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

Survey for the presence of a vitronectin-like protein in micro- and macroalgae and cyanobacteria

Vitronectin (Vn) is a glycoprotein that serves a wide variety of roles in multicellular organisms. It was first identified in multicellular animals but has also been isolated from land plants and some algae, where it appears to serve as an extracellular adhesive molecule. In order to further elucidate presence and localization of a Vn-like protein and its potential role in algae, we surveyed different morphological regions of 24 species of macro- and microalgae and three species of cyanobacteria for the presence of a Vn-like protein. Vn-like proteins were not detected in any of the species of cyanobacteria, microalgae or Rhodophyta investigated. They were detected in several species of the Phaeophyceae and Chlorophyta where their localization was limited to the holdfast and rhizoids of these organisms, respectively. Detection of a Vn-like protein (between 0.0125 and 0.097 μg · μL^-1 protein extract) was therefore limited to locations associated with substrate attachment.

Effect of embryonic development on the chicken egg yolk plasma proteome after 12 days of incubation

To better appreciate the dynamics of yolk proteins during embryonic development, we analyzed the protein quantitative changes occurring in the yolk plasma at the day of lay and after 12 days of incubation, by comparing unfertilized and fertilized chicken eggs. Of the 127 identified proteins, 69 showed relative abundance differences among conditions. Alpha-fetoprotein and two uncharacterized proteins (F1NHB8 and F1NMM2) were identified for the first time in the egg. After 12 days of incubation, five proteins (vitronectin, α-fetoprotein, similar to thrombin, apolipoprotein B, and apovitellenin-1) showed a major increase in relative abundance, whereas 15 proteins showed a significant decrease in the yolks of fertilized eggs. In unfertilized/table eggs, we observed an accumulation of proteins likely to originate from other egg compartments during incubation. This study provides basic knowledge on the utilization of egg yolk proteins by the embryo and gives some insight into how storage can affect egg quality.

Purification of vitronectin

This unit describes the purification of extracellular vitronectin from plasma or serum by using heparin-affinity chromatography. First, the plasma is depleted of fibronectin plus other heparin- and Sepharose-binding proteins and treated with urea to activate the heparin-binding activity of vitronectin, which is subsequently bound to a heparin affinity column and eluted. The resulting vitronectin should be ∼ 98% pure.

Foxa (HNF3) up-regulates vitronectin expression during retinoic acid-induced differentiation in mouse neuroblastoma Neuro2a cells

Accumulation of vitronectin protein increased in the conditioned medium of mouse neuroblastoma Neuro2a cells during retinoic acid-induced differentiation. To study the regulatory mechanism of the increase in vitronectin expression during the differentiation, the activity of the -527/+95 vitronectin promoter was observed in Neuro2a cells with or without retinoic acid treatment. The result showed that the -527/+95 promoter activity increased 2.7-fold with retinoic acid, and despite deletion of regions from -527 to -49 and +54 to +95 base pairs (bp), the -48/+53 promoter preserved the retinoic acid response. We recently showed that the -48/+53 region has two transcription factor Foxa (HNF3)-binding sites (site A from -34 to -25 bp and site B from +15 to +26 bp), suggesting that Foxa may up-regulate the vitronectin expression. Therefore, we examined the change of Foxa expression in Neuro2a cells during the differentiation. The expression of Foxa1 protein was increased during the differentiation, but the expression of Foxa2 protein was not detected. In addition, overexpression of Foxa1 increased the amount of vitronectin protein in the conditioned medium of Foxa1-overexpressed Neuro2a cells, but overexpression of Foxa2 only weakly increased it. The site-A and -B double mutation of the -527/+95 promoter remarkably reduced the promoter activity induced by Foxa overexpression, indicating that Foxa-binding sites in the -527/+95 region are located only on sites A and B. The mutation of site A in the -48/+53 promoter did not affect the retinoic acid response, but the site-B mutation abolished the constitutive promoter activity and remarkably reduced the promoter activity with retinoic acid. These results demonstrate that Foxa up-regulates the vitronectin expression during the retinoic acid-induced differentiation in Neuro2a cells.

Vitronectin regulates Sonic hedgehog activity during cerebellum development through CREB phosphorylation

During development of the cerebellum, Sonic hedgehog (SHH) is expressed in migrating and settled Purkinje neurons and is directly responsible for proliferation of granule cell precursors in the external germinal layer. We have previously demonstrated that SHH interacts with vitronectin in the differentiation of spinal motor neurons. Here, we analysed whether similar interactions between SHH and extracellular matrix glycoproteins regulate subsequent steps of granule cell development. Laminins and their integrin receptor subunit alpha6 accumulate in the outer most external germinal layer where proliferation of granule cell precursors is maximal. Consistent with this expression pattern, laminin significantly increases SHH-induced proliferation in primary cultures of cerebellar granule cells. Vitronectin and its integrin receptor subunits alpha(v) are expressed in the inner part of the external germinal layer where granule cell precursors exit the cell cycle and commence differentiation. In cultures, vitronectin is able to overcome SHH-induced proliferation, thus allowing granule cell differentiation. Our studies indicate that the pathway in granule cell precursors responsible for the conversion of a proliferative SHH-mediated response to a differentiation signal depends on CREB. Vitronectin stimulates phosphorylation of cyclic-AMP responsive element-binding protein (CREB), and over-expression of CREB is sufficient to induce granule cell differentiation in the presence of SHH. Taken together, these data suggest that granule neuron differentiation is regulated by the vitronectin-induced phosphorylation of CREB, a critical event that terminates SHH-mediated proliferation and permits the differentiation program to proceed in these cells.

Sonic hedgehog synergizes with the extracellular matrix protein vitronectin to induce spinal motor neuron differentiation

Patterning of the vertebrate neural tube depends on intercellular signals emanating from sources such as the notochord and the floor plate. The secreted protein Sonic hedgehog and the extracellular matrix protein Vitronectin are both expressed in these signalling centres and have both been implicated in the generation of ventral neurons. The proteolytic processing of Sonic hedgehog is fundamental for its signalling properties. This processing generates two secreted peptides with all the inducing activity of Shh residing in the highly conserved 19 kDa amino-terminal peptide (N-Shh). Here we show that Vitronectin is also proteolitically processed in the embryonic chick notochord, floor plate and ventral neural tube and that this processing is spatiotemporally correlated with the generation of motor neurons. The processing of Vitronectin produces two fragments of 54 kDa and 45 kDa, as previously described for Vitronectin isolated from chick yolk. The 45 kDa fragment lacks the heparin-binding domain and the integrin-binding domain, RGD, present in the non-processed Vitronectin glycoprotein. Here we show that N-Shh binds to the three forms of Vitronectin (70, 54 and 45 kDa) isolated from embryonic tissue, although is preferentially associated with the 45 kDa form. Furthermore, in cultures of dissociated neuroepithelial cells, the combined addition of N-Shh and Vitronectin significantly increases the extent of motor neuron differentiation, as compared to the low or absent inducing capabilities of either N-Shh or Vitronectin alone. Thus, we conclude that the differentiation of motor neurons is enhanced by the synergistic action of N-Shh and Vitronectin, and that Vitronectin may be necessary for the proper presentation of the morphogen N-Shh to one of its target cells, the differentiating motor neurons.

Sperm surface heparin/heparan sulfate is responsible for sperm binding to the uterine envelope in the newt, Cynops pyrrhogaster

The sperm-binding properties of egg envelopes are investigated in the newt, Cynops pyrrhogaster. Sperm binding was only seen on the uterine envelope when acrosome-reacted sperm were inseminated. No acrosome-intact sperm bound to the envelopes. By scanning electron microscopic observation, acrosome-reacted sperm were revealed to bind to a seat-like structure present on the surface of the uterine envelope. Sperm binding to the uterine envelope was inhibited by treatment of eggs with heparin or heparan sulfate, or treatment of acrosome-reacted sperm with heparinase prior to insemination. A molecule with a molecular mass of 75 kDa was purified from the uterine envelope by affinity chromatography with heparin-Sepharose. These results indicated that sperm binding was mediated by heparin-like molecules expressed on the surface of acrosome-reacted sperm and the 75 kDa molecule was present as a constituent of uterine envelopes.

Effect of electron beam irradiation on physical, physiochemical, and functional properties of liquid egg yolk during frozen storage

Raw yolk of 1-d-old eggs was either subjected to linear electron beam irradiation at approximately 2.5 kGy dosage or not processed. Both irradiated and nonprocessed egg yolk samples were stored at -15 C after irradiation. Testing was conducted on 0, 1, 7, 15, 30, and 60 d of storage. Development of storage modulus (G') was delayed in irradiated samples after 7 d, which suggests that less structure was developed in irradiated egg yolk than in nonprocessed egg yolk during storage. Irradiated samples retained more soluble protein within the first 7 d and showed slightly improved emulsion capacity over that from nonprocessed samples. However, irradiated egg yolk was less bright than nonprocessed samples. No differences were observed in SDS-PAGE patterns of soluble proteins and delipidized low density lipoprotein (LDL). The LDL isolated from irradiated liquid egg yolk showed no difference in N-terminal amino acids compared to that of nonprocessed egg yolk, indicating no detectable cleavage of LDL. However, the denaturation temperature of irradiated samples at Day 0 shifted about 1 C lower than that of the nonprocessed sample. Results indicated that electron beam irradiation did not cause significant physical, chemical or functional changes of egg yolk, or cleavage of egg yolk protein. Therefore, electron beam irradiation could serve as a preservation method for liquid egg yolk.

Separation methods for glycoprotein analysis and preparation

Several chromatographic methods have been developed for the isolation and characterization of glycoproteins. In these methods, affinity chromatography, a single-step method, or combined use with general chromatographic methods have now become essential for the purification of many biologically important glycoproteins, including alpha1-acid glycoprotein, immunoglobulins, ceruloplasmin and erythropoietin. On the other hand, almost all glycoproteins exhibit polymorphism associated with their glycan moieties. This feature is wide-spread and has been observed in natural as well as in recombinant DNA glycoproteins. Recently, several sophisticated techniques--such as electromigration method (high-performance capillary electrophoresis) and chromatographic methods (two-dimensional polyacrylamide gel electrophoresis, high-pH anion-exchange chromatography with pulsed-amperometric detection)--have been introduced for qualitative or quantitative estimation of the microheterogeneity of glycoproteins. For gaining further insight into the structure-function relations for microheterogeneity, preparative chromatographic techniques that can yield sufficient quantities of glycoprotein variants must be developed.

Nectinepsin: a new extracellular matrix protein of the pexin family. Characterization of a novel cDNA encoding a protein with an RGD cell binding motif

We report the isolation and characterization of a novel cDNA from quail neuroretina encoding a putative protein named nectinepsin. The nectinepsin cDNA identifies a major 2.2-kilobase mRNA that is detected from ED 5 in neuroretina and is increasingly abundant during embryonic development. A nectinepsin mRNA is also found in quail liver, brain, and intestine and in mouse retina. The deduced nectinepsin amino acid sequence contains the RGD cell binding motif of integrin ligands. Furthermore, nectinepsin shares substantial homologies with vitronectin and structural protein similarities with most of the matricial metalloproteases. However, the presence of a specific sequence and the lack of heparin and collagen binding domains of the vitronectin indicate that nectinepsin is a new extracellular matrix protein. Furthermore, genomic Southern blot studies suggest that nectinepsin and vitronectin are encoded by different genes. Western blot analysis with an anti-human vitronectin antiserum revealed, in addition to the 65- and 70-kDa vitronectin bands, an immunoreactive protein of about 54 kDa in all tissues containing nectinepsin mRNA. It seems likely that the form of vitronectin found in chick egg yolk plasma by Nagano et al. ((1992) J. Biol. Chem. 267, 24863-24870) is the protein that corresponds to the nectinepsin cDNA. This new protein could be an important molecule involved in the early steps of the development.

Specific roles of the alpha V beta 1, alpha V beta 3 and alpha V beta 5 integrins in avian neural crest cell adhesion and migration on vitronectin

To identify potentially important extracellular matrix adhesive molecules in neural crest cell migration, the possible role of vitronectin and its corresponding integrin receptors was examined in the adhesion and migration of avian neural crest cells in vitro. Adhesion and migration on vitronectin were comparable to those found on fibronectin and could be almost entirely abolished by antibodies against vitronectin and by RGD peptides. Immunoprecipitation and immunocytochemistry analyses revealed that neural crest cells expressed primarily the alpha V beta 1, alpha V beta 3 and alpha V beta 5 integrins as possible vitronectin receptors. Inhibition assays of cellular adhesion and migration with function-perturbing antibodies demonstrated that adhesion of neural crest cells to vitronectin was mediated essentially by one or more of the different alpha V integrins, with a possible preeminence of alpha V beta 1, whereas cell migration involved mostly the alpha V beta 3 and alpha V beta 5 integrins. Immunofluorescence labeling of cultured motile neural crest cells revealed that the alpha V integrins are differentially distributed on the cell surface. The beta 1 and alpha V subunits were both diffuse on the surface of cells and in focal adhesion sites in association with vinculin, talin and alpha-actinin, whereas the alpha V beta 3 and alpha V beta 5 integrins were essentially diffuse on the cell surface. Finally, vitronectin could be detected by immunoblotting and immunohistochemistry in the early embryo during the ontogeny of the neural crest. It was in particular closely associated with the surface of migrating neural crest cells. In conclusion, our study indicates that neural crest cells can adhere to and migrate on vitronectin in vitro by an RGD-dependent mechanism involving at least the alpha V beta 1, alpha V beta 3 and alpha V beta 5 integrins and that these integrins may have specific roles in the control of cell adhesion and migration.