Expression of vigilin in chicken cartilage and bone

Investigation of effect of 17α-ethinylestradiol on vigilin expression using an isolated recombinant antibody

Vigilin, a highly conserved protein from yeast to mammals, is a multifunctional protein in eukaryotic organisms. One biological function of vigilin is to stabilize the expression level of vitellogenin (VTG). This study aimed to develop vigilin as a new estrogen-inducible biomarker that correlates with the widely applied estrogen-inducible biomarker VTG and expand the ability to detect it in various species. Here, a recombinant monoclonal antibody with high specificity against the conserved C-terminal region of vigilin from zebrafish (Danio rerio) was successfully isolated from a phage display antibody library and found to recognize vigilin proteins from multiple vertebrate species. The effect of 17α-ethinylestradiol (EE2) on vigilin expression in the liver of zebrafish and juvenile crucian carp (Carassius auratus) was investigated. Although vigilin mRNA was expressed in all tissues analyzed from male zebrafish, vigilin protein was detected exclusively in the testis of male zebrafish, as well as the liver of female zebrafish and juvenile crucian carp at a lower level without exposure to EE2. Significant induction of vigilin mRNA by exposure to EE2 was observed in the liver and testis of male zebrafish, even at a low dose of 6.25 ng/L (21.09 pmol/L). In Hela cells, the expression of vigilin coincided with high protein synthesis activity but not dose-dependently by EE2 exposure. Therefore, the recombinant antibody may be used as a detection tool to screen for mammalian cell lines or organs with estrogen-inducible expression of vigilin.

Labeling and confocal imaging of neurons in thick invertebrate tissue samples

Neuroscience researchers have long sought methods to describe the neural connectivity of the circuits responsible for specific behaviors. One major obstacle is scale: Neural spines can be <1 µm in diameter, but axons can range from millimeters to centimeters (or larger) in length, making tissue imaging and neuron reconstruction a challenging task. New tissue-clearing agents and long-working-distance objectives offer improved imaging conditions, and here we present a complete protocol for invertebrate tissue that uses these advances. In this protocol, tissue-processing steps previously published in separate articles are combined with recent advances in confocal imaging to visualize invertebrate tissue samples that are >500 µm thick and contain dye-filled neurons. The steps describe dye filling, fixing, antibody labeling, clearing, whole tissue mounting, and confocal imaging with matched refractive indexes. Thus, manual sectioning or "flipping" the tissue to image the whole volume is not required. With matched refractive indexes, loss of resolution and signal is avoided. Tissue volumes are imaged in one stack and nonlinear deformations caused by tissue flipping are prevented. We apply the protocol to whole dragonfly thoracic ganglia (2 × 1 × 0.6 mm) and cephalopod skin samples (20 × 2 × 0.6 mm) with minimal tissue deformation. The resulting images will be used to develop a three-dimensional connectivity atlas of dragonfly ganglia and cephalopod skin innervation. This protocol can be applied to other invertebrate species, and has the advantage that it avoids problems with antigen specificity.

Proteomic analysis of mineralising osteoblasts identifies novel genes related to bone matrix mineralisation

Bone matrix mineralisation plays a critical role in the determination of the overall biomechanical competence of bone. However, the molecular mechanisms of bone matrix mineralisation have not been fully elucidated. We used a proteomic approach to identify proteins and genes that may play a role in osteoblast matrix mineralisation. Proteomic differential display revealed a protein band that appeared only in mineralising mouse 7F2 osteoblasts. In-gel protein digestion and mass spectrometry proteomic analysis of this protein band identified 16 proteins. Furthermore, their corresponding transcripts were upregulated. This identification of proteins that may be associated with bone matrix mineralisation presents important new information toward a better understanding of the precise mechanisms of this process.

Vigilin is co-localized with 80S ribosomes and binds to the ribosomal complex through its C-terminal domain

The biological relevance of vigilin a ubiquitous multi (KH)-domain protein is still barely understood. Investigations over the last years, however, provided evidence for a possible involvement of vigilin in the nucleo-cytoplasmic transport of tRNA and in the subsequent association of tRNA with ribosomes. We therefore investigated the potential association of vigilin with 80S ribosomes. Immunostaining, gel filtration, westernblot analysis of polyribosomes and high salt treatment of 80S ribosomes isolated from fresh human placenta were applied to analyze the possible association of vigilin with ribosomes. Overlay assays were performed to examine whether vigilin is capable of binding to ribosomal proteins. Immunostaining of HEp-2 cells, gel filtration of a cytoplasmic extract of HEp-2 cells and westernblot analysis of isolated 80S ribosomes clearly demonstrate that vigilin is bond to the ribosomal complex. Vigilin detaches from the ribosomal complex under the influence of high salt concentrations. We present data that radioactively labeled human vigilin interacts directly with a subset of ribosomal proteins from both subunits. We were able to narrow down the putative binding region to the C-terminal domain by using vigilin mutant constructs. Therefore our results provide strong evidence that vigilin is bond to the ribosomal complex and underline the hypothesis that vigilin might be involved in the link between tRNA-export and the channeled tRNA-cycle on ribosomes.

RNAi-mediated depletion of the 15 KH domain protein, vigilin, induces death of dividing and non-dividing human cells but does not initially inhibit protein synthesis

Vigilin/Scp160p/DDP1 is a ubiquitous and highly conserved protein containing 15 related, but non-identical, K-homology (KH) nucleic acid binding domains. While its precise function remains unknown, proposed roles for vigilin include chromosome partitioning at mitosis, facilitating translation and tRNA transport, and control of mRNA metabolism, including estrogen-mediated stabilization of vitellogenin mRNA. To probe sites of vigilin action in vertebrate cells, we performed nucleic acid binding and RNA interference studies. Consistent with a potential role in chromosome partitioning, human vigilin exhibits a higher affinity for Drosophila dodecasatellite single-stranded DNA than for vitellogenin mRNA 3'-UTR. Direct observation and flow cytometry in non-mitotic, serum-starved, HeLa cells showed that RNAi-mediated vigilin knockdown is rapidly lethal, indicating an essential function for vigilin distinct from its proposed role in chromosome partitioning. Pulse labeling experiments revealed that rates of protein synthesis and degradation are unaffected by the several fold reduction in vigilin levels early in siRNA knockdown indicating that vigilin is not a global regulator of translation. These data show that vigilin is an essential protein in human cells, support the view that vigilin's most essential functions are neither chromosome partitioning nor control of translation, and are consistent with vigilin playing a critical role in cytoplasmic mRNA metabolism.

Regulation of pathways of mRNA destabilization and stabilization

The level of an mRNA in the cytoplasm represents a balance between the rate at which the mRNA precursor is synthesized in the nucleus and the rates of nuclear RNA processing and export and cytoplasmic mRNA degradation. Although most studies of gene expression have focused on gene transcription and in the area of eukaryotic mRNA degradation, but to provide a short general discussion of the importance of mRNA degradation and its regulation and a brief overview of recent findings and present knowledge. The overview is followed by a more in-depth discussion of one of the several pathways for mRNA degradation. We concentrate on the pathway for regulated mRNA degradation mediated by mRNA-binding proteins and endonucleases that cleave within the body of mRNAs. As a potential example of this type of control, we focus on the regulated degradation of the egg yolk precursor protein vitellogenin on the mRNA-binding protein vigilin and the mRNA endonuclease polysomal ribonuclease 1 (PMR-1).

Expression of the ATP-binding cassette transporter gene ABCG1 (ABC8) in Tangier disease

Several members of the ATP-binding cassette (ABC) transporter family are involved in cholesterol efflux from cells. A defect in one member, ABCA1, results in Tangier disease, a condition characterized by cholesterol accumulation in macrophages and virtual absence of mature circulating high-density lipoproteins. Expression of a second member, ABCG1, is increased by cholesterol-loading in human macrophages. We now show that ABCG1, which we identified by differential display RT-PCR in foamy macrophages, is overexpressed in macrophages from patients with Tangier disease compared to control macrophages. On examination by confocal laser scanning microscopy, ABCG1 was present in perinuclear structures within the cell. In addition, a combination of in situ hybridization and indirect immunofluorescence microscopy revealed that ABCG1 is expressed in foamy macrophages within the atherosclerotic plaque. These data indicate that not only ABCA1 but also ABCG1 may play a role in the cholesterol metabolism of macrophages in vitro and in the atherosclerotic plaque.

Scp160p, an RNA-binding, polysome-associated protein, localizes to the endoplasmic reticulum of Saccharomyces cerevisiae in a microtubule-dependent manner

Scp160p is an RNA-binding protein containing 14 tandemly repeated heterogenous nuclear ribonucleoprotein K-homology domains, which are implicated in RNA binding. Scp160p interacts with free and membrane-bound polysomes that are dependent upon the presence of mRNA. Despite its presence on cytosolic polysomes, Scp160p is predominantly localized to the endoplasmic reticulum (ER). Accumulation of Scp160p-ribosome complexes at the ER requires the function of microtubules but is independent of the actin cytoskeleton. We propose that the multi-K-homology-domain protein Scp160p functions as an RNA binding platform, interacting with polysomes that are transported to the ER.

Human macrophages synthesize type VIII collagen in vitro and in the atherosclerotic plaque

Type VIII collagen is a short-chain collagen that is present in increased amounts in atherosclerotic lesions. Although the physiological function of this matrix protein is unclear, recent data suggest an important role in tissue remodeling. Type VIII collagen in the atherosclerotic lesion is mainly derived from smooth muscle cells. We now show that macrophages in the atherosclerotic vessel wall and monocytes in adjacent mural thrombi also express type VIII collagen. We demonstrated this using a novel combined fluorescence technique that simultaneously stains, within the same tissue section, specific RNAs by in situ hybridization and proteins by indirect immunofluorescence. In culture, human monocyte/macrophages expressed type VIII collagen at all time points from 1 h to 3 wk after isolation. Western blotting and immunoprecipitation also revealed secretion of type VIII collagen into the medium of 14-day-old macrophages. Because this is the first report of secretion of a collagen by macrophages, we tested the effect of lipopolysaccharide (LPS) and interferon gamma, substances that stimulate macrophages to secrete lytic enzymes, on macrophage expression of type VIII collagen. LPS and interferon gamma decreased expression of type VIII collagen. By contrast, secretion of matrix metalloproteinase 1 (MMP 1) was increased, indicating a switch from a collagen-producing to a degradative phenotype. Double in situ hybridization studies of expression of type VIII collagen and MMP 1 in human coronary arteries showed that in regions important for plaque stability, the ratio of MMP 1 RNA to macrophage type VIII collagen RNA varies widely, indicating that the transition from one phenotype to the other that we observed in vitro may also occur in vivo.

Expression of type VIII collagen after cholesterol diet and injury in the rabbit model of atherosclerosis

This study presents an analysis of the expression of type VIII collagen mRNA in response to cholesterol diet and balloon injury in the rabbit iliac artery. The design of the animal experiments was as follows: 28 male New Zealand White rabbits were divided into the 3 different treatment groups. Group 1 received regular chow; group 2 was fed with a 1% cholesterol diet for 6 weeks and normal chow for 5 weeks; and group 3 underwent balloon injury, then 6 weeks of a 1% cholesterol diet, which was followed by 5 weeks of normal chow. The expression pattern of type VIII collagen mRNA was compared with that of the fibrillar collagen types I and III, transforming growth factor-beta1, a factor known to exert the most potent stimulatory effect on collagen synthesis in vitro, and matrix metalloproteinase 1, a collagen-degrading enzyme. The cholesterol diet resulted in an upregulation of type VIII collagen, fibrillar collagens, transforming growth factor-beta1, and matrix metalloproteinase I in the adventitia. Although the number of type VIII collagen mRNA-expressing cells in the media increased, no significant difference in overall expression levels was detectable by northern blot analysis. The ratio of medial smooth muscle cells expressing type VIII collagen mRNA to those expressing type I and type III collagen mRNA (CVIII:CI:CIII) changed from 1:1.88:0.03 in the normal media to 1:0.78:0.29. When cholesterol feeding was preceded by balloon injury, type VIII collagen mRNA expression concomitant with the fibrillar collagens was further upregulated over and above that level reported after cholesterol diet alone. In general, low levels of transforming growth factor-beta1 mRNA correlated with high expression of matrix metalloproteinase I. Our study indicates that a cholesterol diet resulted in a balanced reorganization of the collagen composition but did not result in marked collagen accumulation. This may provide an extracellular environment that favors migration and proliferation processes during early atherogenesis. It also demonstrates that type VIII collagen is highly expressed and deposited at later stages, and this may be linked to processes such as tissue reorganization during vascular repair and plaque stabilization.

In vitro genetic analysis of the RNA binding site of vigilin, a multi-KH-domain protein

The function(s) and RNA binding properties of vigilin, a ubiquitous protein with 14 KH domains, remain largely obscure. We recently showed that vigilin is the estrogen-inducible protein in polysome extracts which binds specifically to a segment of the 3' untranslated region (UTR) of estrogen-stabilized vitellogenin mRNA. In order to identify consensus mRNA sequences and structures important in binding of vigilin to RNA, before vigilin was purified, we developed a modified in vitro genetic selection protocol. We subsequently validated our selection procedure, which employed crude polysome extracts, by testing natural and in vitro-selected RNAs with purified recombinant vigilin. Most of the selected up-binding mutants exhibited hypermutation of G residues leading to a largely unstructured, single-stranded region containing multiple conserved (A)nCU and UC(A)n motifs. All eight of the selected down-binding mutants contained a mutation in the sequence (A)nCU. Deletion analysis indicated that approximately 75 nucleotides are required for maximal binding. Using this information, we predicted and subsequently identified a strong vigilin binding site near the 3' end of human dystrophin mRNA. RNA sequences from the 3' UTRs of transferrin receptor and estrogen receptor, which lack strong homology to the selected sequences, did not bind vigilin. These studies describe an aproach to identifying long RNA binding sites and describe sequence and structural requirements for interaction of vigilin with RNAs.

Nonradioactive in situ hybridization for detection of hydrophobin mRNA in the phytopathogenic fungus Claviceps purpurea during infection of rye

Hydrophobins are unique fungal extracellular proteins that produce amphipathic films at interfaces, mediate contact to hydrophobic surfaces and are known to be important in phytopathogenicity. In the pathogenic ascomycete Claviceps purpurea, causing ergot disease in grasses and cereals and ergotism in livestock, a gene encoding an extraordinary type of hydrophobin has been detected, which appeared to be induced during alkaloid synthesis in axenic culture of an ergot-alkaloid producing strain of Claviceps (V. Garre and P. Tudzynski, pers. communication; Arntz and Tudzynski, 1997, Curr. Genet. 31, 357-360). To elucidate presence and function of this hydrophobin during infection of rye, the nonradioactive in situ hybridization technique was successfully adapted to the fungal organism and optimized in the pathogenic interaction system. Semithin cryosections proved to be suitable for microscopical gene expression analysis using immune-mediated alkaline-phosphatase staining for detection of digoxigenin-labeled cRNA probes. Specific hybridization of the prepared antisense riboprobe to hydrophobin mRNA was confirmed in nonradioactive Northern blots. While permeabilization by proteinase K had only a minor effect, the inclusion of detergent into the hybridization solutions enhanced specific RNA-RNA hybridization under maximum stringency. Hydrophobin mRNA was found in fungal cells, growing in axenic culture. In the disease cycle, hydrophobin transcripts were localized in abundance during vegetative fructification in conidiophores that actively produced conidia. No signals were observed in sclerotial hyphae during formation of the alkaloid-containing ergots, although they fluoresced intensely during total RNA detection using acridine orange. Notably, in situ hybridization experiments resulted in specific signals during early infection and colonization phases in the external mycelia and in hyphae penetrating the host epidermal layer. The presumed role of the hydrophobin gene product in ergot pathogenicity is discussed with respect to the described spatio-temporal distribution of the hydrophobin transcripts.

tRNA is entrapped in similar, but distinct, nuclear and cytoplasmic ribonucleoprotein complexes, both of which contain vigilin and elongation factor 1 alpha

Vigilin, which is found predominantly in cells and tissues with high levels of protein biosynthesis, was isolated in its native form from human HEp-2 cells (A.T.C.C. CCL23) by immunoaffinity chromatography. Here we demonstrate that vigilin is part of a novel large tRNA-binding ribonucleoprotein complex (tRNP), found not only in the cytoplasm, but also in the nuclei of human cells. Compositional differences in the protein pattern were detected between the nuclear and cytoplasmic tRNPs, although some properties of the purified nuclear tRNP, such as tRNA protection against nuclease attack, were identical with those of the cytoplasmic tRNP. By using either a pool of total human nuclear RNA or radioactively labelled yeast tRNAAsp in rebinding experiments, we could show that tRNA is specifically recaptured by the RNA-depleted, vigilin-containing nuclear complex. We could also show that vigilin is capable of binding tRNA in vitro. Another tRNA-binding protein is elongation factor 1 alpha, which appears to be enriched in the cytoplasmic and nuclear tRNP complexes. This suggests that the cytoplasmic tRNP may be involved in the channelled tRNA cycle in the cytoplasm of eukaryotic cells. Our results also suggest that the nuclear vigilin-containing tRNP may be related to the nuclear export of tRNA.

Genetic variability in white leghorns revealed by chicken liver expressed sequence tags

A total of 92 expressed sequence tags from chicken liver (CLEST) were searched for homology with known genes. Among the CLEST, 29% had no sequence similarities with known genes, 34% showed sequence similarity to rRNA, 9% to mitochondrial genes, 23% to known nuclear genes, and 5% to human expressed sequence tags. Among the nuclear CLEST (excluding rRNA), clones with sequence similarity to aldolase B were represented four times, whereas all the other clones represented unique genes. The presence of MspI and TaqI restriction fragment length polymorphisms (RFLP) associated with CLEST were analyzed by bulk Southern blotting in 16 strains of White Leghorn chickens derived from five different genetic bases. No RFLP were observed with rRNA CLEST and a single MspI RFLP was observed with mitochondrial CLEST. The nuclear CLEST with sequence similarity to known nuclear genes were grouped into two classes on the basis of their involvement in intermediary metabolism. Among the nine genes coding for metabolic enzymes, all but one were polymorphic at MspI and/or TaqI sites in at least one of the strains, whereas among the other genes six of nine were polymorphic. The average frequency of clones revealing RFLP per cDNA clone and restriction enzyme for the two classes were 0.7 and 0.3, respectively. The analysis indicated that in White Leghorns, RFLP markers in the vicinity of nuclear CLEST are relatively frequent. Further, RFLP in the vicinity of genes coding for metabolic enzymes were significantly more frequent than near genes coding for other proteins.

Smooth muscle cells express granulocyte-macrophage colony-stimulating factor in the undiseased and atherosclerotic human coronary artery

Granulocyte-macrophage colony-stimulating factor (GM-CSF), one of a family of cytokines that regulate proliferation in macrophages and other types of cells, has been implicated in the inflammatory-fibroproliferative response of atherosclerosis. However, previous studies have been restricted to cultured cells and animal models. In the present study, we investigated GM-CSF expression in undiseased and atherosclerotic human coronary arteries at both the mRNA and protein levels. Dual in situ hybridization/cell-marking experiments demonstrated that subpopulations of intimal smooth muscle cells (SMCs) and endothelial cells express the cytokine in the histologically normal human coronary artery and that augmented expression occurs at these sites, and in macrophage accumulations and medial SMCs, in the atherosclerotic vessel. Corresponding data were obtained by in situ hybridization and reverse transcription-polymerase chain reaction and Northern analyses of cultured cells. Cultured human coronary arterial SMCs showed constitutive expression of GM-CSF in cells that had adopted an activated synthetic phenotype. Electron microscope immunocytochemistry revealed that GM-CSF is a protein localized in the cytoplasmic matrix of SMCs of both the undiseased and atherosclerotic vessel wall; extracellular matrix was largely unlabeled, with only occasional small patches of amorphous immunopositive material. The expression of GM-CSF by subpopulations of intimal SMCs in the undiseased artery and the marked upregulation of GM-CSF apparent in atherosclerotic lesions suggest roles for the cytokine in the cellular events underlying initiation and progression of the human atherosclerotic lesion.

High-density lipoprotein-binding protein (HBP)/vigilin is expressed in human atherosclerotic lesions and colocalizes with apolipoprotein E

Accumulation of cholesteryl esters within cells of the arterial intima is a hallmark of atherosclerosis. A small number of proteins have been shown in vitro to be upregulated by cellular cholesterol loading, including apolipoprotein E (apoE) and the recently cloned HDL-binding protein (HBP), but only apoE has been shown to be upregulated in cholesterol-loaded cells in atherosclerosis. To determine whether HBP (also called vigilin) might be expressed in human atherosclerosis, immunohistochemistry and in situ hybridization were performed on coronary arteries of 18 patients. HBP/vigilin was detected on all endothelial cells. HBP/vigilin mRNA and protein also were detected on a subset of macrophages and occasionally on smooth muscle cells (SMC) in atherosclerotic plaques but were not detected on these cell types in nondiseased coronary intima. The majority of HBP/vigilin-expressing macrophages were foam cells, but HBP/vigilin expression also was detected rarely in nonfoam cell macrophages. Foam cell macrophage HBP/vigilin expression was present in 100% of atherosclerotic quadrants, and nonfoam cell macrophage HBP/vigilin expression was present in 6% of atherosclerotic quadrants. HBP/vigilin-expressing human plaque cells also expressed apoE. However, HBP/vigilin was detected in cardiac myocyte foam cells of an apoE-deficient mouse, demonstrating that HBP/vigilin expression can occur independently of apoE. These results suggest that in vivo HBP/vigilin expression is upregulated by intracellular cholesterol loading but also that other factors present in atherosclerotic plaques may upregulate HBP/vigilin. Although the exact function of HBP/vigilin is unknown, its expression in plaque macrophages suggests a role for this molecule in atherogenesis.

Chicken vigilin gene: a distinctive pattern of hypersensitive sites is characteristic for its transcriptional activity

Vigilin, a multidomain hn-ribonucleo-K-homologous protein, is part of a ribonucleoprotein complex with cognate tRNA and is found in both the nucleus and the cytoplasm. In an approach to identify genomic regions involved in regulation of the chicken vigilin gene, we carried out transfection studies with a reporter gene in suitable chicken cells. After including a distantly positioned 5'-sequence in the construct, we observed a 10.5-fold increase in luciferase (EC 1. 13.12.7) expression compared with basal promoter activity. Accordingly, chromatin analysis of freshly isolated embryonic tendon fibroblasts with high levels of vigilin mRNA expression shows a DNase-I-hypersensitive site (DHS1) localized 2.2 kb upstream of the transcriptional start site. Similarly, phytohaemagglutinin-stimulated lymphocytes with a 4-fold elevated expression of vigilin mRNA compared with resting lymphocytes also exhibited this unique DHS, having switched from that found at 3.3 kb (DHS2) in resting lymphocytes. Furthermore, using gel-retardation experiments with DNA representing either DHS1 or DHS2, a specific interaction with chicken nuclear extracts was seen.

Vigilin, a ubiquitous protein with 14 K homology domains, is the estrogen-inducible vitellogenin mRNA 3'-untranslated region-binding protein

RNA-binding proteins containing KH domains are widely distributed. One KH domain protein of unknown function, vigilin (also known as the high density lipoprotein-binding protein), contains 14 KH domains and is ubiquitous in vertebrate cells. We previously used RNA gel mobility shift assays to describe an estrogen-inducible protein which binds specifically to a segment of the 3'-untranslated region (3'-UTR) of vitellogenin mRNA, an area which has been implicated in the estrogen-mediated stabilization of vitellogenin mRNA. Here we show that the vitellogenin mRNA-binding protein (VitRNABP) is vigilin. The VitRNABP was isolated as a 150-155-kDa protein on a vitellogenin mRNA 3'-UTR affinity column. Peptide microsequencing revealed that the purified protein was vigilin, a conclusion confirmed in Western blot analysis with antibodies to vigilin. Direct confirmation that vigilin is the VitRNABP was obtained from RNA gel mobility shift assays which demonstrated that antibodies to chicken vigilin supershifted the Xenopus VitRNABP band. Xenopus liver vigilin mRNA and the VitRNABP exhibited similar induction by estrogen, providing additional confirmation that vigilin is the estrogen-inducible protein which binds to the 3'-UTR of estrogen-stabilized vitellogenin mRNA. These data support a role for vigilin in the hormonal control of mRNA metabolism.

Evidence for a novel cytoplasmic tRNA-protein complex containing the KH-multidomain protein vigilin

Vigilin, a protein found predominantly in cells and tissues with a high biosynthetic capacity, was isolated in its native form from human HEp-2 cells (A.T.C.C. CCL23) by immunoaffinity chromatography. Vigilin forms part of a novel ribonucleoprotein complex that also contains additional, as yet uncharacterized, proteins. Experimental evidence suggests that the nucleic acids entrapped in this complex are protected from RNase and belong to the tRNA family. Using either a pool of total human RNA or radioactively labelled tRNA (tRNA (Asp**)) in rebinding experiments, we could show that tRNA is selectively recaptured by the RNA-depleted vigilin-containing complex.

Expression of vigilin in the uterus of ovariectomized steroid-treated rats and during the estrous cycle

The expression of vigilin in the uterus of rats was investigated by immunoblotting and immunohistochemistry and compared to the ultrastructural features of the endometrial cells. Vigilin could not be detected in the uteri of ovariectomized rats. Administration of estrogen, alone or in combination with progesterone, significantly stimulated the expression of vigilin, mainly in the luminal and glandular epithelial cells. Ultrastructurally, these cells show the morphological features of an increased protein synthesis. Untreated mature rats demonstrate a cyclic pattern of vigilin expression with high levels during the estrogen-dominated proestrus and early estrus stages and low levels at metestrus. The down-regulation of vigilin starts with the occurrence of apoptosis and autophagocytosis in the epithelium, but precedes the vanishing of the secretory granules. At diestrus the vigilin expression is intermediate and the vigilin staining of the epithelial cells is reduced. However, the endometrial fibroblasts show a faint staining. Morphologically, these fibroblasts are characterized by large euchromatic nuclei and dilated cisternae of the rough endoplasmic reticulum. The results suggest that in the uterus of rats the expression of vigilin is stimulated by estrogen. Under the experimental conditions chosen no influence of progesterone on vigilin expression was detected.

Immunocytochemical localization of vigilin, a tRNA-binding protein, after cell fractionation and within the exocrine pancreatic cell of the rat

A polyclonal antibody against a fusion protein composed of two vigilin domains and gamma-galactosidase was used to localize the tRNA-binding protein vigilin at the ultrastructural level. Immunoreactivity for vigilin was found on membranes bearing ribosomes within the microsome fraction derived from rat livers and on the rough endoplasmic reticulum in rat exocrine pancreatic cells, synthesis corroborating the involvement of vigilin in protein synthesis. Gold labeling was also found in the nucleus and in the microsome fraction in an osmiophilic substance resembling heterochromatin. Both of these localizations, the rough endoplasmic reticulum and the nucleus, are in line with the observation that a vigilin-containing ribonucleoprotein complex binds tRNA.

Two additional 5' exons in the human Vigilin gene distinguish it from the chicken gene and provide the structural basis for differential routes of gene expression

Vigilin, a 150-kDa protein, contains 14 tandemly arranged domains, each consisting of a KH RNA-binding motif and a spacer region. Here, we report on the physical structure of the human Vigilin gene with 29 exons, thereby outnumbering the chicken gene by two additional 5' exons. These additional exons, 1A and 1B, are alternatively though concurrently spliced to exon 1C which is homologous to the first exon in the chicken gene. None of the additional human exons code for an amino-terminal extension of Vigilin, due to in-frame stop codons. Structural features of exon 1A, however, would allow the translation of a 13-amino-acid peptide from an upstream open reading frame preceding the vigilin open reading frame. We suggest that exons 1A and 1B have been gained during evolution, allowing alternative routes of expression control of the human Vigilin gene.

Experimental tissue expansion induces changes in expression of procollagen I and III messenger RNA

Experimental tissue expansion was performed in nine dogs following placement of subcutaneous silicone balloons. The balloon expander was then filled with 300 ml saline immediately after implantation. Duration of expansion varied from 3 days to 124 days. Unaffected skin and skin over an empty expander served as control tissue. Dermal procollagen I and procollagen III gene expression in response to tissue expansion was investigated by dot-blot analysis using digoxigenin-labeled RNA probes complementary to either human procollagen-alpha 1(I) mRNA or procollagen-alpha 1(III) mRNA. Cross-hybridization of human probes with canine procollagen mRNA was demonstrated by Northern blot analysis. In response to the trauma of surgery, procollagen I and III mRNA transcriptions were found to be decreased significantly within the first few days after implantation. After 9 days of expansion, increased levels of procollagen I mRNA were found, while after 16 days increased levels of procollagen III mRNA were evident. The present study is the first to demonstrate changes in dermal collagen gene expression as a reaction to tissue expansion.

The human vigilin gene: identification, chromosomal localization and expression pattern

Chick vigilin cRNA clones were used to isolate the cognate human gene, by screening a pWE15 genomic library. Three independent cosmid clones were isolated and characterized by restriction mapping. The gene was identified by sequencing an internal EcoRI fragment containing two exons homologous to exon 24 and 25 of the chicken vigilin gene and corresponding to nucleotides 1973-2104 of the human HBP-cDNA. The homology between the chicken and human sequences was 77% and 82% at the cDNA level, and 91% and 100% at the amino acid level. In addition, the analyzed intron/exon boundaries were invariantly conserved. The 5' and 3' regions of the human gene were mapped by Southern analysis of the respective clones with synthetic oligonucleotides. The entire vigilin gene spans a region of about 50 kb and has been assigned to chromosome 2q36-q37.2 (FL-pter value of 0.96 +/- 0.03) by fluorescence in situ hybridization to metaphase spreads from normal peripheral blood lymphocytes. The vigilin gene is localized in a chromosomal region comprising a cluster of collagen genes (COLIVA3, COLVIA3) and the locus of the Waardenburg syndrome I. Only one mRNA species of 4.4 kb is transcribed from the human vigilin gene. In accordance with previous observations on chicken mRNA, the expression of the human vigilin mRNA depends on the stage of cytodifferentiation both in vitro and in situ.