Vitelline cells

The shell precursors in the vitelline cells - proteins, phenols and phenol oxidase (EC 1.14.18.1, monophenol o-diphenol oxygen oxidoreductase) - can all be stained specifically with cytochemical reagents although the reactions are not as intense as in trematodes (810). The most useful of these reagents are probably (a) Fast Red Salt B, which stains phenolic materials orange/purple, and (b) catechol, which can be used for detecting the phenol oxidase. Details of these techniques are given by Smyth (789). 

In group II eggs, in contrast to those in group I, only a few vitelline cells (often one) interact with the oocyte (Fig. 7.4), with the result that, in some species, little true shell/capsule material is formed. In some species, e.g. Avitellina lahorea, the vitellaria are entirely lacking. This lack of protection by a shell is, however, compensated for in most cases by the presence of a... 

SUBGROUP II.ii FORMATION OF THE TAENIA-TYPE EGG This type of egg is formed essentially in the same way as that of the previous group, only one vitelline cell becoming associated with the fertilised ovum. The embryonic capsule is very thin and almost invisible when laid it is normally lost in faecal eggs. As pointed out earlier, lack of protection by an egg shell is compensated for by the development of a thick embryophore made up of keratin blocks (Fig. 7.1(c)) held together by a cementing substance (442). This gives the egg its characteristically radially striated appearance. 

Swiderski, Z., Eklu-Natey, R. D., Subilia, L. Huggel, H. (1978). Comparative fine structure of vitelline cells in the cestode Proteocephalus longicollis (Proteocephalidea). Proceedings of the 9th international congress of electron microscopy, Grenoble, pp. 669-70. 

Shaw, J. R., Marshall, I. and Erasmus, D. A. (1977) Schistosoma mansoni in vitro stimulation of vitelline cell development by extracts of male worms. Exp. ParasitoL 42 12-20. 

No spermatozoa are seen on the egg surface or on the vitelline coat. After 5 h of treatment with 10 M TBTCl, a few spermatozoa, with very anomalous heads, have been detected. The absence of spermatozoa on the egg surface or on the vitelline coat could be explained by the absence of the follicle cells, which, in S. plicata, primarily play an attracting function. It was previously shown that TBTCl solution, either 10 or 10 M, induces anomalies in spermatozoa, unfertilized, and fertilized eggs of Ascidia malaca. In particular, the follicle cells detach from eggs and the test cells show anomalies in their nucleus and granules. Moreover, damaged spermatozoa are observed in the vitelline coat, but never in... 

The isolated oocytes are still surrounded by the vitelline membrane, an inner glycoprotein matrix layer (Yao et al., 2000). This layer does not interfere with whole-cell recording experiments. It can be removed manually however, for patch-clamp experiments requiring the formation of high-resistance seals. 

All animal eggs are surrounded by egg envelopes which must be traversed by sperm on their journey to the egg surface. These egg envelopes are known by various terms in different organisms, being called the vitelline layer in sea urchins, the vitelline envelope in amphibians, and the zona pellucida in mammals. The fertilizing sperm must penetrate the egg envelope in order to fuse with the plasma membrane and transfer its haploid set of chromosomes into the cell cytoplasm. 

Phospholipids also form complexes with proteins (e.g., vitellin in egg yoUc, animal and plant tissues, lipoproteins in blood serum, and milk), carbohydrates, glycosides, alkaloids, minerals, enzymes, cholesterol, and other substances. Lysophospholipids represent a special class of compounds resulting from the chemical or enzymatic hydrolysis of phospholipids. The role of phospholipases in normal and pathological conditions as well as in cell metabolism is of great biological significance (4). 

Kdn-gp appeared to be synthesized during relatively later stages of oogenesis, since it was undetectable in the oocyte 3 months prior to ovulation. Although the cell types that synthesize Kdn-gp have not been identified, it is most likely synthesized under hormonal control in some extraoocj e cells (i.e. follicle cells), secreted and partly incorporated into the second outermost layer of the vitelline envelope just before ovulation. Kdn-gp may thus be a molecule homologous to the oviduct glycoproteins of mammals that are reported to be secreted and partly incorporated into the egg surface [58-60]. 

In the Oxyurida and the Ascaridida, in addition to the three layers of eggshell originating from the oocyte, additional layers are deposited by the uterine cells over the vitelline layer. Uterine cell contributions to the eggshell have not been studied in depth, although these deposits are thought to be lipoprotein in nature and have been shown to assume a complex architecture (16). 

Fig. 2.39 The schematic structure of an egg I eggshell, 2 outer membrane, 3 inner membrane, 4 Chalaza, 5 exterior albumen (outer thin albumen), 6 middle albumen (inner thick albumen), 7 vitelline membrane, 8 nucleus of pander, 9 germinal disk (blastoderm), 10 yellow yolk, 11 white yolk, 12 internal albumen, 13 chalaza, 14 air cell, 15 Cuticle. (Copyright-free Wikipedia picture)...

Lck, a 56-kDa protein, has originally been characterized as a Src-related tyrosine kinase that is specifically expressed in lymphocytes (Lck is named after lymphocyte kinase). In T-cells, Lck associates with CD4/CD8 cell surface receptor for major histocompatibility complex and, upon interaction with antigen-presenting cells, it will be activated by dephosphorylation in the carboxyl-terminal tyrosine residue, as catalyzed by CD45 phosphatase. In murine eggs, it has been reported that CD4-hke structures on the vitelline membranes are involved in gamete interaction, and that Lck-hke protein could have been detected in association with those CD4-like structures (Mori et al. 2000 Mori et al. 1991). While these studies have been done with the use of sjjedfic monoclonal antibodies (e.g. immunofluorescent and immunochemical approaches), biochemical and molecular biological identifications have not yet been demonstrated. 

Fig. 7. Fine structures in the egg and around the ovary revealed by transmission electron microscopy, (a) Adjacent pronuclei in an egg filled with yolk granules. Bar = 10 pm. (b) Adjacent part of the pronuclei in (a). Bar = 5 pm. (c) The viteUine membrane (indicated by seven arrows). The envelope is still not completed, but interrupted. The vitelline membrane separates the egg with yolk granules (below) from the lyrate organ (above). Bar = 5 pm. (d) Ovary with several oocytes. Presumed sperms are visible around the ovary. Bar = 5 pm. (e) Presumed sperms between an oocyte and lyrate organ. Bar = 5 pm. (Q Detailed structure of a presumed sperm of (e). The detailed structure in the sperm cell is different from that shown in Di Palma Alberti (2001). Black bars are not a staining artifact but an unknown structure. Bar = 1 pm. Abbreviations Nl, N2, nuclei O, oocyte S, presmned sperm Yl, tipid-yolk granule Yp, protein-yolk granule (unpubHshed micrographs by Toyoshima Alberti).

Fig. 1. Full-grown oocyte within its ovarian follicle. The follicle consists of the outer surface epithelium (SE), the middle theca (T), and the inner follicular epithelium, which, in this particular case, is represented almost entirely by the follicle cell nucleus (FCN). Macrovilli (MAV) from the follicle cell and microvilli (MIV) from the oocyte extend into the substance of the vitelline membrane (VM). Also shown are cortical granules (CG), yolk platelets (YP), pigment granules (PG), and lipid droplets (L). See Smith et al. (1968) for additional information.

Fertilization occurs during the time between release of the oocyte and its entry into the end of the oviduct. Sperm penetrate the follicle-derived vitelline membrane to fertilize the oocyte and the second reduction division occurs. The resultant one-cell stage embryo is called a blastodisc. The requirement for rapid fertiUzation following follicle rupture is met hy the female chicken s ability to store sperm in viable form for a number of weeks. 

At the time of laying, the chick embryo is a flat disk consisting of about 60,000 cells. It is made up of two layers, the hypoblast ventrally, lying in close association with the yolk, and the epiblast dorsally, facing the vitelline membrane, the membrane which surrounds the yolk. The disk has a translucent iimer core, the area pellucida, from which the embryo will form, and a denser outer ring of mainly yolk-containing cells, the area opaca. Only the cells at the periphery of the blastoderm are attached to the vitelline membrane, and as they migrate radially, the blastoderm expands. 

As mentioned before, just the cells on the periphery of the blastoderm adhere to the vitelline membrane. It is important not to destroy these delicate contacts. 

Fig. 2. In-ovo electroporation. A pair of electrodes held by a manipulator (A) is inserted intom a window opened on the shell (B). The electrode is placed on the vitelline membrane overlying the embryo (C), and a 25-V 50-ms pulse is charged five times. The entire procedure is monitored under a dissection microscope. Plasmid solution is injected to the E2 (HH stage 10) chick neural tube (D) prior to the pulse charge.The dimensions of the electrode are shown in E. Most of the electrode is insulated (black in the figure) so that only the tip is exposed (white area). One hour after electroporation, some embryos were fixed, processed for paraffin sectioning, and observed with a Nomarski interference microscope (F). The right-hand side of the figure corresponds to the right of the embryo, where injected plasmid was transfected. The morphology of the cells and the structure of neural tube were almost normal. The blue deposit inside the neural tube is a complex of plasmid and the color substrates not removed by washing in dimethylformamide after whole-mount in-situ hybridization. Twenty-four hours after electroporation, the development of yolk sac plexus, vitelline veins, and vitelline arteries are retarded in the area contacted on the electrodes (arrows in G). Bar is 2mm (C) 50 pm (F) 4mm (G). Source (3).

Before fusion of sea urchin eggs, the vitellin layer has to be destroyed enzymatically (pronase 1 mg/ml)[28]. Fused cells can be fertilized and will divide. Simultaneously the membrane becomes stabilized by addition of pronase for higher pulse energies[29]. 

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