The constituent oocytal layers of the avian germ and the origin of the primordial germ cell yolk

By radioactive or trypan blue induced fluorescence yolk labelling (used at certain developmental stages as intravital cytoplasmic markers), it can be demonstrated that the constituent yolk layers of quail blastoderms are formed when the precursor oocyte is growing from 3 to approximately 18 mm (rapid growth period). A previous study ( Callebaut , 1974) and the present study demonstrate that 2 cytoplasmic regions, each with a different constitution and behaviour, can be discerned in the avian germinal disc: 1) a deep and paraxial region, containing yolk that has been in contact with the t.i.c.o.s. (3H-thymidine incorporating cytoplasmic organelles) during oogenesis; 2) a superficial and peripheral region, which has not been in contact with the t.i.c.o. material and which penetrates into the first region along with the cleavage furrows. In the large blastomeres, the originally superficial ooplasm surrounds the deep ooplasm. The area centralis of the unincubated blastoderm must be considered as a heterogeneous cell population, containing both deep and superficial material in variable amounts. After laying and incubation, extra-embryonic tissues such as yolk endoderm and margin of overgrowth develop in the superficial and peripheral region. The embryonic mesoderm also develops from the latter. The yolk, which will be incorporated in the primordial germ cells (germinal yolk), derives only from the original deep and paraxial region of the oocytal germinal disc, i.e. from the region which has been in contact with the t.i.c.o.s. The germinal yolk plasm can be traced in the deep paraxial region of the oocytal germinal disc, in the central region of the unincubated blastoderm, in the endophyll (early primitive streak stage) and finally in the primordial germ cells (P.G.C.s.) at the moment of their separation from the endophyll wall (early somite stage). Thus our results provide evidence for the existence of a germ cell plasm in the avian postlampbrush oocyte.     

Insulin-like growth factor I activity is stored in the yolk of the avian egg

Growth factors of maternal origin may be incorporated into the vertebrate egg and play a role in early phases of embryo growth and differentiation. An avian insulin-like growth factor I (IGF-I) activity from unfertilized chicken egg-yolk has been partially purified by HPLC. The material is slightly more hydrophobic than recombinant human IGF-I. It reacts in a human IGF-I radioimmunoassay and is specifically depleted by anti-human IGF-I antibodies. Like authentic IGF-I, the extracts enriched in IGF-I activity stimulated the accumulation of delta-crystallin mRNA in epithelial cells from chick embryo lens with a potency approximately equivalent to its IGF-I immunoactivity.     

Magnetic resonance imaging study of the structure of the yolk in the developing avian egg

Magnetic resonance imaging (MRI) techniques were used to study the morphology of the latebra and concentric rings seen in the yolk of White Leghorn eggs during development of the avian embryo. Previous studies of the macroscopic structure of avian yolk have revealed the latebra, a vase-shaped structure beneath the blastoderm composed of white yolk. The bulbous portion in the center of the yolk is termed the body of the latebra. The thinner portion extending toward the blastoderm is referred to as the neck of the latebra. As the neck of the latebra approaches the blastoderm, it flares out to become the nucleus of Pander. The remainder of the yolk often features alternating concentric layers of white and yellow yolk. These layers, which appear as rings in sections, are thought to represent the daily accumulation of yolk during oogenesis. In this study eggs were imaged with a single slice spin echo sequence using MRI parameters that maximized the visualization of the latebra and concentric rings in the egg yolk. Some experiments were conducted for 2 to 3 day periods with eggs kept in the bore of the magnet using a small incubator that was constructed using a temperature-controlled water pump. The concentric rings of the yolk and the body of the latebra flatten and become more elliptical during development. The neck of the latebra becomes shorter and disappears around the 7th day of incubation. The body of the latebra starts to become incorporated into the embryo at about the 7th day of incubation and usually disappears by the 13th day. The concentric rings are no longer visible as distinct entities at this time. Histochemical procedures carried out as a result of MRI findings indicate that the latebra is an iron-rich structure.     

Effect of egg yolk and seminal plasma heparin binding protein interaction on the freezability of buffalo cauda epididymal spermatozoa

Egg yolk is routinely used in most of the extenders for cryopreservation of semen, but mechanisms of protection of spermatozoa by egg yolk are not very clear. Investigations with buffalo cauda epididymal sperm have shown that seminal plasma heparin binding proteins have detrimental effects during semen cryopreservation. The present study was conducted to investigate the effect of egg yolk on the detrimental effects of heparin binding proteins during cryopreservation of buffalo cauda epididymal spermatozoa. The results indicated that egg yolk was able to reduce the heparin binding proteins mediated cryoinjury in spermatozoa. One of the mechanisms of protection of spermatozoa from cryoinjury by egg yolk may be due to the inhibition of deleterious actions of heparin binding proteins on the spermatozoa.     

Effect of egg yolk lipids on the freezing of goat semen

Jamunapari goat buck semen contained both phospholipase and lysophospholipase activities which remained active during dilution (Step I) with diluents containing egg yolk, cooling to 5 degrees C (Step II), glycerolization and equilibration (Step III) and freezing and thawing (Step IV). A quantitative estimate of the phosphatidyl choline and phosphatidyl ethanolamine before and after freezing revealed that the lipids in egg yolk added to dilute goat semen were not hydrolysed to lysophospholipids and free fatty acids. Seminal plasma was, therefore, not removed and goat semen was frozen in egg yolk citrate-glucose, egg yolk-tris and skim milk-egg yolk. Dilution of goat semen 20 times with the three extenders containing 7% glycerol and an equilibration time of 3 h yielded optimum results. A comparative evaluation of freezing in the three diluents based on the assessment of sperm motility, live sperm count and acrosomal damage showed egg yolk-tris to be best extender for the successful freezing of goat semen. Insemination trials conducted with frozen semen and the number of actual kiddings yielded a fertility rate of approximately 81% in our study.     

Vitamin D in the avian egg. Its molecular identity and mechanism of incorporation into yolk.

The chemical identity of vitamin D in the egg of the domestic fowl was studied by analysing radioactivity in eggs from hens injected with [3H]cholecalciferol. Labelled molecules were found throughout the egg, but the concentration of total radioactivity in albumin was only 5-7% of that in yolk. In lipid extracts of yolk, more than 90% of the radioactivity was as unchanged cholecalciferol and 5% as 25-hydroxycholecalciferol. Only about 3% of the radioactivity in albumin was chloroform-soluble, and of this 40% was 25-hydroxycholecalciferol and 15% was cholecalciferol. Evidence is presented to support the idea that the specific transport of cholecalciferol into yolk is mediated by a cholecalciferol-binding protein in blood. This protein forms a complex with yolk proteins in transit from liver to ovary via the blood. A cholecalciferol-binding protein, chromatographically similar to that from blood, was found in egg yolk. It is postulated that cholecalciferol forms part of a complex with its specific binding protein, Ca2+ and the yolk phosphoprotein, phosvitin. This complex is then incorporated into yolk by the thecal cells of the ovarian follicle.     

An evaluation of soybean lecithin as an alternative to avian egg yolk in the cryopreservation of fish sperm

Plant-derived lecithin has been used as a more sanitary alternative to avian egg yolk in livestock sperm cryopreservation protocols but its efficacy for cryopreserving fish sperm has not previously been tested comparatively. Here various concentrations of soybean lecithin were evaluated for the cryopreservation of carp (Cyprinus carpio) sperm. Sexually mature fish were induced to spermiation and ovulation with ovopel. The extenders were prepared by using 300 mM glucose, 10% DMSO, supplemented with different ratios of lecithin (5%, 10%, 15%, and 20%) and 10% egg yolk (control I). Negative control was made without egg yolk and soybean lecithin (control II). The pooled semen was diluted separately at ratio of 1:3 (v/v) by using egg yolk and soybean-based extenders. Diluted semen placed into 0.25 ml straws were equilibrated at 4 °C for 15 min and frozen in liquid nitrogen vapor. Fertilization was conducted using a ratio of 1 × 10⁵ spermatozoa/egg. Supplementation of 10% lecithin to extender showed the best cryoprotective effect for sperm motility and duration of motility against freezing damage compared to 15%, 20% and control II groups (p < 0.05). Cryopreserved sperm with extender containing 10% lecithin provided a greater result in terms of fertilization success when compared to extenders containing 20% lecithin or control II (p < 0.05).     

The interaction of egg yolk and ram spermatozoa studied with a fluorescent probe.

The flourescent membrane marker, 1-anilinoaphtalene-8-sulphonate (ANS) was used to investigate the attachment of egg-yolk to the plasma membranes of ram spermatozoa. The degree of fluorescence was assessed using a subjective scoring system. It was found that egg yolk competes with ANS for sites on the plasma membrane. When the diluent contained 10% egg yolk, no ANS could be detected on the membranes. Egg yolk attached to the plasma membrane could be removed by washing twice with a yolk-free diluent. Loss of sperm motility in the presence of ANS was observed but some spermotozoa remained motile after incubation at 37 degrees C for 15 min with 2mM-ANS. Egg yolk protected spermatozoa against this loss of motility. It is suggested that egg yolk protects spermatozoa during chilling and freezing by its attachment to the sperm plasma membrane.     

Cytochemistry of yolk elements in the Amphioxus egg

Summary The Amphioxus egg develops compound yolk and lipid yolk, besides the cortical vacuoles described previously. The compound yolk elements consisting of carbohydrates, proteins, lipoproteins, and triglycerides originate within the ooplasmic masses that are constituted by the yolk nucleus substance and mitochondria. The lipid yolk elements, which are poorly developed, stain for phospholipids; the exact mode of their formation could not be determined. The behaviour and cytochemistry of organelles (yolk nucleus and mitochondria) have also been described.     

Differences in the egg yolk reaction on Baird-Parker medium between bovine and human strains of coagulase-positive staphylococci

Strains of coagulase-positive staphylococci isolated from cases of bovine mastitis did not produce halos on Baird-Parker medium whereas strains from cases of human infections did.     

The protective effect of egg yolk from different avian species during the cryopreservation of Karayaka ram semen

Egg yolk is one of the most widely used cryoprotective components for sperm preservation and a wide range of factors affect its action on sperm motility, viability and fertilizing ability. The aim of this experiment was to determine the effect of different species egg yolk, namely the domestic chicken (Gallus gallus domesticus), the goose (Anatidae anser), turkey (Meleagris gallopavo), duck (Anatidae anas platyrhynchos), Japanase quail (Coturmix japonica) and chucker (Alectoris chukar) on sperm quality following cryopreservation of ram semen. Ejaculates were collected using the artificial vagina from three Karayaka rams and spermatological characteristics assessed for the pooled semen. Semen samples were evaluated as split ejaculates in the trial and samples extended with a Tris-citric acid-glucose extender containing the different avian egg yolk (15%) and glycerol (5%). The semen straws were equilibrated at 4 °C for 2 h, frozen in liquid nitrogen vapour (for 15 min at ?120 °C) and stored in liquid nitrogen (?196 °C). After thawing (37 °C for 30 s), sperm motility, viability, abnormal acrosome and membrane integrity (HOST) were evaluated. Results showed chucker egg yolk to have the best cryoprotective effect in terms of the highest sperm motility (54.0%), compared to the other five avian egg yolks (p < 0.05) evaluated. Sperm frozen in chucker egg yolk also showed a higher percentage viability (59%), than sperm stored in quail and turkey egg yolk (p < 0.05). The percentage of acrosomal abnormalities after thawing was lower in the chucker egg yolk, than the other species (p < 0.05). There was no significant difference in sperm membrane integrity between the egg yolks, except for the quail (p < 0.05). Results suggest that chucker egg yolk could be used as an alternative for chicken egg yolk, in a semen extender in cryopreservation, but it warrants further evaluation in fertility trials.     

Effect of hen's egg yolk on capacitation and acrosome reaction of diluted canine spermatozoa

The aim of this study was to investigate the influence of progesterone, cholesterol and calcium (Ca²⁺) in an egg-yolk-containing extender on capacitation and acrosome reactions (AR) of diluted canine spermatozoa during 4 days of cooled-storage. For this purpose, we first investigated the effect of supplementation of a Tris–citrate–fructose buffer (TCF) with progesterone in a final concentration of 0.1, 0.2 and 1.0 μg progesterone/ml TCF-diluted semen. We then compared the effects of TCF and the same buffer-containing 20% egg yolk (TCF–EY). In egg yolks and the TCF–EY, progesterone was measured by enzyme immunoassay, cholesterol by enzymatic colorimetry and Ca²⁺ by flame atomic absorption spectrophotometry. For both experiments, ejaculates from eight dogs were used. For the comparison of diluents, one ejaculate was divided and one half diluted with TCF, the other with TCF–EY. One half of each TCF- and TCF–EY-diluted sample was evaluated immediately (D1), the other after storage for 4 days at +4 °C (D4). In diluted semen, motility and viability were measured by a computer assisted sperm analyzer (CASA; Sperm Vision, Minitüb, Germany), capacitation and AR were evaluated with a modified chlortetracycline assay (CTC) and the AR additionally by flow cytometry. Results: Supplementation of progesterone revealed, that between D1 and D4, total and progressive motility decreased with all progesterone concentrations, while viability as well as percentage of capacitated and acrosome reacted spermatozoa stayed constant. Progesterone-, cholesterol- and Ca²⁺ concentrations in egg yolks were 524.8 ± 131.4 ng/g, 13.9 ± 2.03 mg/g and 1.27 ± 0.17 mg/g, respectively. In the TCF–EY-diluent, the respective values were 210.9 ng/g, 2.52 mg/g and 1.1 mg/g. In TCF–semen, at D1, motility and viability were significantly higher than in TCF–EY-samples (p < 0.05), however at D4, no significant differences were detectable. Further, in TCF–semen, percentages of spermatozoa with intact membranes decreased significantly (p < 0.05) and capacitated spermatozoa increased (p < 0.05), which was not seen in TCF–EY-samples. In all samples, low percentages of AR were detected and after 4 days, the highest value of AR in TCF–EY-samples was 5.3% on average, as detected by flow cytometry. We therefore conclude that progesterone from egg yolk in routine extenders does not substantially influence semen longevity or AR of canine semen during cold-storage for 4 days. In contrary, egg yolk seems to prevent a significant increase in capacitated spermatozoa.     

Antioxidants in the egg yolk of a wild passerine: differences between breeding seasons

Carotenoids and fat-soluble vitamins play crucial roles in several physiological processes. Yolk carotenoid composition may be influenced by the bird's dietary intake and by the possible discrimination during carotenoid metabolism. Information regarding the pigment composition of passerine eggs is very limited. In the present 2-year study, we determined the carotenoid and vitamin concentrations and the percentage profile of carotenoid components in collared flycatcher (Ficedula albicollis) eggs. The major carotenoid was lutein in both years, followed by cis-lutein, zeaxanthin and beta-carotene as other significant components. Carotenoid concentration was higher in 2000 than in 2001. As caterpillar abundance and ambient temperature was lower in 2001 than in 2000, we suggest that the decreased availability of carotenoid-rich resources and the elevated antioxidant demand of the female restricted the carotenoid allocation to the eggs. Our study is the first to indicate that the concentration and profile of yolk carotenoids may considerably vary in the same wild bird population between breeding seasons with different environmental conditions. Compared to other birds, the yolk of this species was relatively rich in vitamins A and E. Vitamin E concentration was positively correlated with total carotenoid concentration, which may be beneficial for the nestlings as these antioxidants synergistically provide better protection.     

Effect of egg yolk and other reagents upon the zinc of cold-shocked boar spermatozoa

A marked reduction (80.8%) in the zinc uptake by boar spermatozoa cooled to 4 degrees C occurs when the seminal plasma is pretreated with egg yolk-glucose at this temperature. Crude lecithin is less effective (59.8%). Similar pretreatment of the seminal plasma by the polycationic drug Antrypol, which totally removes the zinc-precipitable basic haemagglutinin, does not result in a significant reduction of the sperm zinc uptake at 4 degrees C.     

Lipid-protein globules of avian egg yolk. Isolation and properties of globules stable in concentrated sodium chloride solution.

A new type of globular particle, the 'insoluble yolk globule', was isolated from the egg yolk of three avian species (hen, duck, and emu) by centrifugation or gel-filtration chromatography. These globules are stable in NaCl and urea solutions at concentrations that dissolve or disrupt other constituents of yolk, The isolated globules are about 1% of the dry yolk of hen's and duck's eggs but about 8% emu's-egg yolk. Most of these globules are less than 2 micrometer in diameter. Electron micrographs of sections show a preponderance of globules in the range 0.125-0.25 micrometer, each with a thick shell surrounding a feature-less anterior. Globules with the same appearance were seen in sections of unfractionated yolk. Two kinds of larger particles were also observed: (i) particles with a distinct outer membrane and a vesiculated interior; (ii) featureless spheres, possibly of lipid. The insoluble yolk globules comprise protein (8-11% by dry wt.), phospholipid (31-35% total lipid), triacylglycerols (49-53%), cholesterol (8%) and cholesteryl esters (2-3%); the variations being among species. The phospholipid is accessible to phospholipase C. The isolated protein is heterogeneous and resembles the apoprotein from the yolk low-density lipoprotein.