Yolk Glycoprotein Research Articles

Improvement mechanism of lipid metabolism and gut microbiota in obese mice with Thunnus albacares eggs yolk glycoprotein

Thunnus albacares (T.albacares) is plentiful with a promising research value and application. However, research on lipid-reducing activity and gut microbiota of T.albacares eggs yolk glycoprotein (TGP) remains unreported. In this work, we investigated the potential mechanism of TGP intervention to improve the disorders of lipid metabolism, and regulate gut microbiota in mice induced by high-fat diet (HFD). The results demonstrated that TGP improved the dyslipidemia, liver inflammation, and restored the liver tissue structure caused by HFD. TGP prevented lipid overaccumulation by downregulating the relative mRNA expression of lipid synthesis genes. TGP also prevented differential expansion of microbiota, increased the abundance of beneficial bacteria Lactobacillus and Akkermansia, and decreased the abundance of harmful bacteria Desulfovibrio. Moreover, TGP promoted the production of short-chain fatty acids (SCFAs). All the above results provided some theoretical basis for the in-depth development and application of TGP as a functional food for obesity and hyperlipidemia.

Identification of potent antioxidant bioactive peptides from the soluble proteins of chicken egg yolk

Background: Eggs are an excellent nutrient-dense food containing proteins, fats, carbohydrates, minerals, and vitamins. While many proteins are present in egg yolk, there arefew studies on their health benefits. Objective: The aim of this study was to explore the antioxidant peptides derived from the soluble protein fractions of egg yolk. Lipids and lipoproteins were removed with activated carbon and centrifugation after water dilution at acidic pH. Materials and Methods: Compared with 3.6 grams of protein in egg white, egg yolk contains 2.7 grams of protein in a single large egg. The egg yolk soluble protein (EYsP) was digested with pepsin for 2h at pH 3.0 (P-EYsP), followed by digestion with trypsin (P-EYsP-T), α-chymotrypsin (P-EYsP-α), or both enzymes (P-EYsP-T/α). The most active digest was fractionated using sephacryl S-100 gel filtration, followed by reversed phase-HPLC of the most active fraction. The antioxidant activities were evaluated using a superoxide anion-generating system of xanthine oxidase, DPPH-scavenging assay, and yeast cells as an oxidative-stress tolerance cellular model. Results: The intact proteins (EYsP) showed antioxidant activity, but pepsin hydrolysate (P-EYsP) exhibited greater superoxide-scavenging activities than EYsP, while P-EYsP-T, P-EYsP-α and P-EYsP-T/α lacked activities. The P-EYsP and its subsequent proteases (P-EYsP-T, P-EYsP-α and P-EYsP-T/α) exhibited significant DPPH reduction, but P-EYsP-T, P-EYsP-α and P-EYsP-T/α exhibited the strongest DPPH reduction activities. MALDI-TOF-MS analysis revealed five major antioxidant peptides, two derived from yolk glycoprotein 40 (859 Da, 883Da), two from lipovitelline (901Da, 945 Da), and one from livetin (1089 Da). The peptides exhibited potent superoxide anion as well as DPPH scavenging activities and markedly enhanced the tolerance of yeast cells against peroxide-induced oxidative stress.Conclusion: The results show that these bioactive peptides hold a fascinating opportunity for their potential as nutraceuticals in prevention and combating oxidative stress-associated diseases.Keywords: Egg yolk proteins; bioactive peptides; antioxidant; superoxide-scavenging; DPPH-reduction; yeast tolerance

Search for a Novel Allergen in Hen’s Egg Allergy Using an IgE Immunoblotting Assay

Background: Food allergy is a serious health issue affecting roughly 4% of children, with a substantial effect on quality of life. Chicken egg allergy is frequently observed in infants. Therefore, some of them have to exclude hen’s eggs from their daily diet to avoid allergenic symptoms. Hen’s egg is composed of 2 soluble parts; one is egg white, which has been characterized as the major source of allergenicity, while the other is egg yolk, which is estimated as a miner source. Only 2 allergens from egg yolk, α-livetin (Gal d 5) and YGP42 (Gal d 6), have been described to date. Methods: Sera from 53 patients allergic to hen’s eggs and 2 patients allergic to sesame were obtained from the Department of Pediatrics, Chiba University Hospital. The study was performed using SDS-PAGE, IgE immunoblotting, and dot blotting. Results: Seven bands of egg yolk were detected by IgE immunoblotting. Out of these bands, a possible new allergen was further characterized by LC-MS/MS. The 33-kDa band was identified as yolk glycoprotein (YGP40) by LC-MS/MS. A total of 21 of the 53 patients (47%) had YGP40 detected by dot blotting. Conclusions: We identified YGP40 as a new hen’s egg yolk allergen and detected 4 sites of YGP40 as linear epitopes.

Suppression of Neu1 sialidase delays the absorption of yolk sac in medaka (Oryzias latipes) accompanied with the accumulation of α2-3 sialo-glycoproteins

Sialidase catalyzes the removal of sialic acids from glycoconjugates. Recently, medaka sialidase Neu1 has been cloned and its enzymatic properties were investigated. Although enzymatic properties of this sialidase, such as optimal pH and substrate specificity, exhibits high similarity with human NEU1, Neu1 physiological functions in fish are still unclear. Here, to understand Neu1 significance in medaka embryogenesis, sialidase translation knockdown was carried out with one-cell stage fertilized egg using morpholino oligo injection.Neu1 exhibited desialylation of α2-3 sialic acid linkage in vitro and lysosomal localization in medaka caudal fin primary cells. Chloroquine treatment, inhibitor of lysosomal enzymes, caused an accumulation of α2-3 sialo-glycoproteins in the primary cells. During the embryogenesis neu1 mRNA level was elevated until 3.5 day post fertilization (dpf) while an initial decrease of α2-3 sialo-glycoprotein was observed around the same developmental stage. Neu1 knockdown by morpholino oligo induced some abnormal phenotypes such as delay of yolk sac absorption and small embryos. Sialidase-knockdown embryos also showed increase of heart rate in 5.5 and 6.5 dpf. Furthermore, about 37% decrease of hatching rate was observed in Neu1-MO treated embryos compared with control MO. Embryos showing severe phenotypes stopped embryogenesis at the late stage of development. Alteration of embryonic sialo-glycoproteins induced by morpholino injection was examined by lectin blotting to clarify the mechanism of abnormal development. As a result, degradation of several α2-3 sialo-glycoproteins was suppressed in Neu1-MO embryo, possibly induced by the interruption of lysosomal desialylation toward yolk glycoprotein. Our results suggest that medaka Neu1 could be crucial for embryonic development through the degradation of yolk sac nutrition.

Effects of a Lactobacillus acidophilus D2 enriched diet on yolk protein in hen eggs

Summary The effects of probiotic supplementation on hen egg quality were studied, focusing on yolk protein changes. Electrophoretic analysis and protein spot identification were performed and the relative quantity of each protein was computed. Results showed a higher quantity of ovotransferrin, YGP42 and YGP40 ( P<0.05) together with a reduced quantity of lipovitellin-2 ( P<0.01) in the yolk of treated hens. Noteworthy is the increased concentration of YGP40. This is a yolk glycoprotein of 40 kDa recently suggested to be a potential new allergen. Eggs from treated hens also had a lower fat content than those from the control hens, both because of a lower fat concentration ( P<0.05) and a smaller yolk ( P<0.01).

N-glycan moieties of the crustacean egg yolk protein and their glycosylation sites

Vitellogenin (Vg) is the precursor of the egg yolk glycoprotein of crustaceans. In the prawn Macrobrachium rosenbergii, Vg is synthesized in the hepatopancreas, secreted to the hemolymph, and taken up by means of receptor-mediated endocytosis into the oocytes. The importance of glycosylation of Vg lies in its putative role in the folding, processing and transport of this protein to the egg yolk and in the fact that the N-glycan moieties could provide a source of carbohydrate during embryogenesis. The present study describes, for the first time, the structure of the glycan moieties and their sites of attachment to the Vg of M. rosenbergii. Bioinformatics analysis revealed seven putative N-glycosylation sites in M. rosenbergii Vg; two of these glycosylation sites are conserved throughout the Vgs of decapod crustaceans from the Pleocyemata suborder (N 159 and N 660). The glycosylation of six putative sites of M. rosenbergii Vg (N 151, N 159, N ,168 N ,614 N 660 and N 2300) was confirmed; three of the confirmed glycosylation sites are localized around the N-terminally conserved N-glycosylation site N 159. From a theoretical three-dimensional structure, these three N-glycosylated sites N 151, N 159, and N 168 were localized on the surface of the Vg consensus sequence. In addition, an uncommon high mannose N-linked oligosaccharide structure with a glucose cap (Glc1Man9GlcNAc2) was characterized in the secreted Vg. These findings thus make a significant contribution to the structural elucidating of the crustacean Vg glycan moieties, which may shed light on their role in protein folding and transport and in recognition between Vg and its target organ, the oocyte.

Characterization of the estrogenic response to genistein in Japanese medaka ( Oryzias latipes)

This study was designed to determine the estrogenic effect of the phytoestrogen genistein on several measures of endocrine function in adult Japanese medaka ( Oryzias latipes) relative to 17-β-estradiol. Adult animals of both sexes were exposed to 75, 750 and 30 000 ng/fish (average fish weight equals 0.26 g) of genistein by i.p. injection, with a positive control group treated with 300 ng/fish of 17-β-estradiol, while a negative control group received a vehicle-only (corn oil) injection. Content of vitellogenin, the yolk glycoprotein made in the liver in response to estradiol stimulation, was measured using Western blots. Circulating estradiol and testosterone levels were measured using a steroid-enzyme immunosorbant assay. The ability of ovaries and testes to synthesize and release estradiol and testosterone was determined by ex vivo incubation of gonads with 25-hydroxycholesterol. Vitellogenin, while induced by 17-β-estradiol, was not increased in the liver of individuals treated with genistein. In females, genistein treatment at 750 and 30 000 ng increased the estradiol production of ovaries more than the 17-β-estradiol treatment. In males, genistein treatment resulted in decreased testosterone production from ex vivo testis and a comparable reduction in circulating testosterone level. The changes in vitellogenin, circulating steroids and ex vivo steroidogenesis in medaka in response to genistein are similar to that of 17-β-estradiol. However, some endpoints are more sensitive to estradiol treatment (vitellogenin), while others are more sensitive to genistein (male testosterone and ovarian estrogenesis).

Identification of two discrete peptide: N-glycanases in Oryzias latipes during embryogenesis.

Two different types of peptide:N-glycanase (PNGase) were identified in developing embryos of medaka fish ( Oryzias latipes ). Because the optimum pH values for their activities were acidic and neutral, they were designated as acid PNGase M and neutral PNGase M, respectively. The acid PNGase M corresponded to the enzyme that had been partially purified from medaka embryos (Seko,A., Kitajima,K., Inoue,Y. and Inoue,S. (1991) J. Biol. Chem., 266, 22110-22114). The apparent molecular weight of this enzyme was 150 K, and the optimal pH was 3.5-4.0, and the K m for L-hyosophorin was 44 microM. L-Hyosophorin is a cortical alveolus-derived glycononapeptide with a large N-linked glycan chain present in the perivitelline space of the developing embryo. Acid PNGase M was competitively inhibited by a free de-N-glycosylated nonapeptide derived from L-hyosophorin. This enzyme was expressed in ovaries and embryos at all developmental stages after gastrulation, but activity was not detected in embryos at developmental stages between fertilization and gastrula. Several independent lines of evidence suggested that acid PNGase M may be responsible for the unusual accumulation of free N-glycans derived from yolk glycoproteins (Iwasaki,M., Seko,A., Kitajima,K., Inoue,Y. and Inoue,S. (1992) J. Biol. Chem., 267, 24287-24296). In contrast, the neutral PNGase M was expressed in blastoderms from the 4-8 cell stage and in cells up to early gastrula. The general significance of these findings is that they show a developmental stage-dependent expression of the two PNGase activities, and that expression of the neutral PNGase M activity occurs concomitantly with the de-N-glycosylation of L-hyosophorin. These data thus support our conclusion that the neutral PNGase M is responsible for the developmental-stage-related de-N-glycosylation of the L-hyosophorin.

Precursor-product relationship between chicken vitellogenin and the yolk proteins: the 40 kDa yolk plasma glycoprotein is derived from the C-terminal cysteine-rich domain of vitellogenin II

Chicken vitellogenin, a serum lipoprotein specific for laying hens, has been thought to be proteolytically cleaved into the heavy and light chain lipovitellins and phosvitin, the major yolk granule proteins, during or after transportation into oocyte. In this study, another proteolytic product of vitellogenin has newly been isolated from the ‘β-livetin’ fraction of yolk plasma. It is a yolk glycoprotein of 40 kDa (YGP40) with asparagine-linked carbohydrate chain(s) recognized by Concavanalin A and castor bean lectin (RCA-I), and it is identified as a C-terminal cysteine-rich fragment of the major vitellogenin (vitellogenin II), the cysteine-rich domain homologous to D2 region of von Willebrand factor. Another yolk plasma glycoprotein of 42 kDa is suggested to be one of the proteolytic products of the minor vitellogenin (vitellogenin I). Both 40 kDa and 42 kDa glycoproteins were shown to be present in growing oocytes but absent in laying hen's serum. Limited proteolysis of vitellogenin II with cathepsin D produced a 40 kDa protein with reactivity to anti-YGP40 antibody. Gel filtration analysis of vitellogenin II digested with cathepsin D showed that YGP40 dissociated from lipovitellin-phosvitin complex after the proteolytic cleavage. These results suggest that after incorporation from serum via a specific receptor vitellogenin II is cleaved in the oocyte into four fragments, heavy and light chain lipovitellins, phosvitin and YGP40, and that YGP40 is released into the yolk plasma before or during compartmentation of lipovitellin-phosvitin complex into the yolk granule.

Proteolysis of the major yolk glycoproteins is regulated by acidification of the yolk platelets in sea urchin embryos.

The precise function of the yolk platelets of sea urchin embryos during early development is unknown. We have shown previously that the chemical composition of the yolk platelets remains unchanged in terms of phospholipid, triglyceride, hexose, sialic acid, RNA, and total protein content after fertilization and early development. However, the platelet is not entirely static because the major 160-kD yolk glycoprotein YP-160 undergoes limited, step-wise proteolytic cleavage during early development. Based on previous studies by us and others, it has been postulated that yolk platelets become acidified during development, leading to the activation of a cathepsin B-like yolk proteinase that is believed to be responsible for the degradation of the major yolk glycoprotein. To investigate this possibility, we studied the effect of addition of chloroquine, which prevents acidification of lysosomes. Consistent with the postulated requirement for acidification, it was found that chloroquine blocked YP-160 breakdown but had no effect on embryonic development. To directly test the possibility that acidification of the yolk platelets over the course of development temporally correlated with YP-160 proteolysis, we added 3-(2,4-dinitroanilo)-3-amino-N-methyldipropylamine (DAMP) to eggs or embryos. This compound localizes to acidic organelles and can be detected in these organelles by EM. The results of these studies revealed that yolk platelets did, in fact, become transiently acidified during development. This acidification occurred at the same time as yolk protein proteolysis, i.e., at 6 h after fertilization (64-cell stage) in Strongylocentrotus purpuratus and at 48 h after fertilization (late gastrula) in L. pictus. Furthermore, the pH value at the point of maximal acidification of the yolk platelets in vivo was equal to the pH optimum of the enzyme measured in vitro, indicating that this acidification is sufficient to activate the enzyme. For both S. purpuratus and Lytechinus pictus, the observed decrease in the pH was approximately 0.8 U, from 7.0 to 6.2. The trypsin inhibitor benzamidine was found to inhibit the yolk proteinase in vivo. By virtue of the fact that this inhibitor was reversible we established that the activity of the yolk proteinase is developmentally regulated even though the enzyme is present throughout the course of development. These findings indicate that acidification of yolk platelets is a developmentally regulated process that is a prerequisite to initiation of the catabolism of the major yolk glycoprotein.

The “lecithotrophic” sea urchin Heliocidaris erythrogramma lacks typical yolk platelets and yolk glycoproteins

The sea urchin Heliocidaris tuberculata undergoes typical development, forming an echinoid pluteus larva, whereas H. erythrogramma undergoes direct development via a highly modified, nonfeeding larva. Using a polyclonal antibody prepared against yolk glycoproteins from the typical developer Stronglyocentrotus purpuratus, we found that H. tuberculata contains cross-reactive proteins in abundance, but H. erythrogramma does not. In addition, we used immunoelectron microscopy to demonstrate that unfertilized eggs of H. tuberculata contain yolk platelets, but those of H. erythrogramma do not.

Loss of yolk platelets and yolk glycoproteins during larval development of the sea urchin embryo

The fate of the yolk platelets and their constituent yolk glycoproteins was studied in Stronglyocentrotus purpuratus eggs and embryos cultured through the larval stage. Previous studies have shown that the yolk glycoproteins undergo limited proteolysis during early embryonic development. We present evidence that the yolk glycoproteins stored in the yolk platelets exist as large, disulfide-linked complexes that are maintained even after limited proteolysis has occurred. We provide additional evidence that acidification of the yolk platelet may activate a latent thiol protease in the yolk platelet that is capable of correctly processing the major yolk glycoprotein into the smaller yolk glycoproteins. Because we previously showed that these yolk glycoproteins are not catabolized during early embryonic development, it was of interest to study their fate during larval development. Using a specific polyclonal antibody to a yolk glycoprotein, we found that both yolk glycoproteins and the yolk platelets disappeared in feeding, Day 7, larval stage embryos, but that starvation did not significantly affect the levels of the yolk glycoproteins. We also found that the yolk glycoproteins reappeared in 30-day-old premetamorphosis larvae.

Structure of a major yolk glycoprotein and its processing pathway by limited proteolysis are conserved in echinoids

To study the fate of the yolk glycoproteins found in eggs and embryos of the sea urchin, Strongylocentrotus purpuratus, a polyclonal antibody to a 90-kDa polymannose glycoprotein found in the embryo was prepared. Immunoblot analysis of total proteins over the course of development showed that this antibody recognized a family of glycoproteins. Concomitant with the disappearance of the major 160-kDa yolk glycoprotein of the egg during embryogenesis, glycoproteins with a lower molecular mass appeared. These glycoproteins (115, 108, 90, 83, and 68 kDa) were purified from S. purpuratus and analyzed by limited proteolysis and peptide mapping. This analysis revealed that these glycoproteins were cleavage products derived from the major yolk glycoprotein. The antibody to the 90-kDa glycoprotein in S. purpuratus embryos was used to identify a homologous set of yolk glycoproteins with similar molecular masses in the embryos of three other species in the class Echinoidea: Arbacia punctulata, Lytechinus pictus, and Dendraster excentricus. However, eggs from other echinoderm classes and from Xenopus laevis, Drosophila melanogaster, and the chicken did not contain any cross-reactive molecules. Cross-reactivity within the class Echinoidea was not due to a common carbohydrate epitope, because the antibody recognized the glycoproteins even after the N-linked carbohydrate side chains were enzymatically removed. The major yolk glycoprotein (160–170 kDa) from each of the three sea urchin species was purified and analyzed. Comparison of the physical and chemical properties of these glycoproteins revealed striking similarities in p I and in amino acid and monosaccharide composition. The results of peptide mapping also supported the conclusion that the 160- to 170-kDa glycoproteins from the four echinoids are structurally homologous glycoproteins containing N-linked polymannose chains. Immunolocalization by electron microscopy in S. purpuratus showed that the yolk glycoproteins remained within the yolk platelet throughout development, and that externalization of the 160-kDa glycoprotein or its cleavage products was not detectable.

Developmentally regulated proteolytic processing of a yolk glycoprotein complex in embryos of the sea urchin, Strongylocentrotus purpuratus

We have isolated a yolk glycoprotein complex from eggs and early embryos of the sea urchin, Strongylocentrotus purpuratus. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of these complexes and peptide mapping of their individual glycoprotein components indicate that developmental stage-specific changes in molecular composition of the complex are due to proteolytic processing events. Our data revealed that a 180 kDa glycoprotein of the egg complex is separated by a single proteolytic cleavage into intermediate glycoproteins of 115 and 76 kDa early in development. By the hatched blastula stage, each of these intermediate glycoproteins has been further processed to lower molecular weight forms: the 115 kDa protein is proteolytically clipped to a 84 kDa form, perhaps through 110 and 105 kDa intermediaries, while the 76 kDa molecule is directly processed to a 65 kDa form.

The major yolk glycoprotein precursor in echinoids is secreted by coelomocytes into the coelomic plasma

The echinoid perivisceral coelomic plasma contains a prominent glycoprotein particle which has a sedimentation coefficient of 22S in Dendraster excentricus and 24S in Strongylocentrotus purpuratus. The major constituent of the plasma particles is a 200 kDa glycopeptide which is also an abundant constituent of the major yolk glycoprotein precursor particles stored in the ovarian accessory cells prior to vitellogenesis [Ozaki, H. et al.: Wilhelm Roux' Arch. Dev. Biol. 195, 74–79 (1986)]. Through in vitro culture analysis we have found that the high molecular weight plasma glycoprotein is secreted by coelomocytes of the perivisceral coelom. Moreover, the results of radioisotope labeling experiments in D. excentricus have shown that the synthesis of the high molecular weight glycoprotein took place predominantly in the coelom, and that its synthesis was not detectable in the ovary or digestive tract. It appears, therefore, that the yolk glycoprotein precursor when secreted by the coelomocytes reaches the ovary through the circulatory system.

The effect of estrogen on protein synthesis in echinoid coelomocytes

1. 1. A similar high molecular weight glycoprotein is found in an asteroid egg, Pisaster giganteus, and in echinoid eggs, Dendraster excentricus and Strongylocentrotus purpuratus. 2. 2. Estrogen induced the synthesis of a novel protein in echinoid coelomocytes, 82 K daltons in D. excentricus and 78 K daltons in S. purpuratus; but it did not increase yolk glycoprotein precursor synthesis nor protein synthesis as a whole in these cells during treatment up to 24 hr. However, the induced novel protein may ultimately lead to increased transcription of the yolk glycoprotein precursor gene. Estrogen therefore could be involved in the regulation of reproduction in echinoids, as it is in asteroids and vertebrates.

A glycoprotein in the accessory cell of the echinoid ovary and its role in vitellogenesis.

A high-molecular-weight glycoprotein with a sedimentation coefficient of 22.6 has been isolated and characterized from the accessory cells in the previtellogenic ovary of the echinoid Dendraster excentricus. This glycoprotein is similar to the major yolk glycoprotein of the mature egg in its electrophoretic mobility under non-denaturing conditions, high mannose-type glycan, amino acid composition, constitutive glycopeptides, and immunological determinants. Previous histological and electron microscopical analyses led to the hypothesis that vitellogenesis involves a translocation of material from the accessory cell in the ovary to the oocyte. Because of the close similarities of the accessory cell glycoprotein to the yolk glycoprotein of the mature egg, we conclude that the glycoprotein in the accessory cell is a precursor to the major glycoprotein of the egg yolk. This conclusion is further supported by our additional finding that the accessory cell of another echinoid, Strongylocentrotus purpuratus, also contains a high-molecular-weight (24 S) glycoprotein which shows similarities to the yolk glycoprotein of the mature egg in the carbohydrate moiety and the constitutive glycopeptides.

Analysis of changes in a yolk glycoprotein complex in the developing sea urchin embryo

A sea urchin yolk glycoprotein complex (YGC) was isolated from several developmental stages by velocity centrifugation on sucrose gradients. The YGCs were analyzed by SDS-polyacrylamide gel electrophoresis to determine if the molecular composition of the YGC was changing during development. The mass of the YGC did not change with development. However, as development proceeded there were significant changes in the glycoprotein composition of the YGC isolated from either Lytechinus pictus or Strongylocentrotus purpuratus embryos. In both species the YGC isolated from eggs contained three major glycoproteins. The most abundant one had an apparent molecular weight of 190,000 and was designated GP-190. During development the three major egg YGC glycoproteins decreased in relative amounts as intermediate-molecular-weight glycoproteins increased. While these changes were detected in YGCs isolated from either species, the rate of change was much greater in S. purpuratus than in L. pictus. The most significant difference was observed in the rate of decrease in GP-190. In S. purpuratus, GP-190 showed a significant decrease by 8–10 hr postfertilization, while a similar decrease did not occur in L. pictus YGCs until 72 hr postfertilization. To determine how these changes were occurring, both amino acid and carbohydrate analyses were done on the YGC isolated from various stages. From examination of these data, it appeared that the molecular composition of the YGC was changing via very limited proteolysis. The intermediate and low-molecular-weight glycoproteins generated apparently remain assembled in the YGC, thus conserving its mass.

Ribonucleosides bound to the major yolk components in eggs of the insects Euscelis and Smittia

AbstractThe uptake of radioactive RNA precursors into growing oocytes of insect ovaries was studied. In addition to incorporation of radioactivity into RNA, labelled nucleosides were also observed in the egg. Some of this radioactivity is bound covalently to yolk glycoproteins.