ABSTRACT
The development of the oocyte and of its associated follicle cells in the Nile tilapia, Oreochromis niloticus, has been examined by optical and transmission electron microscopy. During oocyte development the female gamete of Orochromis niloticus increases in size because of the accumulation of yolk in its cytoplasm. As the accumulation of yolk proceeds, the organization of cortex of the oocyte becomes very complex; all of the cytoplasmic organelles and several populations of vesicles can be found. On the other hand follicle cells also undergo a series of modifications: they first become cuboidal then cylindrical and their cytoplasm become densely populated with organelles. The mature egg of Oreochromis niloticus is surrounded by a thin acellular envelope (chorion) assembled during oocyte development. Biochemical analysis of isolated and purified chorions from mature females was also performed. SDS-PAGE under reducing conditions showed a reproducible pattern of three major polypeptides (121, 66 and 50 kD), most of which being glycosylated. The pattern of synthesis and assembly of the egg envelope in Oreochromis niloticus, a mouth-brooding cichlid fish, is also discussed.
Subject(s)
Cichlids/physiology , Oocytes/growth & development , Oogenesis/physiology , Animals , Chorion/chemistry , Electrophoresis, Polyacrylamide Gel , Female , Glycoproteins/analysis , Microscopy, Electron , Oocytes/ultrastructure , Peptides/analysis , Zona Pellucida/chemistry , Zona Pellucida/physiologyABSTRACT
A cDNA encoding the precursor of one of the major components of gilthead sea bream, Sparus aurata, egg envelope has been cloned by reverse transcriptase polymerase chain reaction (RT-PCR) techniques. The clone was isolated starting from total RNA extracted from the liver of spawning female fish and estradiol-17 beta-treated male fish. Sequence analysis revealed that the cDNA encoded a protein of 405 aa corresponding to 49-kDa component (termed gp49), a glycoprotein belonging to the N-linked type. The gp49 protein is homologous to the Zl-3 of medaka Oryzias latipes, the mammalian ZPC and ZPC homologues of Xenopus laevis (xlZPC) and carp Cyprinus carpio (ccZPC). In addition, the open reading frame also encodes an additional aa sequence, the signal peptide, located in the N-terminal region of the protein. RT-PCR and in situ expression analyses evidenced an organ-restricted pattern: the mRNA was detected only in liver of spawning female and estradiol-17 beta-treated male fish but not in other tissues.
Subject(s)
Egg Proteins/genetics , Membrane Glycoproteins/genetics , Ovum/metabolism , RNA, Messenger/metabolism , Receptors, Cell Surface , Amino Acid Sequence , Animals , Base Sequence , Cloning, Molecular , DNA, Complementary , Egg Proteins/biosynthesis , Electrophoresis, Polyacrylamide Gel , Female , Gene Expression , Humans , Membrane Glycoproteins/biosynthesis , Molecular Sequence Data , Ovum/ultrastructure , Perciformes , Polymerase Chain Reaction , Sequence Homology, Amino Acid , Sodium Dodecyl Sulfate , Transcription, Genetic , Zona Pellucida GlycoproteinsABSTRACT
The chorion is the acellular envelope surrounding mature eggs of teleostean fish. The macromolecular composition of the zebrafish (Danio rerio) egg chorion, organised as a three-layered structure, has been analysed. SDS-PAGE analysis, under reducing conditions, of isolated and purified chorions revealed a reproducible pattern of four major polypeptides (116, 97, 50 and 43 kDa) and several minor bands. Lectin binding assays showed that both the 116 kDa and 50 kDa proteins were recognised by concanavalin agglutinin (Con A), Galanthus nivalis agglutinin (GNA), Sambucus nigra bark agglutinin (SNA) and Ricinus communis agglutinin (RCA 120), suggesting that these polypeptides are N-linked glycoproteins. By contrast, neither the 97 kDa nor the 43 kDa polypeptides were stained by these lectins, indicating that these polypeptides are not glycosylated. Amino acid analysis also showed significant differences in the average content of some amino acids, for example serine and proline, when compared with previous reports.
