Identification of novel Fgf enhancers and their role in dental evolution

Mammalian dental morphology is under strong evolutionary pressure because of its importance for mastication and diet. While the mechanisms underlying tooth development have been widely studied in model organisms, the role of genetic regulatory elements in patterning the different elements of the occlusal surface and crown height across species is not well understood. Previous studies showed that Fibroblast Growth Factor (FGF) genes are important regulators of tooth development that influence morphological variation. We hypothesized that inter-specific variation in rodent dental morphology could be governed by nucleotide variation in genetic regulatory elements that modulate the spatial and temporal expression of the genes encoding FGF signaling molecules. In this study, we compared the variation in dental morphology across nine taxa of rodents to the variation in sequences of non-coding evolutionary conserved regions (ECRs) of Fgf3, 4, 8, 9, and 10. We correlated the variation in molar tooth cusp shape and the evolution of high molar crowns (hypsodonty) to the patterns of sequence variation in two ECRs, Fgf10ECR3, and Fgf9ECR1, respectively. By conducting luciferase and electrophoretic mobility shift assays, we determined that these ECRs could function as enhancers. These data suggest that emergence of hypsodonty and occlusal cusp patterning may have happened through the evolutionary changes in enhancers, such as Fgf9ECR1 and Fgf10ECR3, which affected the expression of major signaling molecules involved in tooth development.

Genetic signature of reproductive manipulation in the phylogeography of the bat fly, Trichobius major

The bat fly (Trichobius major) is a blood-feeding ectoparasite of the cave myotis (Myotis velifer). A recent mitochondrial DNA (mtDNA) study examining population structure of T. major in the South Central United States detected a single haplotype from all individuals examined (N = 48 from 12 different caves), representing one of only a few known examples of such widespread mtDNA uniformity. We examined nuclear genetic diversity using amplified fragment length polymorphism and detected high levels of nuclear genetic diversity in all populations sampled. Amplified fragment length polymorphism analyses indicated significant levels of gene flow among caves >700 km apart, suggesting the absence of mtDNA diversity in T. major is the result of a selective sweep, not a demographic event (i.e., a recent bottleneck). One mechanism by which mtDNA sweeps occur in arthropods is through bacterial parasites that manipulate host reproduction and mtDNA inheritance. We used PCR to test for the presence of all known reproductive parasites and detected a widespread infection (91.33% infection rate) of T. major with a novel Arsenophonus bacterium, as well as the infection of 2 individuals (1.16% infection rate) with a novel strain of Rickettsia. We discuss the implications for T. major phylogeography and the necessity of a bigenomic approach in arthropod population genetics.

Conjunctival Lymphoid Follicles in New World Rodents

We report for the first time, the detection of conjunctival lymphoid follicles (CLF) in the eyes of New World rodents. CLF were found in 7 of the 15 species examined, 6 of the 10 genera, and in at least one individual in four families of rodents. These follicles are dense collections of leukocytes in the conjunctival substantia propria with a thinned overlying epithelium lacking in goblet cells. Although the precise location of CLF within the conjunctiva varied from species to species, all CLF were found in the fornix of the conjunctival sac. In general, size and complexity of CLF varied with the size of the eye; the larger the eye, the larger and more complex the CLF. Our findings also reveal that some species of New World rodents, like the majority of Old World rodents examined in this and previous studies might lack CLF. However, until larger samples are examined, this is difficult to state with certainty. Consequently, the presence/absence of CLF at this point might not be informative for phylogenetic comparisons. Our findings also suggest the deer mouse, Peromyscus maniculatus, might serve as a useful model species for studying ocular infections and immunology of the eye.

Intraspecific Phylogeography of Red Squirrels (Tamiasciurus hudsonicus) in the Central Rocky Mountain Region of North America

We used variation in a portion of the mitochondrial DNA control region to examine phylogeography of Tamiasciurus hudsonicus, a boreal-adapted small mammal in the central Rocky Mountain region. AMOVA revealed that 65.66% of genetic diversity was attributable to variation within populations, 16.93% to variation among populations on different mountain ranges, and 17.41% to variation among populations within mountain ranges. Nested clade analysis revealed two major clades that likely diverged in allopatry during the Pleistocene: a southern clade from southern Colorado and a northern clade comprising northern Colorado, Wyoming, eastern Utah, and eastern Idaho. Historically restricted gene flow as a result of geographic barriers was indicated between populations on opposite sides of the Green River and Wyoming Basin and among populations in eastern Wyoming. In some instances genetic structure indicated isolation by distance.

Thermodynamics and kinetics of Hsp70 association with A + U-rich mRNA-destabilizing sequences

Rapid mRNA degradation directed by A + U-rich elements (AREs) is mediated by the interaction of specific RNA-binding proteins to these sequences. The protein chaperone Hsp70 has been identified in a cellular complex containing the ARE-binding protein AUF1 and has also been detected in direct contact with A + U-rich RNA substrates, indicating that Hsp70 may be involved in the regulation of ARE-directed mRNA turnover. By using gel mobility shift and fluorescence anisotropy assays, we have determined that Hsp70 directly and specifically associates with U-rich RNA substrates in solution. With the ARE from tumor necrosis factor alpha (TNFalpha) mRNA, Hsp70 forms a dynamic complex consistent with a 1:1 association of protein:RNA but demonstrates cooperative binding behavior on polyuridylate substrates. Unlike AUF1, the RNA binding activity of Hsp70 is not regulated by ion-dependent folding of the TNFalpha ARE, suggesting that AUF1 and Hsp70 recognize distinct binding determinants on this RNA substrate. Binding of Hsp70 to the TNFalpha ARE is driven entirely by enthalpy at physiological temperatures, indicating that burial of hydrophobic surfaces is likely the principal mechanism stabilizing the Hsp70.RNA complex. Potential roles for the interaction of Hsp70 with ARE-containing mRNAs in the regulation of mRNA turnover and/or translational efficiency are discussed.

Structural remodeling of an A + U-rich RNA element by cation or AUF1 binding

Association of AUF1 with A + U-rich elements (AREs) induces rapid cytoplasmic degradation of mRNAs containing these sequences, involving the recruitment or assembly of multisubunit trans-acting complexes on the mRNA. Recently, we reported that Mg(2+)-induced conformational changes in the ARE from tumor necrosis factor alpha mRNA inhibited AUF1 binding and oligomerization activities on this substrate (Wilson, G. M., Sutphen, K., Chuang, K., and Brewer, G. (2001) J. Biol. Chem. 276, 8695-8704). In this study, resonance energy transfer was employed to characterize structural changes in RNA substrates in response to cation- and AUF1-binding events. An RNA substrate containing the tumor necrosis factor alpha ARE displayed a weak conformational transition in the absence of added cations but was cooperatively stabilized by Mg(2+). Additional assays demonstrated a strong preference for small, multivalent cations, suggesting that the folded RNA structure was stabilized by counterion neutralization at discrete regions of high negative charge density. Association of AUF1 with cognate RNA substrates also induced formation of condensed RNA structures, although distinct from the folded structure stabilized by multivalent cations. Taken together, these experiments indicate that association of AUF1 with an ARE may function to remodel local RNA structures, which may be a prerequisite for subsequent recruitment of additional trans-acting factors.

Folding of A+U-rich RNA elements modulates AUF1 binding. Potential roles in regulation of mRNA turnover

In mammals, A+U-rich elements (AREs) are potent cis-acting determinants of rapid cytoplasmic mRNA turnover. Recognition of these sequences by AUF1 is associated with acceleration of mRNA decay, likely involving recruitment or assembly of multi-subunit trans-acting complexes. Previously, we demonstrated that AUF1 deletion mutants formed tetramers on U-rich RNA substrates by sequential addition of protein dimers (Wilson, G. M., Sun, Y., Lu, H., and Brewer, G. (1999) J. Biol. Chem. 274, 33374-33381). Here, we show that binding of the full-length p37 isoform of AUF1 to these RNAs proceeds via a similar mechanism, allowing delineation of equilibrium binding constants for both stages of tetramer assembly. However, association of AUF1 with the ARE from tumor necrosis factor (TNFalpha) mRNA was significantly inhibited by magnesium ions. Further fluorescence and hydrodynamic experiments indicated that Mg(2+) induced or stabilized a conformational change in the TNFalpha ARE. Based on the solution of parameters describing both the protein-RNA and Mg(2+)-RNA equilibria, we present a dynamic, global equilibrium binding model describing the relationship between Mg(2+) and AUF1 binding to the TNFalpha ARE. These studies provide the first evidence that some AREs may adopt higher order RNA structures that regulate their interaction with trans-acting factors and indicate that mRNA structural remodeling has the potential to modulate the turnover rates of some ARE-containing mRNAs.

Down-regulation of cyclin D1 expression by prostaglandin A(2) is mediated by enhanced cyclin D1 mRNA turnover

Prostaglandin A(2) (PGA(2)), an experimental chemotherapeutic agent, causes growth arrest associated with decreased cyclin D1 expression in several cancer cell lines. Here, using human non-small-cell lung carcinoma H1299 cells, we investigated the mechanisms whereby PGA(2) down-regulates cyclin D1 expression. Transcription rates of the cyclin D1 gene, studied using a cyclin D1 promoter-luciferase construct and nuclear run-on assays, were not affected by PGA(2) treatment. Instead, the cyclin D1 mRNA was rendered unstable after exposure to PGA(2). Since the stability of labile mRNA is modulated through binding of proteins to specific mRNA sequences, we sought to identify protein(s) recognizing the cyclin D1 mRNA. In electrophoretic mobility-shift assays using radiolabeled RNA probes derived from different regions of cyclin D1 mRNA, we observed that (i) lysates prepared from PGA(2)-treated cells exhibited enhanced protein-cyclin D1 RNA complex formation; (ii) the kinetics of complex formation correlated closely with that of cyclin D1 mRNA loss; and (iii) binding occurred within a 390-base cyclin D1 3' untranslated region (UTR) (K12). This binding activity could be cross-linked, revealing proteins ranging from 30 to 47 kDa. The RNA-binding protein AUF1, previously associated with the degradation of target mRNAs, bound cyclin D1 mRNA, because anti-AUF1 antibodies were capable of supershifting or immunoprecipitating cyclin D1 mRNA-protein complexes. Finally, insertion of K12 in the 3'UTR of reporter genes markedly reduced the expression and half-life of the resulting chimeric mRNAs in transfected, PGA(2)-treated cells. Our data demonstrate that PGA(2) down-regulates cyclin D1 expression by decreasing cyclin D1 mRNA stability and implicates a 390-base element in the 3'UTR in this regulation.

Spacing constraints on reinitiation of paramyxovirus transcription: the gene end U tract acts as a spacer to separate gene end from gene start sites

The paramyxovirus gene end U tracts are thought to serve as templates for the addition of a 3' polyA tail to viral mRNAs. The goal of the work described here was to determine the function in transcription of the naturally occurring variability in length of the gene end U tracts of the paramyxovirus simian virus 5 (SV5). An anchored RT-PCR assay was developed to test the hypothesis that the variable U tracts template the addition of variable lengths of polyA tails to mRNAs. The results showed that although the SV5 NP, M, and SH genes encode U tracts of seven, four, and six U residues, respectively, their mRNAs contain similar polyA tails of approximately 250-290 bases. These results indicate that the variable gene end U tracts are functionally equivalent in directing polyadenylation. A reverse genetics system based on a dicistronic minigenome containing the SH-HN gene junction was used to test the hypothesis that the variable U tracks affect the efficiency of transcription termination. Minigenome templates containing an SH gene end with a long U tract of six residues (U6) directed efficient transcription termination and reinitiation at the downstream HN start site with no nucleotide preference for the downstream intergenic region. Surprisingly, truncating the SH gene end U tract to four residues (U4) did not affect SH termination but, rather, reduced downstream HN reinitiation to 20-30% of wild-type levels. Efficient HN reinitiation could be restored to mutant U4 templates in either of two ways: by increasing the U-tract length from four to six residues or by increasing the length of the intergenic region. Efficient HN reinitiation required a minimum of six bases between the last nucleotide in SH and the first nucleotide in HN. We propose that for some paramyxoviruses, the gene end U tract serves a previously unrecognized role as a spacer region between the gene end and gene start sites.

Expression of mouse mammary tumor virus superantigen accelerates tumorigenicity of myeloma cells

To investigate whether superantigen (SAG) from endogenous mouse mammary tumor virus functions as an immunogenic or a tumorigenic factor in tumor development, the BALB/c myeloma cell line FO was transfected with the SAG gene from the 3' Mtv-50 long terminal repeat (LTR) open reading frame (ORF), the product of which was specific for Vbeta6. All five transfectants expressing Mtv-50 LTR ORF mRNA showed stimulatory activity for Vbeta6 T-cell hybridomas in vitro; this activity was inhibited by the addition of anti-Mtv-7 monoclonal antibody (MAb) or anti-major histocompatibility complex class II I-A(d) and I-E(d) MAb. All transfectants with the SAG gene grew more rapidly than did mock transfectants in BALB/c mice after subcutaneous inoculation, whereas all clones, including mock transfectants, grew equally well in athymic nude mice. A significant fraction of Vbeta6 T cells selectively expressed activation markers, including CD44(high), CD62L(low), and CD69(high), and produced large amounts of interleukin 5 (IL-5) and IL-6 in BALB/c mice inoculated with transfectants. These results suggested that the expression of viral SAG enhances the tumorigenicity of a myeloma cell line through the stimulation of SAG-reactive T cells.

A fluorescence-based assay for 3' --> 5' exoribonucleases: potential applications to the study of mRNA decay

A cell-free mRNA decay assay has been adapted to permit the kinetics of 3' --> 5' exoribonuclease activities to be monitored in real time. RNA probes containing 5' caps and 3' poly(A) tails generated by transcription in vitro are 3' labeled using fluorescein-N6-ATP and poly(A) polymerase. Release of fluorescein-conjugated adenosine residues from the 3' end of the RNA substrate is monitored by a time-dependent decrease in fluorescence anisotropy in the presence of cytosolic proteins. To demonstrate the utility of the assay, an RNA probe was constructed containing a fragment of the c-myc 3' untranslated region and an 85-base poly(A) tail. Following 3' fluorescein labeling, the rate of 3'-terminal adenosine excision was monitored in the presence of an S100 cytosolic extract prepared from K562 erythroleukemia cells. Removal of the fluorescein-tagged A residues resolved to a first-order decay function, allowing the rate constant and enzyme-specific activity to be determined in this extract. Further applications and advantages of this technology are discussed.

Assembly of AUF1 oligomers on U-rich RNA targets by sequential dimer association

Many labile mammalian mRNAs are targeted for rapid cytoplasmic turnover by the presence of A + U-rich elements (AREs) within their 3'-untranslated regions. These elements are selectively recognized by AUF1, a component of a multisubunit complex that may participate in the initiation of mRNA decay. In this study, we have investigated the recognition of AREs by AUF1 in vitro using oligoribonucleotide substrates. Gel mobility shift assays demonstrated that U-rich RNA targets were specifically bound by AUF1, generating two distinct RNA-protein complexes in a concentration-dependent manner. Chemical cross-linking revealed the interaction of AUF1 dimers to form tetrameric structures involving protein-protein interactions in the presence of high affinity RNA targets. From these data, a model of AUF1 association with AREs involving sequential dimer binding was developed. Using fluorescent RNA substrates, binding parameters of AUF1 dimer-ARE and tetramer-ARE equilibria were evaluated in solution by fluorescence anisotropy measurements. Using two AUF1 deletion mutants, sequences C-terminal to the RNA recognition motifs are shown to contribute to the formation of the AUF1 tetramer.ARE complex but are not obligate for RNA binding activity. Kinetic studies demonstrated rapid turnover of AUF1.ARE complexes in solution, suggesting that these interactions are very dynamic in character. Taken together, these data support a model where ARE-dependent oligomerization of AUF1 may function to nucleate the formation of a trans-acting, RNA-destabilizing complex in vivo.

Regulation of AUF1 expression via conserved alternatively spliced elements in the 3' untranslated region

The A+U-rich RNA-binding factor AUF1 exhibits characteristics of a trans-acting factor contributing to the rapid turnover of many cellular mRNAs. Structural mapping of the AUF1 gene and its transcribed mRNA has revealed alternative splicing events within the 3' untranslated region (3'-UTR). In K562 erythroleukemia cells, we have identified four alternatively spliced AUF1 3'-UTR variants, including a population of AUF1 mRNA containing a highly conserved 107-nucleotide (nt) 3'-UTR exon (exon 9) and the adjacent downstream intron (intron 9). Functional analyses using luciferase-AUF1 3'-UTR chimeric transcripts demonstrated that the presence of either a spliceable or an unspliceable intron 9 in the 3'-UTR repressed luciferase expression in cis, indicating that intron 9 sequences may down-regulate gene expression by two distinct mechanisms. In the case of the unspliceable intron, repression of luciferase expression likely involved two AUF1-binding sequences, since luciferase expression was increased by deletion of these sites. However, inclusion of the spliceable intron in the luciferase 3'-UTR down-regulated expression independent of the AUF1-binding sequences. This is likely due to nonsense-mediated mRNA decay (NMD) owing to the generation of exon-exon junctions more than 50 nt downstream of the luciferase termination codon. AUF1 mRNA splice variants generated by selective excision of intron 9 are thus also likely to be subject to NMD since intron 9 is always positioned >137 nt downstream of the stop codon. The distribution of alternatively spliced AUF1 transcripts in K562 cells is consistent with this model of regulated AUF1 expression.

The search for trans-acting factors controlling messenger RNA decay

Control of mRNA turnover is an integral component of regulated gene expression. Individual mRNAs display a wide range of stabilities, which in many cases have been linked to discrete sequence elements. The most extensively characterized determinants of rapid constitutive mRNA turnover in mammalian systems are A + U-rich elements (AREs), first identified in the 3' untranslated regions of many cytokine/lymphokine and protooncogene mRNAs. In this article, we describe recent advances in the characterization of ARE-directed mRNA turnover, including links to deadenylation kinetics and functional heterogeneity among AREs from different mRNAs. We then describe strategies employed in the search for trans-acting factors interacting with these elements. Using such techniques, an ARE-binding activity capable of accelerating c-myc mRNA turnover in vitro was identified, and named AUF1. Subsequent cloning and characterization revealed that AUF1 exists as a family of four proteins formed by alternative splicing of a common pre-mRNA and appears to function as part of a multisubunit trans-acting complex to promote ARE-directed mRNA turnover. Investigations using several systems have demonstrated that AUF1 expression and/or activity correlate with rapid decay of ARE-containing mRNAs, and that both expression and activity of AUF1 are regulated by developmental and signal transduction mechanisms.

Identification and characterization of proteins binding A + U-rich elements

A + U-Rich elements (AREs) have been extensively investigated as cis-acting determinants of rapid mRNA turnover. Recently, a number of RNA-binding proteins interacting with AREs have been described. This article presents strategies and techniques used by our laboratory to identify and characterize a family of ARE-binding proteins collectively termed AUF1. However, these techniques may be applied to the study of any protein displaying sequence-specific RNA binding activity. The techniques described here include the purification of native AUF1 from cultured cells as well as the preparation of recombinant AUF1 proteins using a bacterial expression system. Analyses of RNA-protein interactions are also described, including the use of gel mobility shift assays with synthetic RNA probes to monitor specific RNA binding activity in cell extracts or with recombinant proteins. Variations of this technique are also described to evaluate the RNA binding affinity of recombinant proteins and the use of specific RNA competitors to assess RNA determinants of protein binding specificity. Other techniques presented include the identification of specific proteins in RNA:protein complexes using antibody supershifts and the estimation of molecular weights of RNA-binding proteins by UV crosslinking. Results of individual experiments are presented as examples of some techniques. Throughout the article, suggestions are included to avoid commonly encountered problems and to assist in the optimization of these techniques for the study of other RNA-binding proteins.

Stabilization and cytoskeletal-association of LDL receptor mRNA are mediated by distinct domains in its 3' untranslated region

The mRNA encoding the human low density lipoprotein (LDL) receptor is transiently stabilized after phorbol ester treatment of HepG2 cells and has been shown to associate with components of the cytoskeleton in this cell line (G. M. Wilson, E. A. Roberts, and R. G. Deeley, J. Lipid Res. 1997. 38: 437-446). Using an episomal expression system, fragments of the 3' untranslated region (3'UTR) of LDL receptor mRNA were transcribed in fusion with the coding region of beta-globin mRNA in HepG2 cells. Analyses of the decay kinetics of these beta-globin-LDL receptor fusion mRNA deletion mutants showed that sequences in the proximal 3'UTR of LDL receptor mRNA including several AU-rich elements (AREs) were sufficient to confer short constitutive mRNA half-life in the heterologous system. Stabilization of LDL receptor mRNA in the presence of PMA required sequences in the distal 3'UTR, at or near three Alu-like repetitive elements. Furthermore, the 3'UTR of LDL receptor mRNA conferred cytoskeletal association on the otherwise unassociated beta-globin mRNA, by a mechanism involving at least two distinct RNA elements. Comparisons of decay kinetics and subcellular localization of endogenous LDL receptor mRNA and beta-globin-LDL receptor mRNA fusions in HepG2 cells have demonstrated that several cis-acting elements in the receptor 3'UTR contribute to post-transcriptional regulation of receptor expression, and provide further support for involvement of the cytoskeleton in the regulation of LDL receptor mRNA turnover.

Structure and genomic organization of the human AUF1 gene: alternative pre-mRNA splicing generates four protein isoforms

The steady-state levels of many mRNAs are determined in part by their turnover rates. Turnover rates, in turn, are usually controlled by proteins that bind cis-acting sequence elements in mRNAs. One class of cis-acting instability determinants is composed of A + U-rich elements present in the 3'-UTRs of many labile mRNAs. Many A + U-rich elements are bound by the AUF1 family of RNA-binding proteins, which may target these mRNAs for rapid decay. cDNA cloning and immunoblot analyses suggest that the AUF1 family consists of at least four isoforms. Previous genomic cloning combined with FISH and Southern analyses of a panel of monochromosomal mouse/human or hamster/human somatic cell hybrids localized two AUF1 loci to human 4q21.1-q21.2 and Xq12 (B. Wagner et al., 1996, Genomics 34: 219-222). In the present study AUF1 gene organization was examined. The results suggest that the four known AUF1 isoforms are generated by alternative pre-mRNA splicing of a transcript encoded by the chromosome 4 locus. Functionally, this creates isoforms with different RNA-binding affinities and specificities. Thus, alternative pre-mRNA splicing may serve to create functional versatility within the AUF1 family of proteins.

Coincidence of true and false left ventricular aneurysm

Coincidence of true and false left ventricular aneurysm is very rare. To date 6 cases have been reported in the world literature. We present a case of false aneurysm emanating from a posterior true aneurysm of the left ventricle. These findings were demonstrated preoperatively by transesophageal echocardiography and were confirmed at operation. The aneurysms were successfully resected and the ventricle repaired.

Modulation of LDL receptor mRNA stability by phorbol esters in human liver cell culture models

In the human hepatocarcinoma cell lines HepG2 and Hep3B, low density lipoprotein receptor (LDLR) mRNA levels were rapidly and transiently induced after treatment with phorbol-12-myristate-13-acetate (PMA), increasing by approximately 50-fold and 8-fold, respectively, within 4 h before returning to near basal levels by 24 h. The difference in magnitude of mRNA accumulation between these cell lines is at least partly due to a rapid 2- to 2.5-fold stabilization of LDLR mRNA in HepG2 cells after PMA treatment. Stabilization of LDLR mRNA in response to PMA was also observed in HH01 cells, a human hepatocyte coculture system derived from normal human liver. In both HepG2 and HH01 cells, PMA treatment induced a rapid morphological change with characteristics of cytoskeletal reorganization. The changes in morphology and stabilization of LDLR mRNA by PMA were coincident in the cell lines tested and were independent of de novo gene expression. Subcellular fractionation studies indicated that LDLR polysomes may be associated with the cytoskeleton in HepG2 cells. Disruption of the action cytoskeleton but not microtubules abrogated stabilization of LDLR mRNA by PMA. These data suggest that components of the actin cytoskeleton are involved in the regulated decay of LDLR mRNA in some human liver cell culture systems.

Bax- and Bak-induced cell death in the fission yeast Schizosaccharomyces pombe

The effects of the expression of the human Bcl-2 family proteins Bax, Bak, Bcl-2, and Bcl-XL were examined in the fission yeast Schizosaccharomyces pombe and compared with Bax-induced cell death in mammalian cells. Expression of the proapoptotic proteins Bax and Bak conferred a lethal phenotype in this yeast, which was strongly suppressed by coexpression of the anti-apoptotic protein Bcl-XL. Bcl-2 also partially abrogated Bax-mediated cytotoxicity in S. pombe, whereas a mutant of Bcl-2 (Gly145Ala) that fails to heterodimerize with Bax or block apoptosis in mammalian cells was inactive. However, other features distinguished Bax- and Bak-induced death in S. pombe from animal cell apoptosis. Electron microscopic analysis of S. pombe cells dying in response to Bax or Bak expression demonstrated massive cytosolic vacuolization and multifocal nuclear chromatin condensation, thus distinguishing this form of cell death from the classical morphological features of apoptosis seen in animal cells. Unlike Bax-induced apoptosis in 293 cells that led to the induction of interleukin-1 beta-converting enzyme (ICE)/CED-3-like protease activity, Bax- and Bak-induced cell death in S. pombe was accompanied neither by internucleosomal DNA fragmentation nor by activation of proteases with specificities similar to the ICE/CED-3 family. In addition, the baculovirus protease inhibitor p35, which is a potent inhibitor of ICE/CED-3 family proteases and a blocker of apoptosis in animal cells, failed to prevent cell death induction by Bax or Bak in fission yeast, whereas p35 inhibited Bax-induced cell death in mammalian cells. Taken together, these findings suggest that Bcl-2 family proteins may retain an evolutionarily conserved ability to regulate cell survival and death but also indicate differences in the downstream events that are activated by overexpression of Bax or Bak in divergent cell types.

Structure and expression of the messenger RNA encoding the murine multidrug resistance protein, an ATP-binding cassette transporter

In vitro, overexpression of the human multidrug-resistance protein (MRP) causes a form of multidrug resistance similar to that conferred by P-glycoprotein, although the two proteins are only very distantly related. Studies with MRP-enriched membrane vesicles have demonstrated that the protein can bind and transport cysteinyl leukotrienes, as well as some other glutathione conjugates, with high affinity. In contrast, there is no direct evidence of the ability of MRP to bind or transport unmodified forms of the drugs to which it confers resistance. To facilitate studies of the physiological function(s) of MRP and its ability to cause multidrug resistance in vivo, we cloned and characterized the mRNA specifying its murine homolog. The murine MRP mRNA encodes a protein of 1528 amino acids that is 88% identical to human MRP. Although detectable by Northern blotting at variable levels in a wide range of tissues, in situ hybridization experiments revealed that MRP mRNA expression in some tissues is cell-type specific. High levels of the mRNA were detected in epithelia lining bronchi and bronchioles, as well as stage-specific expression in the seminiferous epithelium of the testes. Comparison of the predicted hydropathy profiles of human and murine MRP suggests a highly conserved membrane topology, the most distinctive feature of which is an extremely hydrophobic NH2-terminal region containing five or six potential transmembrane sequences. This structural feature is shared with the sulfonylurea receptor and the yeast cadmium factor 1 but is not present in members of the superfamily, such as the cystic fibrosis transmembrane conductance regulator and P-glycoproteins. Finally, we used overlapping cDNAs to construct an episomally replicating murine MRP expression vector that was stably transfected into HeLa cells. MRP-Transfected cell populations expressed markedly elevated levels of a 180-190-kDa protein that cross-reacted with a polyclonal antiserum raised against a peptide that is completely conserved in murine and human MRPs. The MRP transfectants also displayed increased resistance to vincristine (5-6-fold) and doxorubicin (< 2-fold).

The clinical utility of automatic boundary detection for the determination of left ventricular volume: a comparison with conventional off-line echocardiographic quantification

The aim of this study was to compare measurements of echocardiographic volume with an on-line automatic boundary detection imaging system with those of a conventional off-line method for routine clinical studies. Automatic boundary detection imaging shows promise as a rapid, on-line method for quantitating left ventricular volumes by echocardiography. However, there is little information about the role of automatic boundary detection for routine clinical studies. Ninety-seven patients with a variety of clinical diseases who were referred for clinical transthoracic echocardiographic evaluation were studied in apical four-chamber and two-chamber imaging planes. End-diastolic volume, end-systolic volume, and ejection fraction obtained with automatic boundary detection images were compared with those of conventional off-line analysis. Segmental endocardial definition and border tracking were evaluated on all automatic boundary detection images. Left ventricular end-diastolic volumes obtained by automatic boundary detection correlated well but were systematically under-estimated compared with off-line analysis for the apical two-chamber (r = 0.83; underestimation = 42 +/- 33 ml; p < 0.05) and four-chamber views (r = 0.83; underestimation = 43 +/- 31 ml; p < 0.05). Left ventricular end-systolic volumes also correlated well but were underestimated by automatic boundary detection for the apical two-chamber (r = 0.83; underestimation = 14 +/- 26 ml; p < 0.05) and four-chamber views (r = 0.83; underestimation = 18 +/- 24 ml; p < 0.05). Ejection fraction was not predicted accurately for the entire study population (n = 97). However, for patients with complete endocardial definition (n = 32), automatic boundary detection accurately predicted ejection fraction with no systematic error compared with manually traced images for both the apical two-chamber (r = 0.86; p < 0.05) and four-chamber (r = 0.82; p < 0.05) views. Segmental analysis of endocardial tracking revealed significantly better tracking of the septal and lateral walls compared with other regions (p < 0.05). End-diastolic and end-systolic volumes determined by automatic boundary detection correlate well but underestimate volume compared with conventional off-line analysis. However, ejection fraction compares favorably for the two methods when there is complete endocardial definition.

An episomal expression vector system for monitoring sequence-specific effects on mRNA stability in human cell lines

A plasmid expression system has been developed which allows sequence-specific effects on mRNA degradation rates to be determined. This system uses stable, nonintegrating vectors that provide consistent levels of mRNA expression without the position effects common to integrating vectors. cDNAs encoding putative instability elements may be subcloned into the 5' untranslated region (5'UTR), the coding region, or the proximal 3'UTR of a beta-globin cDNA reporter. The effects of these sequences on mRNA stability may then be determined by actinomycin time course analyses of the fusion mRNAs and recombinant beta-globin mRNA in human cell lines. To demonstrate the utility of the vector system we fused an 820-bp fragment of the cDNA encoding the proximal 3'UTR of human 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase to the 3'UTR of the beta-globin reporter and introduced the vector into the human hepatocarcinoma cell line, HepG2. The fusion mRNA was degraded at a rate 2- to 2.5-fold greater than that of beta-globin alone, at a rate similar to that reported for HMG CoA reductase mRNA in normal rat liver. Similar to a number of other relatively unstable mRNAs, the rate of fusion mRNA degradation was greatly decreased by treatment with cycloheximide.

Pharmacological characterization of multidrug resistant MRP-transfected human tumor cells

We have previously identified and characterized a novel member of the ATP-binding cassette superfamily of transport proteins, multidrug resistance protein (MRP), and subsequently demonstrated that its overexpression is sufficient to confer multidrug resistance on previously sensitive cells (Cole et al., Science (Washington DC), 258: 1650-1654, 1992; Grant et al., Cancer Res. 54: 357-361, 1994). In the present study, we have transfected two different eukaryotic expression vectors containing MRP complementary DNA into HeLa cells to study the pharmacological phenotype produced exclusively by overexpression of human MRP. The drug resistance patterns of the two MRP-transfected cell populations were similar. They were characterized by a moderate (5- to 15-fold) level of resistance to doxorubicin, daunorubicin, epirubicin, vincristine, and etoposide, and a low (< or = 3-fold) level of resistance to taxol, vinblastine, and colchicine. The transfectants were not resistant to 9-alkyl anthracyclines, mitoxantrone, or cisplatin. The MRP-transfected cells were also resistant to some heavy metal anions including arsenite, arsenate, and trivalent and pentavalent antimonials but were not resistant to cadmium chloride. Accumulation of radiolabeled vincristine was reduced by 45% in the MRP-transfected cells and could be restored to the levels found in sensitive cells by depletion of ATP. Rates of vincristine efflux did not differ greatly in the sensitive and resistant cells. The cytotoxic effects of vincristine and doxorubicin could be enhanced in a dose-dependent fashion by coadministration of verapamil. Cyclosporin A also increased vincristine toxicity but had less effect on doxorubicin toxicity. The degree of chemosensitization by verapamil and cyclosporin A was similar in MRP-transfected cells and in cells transfected with the vector alone, suggesting that sensitization involved mechanisms independent of MRP expression. Verapamil and cyclosporin A caused a modest increase in vincristine accumulation in the resistant cells but did not restore levels to those of the sensitive cells. Taken together, these data indicate that drug-resistant cell lines generated by transfection with MRP complementary DNA display some but not all of the characteristics of MRP-overexpressing cell lines produced by drug selection in vitro. They further demonstrate that the multidrug resistance phenotype conferred by MRP is similar but not identical to that conferred by P-glycoprotein and includes resistance to arsenical and antimonial oxyanions.

Mutations in the NTP-binding motif of minute virus of mice (MVM) NS-1 protein uncouple ATPase and DNA helicase functions

The NS-1 protein of minute virus of mice (MVM) is required for viral DNA replication and transcriptional regulation. To define the domain structure of NS-1, we have generated point mutations in its putative NTP-binding/ATPase domain. We show that all mutants were unable to support replication of MVM DNA in a transient DNA replication assay. Furthermore, all mutants, except for the K405S substitution, were able to transactivate the P38 promoter in transient transfection experiments. NS-1 proteins bearing COOH-terminal deletions of 29 and 33 amino acid residues were also transcriptionally inert. Biochemical analysis of recombinant NS-1 expressed in insect cells shows that mutations in the putative NTP-binding/ATPase domain severely reduced helicase activity in vitro. However, affinity labeling experiments indicate that none of these mutations, except for K469T, impaired NTP-binding activity. Finally, all point mutants retained significant levels of ATPase activity, except for the E444Q mutant (1%). These findings suggest that the replication and transcription activities of NS-1 reside in separate functional domains. In addition, NS-1 proteins with mutations in the putative nucleotide binding fold have lost helicase activity, whereas most retain nucleotide binding and ATPase functions, suggesting that the mutations have uncoupled the ATPase and helicase activities.

Severe anaemia and ileocolic anastomotic ulceration

Two children are described with anaemia from ileocolic anastomosic ulceration as a late complication of surgery in the newborn period. The anastomosis was revised in each case but in one child there was early recurrence of ulceration.

Purification and initial characterization of the lymphocyte-specific protein-tyrosyl kinase p56lck from a baculovirus expression system

A baculovirus expression system has been used to express large quantities of the lymphocyte-specific protein-tyrosyl kinase p56lck. A series of chromatographic steps, including the novel application of metalchelate affinity chromatography for protein kinase purification, were employed to obtain p56lck in a highly active form. Recombinant p56lck was purified to apparent homogeneity as determined by polyacrylamide gel electrophoretic analyses and was found to migrate in SDS gels as two related species, both with apparent molecular masses close to 56 kDa. p56lck phosphorylated all assayed substrates exclusively on tyrosyl residues, and underwent autophosphorylation at one principal site, also on a tyrosyl residue. p56lck displayed a high affinity for a synthetic peptide corresponding to the cytoplasmic domain (residues 52-164) of the T-cell receptor zeta-chain (TCR-zeta) (Km approximately 6.5 microM) but a low affinity for a peptide corresponding to its own autophosphorylation site (Km approximately 900 microM). p56lck was also found to be highly active for a purified protein-tyrosyl kinase (Vmax greater than 400 pmol.min-1.micrograms-1 using the TCR-zeta (52-164) as a substrate). A variety of agents were tested for their ability to inhibit p56lck, with zinc ions (I50 approximately 1.7 mM) and staurosporine (I50 approximately 500 nM) proving the most potent.

Expression of minute virus of mice major nonstructural protein in insect cells: purification and identification of ATPase and helicase activities

The gene encoding the major nonstructural (NS-1) protein of minute virus of mice (MVM) has been expressed in insect cells using a baculovirus expression system. This 83-kDa polypeptide was found to be localized in the soluble (cytosolic) fraction in insect cells, in contrast with the nuclear localization of NS-1 expressed in MVM-infected mouse LA-9 cells. The protein was purified by immunoaffinity chromatography using a monoclonal antibody (MAb) prepared to an NS-1 fusion peptide [(Yeung et al., Virology 185, 35-45 (1991)]. Recombinant NS-1 was eluted using either low pH or a synthetic peptide corresponding to the epitope of the MAb. The peptide-eluted material is greater than 95% pure and biologically active in that it has ATPase activity and ATP-dependent helicase activity as determined by a strand displacement assay.

The effect of E1 mutations on biochemical transformation by an adenovirus carrying the herpes simplex virus thymidine kinase gene in region E3

A series of human adenovirus type 5 (Ad5) vectors has been constructed in which a vector containing the human herpes simplex virus thymidine kinase (TK) gene has been recombined with several Ad5 early region 1 (E1) mutants. The resulting viruses were used to study host-virus interactions in TK- rat cells and to examine the importance of E1 functions in a biochemical transformation assay. One of the most important parameters affecting transformation efficiency in this system was the cytotoxicity of the transforming virus. Ad5 viruses expressing the E1a 289 amino acid protein were all highly cytotoxic and induced significantly fewer colonies than did less cytotoxic mutants which were defective in expression of the 289 amino acid product. When correction was made for differential cell viability the variation in transformation efficiencies was considerably reduced although some E1a mutants still demonstrated an enhanced ability to transform in comparison to wt virus. The significance of these results to morphological transformation by adenoviruses is discussed.

Asymptomatic degenerative disk disease and spondylosis of the cervical spine: MR imaging

Evidence on magnetic resonance (MR) images of disk degeneration and herniation, as well as of cord and root impingement, may be regarded either as normal, age-related changes or as causative of symptoms. Individuals referred for MR examinations of the larynx without symptoms referable to the cervical spine were studied retrospectively (35 patients) or prospectively (65 patients) over a 2-year period. With a solenoid surface coil, 5-mm-thick sections were acquired in sagittal, axial, and coronal planes with T1-weighted spin-echo pulsing sequences. Disk protrusion (herniation/bulge) was seen in five of 25 (20%) patients aged 45-54 and 24 of 42 (57%) patients older than 64 years of age. Posterolateral protrusions were seen in only nine of 100 patients and occurred with greatest frequency in patients over 64 years of age. In no patient was obliteration of the intraforaminal fat seen. Spinal cord impingement was observed in nine of 58 (16%) patients under 64 years of age, and in 11 of 42 (26%) patients over 64 years of age. Cord compression was observed in seven of 100 patients and occurred solely secondary to disk protrusion in all cases. The percentage of cord area reduction never exceeded 16% and averaged approximately 7%.

Influence of complex charge and size on the uptake of 99mTc-diphosphonates in osteogenic tissue

The biodistributions of six chromatographically pure 99mTc-HEDP complexes have been determined in soft tissues, normal bone and osteogenic lesions (induced with a Walker 256 tumor) in Fisher 344 rats. The physical properties of each 99mTc-HEDP complex including anionic charge, partial molar volume, molecular weight and spectral characteristics are known; thus allowing structure-activity relationships to be drawn. The results indicate that the smallest, low charged, mononuclear 99mTc-HEDP complexes have the greatest uptake in bone lesions, and the highest lesion to muscle and lesion to normal bone ratios.

Measurement of thyroid size by ultrasound, palpation and scintiscan

Thyroid gland size was calculated from grey-scale ultrasound images in twenty patients with goitre. Results were compared with measurements by palpation and in some cases with measurements by scintiscan and at operation. There was a good correlation between ultrasound measurements and both the size of surgical specimens and clinicians' estimations, although clinicians under-estimated the size of large (greater than 40 ml) goitres compared with ultrasound and surgical specimens. Gland size calculated from scintiscan did not correspond well with measurements by ultrasound or palpation.

Prevention of bone loss following oophorectomy in premenopausal women: a retrospective assessment of the effects of oophorectomy and a prospective controlled trial of the effects of mestranol therapy

Prospective studies of bone mass in women following oophorectomy for benign conditions were done by the double-blind technique. Skeletal response to treatment was measured by photon absorption densitometry. Untreated patients were found to lose bone mass rapidly during the first two years after oophorectomy. When estrogen replacement was started within two months of oophorectomy, it was found to be effective in preventing subsequent bone tissue loss. Three years following oophorectomy, untreated women who had already lost bone tissue, and who were then started on estrogen replacement, showed a highly significant increase in their bone mass. The women in whom this treatment was delayed for six years did not respond. No untoward effects were noted in these women, perhaps, in part, because they had undergone hysterectomy. Long-term effects of this treatment are now being evaluated.

Total thyroidal content of iodine in thyrotoxic patients measured by in vivo neutron activation analysis

This paper describes an in vivo method for measuring total thyroidal iodine stores by activation analysis, its evaluation and measurements in thyrotoxic patients. There was good correlation between measurements of solutions of iodine and post-mortem thyroids by activation analysis and chemical analysis. Measurements in thyrotoxic patients showed low levels in untreated and treated (antithyroid drugs) patients and a marked increase in patients studied whilst in clinical remission. The practical importance of this method of measurement of thyroidal iodine stores is that it is a reliable in vivo measurement obtained at a single visit and should enable the definition of the relationship of thyroidal iodine stores to pathophysiology and prognosis.

General professional training in medicine

A programme of general professional training in medicine based on the Royal Commission report has been in operation at the Western Infirmary, Glasgow, and associated hospitals since 1969. It involves a two-year rotation through general medicine, dermatology, psychiatry, paediatrics, geriatrics, and a variety of medical specialties. A third year is spent as far as possible in one unit of the doctor's choice. The scheme has been popular with trainees and senior staff. A high pass-rate has been achieved in the M.R.C.P.--23 out of 26 being successful within the three-year period. The trainees have subsequently taken up a wide variety of hospital posts within the broad division of medicine or entered general practice. The concept of a broadly based three-year period of general professional training in medicine has proved both practical and useful.

Blood ethanol concentrations in patients attending special clinics in Glasgow

Blood samples for measurement of ethanol concentration were taken on a routine basis from 543 male and 158 female patients attending Special Clinics in Glasgow. Ethanol was detected in 56 (10-3 per cent.) of the men and eight (5-1 per cent.) of the women, and at concentrations in excess of 0-1 g./l. in 37 (6-8 per cent.) and three (1-9 per cent.) respectively. In nine men and one woman, the blood ethanol concentration was over 0-8 g./l. when they attended the clinic. The majority (84 per cent.) of positive findings were obtained in specimens collected after 2 p.m. and one-quarter on Tuesday afternoons, the local half-day. The other peak periods related to attendance at football matches on Wednesday evenings, and to receiving wages on Friday mornings. Male new patients attending a clinic for the first time had the highest incidence, 32 (11-6 per cent.) having detectable amounts of ethanol among whom 26 (9-4 per cent.) had levels in excess of 0-1 g./l., compared with only 4-1 per cent. among those either returning to the clinics with a fresh infection or on surveillance. Only 5 per cent. of female patients attending for the first time and 3 per cent. of those on surveillance had detectable amounts of ethanol in the blood, compared with 9 per cent. of those few returning with fresh infections. Levels in excess of 0-1 g./1. were only found in promiscuous women. Those with concentrations in excess of 0-8 g./1. were unreliable attenders. Only one, a known alcoholic, completed surveillance; one defaulted after his fourth visit, four after the second, and four after the first visit.