and Masui, Y. (1984). Roles of cytosol and cytoplasmic particles in nuclear envelope assembly and sperm pronuclear formation in cell free preparations from amphibian eggs. J. Cell Biol. 9si 1222-1230. 

Gurdon, J. B and Melton, D. A. (1981). Gene transfer in amphibian eggs and oocytes. Anna. Rev. 

Indeed, using extracts from amphibian eggs, it has been shown that the acidic protein nucleoplasmin, previously shown to function as a nucleosome assembly factor (for review, see Laskey and Leno, 1990), also plays a key role in the decondensation and remodeling of sperm chromatin at fertilization (Philpott et... 

In general, the remodeling of sperm chromatin that accompanies stage I decondensation involves the replacement of sperm-specific basic proteins with histones from the egg and results in the formation of nucleosomes. It now seems clear, at least in amphibian egg and Drosophila embryo extracts, that this remodeling is mediated by specific factors that participate in both assembly and disassembly processes. These changes in chromatin composition and structure can be analyzed by one- or two-dimensional polyacrylamide gel electrophoresis and micrococcal nuclease digestion. 

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