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

Importance for humans of recently discovered protein compounds - yolkin and yolk glycopeptide 40, present in the plasma of hen egg yolk

Vitellogenin (Vt) is considered the primary protein precursor of egg yolk, serving as a source of protein- and lipid-rich nutrients for the developing embryo. However, recent research has revealed that the functions of Vt and Vt-derived polypeptides, such as yolkin (Y) and yolk glycopeptide 40 (YGP40), extend beyond their nutritional roles as a source of amino acids. Emerging evidence has demonstrated that both Y and YGP40 possess immunomodulatory properties and can contribute to host immune defenses. Additionally, Y polypeptides have been shown to exhibit neuroprotective activity, participating in the modulation of neurons' survival and activity, inhibiting neurodegeneration processes, and improving cognitive functions in rats. These non-nutritional functions not only enhance our understanding of the physiological roles of these molecules during embryonic development but also offer a promising basis for the potential application of these proteins in human health.

Excretory/Secretory Proteome of Females and Males of the Hookworm Ancylostoma ceylanicum

The dynamic host-parasite mechanisms underlying hookworm infection establishment and maintenance in mammalian hosts remain poorly understood but are primarily mediated by hookworm's excretory/secretory products (ESPs), which have a wide spectrum of biological functions. We used ultra-high performance mass spectrometry to comprehensively profile and compare female and male ESPs from the zoonotic human hookworm Ancylostoma ceylanicum, which is a natural parasite of dogs, cats, and humans. We improved the genome annotation, decreasing the number of protein-coding genes by 49% while improving completeness from 92 to 96%. Compared to the previous genome annotation, we detected 11% and 10% more spectra in female and male ESPs, respectively, using this improved version, identifying a total of 795 ESPs (70% in both sexes, with the remaining sex-specific). Using functional databases (KEGG, GO and Interpro), common and sex-specific enriched functions were identified. Comparisons with the exclusively human-infective hookworm Necator americanus identified species-specific and conserved ESPs. This is the first study identifying ESPs from female and male A. ceylanicum. The findings provide a deeper understanding of hookworm protein functions that assure long-term host survival and facilitate future engineering of transgenic hookworms and analysis of regulatory elements mediating the high-level expression of ESPs. Furthermore, the findings expand the list of potential vaccine and diagnostic targets and identify biologics that can be explored for anti-inflammatory potential.

IgY technology: Methods for developing and evaluating avian immunoglobulins for the in vitro detection of biomolecules

The term “IgY technology” was introduced in the literature in the mid 1990s to describe a procedure involving immunization of avian species, mainly laying hens and consequent isolation of the polyclonal IgYs from the “immune” egg yolk (thus avoiding bleeding and animal stress). IgYs have been applied to various fields of medicine and biotechnology. The present article will deal with specific aspects of IgY technology, focusing on the currently reported methods for developing, isolating, evaluating and storing polyclonal IgYs. Other topics such as current information on isolation protocols or evaluation of IgYs from different avian species are also discussed. Specific advantages of IgY technology (e.g., novel antibody specificities that may emerge via the avian immune system) will also be discussed. Recent in vitro applications of polyclonal egg yolk-derived IgYs to the field of disease diagnosis in human and veterinary medicine through in vitro immunodetection of target biomolecules will be presented. Moreover, ethical aspects associated with animal well-being as well as new promising approaches that are relevant to the original IgY technology (e.g., development of monoclonal IgYs and IgY-like antibodies through the phage display technique or in transgenic chickens) and future prospects in the area will also be mentioned.

C-Terminal Fragment of Vitellogenin II, a Potential Yolkin Polypeptide Complex Precursor Protein-Heterologous Expression, Purification, and Immunoregulatory Activity

The aim of this research was to analyze the heterologous expression, purification, and immunoregulatory activity of recombinant YGP40 (rYGP40), the potential precursor of the yolkin peptide complex. The ygp40 coding sequence was codon optimized, successfully expressed in the E. coli system, and purified from inclusion bodies with a yield of about 1.1 mg/L of culture. This study showed that the protein exhibits immunomodulatory activity, expressed by the stimulation of TNF-α and IL-10 production and nitric oxide induction at a level comparable to that of the natural yolkin peptide complex obtained by other authors from hen egg yolk. At the highest dose of 100 µg/mL, rYGP40 also caused the up-regulation of iNOS expression in murine bone marrow-derived macrophages (BMDM). Moreover, no cytotoxic effects of rYGP40 on the BMDM cell line were observed.

Comparative Studies of Yolkin Preparations Isolated from Egg Yolks of Selected Bird Species

The results of our research have proven that yolkin preparations isolated from eggs of different bird species show a high similarity in polypeptide composition. Despite the small differences in protein patterns, all of yolkin preparations showed also strong immunomodulatory activity, comparable with yolkin obtained previously from hen egg yolk. It can therefore be deducted that the presence of this polypeptide complex in the egg is not accidental and performs an important biological function for developing embryo.

Quantitative Comparative Integrated Proteomic and Phosphoproteomic Analysis of Chicken Egg Yolk Proteins under Diverse Storage Temperatures

To investigate the alterations of egg yolk protein abundances and their phosphorylation status at different storage temperatures, a comparative quantitative study of unfertilized chicken egg yolk after 15 days of storage at 4 and 37 °C was performed. Altogether, 445 proteins were identified in our study, of which the abundances of 154 proteins were significantly changed when comparing high-temperature storage with low-temperature storage, including 42 up-regulated and 112 down-regulated proteins. In the phosphoproteome, we identified a total of 137 phosphorylated sites on 326 peptides corresponding to 51 proteins. The results showed that the degree of phosphorylation for most egg yolk proteins was enhanced during high-temperature storage. Furthermore, GO analysis indicated that these phosphoproteins of egg yolk may be closely related to the binding, catalysis, and transport functions. The results provide further insights into the effect of storage temperature on egg proteome changes and their phosphorylation level. Moreover, this study can provide a theoretical basis for the improvement of egg quality during storage by phosphorylation modification in the food industry.

Reproductive management of poultry

Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems.

Comparative Quantitative Phosphoproteomic Analysis of the Chicken Egg during Incubation Based on Tandem Mass Tag Labeling

Protein phosphorylation plays an important role in protein structure and function. To investigate the role of egg protein phosphorylation in chicken embryonic development, a comparative and quantitative phosphoproteomic analysis of fertilized chicken egg white and yolk was performed during incubation. Overall, 215 phosphosites mapped onto 205 phosphopeptides corresponding to 100 phosphoproteins were identified. Among these phosphoproteins, 123 phosphosites from 62 egg proteins were found significantly changed (p < 0.05) at day 12 during incubation. Furthermore, GO analysis suggested that these differentially phosphorylated proteins were associated with various molecular functions, primarily including binding, molecular function regulator, and transport activity. Such findings in this study improved our understanding of the protein molecular functions involved in chicken embryonic development from a protein phosphorylation perspective.

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.

Comparative proteome analysis of egg yolk plasma proteins during storage

BACKGROUND

Physical changes such as chicken egg white thinning and egg yolk flattening occur during storage, implying a decline in egg quality. To reveal the deteriorative process related to chicken egg internal quality, a comparative proteomic method was used in this study to analyze the alterations in egg yolk plasma proteins at different storage times (0, 20 and 40 days) under an ambient temperature of 22 ± 2 °C.

RESULTS

Using two-dimensional electrophoresis followed by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry, 33 protein spots representing 12 proteins were identified with significant (P < 0.05) alterations in abundance at different storage times. The proteins that showed significant changes in abundance included serum albumin, vitellogenin fragments, IgY chains, ovalbumin, ovoinhibitor, α₂ -macroglobulin-like protein 1-like, hemopexin, transthyretin, apolipoprotein A-I and β₂ -glycoprotein I precursor. Accelerating degradation for most egg yolk plasma proteins was observed after prolonged storage (from day 20 to day 40).

CONCLUSION

It is likely that the increased degradation of protease inhibitors such as ovoinhibitor and α₂ -macroglobulin-like protein 1-like during prolonged storage lead to an imbalance of protease and antiprotease in egg yolk, which may play a key role in the degradation of egg yolk proteins. These findings will provide an insight into the effects of storage on egg yolk protein changes and give a deeper understanding of the deteriorative process of chicken egg yolk. © 2016 Society of Chemical Industry.

A simple and rapid method of isolation of active polypeptide complex, yolkin, from chicken egg yolk

A large number of bioactive peptides isolated from natural sources are known to play important physiological roles in the human body. It is possible to use these as alternative therapy agents. One example is yolkin which can be useful as a food supplement, a natural therapeutic agent for preventing and treating cognitive disorders of various origins, preferably in patients with unsatisfactory responses to known therapies. A new simple method of isolation of yolkin based on precipitation with ethanol or acetone was developed. The best precipitation efficiency of both ethanol and acetone was achieved when stirred into the starting material to a final concentration of 70%. These methods preserved the ability of yolkin to stimulate human whole blood cells to release anti-inflammatory cytokines and neurotrophins. At first we indicated that yolkin displayed a potential neuroprotective effect by the ability to stimulate cells to produce pro-survival brain derived neurotrophic factor (BDNF).

The hookworm Ancylostoma ceylanicum intestinal transcriptome provides a platform for selecting drug and vaccine candidates

Background

The intestine of hookworms contains enzymes and proteins involved in the blood-feeding process of the parasite and is therefore a promising source of possible vaccine antigens. One such antigen, the hemoglobin-digesting intestinal aspartic protease known as Na-APR-1 from the human hookworm Necator americanus, is currently a lead candidate antigen in clinical trials, as is Na-GST-1 a heme-detoxifying glutathione S-transferase.

Methods

In order to discover additional hookworm vaccine antigens, messenger RNA was obtained from the intestine of male hookworms, Ancylostoma ceylanicum, maintained in hamsters. RNA-seq was performed using Illumina high-throughput sequencing technology. The genes expressed in the hookworm intestine were compared with those expressed in the whole worm and those genes overexpressed in the parasite intestine transcriptome were further analyzed.

Results

Among the lead transcripts identified were genes encoding for proteolytic enzymes including an A. ceylanicum APR-1, but the most common proteases were cysteine-, serine-, and metallo-proteases. Also in abundance were specific transporters of key breakdown metabolites, including amino acids, glucose, lipids, ions and water; detoxifying and heme-binding glutathione S-transferases; a family of cysteine-rich/antigen 5/pathogenesis-related 1 proteins (CAP) previously found in high abundance in parasitic nematodes; C-type lectins; and heat shock proteins. These candidates will be ranked for downstream antigen target selection based on key criteria including abundance, uniqueness in the parasite versus the vertebrate host, as well as solubility and yield of expression.

Conclusion

The intestinal transcriptome of A. ceylanicum provides useful information for the identification of proteins involved in the blood-feeding process, representing a first step towards a reverse vaccinology approach to a human hookworm vaccine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1795-8) contains supplementary material, which is available to authorized users.

Complexity of Yolk Proteins and Their Dynamics in the Sea Star Patiria miniata

Oviparous animals store yolk proteins within the developing oocyte. These proteins are used in gametogenesis and as a nutritional source for embryogenesis. Vitellogenin and the major yolk protein are two of the most important yolk proteins among diverse species of invertebrates and vertebrates. Among the echinoderms, members of the subphyla Echinozoa (sea urchins and sea cucumbers) express the major yolk protein (MYP) but not vitellogenin (Vtg), while an initial report has documented that two Asterozoa (sea stars) express a vitellogenin. Our results show that sea stars contain two vitellogenins, Vtg 1 and Vtg 2, and MYP. In Patiria miniata, these genes are differentially expressed in the somatic and germ cells of the ovary: Vtg 1 is enriched in the somatic cells of the ovary but not in the oocytes, and Vtg 2 accumulates in both oocytes and somatic cells; MYP is not robustly present in either. Remarkably, Vtg 2 and MYP mRNA reappear in larvae; Vtg 2 is detected within cells of the ectoderm, and MYP accumulates in the coelomic pouches, the intestine, and the posterior enterocoel (PE), the site of germ line formation in this animal. Additionally, the Vtg 2 protein is present in oocytes, follicle cells, and developing embryos, but becomes undetectable following gastrulation. These results help elucidate the mechanisms involved in yolk dynamics, and provide molecular information that allows for greater understanding of the evolution of these important gene products.

Pro-Cognitive Properties of the Immunomodulatory Polypeptide Complex, Yolkin, from Chicken Egg Yolk and Colostrum-Derived Substances: Analyses Based on Animal Model of Age-Related Cognitive Deficits

The study aimed to assess the effect of the polypeptide Y complex (Yolkin), isolated from chicken egg yolk, on behavioural and cognitive functions. It also aimed to compare this activity with colostrum-derived substances (Colostrinin, Coloco), which have a confirmed impact on learning and memory. In the study, the effect of Yolkin, administered to rats of different ages, who performed various tasks involving spatial and episodic memory, motor functions and exploratory behavior, was assessed. The experiment was carried out in rats which were 6 and 12 months old. Two different doses of the studied specimens based on previous comparative studies and two different routes of administration (oral and retroperitoneal) were used. A series of behavioural tests were carried out, including an open field test, a novel object recognition test and a Morris water maze. They were used to evaluate the impact of the studied specimen on improving locomotor function and exploratory behaviour, preventing their decline and assess the functioning of episodic and spatial memory in aging rats. The administration of Yolkin gave distinct effects compared to colostrum-derived substances, although confirmed its suggested pro-cognitive action. Therefore, it may be used to enhance cognitive functions and inhibit the progression of dementia in the course of neurodegenerative disorders.

Characterisation and expression analysis of cathepsins and ubiquitin-proteasome genes in gilthead sea bream (Sparus aurata) skeletal muscle

Background

The proteolytic enzymes involved in normal protein turnover in fish muscle are also responsible for post-mortem softening of the flesh and are therefore potential determinants of product quality. The main enzyme systems involved are calpains, cathepsins, and the ubiquitin-proteasome (UbP). In this study on Sparus aurata (Sa), the coding sequences of cathepsins (SaCTSB and SaCTSDb) and UbP family members (SaN3 and SaUb) were cloned from fast skeletal muscle, and their expression patterns were examined during ontogeny and in a fasting/re-feeding experiment.

Results

The amino acid sequences identified shared 66-100% overall identity with their orthologues in other vertebrates, with well conserved characteristic functional domains and catalytic residues. SaCTSDb showed phylogenetic, sequence and tissue distribution differences with respect to its paralogue SaCTSDa, previously identified in the ovary. Expression of gilthead sea bream cathepsins (B, L, Da, Db) and UbP members (N3, Ub, MuRF1 and MAFbx) in fast skeletal muscle was determined at three different life-history stages and in response to fasting and re-feeding in juveniles. Most of the proteolytic genes analysed were significantly up-regulated during fasting, and down-regulated with re-feeding and, between the fingerling (15 g) and juvenile/adult stages (~50/500 g), consistent with a decrease in muscle proteolysis in both later contexts. In contrast, SaCTSDa and SaMuRF1 expression was relatively stable with ontogeny and SaUb had higher expression in fingerlings and adults than juveniles.

Conclusions

The data obtained in the present study suggest that cathepsins and UbP genes in gilthead sea bream are co-ordinately regulated during ontogeny to control muscle growth, and indicate that feeding regimes can modulate their expression, providing a potential dietary method of influencing post-mortem fillet tenderisation, and hence, product quality.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1121-0) contains supplementary material, which is available to authorized users.

Immunologically active peptides that accompany hen egg yolk immunoglobulin Y: separation and identification

The protein mixture of cytokine-inducing activity accompanying chicken immunoglobulin Y, named yolkin, consists of several peptides of molecular weight (MW) ranging from over 1 to 35 kDa. Yolkin and its constituent peptides were found to be efficient inducers of interleukin (IL)-1β, IL-6 and IL-10 secretion. N-terminal amino acid sequences of eight of the electrophoretically purified yolkin constituents revealed that all of them are homological to some fragments of the C-terminal domain of vitellogenin II. The fractions of MW about 4 and 12 kDa are free of carbohydrates and start at position 1732 in the vitellogenin amino acid sequence; whereas the other fractions (MW about 16, 19, 23, 29, 32 and 35 kDa) appeared to be glycoproteins corresponding to the amino acid sequence of vitellogenin starting at position 1572. From these data, it is concluded that yolkin most likely represents vitellogenin-derived peptides that possess cytokine-inducing activity and are, at least partially, responsible for such properties of separated immunoglobulin Y preparation. This finding reveals a new role for vitellogenin as a reservoir of polypeptides that may play an important role in the innate immune system of the developing embryo.

Evolution of yolk protein genes in the Echinodermata

Vitellogenin genes (vtg) encode large lipid transfer proteins (LLTPs) that are typically female-specific, functioning as precursors to major yolk proteins (MYPs). Within the phylum Echinodermata, however, the MYP of the Echinozoa (Echinoidea + Holothuroidea) is expressed by an unrelated transferrin-like gene that has a reproductive function in both sexes. We investigated egg proteins in the Asterozoa (Asteroidea + Ophiuroidea), a sister clade to the Echinozoa, showing that eggs of the asteroid Parvulastra exigua contain a vitellogenin protein (Vtg). vtg is expressed by P. exigua, a species with large eggs and nonfeeding larvae, and by the related asterinid Patiriella regularis which has small eggs and feeding larvae. In the Asteroidea, therefore, the reproductive function of vtg is conserved despite significant life history evolution. Like the echinozoan MYP gene, asteroid vtg is expressed in both sexes and may play a role in the development of both ovaries and testes. Phylogenetic analysis indicated that a putative Vtg from the sea urchin genome, a likely pseudogene, does not clade with asteroid Vtg. We propose the following sequence as a potential pathway for the evolution of YP genes in the Echinodermata: (1) the ancestral echinoderm produced YPs derived from Vtg, (2) bisexual vtg expression subsequently evolved in the echinoderm lineage, (3) the reproductive function of vtg was assumed by a transferrin-like gene in the ancestral echinozoan, and (4) redundant echinozoan vtg was released from stabilizing selection.

Evidence for the fragmentation of VtgAb LvH in common dentex (Dentex dentex), a marine pelagophil teleost

Since the timing of the lipovitellin heavy chain (LvH) of vitellogenin Ab (VtgAb) degradation during marine teleosts ontogeny is poorly understood, the current study was planned to address some aspects of this shortcoming. Fertilized eggs (before epiboly) of Dentex dentex were analysed. Vtg-derived proteins, that appeared as 6 protein bands after SDS-PAGE, were purified using specific ion exchange chromatography. Five bands (i.e., ∼78, ∼57, ∼22, ∼19, and ∼17 kDa) were merely stained with Coomassie Blue and one band (i.e., ∼16 kDa) only with Periodic Acid Schiff (PAS). The ∼16 kDa protein band was subjected to a mass spectrometry-based sequencing. These results showed that the ∼16 kDa protein band contains a mixture of "LvH-Ab" derivatives with the same molecular weight. The specific staining system (i.e., PAS) also revealed the glycosylation of some of the LvH-Ab fragments inside the ∼16 kDa protein band. The study provides new data about fragmentation of the LvH-Ab in marine pelagophil teleosts.

Lipovitellin is a non-self recognition receptor with opsonic activity

Lipovitellin (Lv), a glycolipoprotein, is a major component of the egg yolk, which is usually regarded as an energy reserve of nutrients essential for growth and development. We have purified Lv from ovulated eggs of the rosy barb Puntius conchonius by two-step chromatography and characterized it by staining with periodic acid/Schiff reagent and Sudan black B, amino acid composition analysis, and peptide mass fingerprinting. The results of ligand and bacterial binding assays, an enzyme-linked immunosorbent assay (ELISA), and the phagocytosis test revealed, for the first time, that the purified native form of P. conchonius Lv acts as a pattern recognition molecule with multiple specificities capable of identifying pathogen-associated molecular patterns (PAMPs), including those of lipopolysaccharide, lipoteichoic acid, and peptidoglycan, rather than self components and that it can bind Gram-negative and -positive bacteria, such as Escherichia coli and Staphylococcus aureus. These tests also showed that the P. conchonius Lv functions as an opsonin capable of enhancing macrophage phagocytosis. Taken together, these characteristics suggest that in developing embryos/larvae of P. conchonius, the native form of Lv may be physiologically involved in the sensing of invading pathogens via interaction with PAMPs and in the recruitment of the primitive macrophages that appear in early embryos to phagocytose and digest the pathogens, thereby protecting them from pathogenic attacks.

Conserved and variant molecular and functional features of multiple egg yolk precursor proteins (vitellogenins) in white perch (Morone americana) and other teleosts

Three complete cDNAs encoding different forms of vitellogenin (Vtg) were isolated from a white perch (Morone americana) liver cDNA library and characterized with respect to immunobiochemical and functional features of the three Vtgs and their product yolk proteins (YPs) in this species and in the congeneric striped bass (Morone saxatilis). The two longest cDNAs encoded Vtgs with a complete suite of yolk protein domains that, based on comparisons with vtg sequences from other species, were categorized as VtgAa and VtgAb using the current nomenclature for multiple teleost Vtgs. The shorter cDNA encoded a Vtg that lacked a phosvitin domain, had a shortened C-terminus, and was categorized as VtgC. Mapping of peptide sequences from the purified Vtgs and their derived YPs to Vtg sequences deduced from the cDNAs definitively identified the white perch VtgAa, VtgAb, and VtgC proteins. Detailed comparisons of the primary structures of each Vtg with partial or complete sequences of Morone yolk proteins or of Vtgs from other fishes revealed conserved and variant structural elements of teleost Vtgs with functional significance, including, as examples, signal peptide cleavage sites, dimerization sites, cathepsin D protease recognition sites, and receptor-binding domains. These comparisons also yielded an interim revision of the classification scheme for multiple teleost Vtgs.

New insights into the structure of apolipoprotein B from low-density lipoproteins and identification of a novel YGP-like protein in hen egg yolk

Apoproteins of low-density lipoproteins (LDL) and soluble proteins (livetins) contained in hen egg yolk plasma have been demonstrated as being essential to the interfacial and emulsifying properties of yolk. The knowledge of their structure is necessary to better understand these properties. Purified protein fractions were separated by SDS-PAGE or 2D-PAGE and identified through the LC-MS/MS of their trypsin peptides. Hen blood apolipoprotein B gives rise to nine different apoproteins in LDL after maturation and proteolysis. Among these apoproteins, two protein fragments appeared to be less accessible to proteases and could be enriched in beta-sheets and firmly associated with lipids. Plasma soluble proteins were constituted by approximately 45% of yolk immunoglobulins with a high heterogeneity of the variable regions of both heavy and light chains, 41% of glycoproteins constituted by YGP42 and YGP40, 14% of albumins, and one new minor protein we called YGP30, showing 75% similarity to YGP40.

Changes in cathepsin gene expression and relative enzymatic activity during gilthead sea bream oogenesis

The aim of this study was to provide evidence on the modulation of lysosomal enzymes in terms of both gene expression and enzymatic activity during follicle maturation. For this purpose three lysosomal enzymes, cathepsins B, D, and L, were studied in relation to yolk formation and degradation, during the main phases of ovarian follicle growth in the pelagophil species, the sea bream Sparus aurata. Specific attention was focused on the gene expression quantification method, on the assay of enzymatic activities, and on the relationship between the proteolytic cleavage of yolk proteins (YPs), cathepsin gene expression and cathepsin activities. For the gene expression study, the cathepsins B-like and L-like mRNAs were isolated and partially or fully characterized, respectively; the sequences were used as design specific primers for the quantification of cathepsin gene expression by real-time PCR, in follicles at different stages of maturation. The enzymatic assays for cathepsins B, D, and L were optimized in terms of specificity, sensitivity and reliability, using specific substrates and inhibitors. In ovulated eggs, the lipovitellin I (LV I) was degraded and the changes in electrophoretic pattern were preceded by an increase in the activity of a cysteine proteinase, cathepsin L, and its mRNA. Cathepsin B did not appear to be involved in YP changes during the final maturation stage.

Association of chicken zona pellucida glycoprotein (ZP) B1 with ZPC induces formation of ZPB1-ZPC fibrous aggregates containing disulfide-bridged ZPB1 dimer

Egg-envelope, a fibrous extracellular matrix, surrounding an oocyte is constructed from ZPC, ZPX2, both of which are secreted from ovarian granulosa cells, and ZPB1 which is secreted from liver cells and transported into ovary in birds. We report here that in vitro incubation of ZPB1 with ZPC spontaneously produced fibrous aggregates of ZPB1-ZPC hetero-complexes, which were visible under optical microscopy and morphologically resembled the aggregates obtained from mechanically decomposed chicken egg-envelope. Formation of such fibrous aggregates depended on ZPC/ZPB1 ratio, and involved ZPB1 dimerization through disulfide cross-linking, which had been found in authentic egg-envelope developed in hen's ovary. Furthermore, addition of excessive amounts of ZPC to ZPB1 produced soluble but high molecular weight hetero-complexes with increased adherence property against polystyrene ELISA plates. Thus, the specific association between ZPB1 and ZPC could play pivotal roles to initiate complex formation of hetero-polymers of ZP proteins in egg-envelope matrix construction.

Egg yolk proteins in gray mullet (Mugil cephalus): purification and classification of multiple lipovitellins and other vitellogenin-derived yolk proteins and molecular cloning of the parent vitellogenin genes

Seven yolk proteins (YPs), four large lipoproteins (YPs1-4) and three minor yolk components (YPs5-7) including one phosphoprotein (YP7), were purified from extracts of vitellogenic ovaries of grey mullet (Mugil cephalus) by combinations of hydroxylapatite, ion exchange, immunoadsorbent, and gel filtration chromatography. The molecular masses of native YP1, YP2, YP3, and YP4 were estimated to be 330, 325, 335, and 570 kDa, respectively. The tertiary structures of YP1, YP2, and YP3 revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis were typical of teleost lipovitellins (Lvs), consisting of a heavy chain ( approximately 110, approximately 99, and approximately 97 kDa, respectively) and a light chain ( approximately 30, approximately 29, and approximately 21.5 kDa, respectively), while YP4 exhibited a heavy chain ( approximately 110 kDa) and two more polypeptide bands ( approximately 70 and approximately 54 kDa). Mapping of N-terminal peptide sequences of the purified YPs to the primary structure of multiple mullet vitellogenins (Vgs) deduced from their respective complete cDNAs, which were cloned and sequenced, conclusively identified YP1, YP2, and YP3 as Lvs derived from mullet VgA, VgB, and VgC, respectively. The fourth YP (YP4) appeared to be a proteolytic variant consisting of Lv and phosvitin components of VgA. Two other YPs (YP5 and YP6) were identified as beta'-components derived from VgA and VgB based on their structures and common, but not identical, antigenicity to salmonid beta'-component, while purified YP7, a phosphoprotein with a high content of serine residues, was identified as a phosvitin derived from VgB. This is the first report, of which we are aware, on purification and molecular classification of three distinct forms of Lv from any oviparous vertebrate.

Vertebrate Yolk Complexes and the Functional Implications of Phosvitins and Other Subdomains in Vitellogenins1

In nonplacental or nontrophotenic vertebrates, early development depends on the maternal provision of egg yolk, which is mainly derived from large multidomain vitellogenin (Vtg) precursors. To reveal the molecular nature of the protein pools in vertebrate oocytes, published data on the N-termini of yolk proteins has been mapped to the deduced primary structures of their parent Vtgs. The available evidence shows that the primary cleavage sites of Vtgs are conserved, whereas the cleavage products exist as multidomain variants in the yolk protein pool. The serine-rich phosvitin (Pv) domains are linearly related to the molecular masses of the lipovitellin heavy chain. The 3-D localization of Pv maps to the outer edges of the Vtg monomer, where it is proposed to form amphipathic structures that loop up over the lipid pocket. At this locus, it is proposed that Pv stabilizes the nascent Vtg while it receives its lipid cargo, thereby facilitating the hepatic loading and locking of lipid within the Vtg (C-sheet)-(A-sheet)-(LvL) cavity, and enhances its solubility following secretion to the circulating plasma. The C-terminal regions of Vtgs are homologous to human von Willebrand factor type D domains (Vwfd), which are conserved cysteine-rich molecules with homologous regions that are prevalent in Vtgs, lipophorins, mucins, integrins, and zonadhesins. Unlike human VWFD, lower vertebrate Vwfds do not contain RGD motifs, which are associated with extracellular matrix binding. Although its function in Vtg is unknown, the lubricant properties associated with mucins and the cell adhesion properties associated with integrins and zonadhesins implicate Vwfd in the genesis of hemostatic platelet aggregation. Similarly, the proteolytic inhibitory properties associated with the binding of factor VIII in humans suggest that Vwfd stabilizes Vtg during passage in the systemic circulation.

Insights into protein structure and function from disorder-complexity space

Intrinsically disordered proteins have a wide variety of important functional roles. However, the relationship between sequence and function in these proteins is significantly different than that for well-folded proteins. In a previous work, we showed that the propensity to be disordered can be recognized based on sequence composition alone. Here that analysis is furthered by examining the relationship of disorder propensity to sequence complexity, where the metrics for these two properties depend only on composition. The distributions of 40 amino acid peptides from both ordered and disordered proteins are graphed in this disorder-complexity space. An analysis of Swiss-Prot shows that most peptides have high complexity and relatively low disorder. However, there are also an appreciable number of low complexity-high disorder peptides in the database. In contrast, there are no low complexity-low disorder peptides. A similar analysis for peptides in the PDB reveals a much narrower distribution, with few peptides of low complexity and high disorder. In this case, the bounds of the disorder-complexity distribution are well defined and might be used to evaluate the likelihood that a peptide can be crystallized with current methods. The disorder-complexity distributions of individual proteins and sets of proteins grouped by function are also examined. Among individual proteins, there is an enormous variety of distributions that in some cases can be rationalized with regard to function. Groups of functionally related proteins are found to have distributions that are similar within each group but show notable differences between groups. Finally, a pattern matching algorithm is used to search for proteins with particular disorder-complexity distributions. The results suggest that this approach might be used to identify relationships between otherwise dissimilar proteins.

Oogenesis: Single cell development and differentiation

Oocytes express a unique set of genes that are essential for their growth, for meiotic recombination and division, for storage of nutrients, and for fertilization. We have utilized the newly sequenced genome of Strongylocentrotus purpuratus to identify genes that help the oocyte accomplish each of these tasks. This study emphasizes four classes of genes that are specialized for oocyte function: (1) Transcription factors: many of these factors are not significantly expressed in embryos, but are shared by other adult tissues, namely the ovary, testis, and gut. (2) Meiosis: A full set of meiotic genes is present in the sea urchin, including those involved in cohesion, in synaptonemal complex formation, and in meiotic recombination. (3) Yolk uptake and storage: Nutrient storage for use during early embryogenesis is essential to oocyte function in most animals; the sea urchin accomplishes this task by using the major yolk protein and a family of accessory proteins called YP30. Comparison of the YP30 family members across their conserved, tandem fasciclin domains with their intervening introns reveals an incongruence in the evolution of its major clades. (4) Fertilization: This set of genes includes many of the cell surface proteins involved in sperm interaction and in the physical block to polyspermy. The majority of these genes are active only in oocytes, and in many cases, their anatomy reflects the tandem repeating interaction domains essential for the function of these proteins. Together, the expression profile of these four gene classes highlights the transitions of the oocyte from a stem cell precursor, through stages of development, to the clearing and re-programming of gene expression necessary to transition from oocyte, to egg, to embryo.

Role of cathepsins in ovarian follicle growth and maturation

Several complex processes are involved in the production of viable eggs. The aim of this review is to provide an overview on the role played by lysosomal enzymes, especially cathepsins B, D, and L, during ovarian follicle growth and maturation. Specific attention is focused on the relationship between the second proteolytic cleavage of yolk proteins (YP) and the resumption of the meiosis during germinal vesicle break down (GVBD). Maturation represents the final stage of oocytes development prior to ovulation. Oocytes in this phase appear translucent. In many teleosts GVBD is accompanied by water uptake and among marine teleosts with pelagic eggs, most of the final volume is reached by this process. The last phase of maturation in benthonic eggs also occurs concomitant to a second proteolytic cleavage and is related with a slight hydration process. In vitro maturation by 17alpha,20beta-dihydroxy-4-pregnen-3one in class III Danio rerio oocytes, induced 80% of GVBD. The maturation of these oocytes is known to be associated with proteolysis of their major yolk components. In the present study, we show that inhibition of specific enzymes (cathepsins) involved in the second YP processing, did not affect the occurrence of GVBD as the oocytes become translucent and display a slight increase in size. More specifically, in vitro incubation of the maturing oocytes with a cathepsin B inhibitor suppressed both cathepsin B and L activities and the proteolysis of YP. On the contrary, the addition of cathepsin L inhibitor, only affected cathepsin L activity, indicating that cathepsin B is probably involved in Cathepsin L activation, and this enzyme is probably responsible for the second YP processing. These results, together with previous studies, indicate that the GVBD process is independent of the occurrence of the second proteolytic process. It supports the hypothesis that the maturation process is under K+ ion flux control, while yolk proteolysis is related to the temporal and specific activation of cathepsins by acidification of yolk spheres.

Proteome analysis of chick embryonic cerebrospinal fluid

During early stages of embryo development, the brain cavity is filled with embryonic cerebrospinal fluid (E-CSF), a complex fluid containing different protein fractions that contributes to the regulation of the survival, proliferation and neurogenesis of the neuroectodermal stem cells. Using 2-DE, protein sequencing and database searches, we identified and analyzed the proteome of the E-CSF from chick embryos (Gallus gallus). We identified 26 different gene products, including proteins related to the extracellular matrix, proteins associated with the regulation of osmotic pressure and metal transport, proteins related to cell survival, MAP kinase activators, proteins involved in the transport of retinol and vitamin D, antioxidant and antimicrobial proteins, intracellular proteins and some unknown proteins. Most of these gene products are involved in the regulation of developmental processes during embryogenesis in systems other than E-CSF. Interestingly, 14 of them are also present in adult human CSF proteome, and it has been reported that they are altered in the CSF of patients suffering neurodegenerative diseases and/or neurological disorders. Understanding these molecules and the mechanisms they control during embryonic neurogenesis is a key contribution to the general understanding of CNS development, and may also contribute to greater knowledge of these human diseases.

Excision of foreign gene product with cathepsin D in chicken hepatoma cell line

To easily and rapidly recover exogenous gene products from chicken egg yolk, we constructed pVTG-catD (VTG, vitellogenin; catD, cathepsin D), a vector cassette carrying two catD-recognition signal peptides (catD-RSPs) in addition to the cloning site. An enhanced green fluorescence protein (EGFP)-encoding DNA fragment was ligated into the pVTG-catD. When the resultant construct pVTG-EGFP-catD containing histidine- and myc-tags was transfected into the chicken hepatoma cell line LMH, EGFP-expression at 24h post-cultivation was confirmed by fluorescence microscopy. Because a signal peptide (NTVLAEF) encoded in pVTG-EGFP-catD is recognized by catD, the VTG-EGFP fusion protein digested with catD was detectable by Western blotting. Digested exogenous gene product was recovered with nickel resin. These results indicate that catD-recognition sites bearing pVTG-catD and His-tags are functional in chicken LMH cells. Therefore, the system described here may be of use in making excision exogenous gene products in the chicken and in creating homozygous knock-in chickens.

Derivation of major yolk proteins from parental vitellogenins and alternative processing during oocyte maturation in Fundulus heteroclitus

Various Coomassie blue-staining yolk proteins (YPs) present in oocytes and eggs of Fundulus heteroclitus, a teleost that produces low hydrated, demersal eggs (benthophil species), were subjected to N-terminal microsequencing. Four YPs were N-terminally blocked, while five yielded sequence information. Of the latter, four corresponded to internal sequences of vitellogenin 1 (Vg1), whereas a fifth band corresponded to the N-terminal sequence of Vg2. Phosphorylated YPs (phosvitins and phosvettes) derived from the polyserine domain of Vg were not successfully sequenced. The major N-terminally blocked 122-and 103-kDa YPs both represented the lipovitellin heavy chain of Vg1 (LvH1), and thus most of the oocyte YPs were derived from Vg1. During oocyte maturation in vivo and in vitro, the LvH1 122 is degraded, concomitant with an increased enzymatic activity of cathepsin B, while the 45-kDa YP is converted to a 42-kDa YP. The LvH1 122 was found to contain a consensus site for proteolytic degradation (PEST) near its C-terminus, which is missing from its stable, but truncated twin sequence, LvH1 103. We suggest that this site becomes exposed to cathepsin B during the hydration process that accompanies oocyte maturation and renders the LvH1 122 susceptible to proteolysis. PEST sites are found in Vg sequences from other benthophil fish, whereas, interestingly, they are missing in marine teleosts that spawn highly hydrated, pelagic eggs (pelagophil species), displaying a different pattern of Vg incorporation into YPs and LvH1 and LvH2 processing to that found in F. heteroclitus. Thus, different models of Vg/YP precursor/product relationship and further processing during oocyte maturation and hydration are proposed for pelagophil and benthophil teleosts.

Multiple vitellogenins (Vgs) in mosquitofish (Gambusia affinis): identification and characterization of three functional Vg genes and their circulating and yolk protein products

The objectives of this study were to characterize multiple forms of vitellogenin (Vg) in mosquitofish (Gambusia affinis) and to discover the fate of each Vg during its processing into product yolk proteins. Two Vg preparations, with apparent masses of 600 kDa (600 Vg) and 400 kDa (400 Vg), were isolated from the plasma of fish treated with estradiol-17beta (E(2)) by various chromatographic procedures. Immunological analyses verified the presence of two different Vg proteins (600 VgA and 600 VgB) in the 600 Vg preparation and of a single protein in the 400 Vg preparation. Three major yolk proteins (Yps) with apparent masses of 560, 400, and 28 kDa were observed in extracts of ovarian follicles from vitellogenic females. Immunological analyses demonstrated that the 400 Vg underwent no change in native mass after being incorporated into oocytes. The 600 Vgs gave rise to a 28 kDa beta'-component and a native 560 kDa Yp, which was heterodimeric in structure, consisting of two types of complexes between phosvitin (Pv) and lipovitellin (Lv) heavy- and light-chains. Full-length cDNAs encoding the 600 VgA, 600 VgB, and 400 Vg were isolated from a liver cDNA library of E(2) treated fish. Similar to the zebrafish vg3 gene, the 400 Vg cDNA lacked a Pv domain and was classified as an incomplete or phosvitinless (C-type) Vg. The deduced primary structures of 600 VgA and 600 VgB were complete, and these were categorized as type A and type B Vgs, respectively, according to our recent classification scheme. This is the first report on the characterization of three functional Vg genes and their circulating and yolk protein products in any vertebrate species.

Two-step consumption of yolk granules during the development of quail embryos

The mechanism of yolk consumption was studied morphologically and biochemically in Japanese quail Coturnix japonica. The amount of yolk granules in the yolk (or 'yolk cell') decreased in two steps during embryonic development. In the first step, during days 0-4 of incubation, the yolk-granule weight decreased at a rate of 13 mg/day. This decrease was due to segregation by endodermal cells that were newly formed in the developing yolk sac. In the second step after day 6, the decrease was drastic at a rate of 29.8 mg/day during days 6-12 and very slow thereafter. The decrease at the second step was due to the enzymatic digestion of yolk granules by cathepsin D that coexisted in yolk spheres. This digesting reaction was triggered by the solubilization of the granules with high concentrations of salts that were supplied after disruption of the limiting membrane of yolk spheres. The 'yolk cell' seemed to die around day 5 of incubation. Thus the digestion products might be taken up together with yolk lipids by endocytosis into the endodermal cells and transported to blood vessels.

Multihormonal control of vitellogenesis in lower vertebrates

The comparative approach on how and when vitellogenesis occurs in the diverse reproductive strategies displayed by aquatic and terrestrial lower vertebrates is presented in this chapter; moreover, attention has been paid to the multihormonal control of hepatic vitellogenin synthesis as it is related to seasonal changes and to vitellogenin use by growing oocytes. The hormonal mechanisms regulating vitellogenin synthesis are also considered, and the effects of environmental estrogens on the feminization process in wildlife and humans have been reported. It is then considered how fundamental nonmammalian models appear to be, for vitellogenesis research, addressed to clarifying the yolkless egg and the evolution of eutherian viviparity.

Purification and characterization of Mr 43,000 protein similar to Mr 25,000 protein, a substrate for protein Ser/Thr kinases, identified as a part of Xenopus laevis vitellogenin B1

Mr 25,000 protein (pp25), a substrate for protein Ser/Thr kinases, was recently shown to consist of a portion of the Xenopus laevis vitellogenin B1 protein. By Western blot analyses using antibodies against pp25, a minor protein band with Mr 43,000 (pp43) was detected in purified preparations of pp25. In this study, pp43 was highly purified through several column chromatography steps and its protein structure was analyzed. The amino acid sequence of the amino-terminal region of pp43 was the same as that of pp25. pp43 contained about two times more phosphates than pp25. These phosphates in pp43 were more resistant to acid phosphatase attack than those of pp25. pp43 was able to bind to pNiXa, a binding protein of pp25. Alpha-chymotryptic digestion generated a common fragment with molecular mass of 23,000 from both pp43 and pp25. These results suggest that pp43 may be a precursor of pp25 generated during processing of vitellogenin B1.

Mr 25 000 protein, a substrate for protein serine/threonine kinases, is identified as a part of Xenopus laevis vitellogenin B1

A phosphorylated protein with a molecular mass of 25 000 (pp25) previously purified from the cytosolic fraction of Xenopus laevis oocytes is an effective phosphate acceptor for casein kinases and protein kinase C. In this study, based on the partial amino acid sequence of pp25, a cDNA was isolated that encodes a new yolk precursor protein, Xenopus vitellogenin B1, which contained the sequence encoding pp25. Both mRNA and protein of vitellogenin B1 were expressed in all of the female organs examined. In agreement with a previous report, the amount of vitellogenin B1 protein in the liver increased after stimulation with estrogen. These results suggest that pp25 is a cytosolic non-crystallized yolk protein nutrient source, but it might also play a role in rapid development.

Vitellogenin-derived yolk proteins of white perch, Morone americana: purification, characterization, and vitellogenin-receptor binding

The objectives of this study were to 1) purify and characterize vitellogenin-derived yolk proteins of white perch (Morone americana), 2) develop a nonisotopic receptor binding assay for vitellogenin, and 3) identify the yolk protein domains of vitellogenin recognized by the ovarian vitellogenin receptor. Four yolk proteins derived from vitellogenin (YP1, YP2 monomer [YP2m] and dimer [YP2d], and YP3) were isolated from ovaries of vitellogenic perch by selective precipitation, ion exchange chromatography, and gel filtration. The apparent molecular masses of purified YP1, YP2m, and YP2d after gel filtration were 310 kDa, 17 kDa, and 27 kDa, respectively. YP3 appeared in SDS-PAGE as a approximately 20-kDa band plus some diffuse smaller bands that could be visualized by staining for phosphoprotein with Coomassie Brilliant Blue complexed with aluminum nitrate. Immunological and biochemical characteristics of YP1, YP2s, and YP3 identified them as white perch lipovitellin, beta'-components, and phosvitin, respectively. A novel receptor-binding assay for vitellogenin was developed based on digoxigenin (DIG)-labeled vitellogenin tracer binding to ovarian membrane proteins immobilized in 96-well plates. Lipovitellin from white perch and vitellogenin from perch and other teleosts effectively displaced specifically bound DIG-vitellogenin in the assay, but phosvitin and the beta'-component could not, demonstrating for the first time that the lipovitellin domain of teleost vitellogenin mediates its binding to the oocyte receptor. Lipovitellin was less effective than vitellogenin in this regard, suggesting that the remaining yolk protein domains of vitellogenin may interact with its lipovitellin domain to facilitate binding of vitellogenin to its receptor.