Influence of soil pH and application rate on the oxidation of calcium sulfite derived from flue gas desulfurization.

Calcium sulfite hemihydrate (CaSO(3).0.5H2O), a common byproduct of coal-fired utilities, is fairly insoluble and can decompose to release toxic SO2 under highly acidic soil conditions; however, it can also oxidize to form gypsum. The objective of this study was to examine the effects of application rate and soil pH on the oxidation of calcium sulfite under laboratory conditions. Oxidation rates measured by release of SO4-S to solution decreased with increasing application rate. Leachate SO4-S from soils amended with 1.0 to 3.0 g kg-1 CaSO3 increased over a 21 to 28 d period before reaching a plateau. At 4 g kg-1, maximum SO4-S release was delayed until Week 7. Oxidation and release of SO4-S from soil amended with 3.0 g kg-1 calcium sulfite increased markedly with decreasing soil pH. After only 3 d incubation, the concentrations of SO4-S in aqueous leachates were 77, 122, 170, 220, and 229 mg L-1 for initial soil pH values of 7.8, 6.5, 5.5, 5.1, and 4.0, respectively. At an initial soil pH value of 4.0, oxidation/dissolution did not increase much after 3 d. At higher pH values, oxidation was maximized after 21 d. These results suggest that autumn surface applications of calcium sulfite in no-till systems should permit ample time for oxidation/dissolution reactions to occur without introducing biocidal effects related to oxygen scavenging. Soil and annual crops can thus benefit from additions of soluble Ca and SO4 if calcium sulfite is applied in advance of spring planting.

The tenascin family of ECM glycoproteins: structure, function, and regulation during embryonic development and tissue remodeling.

The determination of animal form depends on the coordination of events that lead to the morphological patterning of cells. This epigenetic view of development suggests that embryonic structures arise as a consequence of environmental influences acting on the properties of cells, rather than an unfolding of a completely genetically specified and preexisting invisible pattern. Specialized cells of developing multicellular organisms are surrounded by a complex extracellular matrix (ECM), comprised largely of different collagens, proteoglycans, and glycoproteins. This ECM is a substrate for tissue morphogenesis, lends support and flexibility to mature tissues, and acts as an epigenetic informational entity in the sense that it transduces and integrates intracellular signals via distinct cell surface receptors. Consequently, ECM-receptor interactions have a profound influence on major cellular programs including growth, differentiation, migration, and survival. In contrast to many other ECM proteins, the tenascin (TN) family of glycoproteins (TN-C, TN-R, TN-W, TN-X, and TN-Y) display highly restricted and dynamic patterns of expression in the embryo, particularly during neural development, skeletogenesis, and vasculogenesis. These molecules are reexpressed in the adult during normal processes such as wound healing, nerve regeneration, and tissue involution, and in pathological states including vascular disease, tumorigenesis, and metastasis. In concert with a multitude of associated ECM proteins and cell surface receptors that include members of the integrin family, TN proteins impart contrary cellular functions, depending on their mode of presentation (i.e., soluble or substrate-bound) and the cell types and differentiation states of the target tissues. Expression of tenascins is regulated by a variety of growth factors, cytokines, vasoactive peptides, ECM proteins, and biomechanical factors. The signals generated by these factors converge on particular combinations of cis-regulatory elements within the recently identified TN gene promoters via specific transcriptional activators or repressors. Additional complexity in regulating TN gene expression is achieved through alternative splicing, resulting in variants of TN polypeptides that exhibit different combinations of functional protein domains. In this review, we discuss some of the recent advances in TN biology that provide insights into the complex way in which the ECM is regulated and how it functions to regulate tissue morphogenesis and gene expression.

Synthetic promoter elements obtained by nucleotide sequence variation and selection for activity.

Eukaryotic transcriptional regulation in different cells involves large numbers and arrangements of cis and trans elements. To survey the number of cis regulatory elements that are active in different contexts, we have devised a high-throughput selection procedure permitting synthesis of active cis motifs that enhance the activity of a minimal promoter. This synthetic promoter construction method (SPCM) was used to identify >100 DNA sequences that showed increased promoter activity in the neuroblastoma cell line Neuro2A. After determining DNA sequences of selected synthetic promoters, database searches for known elements revealed a predominance of eight motifs: AP2, CEBP, GRE, Ebox, ETS, CREB, AP1, and SP1/MAZ. The most active of the selected synthetic promoters contain composites of a number of these motifs. Assays of DNA binding and promoter activity of three exemplary motifs (ETS, CREB, and SP1/MAZ) were used to prove the effectiveness of SPCM in uncovering active sequences. Up to 10% of 133 selected active sequences had no match in currently available databases, raising the possibility that new motifs and transcriptional regulatory proteins to which they bind may be revealed by SPCM. The method may find uses in constructing databases of active cis motifs, in diagnostics, and in gene therapy.

Differential regulation by multiple promoters of the gene encoding the neuron-restrictive silencer factor.

NRSF/REST is a protein that silences transcription of a number of genes that contain a DNA element called the neuron-restrictive silencer element (NRSE). During embryogenesis, REST is expressed ubiquitously in nonneural cells, but is down-regulated during differentiation of neural progenitors into neurons. REST is also up-regulated in adult neurons by activity, suggesting a possible role for the protein in synaptic plasticity. To understand mechanisms that control expression of REST, we identified and characterized the promoter region of the mouse REST gene (mREST). A 4.5-kb DNA segment containing three exons (A, B, and C) that correspond to alternatively spliced 5' untranslated regions (5'UTRs) was isolated and its DNA sequence was determined. Reverse transcription-PCR analyses of fibroblasts, astrocytes, and neural progenitors identified variants in which these exons were spliced to exon D, suggesting that exons A, B, and C may each have a promoter. Consistent with this hypothesis, primer extension and in vitro transcription experiments revealed clusters of RNA transcription initiation sites upstream of exons A, B, and C. Tests of REST/luciferase reporter constructs in Neuro2A and NIH 3T3 cells revealed promoters upstream of exons A and B that were active in both cell lines, and a promoter upstream of exon C that was weakly active only in NIH 3T3 cells. Six enhancer and two repressor regions were found to overlap each of the three promoters, and some of these were found to be cell type-specific. Combinatorial arrangements of these promoters with enhancer and repressor regions may allow modulation of REST expression in particular contexts.

Gene regulation of cell adhesion: a key step in neural morphogenesis.

A mounting body of evidence suggests that cell adhesion molecules (CAMs) play important roles in morphogenetic patterning of the nervous system. The combined factors that control the expression of CAMs during early neural development are, however, largely unknown. We have hypothesized that the coordinate expression of homeobox (Hox) and paired box (Pax) proteins in the neural axis leads to the differential expression of particular CAM genes. Following this hypothesis, we have characterized the promoters and identified cis-regulatory sequences that bind to and respond to Hox and Pax proteins in the genes for three neurally expressed CAMs - the neural cell adhesion molecule, N-CAM, the neuron-glia cell adhesion molecule, Ng-CAM, and L1. Experiments on transgenic mice carrying N-CAM promoter/lacZ reporter gene constructs indicated that mutation of either the HBS or the PBS disrupted patterning of N-CAM expression in the embryonic spinal cord. To examine the factors that restrict the expression of certain CAMs to the nervous system, we identified regulatory elements that block expression of the Ng-CAM and L1 genes in non-neural cells. We characterized a 310 base pair region of the first intron of the Ng-CAM gene containing five neural restrictive silencer elements (NRSEs) and a binding site for the Pax-3 protein. These elements silenced activity of the Ng-CAM promoter in NIH3T3 fibroblasts, but had no effect on its activity in N2A neuroblastoma cells line. Similar analyses of the L1 gene revealed a single NRSE within the second intron that was important for silencing in this cellular transfection system. To analyze the role of the NRSE in vivo, we prepared transgenic mice containing two L1 gene/lacZ constructs, one containing the NRSE and another in which the NRSE was deleted. The wild type L1lacZ transgene showed a neurally restricted pattern of expression, whereas the NRSE-mutated L1 construct showed extensive extraneural expression of the L1 gene. Thus, neural specificity of CAM expression is controlled by the NRSE. The general significance of these observations is that they connect the expression of important families of transcriptional regulators with gene products capable of direct cellular mechanochemistry.

Multiple promoter elements differentially regulate the expression of the mouse tenascin gene.

Tenascin (TN) is an extracellular matrix glycoprotein that is expressed in a characteristic spatiotemporal pattern during development and is up-regulated in the adult during tumorigenesis, wound healing, and nerve regeneration. In previous studies, we identified a promoter within the proximal 250 bp upstream of the mouse TN gene that contains several putative regulatory elements that are conserved among vertebrate TN genes. We have identified four different DNA elements within this promoter and show that they contribute in different ways to TN gene expression in NIH 3T3 fibroblasts, C6 glioma cells, and N2A neuroblastoma cells. These elements comprise a binding site for Krox proteins, one for nuclear factor 1, an octamer motif that binds POU-homeodomain proteins, and a novel TN control element. The nuclear factor 1 and TN control element had positive effects on TN promoter activity and formed similar DNA-protein complexes with nuclear extracts from all three cell lines. The Krox element had a negative effect on TN promoter activity in N2A cells, a positive effect in C6 cells, and no effect in NIH 3T3 cells. Two DNA binding complexes, one correlated with the negative and the other with the positive activities of the Krox element, were found to contain the protein Krox24. In cotransfection experiments, the octamer motif was required for induction of TN promoter activity by the POU-homeodomain protein Brn2 in N2A cells but was inactive in C6 cells. Consistent with these findings, N2A cells transfected with Brn2 formed octamer-binding complexes containing N-Oct3, the transcriptionally active form of Brn2, whereas complexes formed in C6 cells contained only N-Oct5A and N-Oct5B. Our results provide a striking example of the diversity of regulatory mechanisms that can be called forth by combining different promoter motifs with transcriptional activators or repressors.

Silencer elements modulate the expression of the gene for the neuron-glia cell adhesion molecule, Ng-CAM.

The combined factors that regulate the expression of cell adhesion molecules (CAMs) during development of the nervous system are largely unknown. To identify such factors for Ng-CAM, the neuron-glia CAM, constructs containing portions of the 5' end of the Ng-CAM gene were examined for activity after transfection into N2A neuroblastoma and NIH3T3 cells. Positive regulatory elements active in both cell types included an Ng-CAM proximal promoter with SP1 and cAMP response element motifs extending 447 base pairs upstream of a single RNA start site and a region within the first exon corresponding to 5'-untranslated sequences. Negative regulatory elements included five neuron-restrictive silencer elements (NRSEs) and a binding site for Pax gene products in a 305-base pair segment of the first intron. Constructs containing the promoter together with the entire first intron were active in N2A cells but were silenced in NIH3T3 cells. This silencer activity was mapped to the NRSEs. In contrast, the Pax motif inhibited activity of Ng-CAM constructs in both cell types. The DNA elements defined in these transfection experiments were examined for their ability to bind nuclear factors. The region within the first exon formed a DNA-protein complex after exposure to nuclear extracts prepared from both NIH3T3 and N2A cells. The NRSE region formed a more prominent complex with proteins prepared from NIH3T3 cells than it did with extracts from N2A cells. A member of the Pax protein family, Pax-3 bound to the Pax motif. Mutations introduced within the Pax motif in its ATTA sequence eliminated this binding whereas mutations in its GTTCC sequence did not, suggesting that paired homeodomain interactions are important for the recognition of Pax-3 by this DNA target sequence. The combined data suggest that negative regulation by NRSEs and Pax proteins may play a key role in the place-dependent expression patterns of Ng-CAM during development.

Structural and functional similarities between the promoters for mouse tenascin and chicken cytotactin.

Cytotactin/tenascin is an extracellular matrix glycoprotein expressed in a restricted anteroposterior pattern during vertebrate development and is reexpressed in the adult during wound healing, tumorigenesis, and nerve regeneration. Previously, we have characterized the chicken cytotactin promoter and have shown its regulation by homeobox gene products in vitro. We have now isolated the promoter for the mouse tenascin gene in order to determine whether common or different DNA regulatory elements control the expression of this gene in these two species. Like the chicken cytotactin gene, the mouse tenascin gene has a single RNA start site that lies 27 bp downstream of a TATA box. A 4028-bp region of DNA upstream of the mouse tenascin gene was sequenced and examined for regulatory motifs in common with the upstream sequence from the chicken cytotactin promoter. Two hundred thirty base pairs of the proximal promoter regions from both genes had an extended sequence similarity and contained common regulatory motifs such as two tracts of homopolymeric dA.dT sequence, an octamer motif, an ATTA (TAAT) motif which is a common core sequence for binding of homeodomain transcription factors, and a TATA-box/cap-site region. Reporter gene constructs with various 5' deletions of the mouse tenascin upstream sequence were tested in transient transfections of mouse NIH 3T3 and chicken embryo fibroblasts. The conserved proximal promoter region of tenascin was responsible for most of the positive regulatory activity. In addition, an upstream region (-2478 to -247) repressed proximal promoter activity in mouse fibroblasts and also in chicken embryo fibroblasts. These data indicate that both the structure and function of the cytotactin/tenascin proximal promoters have remained conserved over 250 million years.

Binding and activation of the promoter for the neural cell adhesion molecule by Pax-8.

The neural cell adhesion molecule (N-CAM), is expressed in definite spatiotemporal patterns during development. To identify factors that may influence place-dependent n-cam gene expression, we have studied the binding and activation of the n-cam promoter by Pax-8, a member of the Pax family of transcription factors. Pax-8 increased n-cam promoter activity 13.4-fold in cellular co-transfection experiments, and a short segment of the promoter (-143 to -15) mediated the response. This region of the n-cam promoter produced a DNA-protein complex when incubated with either extracts from COS-7 cells transfected with the Pax-8 expression vector or a Pax-8/GST fusion protein. Pax-8 bound to the n-cam promoter through two TGCTCC motifs (designated PBS-1 and PBS-2) that resemble paired domain binding sites. Mutation of PBS-1 and PBS-2 eliminated Pax-8 activation of the n-cam promoter. Transfection of N2A neuroblastoma cells with the Pax-8 expression vector resulted in a 5-fold increase in the transcription of the endogenous n-cam gene. The combined results suggest that Pax-8 activates transcription of the n-cam gene through binding of sequences resembling paired domain binding sites in the n-cam promoter. The data raise the possibility that the n-cam promoter may be regulated by other members of the Pax gene family.

Regulation in vitro of an L-CAM enhancer by homeobox genes HoxD9 and HNF-1.

Previous studies have shown that in vitro expression of the neural cell adhesion molecule (N-CAM) can be regulated by the products of homeobox genes HoxB9, -B8, and -C6. N-CAM is a Ca(2+)-independent immunoglobulin-related CAM that plays an important role in neural development. In the present study, we investigated whether the liver cell adhesion molecule (L-CAM) a member of the Ca(2+)-dependent CAM family (cadherins) is also regulated by homeobox-containing genes. In transient cotransfection experiments of NIH 3T3 cells, we observed that both HoxD9 and liver-enriched POU-homeodomain transcription factor, HNF-1, activated chloramphenicol acetyltransferase gene reporter constructs containing the L-CAM promoter and an enhancer present in the second intron of the chicken L-CAM gene. Using electrophoretic mobility-shift assays, we found that components of cell extracts from NIH 3T3 cells transfected with HoxD9 bound to a small region of the L-CAM enhancer having a consensus sequence that is a putative binding site for HNF-1. Components of extracts from the chicken hepatoma cell line LMH that had been transfected with an HNF-1 expression vector also bound to this same site. In nuclear run-on experiments with nuclei from LMH cells that were transfected with expression vectors for HoxD9 or HNF-1, L-CAM RNA levels were increased 33-fold and 4-fold respectively. Using the same run-on procedure, it was confirmed that nuclei prepared from normal embryonic chicken liver cells expressed the RNAs for HoxD9, HNF-1, and L-CAM. Taken together with previous observations, these data raise the possibility that homeobox-containing genes will have a widespread role in the place-dependent expression of CAMs belonging both to immunoglobulin-related and to cadherin families.

Identification of the promoter and a transcriptional enhancer of the gene encoding L-CAM, a calcium-dependent cell adhesion molecule.

L-CAM is a calcium-dependent cell adhesion molecule that is expressed in a characteristic place-dependent pattern during development. Previous studies of ectopic expression of the chicken L-CAM gene under the control of heterologous promoters in transgenic mice suggested that cis-acting sequences controlling the spatiotemporal expression patterns of L-CAM were present within the gene itself. We have now examined the L-CAM gene for sequences that control its expression and have found an enhancer within the second intron of the gene. A 2.5-kb Kpn I-EcoRI fragment from the intron acted as an enhancer of a simian virus 40 minimal promoter driving a chloramphenicol acetyltransferase (CAT) reporter gene and produced 14.0-fold induction of CAT activity in MDCK cells. To narrow down the region responsible for enhancer activity and to determine whether the enhancer could function in a cell type-specific manner, a number of smaller restriction fragments from the intron were tested for activity in two chicken cell lines, the LMH hepatoma line, which produces high levels of L-CAM, and the SL-29 fibroblast line, which produces little, if any, L-CAM. Four L-CAM enhancer plasmids containing shorter segments derived from the intron showed enhanced CAT activity levels (between 9.4- and 16.5-fold) in extracts from transfected LMH cells but not from SL-29 cells. DNA sequence analysis of the L-CAM enhancer region revealed putative binding sites for the transcription factors SP1, E2A, and AP-2. In addition, LE-9, the smallest L-CAM enhancer segment (310 bp), contained a consensus binding site for the liver-enriched POU-homeodomain transcription factor, HNF-1. Tests of upstream sequences showed that a 630-bp fragment, corresponding to nearly the entire intergenic region between L-CAM and its neighboring CAM gene, K-CAM, could function as a promoter. In combination with the L-CAM enhancer, this fragment directed cell type-specific expression of the CAT reporter gene in LMH cells at a level comparable to that observed with enhancer constructs using the simian virus 40 minimal promoter. These combined observations define a promoter and an enhancer for the chicken L-CAM gene. They raise the possibility that these cis-acting regulatory sequences may be instrumental in directing specific place-dependent expression of the L-CAM gene in the chicken.

Binding and transcriptional activation of the promoter for the neural cell adhesion molecule by HoxC6 (Hox-3.3).

Scores of homeobox gene-encoded transcription factors are expressed in a definite spatiotemporal pattern during embryogenesis and regulate a series of as yet unidentified target genes to help coordinate the morphogenetic process. We have suggested that homeobox gene products modulate the expression of adhesion molecule genes and have shown in cotransfection experiments that the promoters for the neural cell adhesion molecule (N-CAM) and cytotactin/tenascin genes respond to cues from different homeobox-containing genes. In this study, we show that the HoxC6 (Hox-3.3)-encoded homeoprotein binds to a DNA sequence in the N-CAM promoter CCTAATTATTAA, designated homeodomain binding site I (HBS-I). To test whether HoxC6 regulated N-CAM promoter activity, we cotransfected the Long and Short reading frame variants of Xenopus HoxC6 (CMV-HoxC6-L and CMV-HoxC6-S) driven by the human cytomegalovirus (CMV) promoter together with a chloramphenicol acetyltransferase (CAT) reporter gene driven by the mouse N-CAM promoter (N-CAM-Pro-CAT). Cotransfection of NIH 3T3 cells with either of the CMV-HoxC6 expression vectors stimulated N-CAM promoter-driven CAT expression. A 47-bp region from the N-CAM promoter that included HBS-I and an adjacent potential HBS, HBS-II, conferred HoxC6 regulation on a simian virus 40 minimal promoter. HBS-I was sufficient for transactivation of the minimal promoter by CMV-HoxC6-S. However, transcriptional activation by CMV-HoxC6-L required both HBS-I and HBS-II, inasmuch as mutation of either HBS-I, HBS-II, or both motifs abolished the response. These studies suggest that HBS-I is a target site for binding and transcriptional control of the N-CAM promoter by homeoproteins, although accessory DNA sequences (such as HBS-II) may also be required. Together with previous studies, these results support the notion that N-CAM gene expression may be controlled by different combinations of homeoproteins that appear in a place-dependent manner during embryogenesis.

Identification and characterization of the promoter for the cytotactin gene.

The extracellular glycoprotein cytotactin is expressed in a characteristic and complex spatiotemporal sequence during development of the chicken embryo. To identify the various control elements underlying its expression, the promoter region of the cytotactin gene has been isolated and characterized. Clones were isolated from genomic libraries by using a fragment near the 5' end of the cDNA sequence. The sequence of this cDNA fragment was found to be distributed over two exons separated by a large first intron. The site of transcription initiation was determined by S1 nuclease and primer-extension mapping. Sequencing of a 4.3-kilobase (kb) genomic DNA clone that contains 3986 base pairs (bp) upstream of the RNA start site, the first exon, and part of the first intron revealed a number of sequence motifs implicated in the regulation and expression of eukaryotic genes. These included CCAAT boxes, phorbol ester-responsive elements, enhancer elements, and a consensus TATA sequence located 24 bp upstream of the major RNA cap site. The flanking sequence also contained a number of regions of dyad symmetry and direct repeats unique to cytotactin, as well as an array of A + T-rich sequences that resemble engrailed elements. Constructs containing fragments of the upstream region of the cytotactin gene fused to a promoterless gene for chloramphenicol acetyltransferase were transiently transfected into chicken embryo fibroblasts to define functional promoter sequences. Although sequences from -721 to +121 exhibited minimal promoter activity, the entire region between -3986 to +374 was required to yield maximal expression in chicken embryo fibroblasts. Transfection of the -3986/+374 chloramphenicol acetyltransferase plasmid into the human U251MG astrocytoma cells but not HT1080 fibrosarcoma cells resulted in chloramphenicol acetyltransferase expression, consistent with the observed synthesis of cytotactin protein only by the U251MG cell line. These data indicate that the chicken cytotactin promoter can control expression in a cell type-specific fashion within cells of another species. These studies provide a basis for the dissection of cis elements and trans factors that govern the developmental expression of the cytotactin gene.

Localization during development of alternatively spliced forms of cytotactin mRNA by in situ hybridization.

Cytotactin, an extracellular glycoprotein found in neural and nonneural tissues, influences a variety of cellular phenomena, particularly cell adhesion and cell migration. Northern and Western blot analysis and in situ hybridization were used to determine localization of alternatively spliced forms of cytotactin in neural and nonneural tissues using a probe (CT) that detected all forms of cytotactin mRNA, and one (VbVc) that detected two of the differentially spliced repeats homologous to the type III repeats of fibronectin. In the brain, the levels of mRNA and protein increased from E8 through E15 and then gradually decreased until they were barely detectable by P3. Among the three cytotactin mRNAs (7.2, 6.6, and 6.4 kb) detected in the brain, the VbVc probe hybridized only to the 7.2-kb message. In isolated cerebella, the 220-kD polypeptide and 7.2-kb mRNA were the only cytotactin species present at hatching, indicating that the 220-kD polypeptide is encoded by the 7.2-kb message that contains the VbVc alternatively spliced insert. In situ hybridization showed cytotactin mRNA in glia and glial precursors in the ventricular zone throughout the central nervous system. In all regions of the nervous system, cytotactin mRNAs were more transient and more localized than the polypeptides. For example, in the radial glia, cytotactin mRNA was observed in the soma whereas the protein was present externally along the glial fibers. In the telencephalon, cytotactin mRNAs were found in a narrow band at the edge of a larger region in which the protein was wide-spread. Hybridization with the VbVc probe generally overlapped that of the CT probe in the spinal cord and cerebellum, consistent with the results of Northern blot analysis. In contrast, in the outermost tectal layers, differential hybridization was observed with the two probes. In nonneural tissues, hybridization with the CT probe, but not the VbVc probe, was detected in chondroblasts, tendinous tissues, and certain mesenchymal cells in the lung. In contrast, hybridization with both probes was observed in smooth muscle and lung epithelium. Both epithelium and mesenchyme expressed cytotactin mRNA in varying combinations: in the choroid plexus, only epithelial cells expressed cytotactin mRNA; in kidney, only mesenchymal cells; and in the lung, both of these cell types contained cytotactin mRNA. These spatiotemporal changes during development suggest that the synthesis of the various alternatively spliced cytotactin mRNAs is responsive to tissue-specific local signals and prompt a search for functional differences in the various molecular forms of the protein.

A detailed structural model of cytotactin: protein homologies, alternative RNA splicing, and binding regions.

A combination of cDNA sequencing of the complete coding region, protein comparisons, binding site mapping, and electron microscopic imaging has permitted the formulation of a structural model of cytotactin. Cytotactin is a large extracellular matrix glycoprotein that displays a restricted tissue distribution during development. Although there appears to be a single cytotactin gene, multiple cytotactin polypeptides and mRNAs are detected in a variety of tissues. We report here the sequences and relationships of cDNAs that encode the complete amino acid sequences of two cytotactin polypeptides in chicken brain. The translated cDNA sequences agree with those obtained by direct analysis of cytotactin and fragments of the molecule. All regions of the polypeptides appear to be identical except for a 273 amino acid segment found in the larger but not in the smaller. At their amino termini, both polypeptides contain a cysteine-rich segment that probably includes those residues that link monomers into hexamers. This segment is followed by 13 epidermal growth factor-like (EGFL) repeats and then 8 consecutive segments that each resemble the type III repeats found in fibronectin. At their carboxyl termini, the polypeptides are similar to the beta and gamma chains of fibrinogen, including a calcium-binding segment. The additional sequence in the large polypeptide is inserted after the fifth type III repeat and includes three additional type III repeats. On RNA transfer blot analyses, cytotactin cDNA probes detected a 6.4-kilobase (kb) component in both brain and gizzard and larger mRNAs in both tissues, but those in gizzard were larger by about 1 kb than those in brain. A probe specific to the insert did not hybridize to the 6.4-kb mRNA in either tissue but detected the larger mRNAs in both tissues. At least a portion of the insert is thus present in both tissues, but there may be additional inserts in the gizzard mRNAs. The proposed model of cytotactin specifies the orientation of the polypeptides, the localization of interchain disulfide bonds, the structural elements constituting the thin and thick segments (EGFL repeats and type III repeats, respectively), the terminal fibrinogen-like nodular region, and the relative location of the cell-binding region.

A cDNA clone for cytotactin contains sequences similar to epidermal growth factor-like repeats and segments of fibronectin and fibrinogen.

Cytotactin is an extracellular glycoprotein that influences neuron-glia interactions. It has been shown to appear in multiple forms that are differentially expressed in neural and non-neural tissues during vertebrate development. We report here the isolation and characterization of a cytotactin cDNA clone (lambda C801) that encodes 933 amino acids, equivalent to about half of a cytotactin polypeptide. Clone lambda C801 is an authentic cytotactin cDNA: it encodes a polypeptide that reacts with a monoclonal anti-cytotactin antibody and its deduced amino acid sequence is identical for 15 amino acids to the directly determined sequence of a CNBr fragment that reacted with the same antibody. Southern blot analyses with fragments of lambda C801 suggested that there may be only one cytotactin gene, but RNA transfer blots detected multiple mRNAs ranging in size from 6.5 to 8.0 kilobases. An 8.0-kilobase message and a Mr 240,000 cytotactin polypeptide were present in embryonic gizzard but not brain, while a 7.2-kilobase message and a Mr 220,000 polypeptide were present in brain but not gizzard. These results indicate that differential splicing of primary transcripts of the cytotactin gene yields various site-specific polypeptides. Sequence analyses of lambda C801 indicated that it specifies a region with extensive similarities to other proteins: the sequence begins with four consecutive epidermal growth factor-like repeats that are followed by eight segments that closely resemble each other and the type III repeats in fibronectin, and it ends with a 66 amino acid sequence similar to part of the beta and gamma chains of fibrinogen. One fibronectin-like repeat contains a single Arg-Gly-Asp sequence. The similarities with all three of these apparently unrelated proteins are extensive, suggesting that cytotactin has an evolutionary and possibly a functional relationship to each.

The clearance of a monoclonal anti-DNA antibody following administration of DNA in normal and autoimmune mice.

To study the assembly of DNA-anti-DNA complexes in vivo, we have measured the clearance from blood and organ localization of a murine IgG2a monoclonal anti-DNA antibody, called 6/0, following the infusion of DNA intravenously or intraperitoneally. Intraperitoneal DNA caused a profound acceleration of 6/0 anti-DNA clearance that was dose dependent and demonstrable after the infusion of as little as 1.9 microgram per gram of body weight of single-stranded DNA. The antibody was cleared primarily in the liver without increased deposition in the kidney. Intraperitoneal infusions of DNA also accelerated the clearance of 6/0 in autoimmune MRL-lpr/lpr mice. In contrast, intravenous DNA given in comparable doses caused only a slight increase in 6/0 antibody clearance; this accelerated clearance was seen only at low antigen doses and only during the first 10 min following DNA infusion. Using double-radiolabeling techniques, 6/0 and Cl.18, an IgG2ak myeloma protein without anti-DNA activity, were found to disappear from blood at a comparable rate in both B6D2 mice and MRL-lpr/lpr mice. These results suggest that the DNA-anti-DNA immune complexes can form in vivo but that this process is profoundly affected by the manner in which DNA enters the circulation. In addition, the results suggest that DNA-dependent clearance is not a major pathway for anti-DNA metabolism in normal or at least one strain of autoimmune mice.

A case-control study of bladder cancer in the United States rubber and tyre industry.

A case-control study of bladder cancer was conducted in five United States rubber and tyre companies to determine if there were high-risk jobs and work areas within the industry. The study included 220 male cases of bladder cancer, of whom 107 were identified from hospital record reviews and 113 from death certificates. Each case was matched individually with two industry controls by sex, race, year of birth, and company. One control was matched additionally by year of hire and duration of employment. Comparisons of cases and controls not matched by year of hire and age of hire showed no differences for those variables, which suggests that age and calendar period of first exposure to the industry were not risk determinants. When the work histories of both cases and controls were contrasted it was found that cases were more likely than controls to have worked in milling (odds ratio (OR) = 1.91) and calender operation (OR = 2.21) jobs. The relative risk estimates for milling and calender operation both exhibited linear trends of increase with duration of exposure. Milling and calender operation jobs entail potential exposures to volatilised reaction products from heated rubber stock. A better understanding of aetiological associations with job type will require more detailed characterisation of the work environment with regard to the sources and levels of aromatic amines and other suspected bladder carcinogens.

Dexamethasone-inhibited pertechnetate uptake in metastatic carcinoma of the cerebellum.

Two sodium pertechnetate Tc 99m brain scans, done within several days of each other, demonstrated inhibition of pertechnetate localization in a cerebellar lesion after dexamethasone therapy for cerebral edema. The lesion, a metastasis from a bronchogenic mucinous adenocarcinoma, was clearly present in the first scan, which was done before treatment.