Subcellular organization of the yolk syncytial-endoderm complex in the preimplantation yolk sac of the shark,Rhizoprionodon terraenovae

Summary The structure of the yolk syncytial-endoderm complex of the preimplantation yolk sac of the shark is examined by light- and transmission electron microscopy. The yolk syncytium is bounded by a membrane that is anchored to the plasmalemma of adjacent endoderm cells by desmosomes. Enlarged nuclei, rough endoplasmic reticulum, Golgi complexes, mitochondria, and other cellular organelles populate the syncytium. Microtubules and filamentous elements are also observed free in the syncytium. Yolk is present as pleomorphic droplets, the profiles of which are generally spherical but may be vesicular, especially at the periphery of large yolk droplets. Occasionally, large yolk droplets have a paracrystalline configuration. Small yolk droplets are modulated through the Golgi complex of the yolk syncytium, and it is suggested that acid hydrolases are added there. Small yolk droplets released from the maturing face of the Golgi complex are sequestered in membrane-limited packets. The membrane of the packets fuses with the membrane enveloping the yolk syncytium and the yolk droplets are released into the yolk syncytialendoderm interspace. Subsequently, the yolk droplets are endocytosed by the endoderm. Yolk droplets disperse and fuse to form the large irregular yolk inclusions of the endoderm. Yolk metabolites are transported out of the endoderm through the yolk sac endothelium. The yolk sac endoderm thus mediates the transfer of metabolites from the yolk mass to the extraembryonic circulation.     

Yolk vitronectin. Purification and differences from its blood homologue in molecular size, heparin binding, collagen binding, and bound carbohydrate.

This is the first report on a unique vitronectin molecule, yolk vitronectin, which is similar to its blood homologue in cell spreading activity but different in molecular size, bound carbohydrate, and heparin and collagen binding activity. Yolk vitronectin was purified 2,500-fold from chick egg yolk by a combination of hydroxylapatite, DEAE-cellulose, and anti-vitronectin-Sepharose column chromatographies. In SDS-polyacrylamide gel electrophoresis under reducing conditions, yolk vitronectin was separated into 54- and 45-kDa bands, which are 16 and 25 kDa smaller, respectively, than the 70-kDa major band of chick blood vitronectin. The 54-kDa band shares the same NH2-terminal sequence as chick blood vitronectin. In contrast, the NH2-terminal sequence of the 45-kDa band is somewhat homologous with the internal sequences of mammalian vitronectins beginning at the 50th amino acid from the NH2 terminus. The bound carbohydrate of the 54- and 45-kDa species of yolk vitronectin is similar to, but distinct from, that of blood vitronectin. Unlike blood vitronectin, yolk vitronectin cannot bind to either heparin or collagen.     

Non-analytical methods for the estimation of total yolk carotenoids in passerine eggs

Carotenoids are essential antioxidant micronutrients. Oviparous species acquire carotenoids from their food and deposit them in the egg yolk, where they support embryonic development. The total carotenoid concentration in the egg yolk is typically measured analytically, which requires time, equipment and expertise, and can limit the sample available for other measurements, at least in species laying small eggs. Here we evaluate whether yolk colour can be used as a reliable alternative measure for total yolk carotenoid concentration. We compare two non-analytical methods, digital photography and visual colour scoring, using eggs from a wild population of Blue Tits Cyanistes caeruleus. Yolk hue estimated from digital photographs correlated more strongly with total yolk carotenoid concentration measured by high-performance liquid chromatography (HPLC) than did the visually assessed colour score based on a Yolk Colour Fan. Previous results based on HPLC measurements of total carotenoid concentration could be reproduced using yolk hue measurements. The results suggest that measuring yolk hue is a suitable proxy for assessing natural variation in total yolk carotenoid concentration in eggs of free-living birds.     

Comparison of the nucleotide sequence of cloned DNA coding for an apolipoprotein (apoVLDL-II) from avian blood and the amino acid sequence of an egg-yolk protein (apovitellenin I): equivalence of the two sequences

We have compared the amino acid sequences of two low-molecular-weight avian apoproteins: apoVLDL-II from very low-density lipoproteins of hen plasma and apovitellenin I from hen egg yolk. The sequence of White Leghorn apoVLDL-II was derived from the nucleotide sequence of cloned apoVLDL-II DNA (Chan et al., 1980). The sequenator was used to determine the amino acid sequence of apovitellinin I from two breeds of hen (White Leghorn and Australorp). The sequences from the two breeds were not only identical, but they also completely matched the predicted sequence derived from the apoVLDL-II DNA sequence. The identity reported here establishes that this protein is transported intact from the blood to the egg yolk.     

Osmotic changes during the development of eggs and larvae of the lumpsucker, Cydopterus lumpus L.

The demersal eggs of Cyclopterus appear to osmoregulate like the pelagic eggs of cod and plaice. Unfertilized eggs in ovarian fluid exhibited ovoplasm osmolarities similar to those of adult blood and ovarian fluid (356–359 mosmol kg⁻¹). Yolk osmolarities remained virtually constant from fertilization and during development (356–366 mosmol), with a slight decrease near hatching (to 332 mosmol). Yolk and body fluids of larvae (338 mosmol) had osmoconcentrations similar to egg yolk values near hatching. Yolk osmoconcentration of unfertilized eggs remained unchanged during the first 12 h in sea water, with a slow increase thereafter. Fertilized eggs of bad quality cultures exhibited higher yolk osmoconcentrations than eggs of good quality. Cyclopterus eggs were found to develop normally and survive in 20–34%o salinity, larvae seemed to have the same salinity range.     

Mineral metabolism in the developing turkey embryo--II. The role of the yolk sac.

1. Turkey embryos were incubated in ovo or in long-term shell-less culture (ex ovo) for 14, 18, 22 or 26 days, at which time the concentrations of zinc, copper, iron, manganese and calcium in yolk and yolk sac membrane were determined. 2. Yolk manganese and calcium concentrations increased during incubation in ovo while the concentrations of zinc, copper and iron declined. The concentrations of zinc, copper and iron in yolk from ex ovo embryos did not decline. Yolk calcium concentration increased during incubation ex ovo, although to a much lesser extent than that observed in ovo. 3. The concentration of zinc, copper and iron declined in yolk sac tissue during incubation in ovo whereas no decline was observed for yolk sac tissue from ex ovo embryos. Yolk sac calcium and manganese concentrations increased during incubation in ovo and ex ovo, although the increase in calcium concentration for ex ovo yolk sac was much smaller than that observed in ovo. 4. A peak corresponding to metallothionein (MT) which bound both zinc and copper was isolated from yolk sac cytosol on day 14 of incubation in ovo using gel-permeation column chromatography. 5. Further fractionation of the MT peak by anion exchange chromatography revealed three metal-binding peaks designated MT-1, MT-2a and MT-2b. The majority of the zinc was bound to MT-2a and MT-2b whereas most of the copper was bound to a single peak (MT-2b). 6. The concentrations of zinc and copper in yolk sac cytosol reached a maximum on day 14 of incubation in ovo and declined through to day 28 (hatching).(ABSTRACT TRUNCATED AT 250 WORDS)     

Procathepsin and acid phosphatase are stored in Musca domestica yolk spheres

Yolk spheres present in mature invertebrate oocytes are composed of yolk proteins and proteolytic enzymes. In the fly Musca domestica, yolk proteins are degraded during embryogenesis by a cathepsin-like proteinase that is stored as a zymogen. An acid phosphatase is also active in the yolk spheres during Musca embryogenesis. In this paper we show that procathepsin and acid phosphatase are initially stored by a different pathway from the one followed by yolk protein precursors. Both enzymes are taken up by the oocytes and transitorily stored into small vesicles (lysosomes) surrounding the early yolk spheres. Fusion of both structures, the early yolk spheres and lysosomes, creates the mature yolk spheres.     

Experimental manipulation of the rodent visceral yolk sac

The visceral yolk sac (VYS) is an especially important placental organ in the rodent because it is the primary source of exchange between the embryo and mother during early organogenesis before the chorioallantoic placenta circulation is established. The VYS is involved with nutritional, endocrine, metabolic, immunologic, secretory, excretory, and hematopoietic functions. The VYS also plays a role in steroid metabolism and interacts with a variety of blood-borne factors: parathyroid hormone, glucocorticoids, insulin, and vitamin D metabolites. The importance of the VYS during development is emphasized by the embryotoxicity resulting from exposure to agents which cause VYS dysfunction when administered to the pregnant animal during organogenesis. Several experimental procedures have provided useful information concerning a variety of VYS functions from early organogenesis to term: Culture of the Embryo, Fetal Incubation, Culture of the Fetus, Giant Yolk Sac, Short- and Long-Term Culture of the Yolk Sac, Modified Ussing's Chamber, Single or Double Diffusion Chamber, and the use of Heterologous Rodent Visceral Yolk Sac Antibodies. Since human yolk sac pathology has been associated with developmental toxicity and spontaneous abortion, it is important to discover whether there are some common functional roles among different mammalian species and to determine if other experimental animal models can be used to study the possible contribution of human yolk sac dysfunction to some human reproductive problems.     

Detection of chromosome aberrations in paraffin sections of seven gonadal yolk sac tumors of childhood

Yolk sac tumors are the most frequent kind of malignant pediatric germ cell tumor and may have a fundamentally different pathogenesis than adult germ cell tumors. Since few cytogenetic studies have been performed so far, in situ hybridization was applied to interphase cell nuclei of seven gonadal yolk sac tumors of childhood in routine paraffin-embedded tissue sections. The panel of chromosome-specific DNA probes was selected on the basis of their relevance in adult germ cell tumors and consisted of five DNA probes specific for the (peri)centromeric regions of chromosomes 1, 8, 12, 17 and/or X and/ or one DNA probe specific for the subtelomeric region of chromosome 1 (p36.3). As in adult germ cell tumors, all pediatric gonadal yolk sac tumors had an increased incidence of numerical chromosome aberrations. All tumors showed an overrepresentation of at least three chromosomes. Gains of chromosome 12, which is highly specific in adult germ cell tumors, were diagnosed in six pediatric gonadal yolk sac tumors. The DNA indices determined in the paraffin-embedded tumor material correlated well with the in situ hybridization findings. A chromosome was either over- or underrepresented, compared with the corresponding DNA indices, in only a few cases. The short arm of chromosome 1 in adult germ cell tumors is often involved in structural aberrations. In pediatric germ cell tumors, the short arm of chromosome 1 is also a nonrandom site of structural aberrations. Moreover, the presence of a deletion at 1p36.3 in four out of five tumors suggests that the loss of gene(s) in this region is an important event in the pathogenesis of gonadal yolk sac tumors of childhood.     

Metabolism and distribution of yolk DNA in embryos ofOphryotrocha labronica La Greca and Bacci

Summary Exposure of the polychaeteOphryotrocha labronica to³H-thymidine during vitellogenesis leads to substantial incorporation of label in the ooplasm, especially in yolk granule DNA. In embryos from oocytes labelled in this way it was possible to follow the amount and localization of the labelled material (DNA) throughout early development by means of light microscopical and electron microscopical autoradiography; liquid scintillation measurements also were carried out.Within the embryonic cells the bulk of the labelled DNA was localized in the yolk granules and noticeable amounts were associated with minor structural elements, whereas mitochondria and lipid droplets were only slightly labelled. Nuclear labelling was weak. Early development was found to be characterized by rapid loss of labelled DNA, so that larvae, ready to leave the egg packs, retained only about 30% of the amount originally present.It was concluded that yolk granule DNA cannot be a store of precursor material for nuclear DNA synthesis, as has been suggested sometimes, but most likely represents an informative DNA which upon release from the yolk granules is rapidly metabolized. Possible roles for yolk granule DNA is discussed.The excellent technical assistance of Mrs. Siv Nilsson and Mrs. Annagreta Petersen is gratefully acknowledged. This work has been supported by the Swedish Natural Science Research Council and Kungliga Fysiografiska Sällskapet, Lund.     

Probable evolution of the coelacanth's reproductive style: lecithotrophy and orally feeding embryos in cichlid fishes and in Latimeria chalumnae

Synopsis The living coelacanth is a livebearer. Yolk seems to be the main source of nutrients and of oxygen to the embryo (fetus). Long before birth, young may also possibly feed orally on histotrophe secretion and egg debris. This type of reproduction evolved, as in most other fishes, from oviparity. The Carboniferous coelacanth Rhabdoderma exiguum had eggs of much lesser yolk volume and may represent an earlier form of oviparity with hiding, guarding or brooding type of parental care. The Jurassic coelacanth Holophagus (Undina) and the Cretaceous Axelrodichthys appear to have already evolved the internal-bearing style. Much of this evolutionary sequence is similar to that in cichlids. Ancestral cichlids are substrate tenders and nesters, with small eggs, little yolk and a feeding larva with indirect development. Mouthbrooding cichlids evolved a few, large eggs with denser yolk, direct development and, ultimately, orally feeding embryos while yolk is still in ample supply. Mixed feeding from yolk and orally ingested food in cichlids and in coelacanths is shown to be an enhanced mode of food delivery to the embryos over that from each source separately, in order to produce directly a better developed or larger young at the time of release, i.e. independence. Increase in egg size is regarded as an environmentally induced, altered pattern of yolk synthesis and an initial component of the epigenetic mechanism leading towards greater specialization. Carotenoids are incorporated within the yolk to assist the oxidative metabolism of the developing embryo.     

The origin of protein and fatty yolk in Rana pipiens. III. Intramitochondrial and primary vesicular yolk formation in frog oocytes.

The precise origin of the primary yolk precursor complex or primary vesicular yolk is obscure but in its earliest recognizable stage it is a typical multivesicular body which first acquires a moderately electron-dark matrix. Following this, an extremely electron-dark amorphous material, the yolk protein, appears within the precursor. This yolk protein increases in amount as the yolk vesicle grows and by the time the precursors are about 1 micrometer in diameter this protein is partly to almost completely crystalline. Yolk originating within mitochondrial cristae unlike that in the yolk precursor complexes is crystalline from its earliest appearance. Intracristae mitochondrial yolk crystals have a spacing of 70--85 A. Their molecular organization appears in some sections as electron-dark lamellae and in others as light cylinders surrounded by an electron-dark matrix.     

Yolk androgens reduce offspring survival

Females may favour some offspring over others by differential deposition of yolk hormones. In American kestrels (Falco sparverius), we found that yolks of eggs laid late in the sequence of a clutch had more testosterone (T) and androstenedione (A4) than yolks of first-laid eggs. To investigate the effects of these yolk androgens on nestling 'fitness', we injected both T and A4 into the yolks of first-laid eggs and compared their hatching time, nestling growth and nestling survival with those of first-laid eggs in which we injected vehicle as a control. Compared to controls, injection of T and A4 at a dose intended to increase their levels to those of later-laid eggs delayed hatching and reduced nestling growth and survival rates. Yolk androgen treatment of egg 1 had no effect on survival of siblings hatching from subsequently laid eggs. The adverse actions of yolk androgen treatment in the kestrel are in contrast to the favourable actions of yolk T treatment found previously in canaries (Serinus canaria). Additional studies are necessary in order to determine whether the deposition of yolk androgens is an adaptive form of parental favouritism or an adverse by-product of endocrine processes during egg formation. Despite its adaptive significance, such 'transgenerational' effects of steroid hormones may have helped to evolutionarily shape the hormonal mechanisms regulating reproduction.     

Do group size and laying order influence maternal deposition of testosterone in smooth-billed ani eggs?

The avian egg contains maternal hormones that affect behavior, growth, morphology, and offspring survival. Evidence to date suggests that patterns of yolk androgen deposition could provide females with a means to manipulate sibling competition and, thereby, increase their fitness. We examined yolk testosterone (T) concentrations in eggs of the smooth-billed ani (Crotophaga ani) to understand patterns of androgen deposition in eggs of this plural-breeding joint-nesting cooperatively breeding species. We tested the hatching asynchrony adjustment hypothesis, which states that increases in yolk androgen levels over the laying sequence function to mitigate the disadvantage of being a later-hatched chick in species without adaptive brood reduction. We also investigated the effect of group size on yolk T deposition to test the hypothesis that females in multi-female groups could give a competitive edge to their own chicks by depositing higher T levels in their eggs. Predictions of the hatching asynchrony adjustment hypothesis were supported in both single- and multi-female groups as yolk testosterone levels increased from early- to late-laid eggs. This suggests that ani females can influence nestling competition and chick survival by within-clutch differential T allocation. Unexpectedly, we did not observe an effect of group size on yolk T deposition. Yolk testosterone concentrations may not be a mere reflection of a female's hormonal status as female plasma circulating levels of T did not vary in the same direction as yolk T levels. Results of this study therefore support the idea that females may adaptively manipulate chick behavior through hormonal deposition in eggs.     

Ontogeny of the umbilical cord and placenta in the Atlantic sharpnose shark,Rhizoprionodon terraenovae

Synopsis The Atlantic sharpnose shark is a viviparous anamniote that develops an epitheliochorial yolksac placenta. Initially, contents of the yolksac nourish the embryos. Yolk is partially digested in the yolk syncytial-endoderm complex and subsequently transferred to the vitelline circulation. Yolk is also transported by ciliary activity of the yolk stalk ductus to the fetal gut for digestion. When embryos are 4.0cm in length, vascular ridges, termed appendiculae, develop on the yolk stalk. As yolk stores are depleted, the yolksac differentiates into the fetal portion of the placenta and the uterus abutting the yolksac differentiates into the maternal portion of the placenta. The yolk stalk differentiates into an elongate umbilical cord. The uterine epithelium produces secretions that are positive by the periodic acid-Schiff and alcian blue methods and metachromatic when stained with toluidine blue. Uterine capillaries are continuous and the surface epithelium is active both in secretion and transport of nutrients. When the embryos are 7–10cm in length, appendiculae are elongate, branched and populated by separate microvillar and granulated cells. Appendiculae may function as a paraplacental nutrient absorptive organ and be involved in the regulation of osmolarity of periembryonic fluids. The fetal placenta has two functional regions: a proximal portion that is presumed to function as a steroid producing organ and a distal portion that effects nutrient and metabolic exchange between the mother and fetus. Characteristics of the fetal placenta include endocytotic activity, crystalline-like cytoplasmic bodies and fenestrated capillaries. Fetal and maternal components of the placenta are separated by the egg envelope.     

Correlation of yolk phosphatase expression with the programmed proteolysis of vitellin in Blattella germanica during embryonic development

Proteolytic processing of the vitellin in Blattella germanica eggs occurs 4 days postovulation and is correlated with both the onset of its utilization and the major portion of the embryo's growth. Yolk phosphatase is also expressed coincident with this event, and some aspects of its activation have been investigated. The enzyme is absent from the ooplasm (yolk) during the first 2 days following ovulation but increases approximately 20-fold in specific activity between days 3 and 4, when assayed at pH 3.9 or 4.8 and 9-fold at pH 6.5. No activation is observed for yolk-bound α-mannosidase, its specific activity remains elevated through the first 6 days following ovulation. This suggests that expression of the phosphatase is regulated independently of that of α-mannosidase in the yolk. Yolk with active phosphatase can dephosphorylate native vitellin, delipidated vitellin, and phosphocasein. Sucrose density gradient centrifugation of yolk obtained from eggs 4 days postovulation, revealed that phosphatase activity cosediments with material which reacts with antivitellin antibodies, while α-mannosidase and β-N-acetyl glucosaminidase are found near the top of the gradient. Oothecae derived from crossing certain translocational heterozygote males and wild-type females contain some eggs with severely depressed levels of yolk phosphatase in which embryos do not grow. Vitellin in these eggs fails to undergo proteolytic processing as late as day 5 postovulation and retains the subunit composition of freshly ovulated vitellin.     

Changes in teleost yolk proteins during oocyte maturation: correlation of yolk proteolysis with oocyte hydration

Yolk proteins of prematuration occytes and postmaturation eggs were compared by SDS gel electrophoresis in several teleosts, including freshwater species that produce demersal eggs, estuarine and marine species with demersal eggs, and marine species with pelagic eggs. In certain teleosts distinct changes in yolk protein banding patterns during oocyte maturation are suggestive of extensive secondary proteolysis of yolk proteins at this time; proteolysis is most pronounced in marine fishes with pelagic eggs. In many teleosts the oocyte swells by hydration during maturation; this hydration is also most pronounced in marine fishes with pelagic eggs. The extent of yolk proteolysis is well correlated with the extent of oocyte hydration during maturation.     

An electron microscope study on the developing oocytes of the crab Cancer pagurus L. with special reference to yolk formation (Crustacea)

Summary The developing oocytes of the crab Cancer pagurus L. were studied with the light and electron microscope.Protein yolk formation was found to take place in two different ways. Yolk precursors of type 1 accumulate within the cisternae of an extensively developed granular endoplasmic reticulum. Also further growth and transformation into the definite yolk body occur within the reticular membranes. There is no structural indication that any other cell organelle contributes to the synthesis of this type of yolk building.Protein yolk formation of type 2 involves accumulation and transformation of material within a limiting membrane of the smooth type. The enclosed material is presumably derived from micropinocytosis, enclosed cellular elements and vesicles originating from the Golgi complex.It thus appears that the cell organelles play an important role in the process of drotein yolk formation in the growing oocytes of Cancer pagurus.