Solute carrier family 3 member 2 (Slc3a2) controls yolk syncytial layer (YSL) formation by regulating microtubule networks in the zebrafish embryo.

The yolk syncytial layer (YSL) in the zebrafish embryo is a multinucleated syncytium essential for embryo development, but the molecular mechanisms underlying YSL formation remain largely unknown. Here we show that zebrafish solute carrier family 3 member 2 (Slc3a2) is expressed specifically in the YSL and that slc3a2 knockdown causes severe YSL defects including clustering of the yolk syncytial nuclei and enhanced cell fusion, accompanied by disruption of microtubule networks. Expression of a constitutively active RhoA mimics the YSL phenotypes caused by slc3a2 knockdown, whereas attenuation of RhoA or ROCK activity rescues the slc3a2-knockdown phenotypes. Furthermore, slc3a2 knockdown significantly reduces tyrosine phosphorylation of c-Src, and overexpression of a constitutively active Src restores the slc3a2-knockdown phenotypes. Our data demonstrate a signaling pathway regulating YSL formation in which Slc3a2 inhibits the RhoA/ROCK pathway via phosphorylation of c-Src to modulate YSL microtubule dynamics. This work illuminates processes at a very early stage of zebrafish embryogenesis and more generally informs the mechanism of cell dynamics during syncytium formation.

Transcriptomic profiling of proteases and antiproteases in the liver of sexually mature hens in relation to vitellogenesis.

BACKGROUND: Most egg yolk precursors are synthesized by the liver, secreted into the blood and transferred into oocytes, to provide nutrients and bioactive molecules for the avian embryo. Three hundred and sixteen distinct proteins have been identified in egg yolk. These include 37 proteases and antiproteases, which are likely to play a role in the formation of the yolk (vitellogenesis), as regulators of protein metabolism. We used a transcriptomic approach to define the protease and antiprotease genes specifically expressed in the hen liver in relation to vitellogenesis by comparing sexually mature and pre-laying chickens showing different steroid milieu. RESULTS: Using a 20 K chicken oligoarray, a total of 582 genes were shown to be over-expressed in the liver of sexually mature hens (1.2 to 67 fold-differences). Eight of the top ten over-expressed genes are known components of the egg yolk or perivitelline membrane. This list of 582 genes contains 12 proteases and 3 antiproteases. We found that "uncharacterized protein LOC419301/similar to porin" (GeneID:419301), an antiprotease and "cathepsin E-A-like/similar to nothepsin" (GeneID:417848), a protease, were the only over-expressed candidates (21-fold and 35-fold difference, respectively) that are present in the egg yolk. Additionally, we showed the 4-fold over-expression of "ovochymase-2/similar to oviductin" (GeneID:769290), a vitelline membrane-specific protease. CONCLUSIONS: Our approach revealed that three proteases and antiproteases are likely to participate in the formation of the yolk. The role of the other 12 proteases and antiproteases which are over-expressed in our model remains unclear. At least 1/3 of proteases and antiproteases identified in egg yolk and vitelline membrane proteomes are expressed similarly in the liver regardless of the maturity of hens, and have been initially identified as regulators of haemostasis and inflammatory events. The lack of effect of sex steroids on these genes expressed in the liver but the products of which are found in the yolk suggests that these may be passively incorporated into the yolk rather than actively produced for that purpose. These results raise the question of the biological significance of egg yolk proteases and antiproteases, and more generally of all minor proteins that have been identified in egg yolk.

Influence of canthaxanthin on broiler breeder reproduction, chick quality, and performance.

To investigate the effect of canthaxanthin supplied via a maternal route on the production of both breeder hens and chickens, 270 Chinese Three-Yellow breeder hens were randomly divided into 2 groups consisting of 135 birds each (5 replicates of 27) for study. The breeder hens were fed either a basal diet or the basal diet supplemented with 6 mg of canthaxanthin/kg for 24 wk. At the end of the 24-wk breeder experiment, all hatching eggs laid in 5 consecutive days of each group were collected and incubated. For each breeder group, 100 newly hatched chicks (5 replicates of 20) were reared under environmentally controlled conditions for 21 d. Canthaxanthin supplementation resulted in the following outcomes: an enhancement of the serum total antioxidant capacity (TAC) of breeder hens (P = 0.029), a significant increase in the yolk colorimetric score of Roche Yolk Color Fan (RYCF; P < 0.001), and a significant improvement of the antioxidant status of the egg yolk (P < 0.05). The chicks that hatched from eggs laid by breeder hens fed the canthaxanthin supplementation diet demonstrated a higher pigmentation colorimetric score of RYCF for their shank skin (P < 0.05), and the antioxidant capacity of the newly hatched chicks was significantly increased (P < 0.05). Both of these positive effects on shank skin pigmentation colorimetric score of RYCF and antioxidant capacity were observed for at least 7 d posthatching, and the chicks that hatched from canthaxanthin-enriched eggs showed a lower mortality (0 vs. 4%) during the first 21 d posthatching. These findings support the hypothesis that canthaxanthin supplementation of the maternal diet enhances the protective capacity of tissues against oxidative stress in vivo, which might be beneficial for poultry producers.

Inorganic polyphosphate inhibits an aspartic protease-like activity in the eggs of Rhodnius prolixus (Stahl) and impairs yolk mobilization in vitro.

Inorganic polyphosphate (poly P) is a polymer of phosphate residues that has been shown to act as modulator of some vertebrate cathepsins. In the egg yolk granules of Rhodnius prolixus, a cathepsin D is the main protease involved in yolk mobilization and is dependent on an activation by acid phosphatases. In this study, we showed a possible role of poly P stored inside yolk granules on the inhibition of cathepsin D and arrest of yolk mobilization during early embryogenesis of these insects. Enzymatic assays detected poly P stores inside the eggs of R. prolixus. We observed that micromolar poly P concentrations inhibited cathepsin D proteolytic activity using both synthetic peptides and homogenates of egg yolk as substrates. Poly P was a substrate for Rhodnius acid phosphatase and also a strong competitive inhibitor of a pNPPase activity. Fusion events have been suggested as important steps towards acid phosphatase transport to yolk granules. We observed that poly P levels in those compartments were reduced after in vitro fusion assays and that the remaining poly P did not have the same cathepsin D inhibition activity after fusion. Our results are consistent with the hypothesis that poly P is a cathepsin D inhibitor and a substrate for acid phosphatase inside yolk granules. It is possible that, once activated, acid phosphatase might degrade poly P, allowing cathepsin D to initiate yolk proteolysis. We, therefore, suggest that degradation of poly P might represent a new step toward yolk mobilization during embryogenesis of R. prolixus.

Effects of dietary supplementation of natural astaxanthin from Haematococcus pluvialis on antioxidant capacity, lipid metabolism, and accumulation in the egg yolk of laying hens.

The present study evaluated the effects of natural astaxanthin (ASTA) from Haematococcus pluvialis on the antioxidant capacity, lipid metabolism, and ASTA accumulation in the egg yolk of laying hens. Hy-Line Brown layers (n = 288, 50 wk old) were randomly assigned to 1 of 4 dietary treatment groups. Each group had 6 replicates of 12 hens each. All birds were given a corn-soybean meal-based diet containing 0, 25, 50, or 100 mg/kg ASTA for 6 wk. The results showed that the total antioxidant capacity, superoxide dismutase level, and glutathione peroxidase level in the plasma, livers, and egg yolks were significantly increased in the ASTA groups compared with those of the control group (P < 0.05), whereas the content of malondialdehyde linearly decreased (P < 0.05). The plasma levels of high-density and very-low-density lipoprotein cholesterol in the ASTA groups were significantly higher than those in the control group (P < 0.05). In addition, ASTA supplementation decreased low-density lipoprotein cholesterol and triglyceride plasma levels (P < 0.05). However, there were no significant differences in the other lipid metabolism parameters among the ASTA-supplemented groups relative to the control group except for an increase in high-density lipoprotein cholesterol in the liver. Compared with the control, dietary ASTA supplementation significantly increased the enrichment of ASTA in egg yolks at the end of week 2, 4, and 6 (P < 0.05). The mRNA expression of scavenger receptor class B type 1 (SCARB1) and very-low-density lipoprotein receptor (VLDLR) in the ASTA groups was markedly higher (P < 0.05) than that in the control group in the liver and ovaries, respectively. In conclusion, these results suggest that dietary ASTA enhances the antioxidant capacity and regulates lipid metabolism in laying hens. ASTA enrichment in egg yolks may be closely related to the upregulation of SCARB1 and VLDLR gene expression.

Phylogenetic relationships and gene expression pattern of three different cathepsin L (Ctsl) isoforms in zebrafish: Ctsla is the putative yolk processing enzyme.

Certain cysteine proteases, such as cathepsin L (Ctsl), have been involved in yolk processing mechanisms in oocytes and embryos of lower vertebrates. In zebrafish (Danio rerio), three different ctsl genes, ctsla, ctslb and ctslc, have been found in the genome, but their pattern of expression, as well as information on which the encoded enzymes are potentially involved in yolk absorption during embryogenesis, is unknown. Here, phylogenetic and gene structure analysis revealed that zebrafish ctsla and ctslb genes are similar, showing a highly conserved structure in comparison with human ctsl, while ctslc presents different exon organization together with an earlier evolution. Thus, ctslc appears to be evolved from a common ancestral ctsl-like gene, possibly through an early duplication event, whereas ctsla and ctslb may be originated from a second duplication mechanism. Zebrafish ctsla, ctslb and ctslc also showed different patterns of mRNA expression during embryogenesis and in adult tissues. While Ctsla transcripts were accumulated in embryos throughout development and in the adult ovary, those encoding Ctslb were detected only in embryos around the time of hatching as previously reported, and those for Ctslc appeared only in larvae and in some adult tissues, but not in the ovary. In zebrafish and killifish (Fundulus heteroclitus) embryos, Ctsla mRNA was first detected in blastomers, and later in development it was localized in cells of the yolk syncytial layer, an embryonic structure involved in yolk absorption. These data therefore suggested that Ctsla is most likely the putative protease involved in yolk processing in fish embryos, while Ctslc seems not to be required during early embryogenesis in zebrafish.

Arsanilic acid modified superparamagnetic iron oxide nanoparticles for Purification of alkaline phosphatase from hen's egg yolk.

Recent studies of magnetic carrier technology have focused on its applications in separation and purification technologies, due to easy separation of the target from the reaction medium by applying an external magnetic field. In the present study, Fe3O4 superparamagnetic nanoparticles were prepared to utilize a chemical co-precipitation method, then the surfaces of the nanoparticles were modified with arsanilic acid derivatives which were used as the specific nanocarriers for the affinity purification of alkaline phosphatase from the hen's egg yolk. The six different types of magnetic nanocarriers with varied lengths of the linkers were obtained. All samples were characterized step by step and validated using FTIR, SEM, EDX, VSM and XRD analysis methods As the results were shown, the use of inflexible tags with long linkers on the surface of the nanocarrier could lead to better results for separation of alkaline phosphatase from the hen's egg yolk with 76.2% recovery and 1361.7-fold purification. The molecular weight of the purified alkaline phosphatase was estimated to be 68kDa by SDS-PAGE. The results of this study showed that the novel magnetic nanocarriers were capable of purifying alkaline phosphatase in a practically time and cost effective way.

Expression of ornithine-urea cycle enzymes in early life stages of air-breathing walking catfish Clarias batrachus and induction of ureogenesis under hyper-ammonia stress.

The air-breathing walking catfish Clarias batrachus is a potential ureogenic teleost with having a full complement of ornithine-urea cycle (OUC) enzymes expressed in various tissues. The present study was aimed at determining the pattern of nitrogenous waste excretion in the form of ammonia-N and urea-N along with the changes of tissue ammonia and urea levels, and the expression of OUC enzymes and glutamine synthetase (GSase) in early life stages of this teleost, and further, to study the possible induction of ureogenesis in 15-day old fry under hyper-ammonia stress. The ammonia and urea excretion was visible within 12 h post-fertilization (hpf), which increased several-fold until the yolk was completely absorbed by the embryo. Although all the early developing stages were primarily ammoniotelic, they also excreted significant amount of nitrogen (N) in the form of urea-N (about 35-40% of total N). Tissue levels of ammonia and urea also increased along with subsequent developmental stages at least until the yolk absorption stage. All the OUC enzymes and GSase were expressed within 4-12 hpf showing an increasing trend of activity for all the enzymes until 350 hpf. There was a significant increase of activity of GSase, carbamyl phosphate synthetase III (CPSase III) and argininosuccinate lyase enzymes (ASL), accompanied with significant increase of enzyme protein concentration of at least two enzymes (GSase and CPSase III) in the 15-day old fry following exposure to 10 mM NH4Cl as compared to respective controls kept in water over a period of 72 h. Thus, it appears that the OUC enzymes are expressed in early life stages of walking catfish like other teleosts, but at relatively high levels and remain expressed all through the life stages with a potential of stimulation of ureogenesis throughout the life cycle as a sort of physiological adaptation to survive and breed successfully under hyper-ammonia and various other environmental-related stresses.

The novel medaka transglutaminase gene is expressed in developing yolk veins.

The vascular system is highly conserved in all vertebrates in the aspects of anatomy as well as in the genetic mechanism governing it. The embryo of the medaka, Oryzias latipes is small and transparent, providing many advantages for the experimental analysis of the vertebrate vascular system. We isolated a novel medaka transglutaminase gene, termed embryonic transglutaminase, and found that it showed the highest homology to the coagulation factor XIII A subunit of mammals. This gene is expressed in the anterior lateral plate mesoderm, and then expressed specifically in yolk veins consisting two ducts of Cuvier and the vitellocaudal vein. Our data is the first finding that a coagulation factor XIII-like gene is expressed in the early vascular development of vertebrates.

Molecular cloning and functional characterization of chicken cathepsin D, a key enzyme for yolk formation.

Upon receptor-mediated endocytosis of very-low-density lipoprotein (VLDL) and vitellogenin into growing chicken oocytes, the protein moieties of these lipoproteins are proteolytically cleaved. Unlike the complete lysosomal degradation in somatic cells, enzymatic ligand breakdown in oocytes generates a characteristic set of polypeptides, which enter yolk storage compartments for subsequent utilization by the embryo. Here, we demonstrate directly that the catalyst for the intraoocytic processing of both apolipoprotein B and vitellogenin is cathepsin D. The enzyme was purified from oocytic yolk, preovulatory follicle homogenates, and liver by affinity chromatography. When plasma VLDL and vitellogenin were incubated with the purified enzyme, fragments indistinguishable from those found in yolk were generated from both precursors under identical, mildly acidic conditions. Amino-terminal sequencing of the pure enzyme demonstrated 88% identity with mammalian cathepsin Ds over 34 residues. On the basis of this information, a full-length clone specifying chicken preprocathepsin D was isolated from a chicken follicle cDNA library by screening with a human cathepsin D probe. Whereas previous studies have demonstrated that the receptors for lipoproteins in somatic cells and oocytes, respectively, of the chicken are the products of different genes, Southern and Northern blot hybridization experiments showed that the enzymes expressed in oocytes and liver are the product of a single gene, giving rise to a 3.3-kb transcript. The primary structure of the 335-residue mature protein suggests a high degree of conservation of known crucial features of aspartyl proteases; however, the absence of the so-called processing region and of an aromatic residue in a region thought to partake in catalysis raise questions with possible evolutionary implications.

Isolation and characterization of cDNA encoding chicken egg yolk aminopeptidase Ey.

Aminopeptidase Ey (EC 3.4.11.20) from chicken (Gallus gallus domesticus) egg yolk is a homodimeric exopeptidase with a broad specificity for N-terminal amino acid residues at P1 position of the substrate. Aminopeptidase Ey is a 300-k metalloexopeptidase, containing 1.0 g atom of zinc per mole of a subunit with a relative molecular mass of 150 k. A full-length cDNA was cloned from chicken (female) liver cDNA library. Analysis of the 3196-base pairs (bp) nucleotide sequence of the cDNA revealed a single open reading frame coding for 967 amino acid residues. The coding region of aminopeptidase Ey gene, apdE, occupies 2901 bp of the cDNA. The predicted amino acid sequence of the enzyme is 66, 65, 64 and 63% identical with those of aminopeptidases N (EC 3.4.11.2) from human, pig, rabbit and rat, respectively. Aminopeptidase Ey contains the metallo-binding sequence motif, His-Glu-Xaa-His, found in zinc metallopeptidases. Zinc binding sites, His-386, His-390 and Glu-409, and catalytic site, Glu-387, were conserved in the homologous aminopeptidases N.

Amylase activity increases in the yolk of fertilized eggs during incubation in chickens.

Amylase activity was detected in the egg of chickens. In unfertilized eggs, no change of amylase activity was observed during 22 days incubation, however, in fertilized eggs, amylase activity increased markedly during embryonic development. The increase depended upon an increase of amylase in the yolk, not in the albumen. Isoamylases in the yolk were electrophoretically identical to those in the pancreas of the embryo or the hen.

Cytochrome c interaction with neutral lipid membranes: influence of lipid packing and protein charges.

The interaction of cytochrome c (cyt c) with fluid/gel neutral supported lipid membranes was investigated by time-lapse atomic force microscopy (AFM). AFM revealed the random formation of depressed areas in fluid membranes promoted by cyt c. These depressions corresponded to the desorption of fluid bilayer patches induced by cyt c. By contrast, the gel domains were never desorbed but they were progressively thickened in the presence of the protein. These results suggest that cyt c molecules might intercalate between the mica and the lipid bilayer. Although the interaction of cyt c with the mica surface is likely to be an artifact, this work is the first direct observation of cyt c ability to cross membranes. Furthermore, our data show that the net positive charge of cyt c molecules plays a pivotal role but it is not the sole factor responsible for cyt c insertion in the membrane.

The chicken egg yolk plasma and granule proteomes.

Using 1-D SDS-PAGE, LC-MS/MS, and MS(3), we identified 119 proteins from chicken egg yolk, 86 of which were not identified in yolk previously. Proteins were roughly quantitated by calculating their exponentially modified protein abundance index (emPAI) to classify them as major or minor yolk components, and to estimate their distribution between yolk plasma and yolk granular fraction. The proteins with highest abundance were serum albumin, the vitellogenin cleavage products, apovitellenins, IgY, ovalbumin, and 12 kDa serum protein with cross-reactivity to beta2-microglobulin. In addition yolk contained many other serum and egg white proteins, the proteases nothepsin and thrombin, numerous protease inhibitors, and antioxidative enzymes, such as superoxide dismutase and glutathione peroxidase. Among the moderately abundant proteins were two alpha2-macroglobulin-like proteins different from egg white alpha2-macroglobulin, and the major biotin-binding protein of yolk. An unexpected identification was that of the eggshell matrix protein ovocleidin-116, which was previously thought to be eggshell-specific. The list of chicken egg yolk proteins provided in this report is by far the most comprehensive at present and may serve as a starting point for the characterization of less well-known yolk proteins.

Identification and characterization of the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) in hen egg.

Using zymography and mass spectrometry, we identified for the first time the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) as a complex with TIMP-2 (tissue inhibitor of metalloproteinases) in egg white and yolk. Real-time polymerase chain reaction confirmed that MMP-2 and its inhibitors TIMP-2 and TIMP-3 were expressed all along the oviduct and in the liver of laying hens. We also demonstrated that the processing of pro-MMP-2 into mature MMP-2 by serine proteases does not occur in vivo, although purified pro-MMP-2 undergoes proteolytic maturation by these proteases in vitro. Moreover, the relative pro-MMP-2 activity assessed by gelatin zymography was shown to decrease in egg white during the storage of unfertilized or fertilized eggs. However, the mature form of 62 kDa MMP-2 could not be detected. The fact that MMP-2 is found as a proform in fresh eggs suggests that the activity of this metalloprotease is regulated under specific conditions during embryonic development.

Utility of a fluorescent vitamin E analogue as a probe for tocopherol transfer protein activity.

The tocopherol transfer protein (TTP) is a member of the CRAL-TRIO family of lipid binding proteins that facilitates vitamin E transfer between membrane vesicles in vitro. In cultured hepatocytes, TTP enhances the secretion of tocopherol to the media; presumably, tocopherol transfer is at the basis of this biological activity. The mechanism underlying ligand transfer by TTP is presently unknown, and available tools for monitoring this activity suffer from complicated assay procedure and poor sensitivity. We report the characterization of a fluorescent vitamin E analogue, (R)-2,5,7,8-tetramethylchroman-2-[9-(7-nitrobenz[1,2,5]oxadiazol-4-ylamino)nonyl]chroman-6-ol (NBD-TOH), as a sensitive and convenient probe for the ligand binding and transfer activities of TTP. Upon binding to TTP, NBD-TOH fluorescence is blue shifted, and its intensity is greatly enhanced. We used these properties to accurately determine the affinity of NBD-TOH to TTP. The analogue binds to TTP reversibly and with high affinity (K(d) = 8.5 +/- 6 nM). We determined the affinity of NBD-TOH to a TTP protein in which lysine 59 is replaced with a tryptophan. When occurring in humans, this heritable mutation causes the ataxia with vitamin E deficiency (AVED) disorder. We find that the affinity of NBD-TOH to this mutant TTP is greatly diminished (K(d) = 71 +/- 19 nM). NBD-TOH functioned as a sensitive fluorophore in fluorescent resonance energy transfer (FRET) experiments. Using the fluorescent lipids TRITC-DHPE or Marina Blue-DHPE as a donor or an acceptor for NBD-TOH fluorescence, we obtained high-resolution kinetic data for tocopherol movement out of lipid bilayers, a key step in the TTP-facilitated ligand transfer reaction.

Expression of four glutamine synthetase genes in the early stages of development of rainbow trout (Oncorhynchus mykiss) in relationship to nitrogen excretion.

The incorporation of ammonia into glutamine, catalyzed by glutamine synthetase, is thought to be important in the detoxification of ammonia in animals. During early fish development, ammonia is continuously formed as yolk proteins and amino acids are catabolized. We followed the changes in ammonia and urea-nitrogen content, ammonia and urea-nitrogen excretion, glutamine synthetase activity, and mRNA expression of four genes coding for glutamine synthetase (Onmy-GS01-GS04) over 3-80 days post fertilization and in adult liver and skeletal muscle of the rainbow trout (Oncorhynchus mykiss). Both ammonia and urea-nitrogen accumulate before hatching, although the rate of ammonia excretion is considerably higher relative to urea-nitrogen excretion. All four genes were expressed during early development, but only Onmy-GS01 and -GS02 were expressed at appreciable levels in adult liver, and expression was very low in muscle tissue. The high level of expression of Onmy-GS01 and -GS03 prior to hatching corresponded to a linear increase in glutamine synthetase activity. We propose that the induction of glutamine synthetase genes early in development and the subsequent formation of the active protein are preparatory for the increased capacity of the embryo to convert the toxic nitrogen end product, ammonia, into glutamine, which may then be utilized in the ornithine-urea cycle or other pathways.

Yolk granules are the major compartment for bullfrog (Rana catesbeiana) oocyte-specific ribonuclease.

Rana catesbeiana ribonuclease (RC-RNase) is a pyrimidine guanine sequence-specific ribonuclease found only in R. catesbeiana (bullfrog) oocytes, not in other organs. An immunohistochemical assay showed that RC-RNase was present in the regular yolk granules, but not in forming yolk granules, yolk platelets, pigment granules, mitochondria clouds or the nucleus. The RC-RNase was restricted to the lateral amorphous area of the yolk granules, and was absent from the central area that has a vitellogenin crystal lattice. The RC-RNase was extracted from yolk granules by 0.5 M NaCl and purified by dialysis and affinity chromatography. Most of the RC-RNase (94%) was found in the yolk granules, the rest RC-RNase (6%) was found in the cytosol in the form of free RNase and latent RNase. The RC-RNase extracted from yolk granules was further analyzed by immunoprecipitation and RNase activity assay on an SDS/polyacrylamide gel. Our results suggest that the RC-RNase activity is regulated by both compartmentation and inhibitor binding.

The embryo pancreas is a source of increased yolk amylase in the fertilized eggs of domestic fowls.

The amylases were studied in the yolk of fertilized eggs and in the pancreases of the embryos of domestic fowls. The amylase activity in the yolk increased markedly from 13 days of incubation until hatching, but the activity decreased when the embryos were taken out of the eggs. The isoamylases in the yolk and in the pancreas of the embryo were identical electrophoretically. The amylase occurs mainly in the pancreas of the embryo. We think that the increase in amylase activity in the yolk of fertilized eggs during incubation depends upon the accumulation of pancreatic amylase synthesized by the developing embryo in the egg.