Exencephaly and axial skeletal malformations induced by maternal administration of sodium valproate in the MF1 mouse

Clinical and epidemiological studies indicate that maternal use of valproic acid (VPA) during pregnancy causes an increased risk for spina bifida in the fetus. A proportion of infants exposed to VPA in utero exhibit a characteristic pattern of facial malformations. Despite the developmental interdependence of the neural plate and paraxial mesoderm during normal morphogenesis, the possible involvement of the axial skeleton in VPA-induced NTD has not been clearly documented. So the objective of this investigation was to determine the nature and extent of involvement of the axial skeleton in VPA-induced exencephaly in the mouse. A single dose of 600 mg/kg of sodium valproate was administered (IP) to MF1 mouse on day 8 of gestation. This treatment resulted in significant increase in resorption, reduction in mean fetal weight, and exencephaly (25%) of live fetuses. Several craniofacial malformations and subcutaneous haematomas were associated with exencephaly. Alizarin red-stained skeletal preparations revealed maxillary-, mandibular hypoplasia, absence of skull vault, hypoplasia and/or agenesis of basicranial bones, and obtuse angulation of the craniovertebral junction. Hemivertebrae, longitudinal fusion of the vertebral arches and bodies, accessory ribs (cervical and lumbar), fusion of thoracic ribs, and several patterns of sternal variations were observed. Nonexencephalic VPA-treated embryos exhibited mandibular, maxillary hypoplasia, arched and cleft palates, cleft lip, kinky tail, and vertebral and sternal anomalies. Treated embryos at early stages of development revealed delay in elevation and fusion of neural folds, distended IVth ventricle, kinky spinal cord, incomplete separation of somites and growth retardation. When viewed in light of the published work on VPA action on embryonic systems, these observations suggest that abnormalities associated with VPA-induced exencephaly may be due to either a direct action of VPA on the precursors of these organs or secondary to its action on neural tube. A significantly high incidence of NTD and their consistent association with defective development of the axial skeleton suggest that this is an excellent experimental model for investigating the pathogenetic mechanism(s) of VPA induced NTD.

Phosphorylation-dependent interaction of adenovirus preterminal protein with the viral origin of DNA replication

Adenovirus preterminal protein (pTP) exists as a heterodimer with the viral DNA polymerase (AdPol) and becomes covalently linked to a dCMP residue during initiation of DNA replication. The in vivo phosphorylation of pTP could be demonstrated when pTP is overproduced using recombinant vaccinia viruses, or by a large scale metabolic labeling of adenovirus 2 (Ad2)-infected HeLa cells. Phosphoserine was the only phosphoamino acid obtained by acid hydrolysis of 32P-labeled pTP immunoprecipitated from metabolically labeled HeLa cells infected with either Ad2 or recombinant vaccinia virus. Tryptic peptide maps of pTP expressed using recombinant vaccinia virus system in HeLa cells revealed that phosphorylation of pTP occurred on multiple sites. Dephosphorylation of pTP with calf intestinal alkaline phosphatase resulted in a significant decrease in its activity in the in vitro DNA replication initiation assays. Further characterization of the phosphatase-treated pTP indicated that although dephosphorylation did not affect its interaction with AdPol, the specific recognition of the DNA replication origin by pTP was significantly reduced as determined by gel electrophoresis-based DNA mobility shift assays.

Expression of the extracellular domain of the rat liver prolactin receptor and its interaction with ovine prolactin

A clone of the extracellular domain of the rat liver prolactin receptor was generated by the RNA-based polymerase chain reaction, and the NH2-terminal 210 amino acids were expressed in HeLa cells using a vaccinia virus/T7 hybrid expression system. The protein was isolated from serum-free culture medium directly by chromatography on an ovine prolactin affinity column and yielded approximately 1.5 mg of protein/liter of suspension culture. The extracellular domain of the rat prolactin receptor inhibited the ovine prolactin-dependent mitogenesis of rat lymphoma Nb2 cells with an IC50 of 7.1 pM and bound 125I-labeled ovine prolactin with a Kd of 1.21 +/- 0.19 nM. In contrast, the binding of the 125I-labeled extracellular domain to ovine prolactin exhibited positive cooperativity with a Hill coefficient of 1.73. High pressure gel filtration chromatography was used to demonstrate the formation of a complex consisting of one molecule of ovine prolactin and two molecules of the extracellular domain of the rat prolactin receptor. Complex formation occurred with human growth hormone, but not with ovine growth hormone, a non-lactogen.

Modified Doppler flowmetry in the splanchnic circulation

BACKGROUND

Absolute measurements of blood flow by Doppler ultrasonography are subject to substantial error. A simplified method of Doppler flowmetry using conventional duplex Doppler equipment was studied to establish its validity in determining short-term changes in flow in the splanchnic circulation in portal hypertension.

METHODS

Two simple indices were measured: peak velocity averaged over two cardiac cycles and vessel diameter. The relationship between peak and mean velocity was studied using a Doppler phantom. The feasibility of studying relevant vessels and the constancy of regional flow was determined by performing Doppler flowmetry in a basal state twice within 2 hours.

RESULTS

Constancy of relationship between peak and mean velocities was confirmed (r > 0.98). Examination was successful in the majority of 28 consecutive patients with portal hypertension for superior mesenteric, main portal, right portal, and paraumbilical (when patent) veins, but was successful in only 54% for the hepatic artery. Constancy of basal flow was found in 11 selected patients when group data were considered, but in individuals, substantial and unpredictable variance was found.

CONCLUSIONS

Modified Doppler flowmetry appears valid in the assessment of short-term changes in splanchnic blood flow of patients with portal hypertension. Individual variance in baseline flow is identified as a potential problem and is further reason for caution in the interpretation of measurements of Doppler flow.

Adenovirus DNA polymerase is phosphorylated by a stably associated histone H1 kinase

Adenovirus DNA polymerase (AdPol) exists as a complex with the preterminal protein (pTP) and is essential for both initiation and elongation stages of viral DNA replication. Recent evidence from our laboratory indicates that AdPol is a phosphoprotein and that the major in vivo phosphorylation site, serine 67, occurs within the consensus substrate recognition sequence for cdc2 kinases. In this study, we found that a protein kinase which also exhibits histone H1 phosphorylation activity is stably associated with AdPol. AdPol forms a multimeric complex with this histone H1 kinase and pTP in HeLa cells infected with adenovirus or coinfected with recombinant vaccinia viruses encoding AdPol and pTP. The associated protein kinase and the p34cdc2 kinase phosphorylate AdPol at the same sites which are utilized in vivo, suggesting that the p34cdc2 kinase or a related kinase may be involved in the in vivo phosphorylation of AdPol. Serine 67 is also one of the major in vitro phosphorylation sites, and the substitution of alanine for serine at this position abolishes DNA replication initiation activity of AdPol.

Role of protein conformation in the processing of dengue virus type 2 nonstructural polyprotein precursor

The dengue virus type-2 (DEN-2) genome is a positive-strand RNA encoding a single polyprotein precursor, C-prM(M)-E-NS1-NS2A-NS2B-NS3-NS4A-NS4B- NS5, consisting of 3391 amino acids (aa). The N-terminal region of the polyprotein precursor, C-prM(M)-E, encodes the structural proteins and is processed cotranslationally by the host signal peptidase. The nonstructural region NS1-->NS5 is processed by the viral protease(s), as well as by the signal peptidase. A two-component viral protease consisting of NS2B and the serine protease domain of NS3 has been shown to be required for cleavages having the consensus sequence of dibasic aa (K-R, R-R, R-K, or Q-R). In this study, the region encoding all the nonstructural proteins, NS1-->NS5, was expressed using a recombinant vaccinia virus system. Cleavages at the consensus viral protease recognition sites, 2B-3 at the N terminus and 3-4A at the C terminus, are prerequisites to the release of mature NS3 protease. Although the 2B-3 site was cleaved readily in a variety of polyprotein precursors containing the intact NS2B and the NS3 protease domain, the 3-4A site was most efficiently cleaved, similar to that found in DEN-2-infected cells, only in the polyprotein precursor encoding the entire nonstructural region. Removal of NS1 at the N terminus or of NS5 coding sequences at the C terminus affected the cleavage at the 3-4A site to produce the processing intermediate, NS3-NS4A. These results indicate that the conformation of the nonstructural polyprotein precursor, NS1-->NS5, plays a major role in the efficient cleavage at the 3-4A site.

Characterization of an unusual mutant of human melanoma cells resistant to anticancer drugs that inhibit topoisomerase II

The topoisomerase II inhibitor, VP-16 (etoposide), is an important component in many chemotherapeutic regimens. To characterize resistance to this drug, the human melanoma cell line, FEM-X, was selected in multiple steps with VP-16. To prevent the development of typical multidrug resistance, an inhibitor of P-glycoprotein, the tiapamil analog, RO-11-2933, was added to the selections. The resultant clone FVP3 is 56-fold resistant to VP-16 and cross-resistant to doxorubicin (Adriamycin) (9-fold) and VM-26 (27-fold). These cells are also two- to four-fold resistant to m-AMSA, daunorubicin, and mitoxantrone. FVP3 is not resistant to the P-glycoprotein substrates vinblastine, does not express the MDR1 gene at detectable levels, and does not show reduced 3H-VP-16 accumulation. Unlike other cell lines that exhibit resistance to inhibitors of topoisomerase II, FVP3 has the same level of topoisomerase II expression and activity as FEM-X. Using live cells treated with VP-16, band depletion assays and KCI/SDS precipitation assays show that topoisomerase II from FVP3 is much less susceptible to drug-induced cleavable complex formation than is that from FEM-X. This difference in sensitivity to VP-16 is also detected using lysates from disrupted cells, but not with isolated nuclei devoid of cytoplasmic and membrane components. In addition, the topoisomerase II present in nuclear extracts from FVP3 is not resistant to the effects of VP-16 as measured by: (1) inhibition of strand passing activity during decatenation of kinetoplast DNA, (2) drug-induced linearization of plasmid DNA, and (3) immunodepletion by VP-16. These results suggest that some component of the cytoplasm or cellular membranes, or a factor depleted from nuclei during their isolation, is responsible for the resistance to VP-16 in FVP3.

K-ras and p53 point mutations in 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced hamster lung tumors

Lung tumors were induced in Syrian golden hamsters by s.c. injection of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). After 40 weeks lung tumor tissue was isolated. Administration of the NNK and exposure of the animals to an atmosphere of 65% oxygen resulted in a statistically significant reduction in tumor size but did not alter the histological tumor type or tumor incidence when compared with carcinogen treated animals maintained under ambient air. Histologically, lung tumors had the morphologic features of adenomas and adenocarcinomas with approximately 15% being squamous cell carcinomas. Lung tumors were examined for mutations in the Ki-ras oncogene and the p53 tumor suppressor gene by direct sequencing. The Ki-ras mutation frequency in RNA isolated from pooled tumors and in DNA isolated from individual tumors were found to be identical. Activated Ki-ras alleles were detected in 77-94% of tumors. All mutations observed (from a total of 65) except one were GC-AT. The Ki-ras mutations resulted in amino acid substitutions at either codons 12 or 13. No mutations were detected at the 61st codon. Examination of the same tumors for p53 mutations showed only one point mutation. We conclude that the NNK treatment in Syrian golden hamsters results in a distinctive mutation pattern in the Ki-ras gene whereas p53 gene mutations may not play a major role at this stage in hamster lung tumorigenesis.

Adenovirus DNA polymerase is a phosphoprotein

Biological activities of many of the eukaryotic DNA replication proteins are modulated by protein phosphorylation. Investigations of the phosphorylation of adenovirus DNA polymerase (AdPol) have been difficult mainly because of its low level of synthesis in adenovirus-infected HeLa cells. However, when AdPol was overproduced using the recombinant vaccinia virus (RV-AdPol) and the baculovirus expression systems, or by a large scale metabolic labeling of adenovirus 2-infected HeLa cells (native AdPol), in vivo phosphorylation of AdPol could be demonstrated. Phosphoamino acid analysis of [32P]AdPol indicated the presence of phosphoserine independent of the source of AdPol. Comparison of tryptic peptide maps of native AdPol and RV-AdPol revealed that the majority of phosphopeptides were common. Fractionation by high performance liquid chromatography and sequencing of one of the major phosphopeptides revealed serine 67 as a site of phosphorylation. Interestingly, this site is located close to the nuclear localization signal of AdPol and has a consensus substrate recognition sequence for histone H1 (cdc2-related) kinases and mitogen-activated protein kinases. Dephosphorylation of AdPol with calf intestinal alkaline phosphatase resulted in significant decrease in its activity in the in vitro DNA replication initiation assay, suggesting that phosphorylation is important for its biological activity.

Processing and localization of Dengue virus type 2 polyprotein precursor NS3-NS4A-NS4B-NS5

Processing of dengue virus type 2 polyprotein precursor NS3-NS4A-NS4B-NS5 could be mediated by the catalytically active NS3 protease domain and NS2B in trans at the dibasic sites NS3-NS4A and NS4B-NS5. Subcellular localization of the unprocessed precursor NS3-NS4A-NS4B-NS5 showed that it was confined to a distinct subcellular organelle in the cytoplasm, which was distinct from the distribution of the mature NS5.

ATP and GTP as alternative energy sources for vinblastine transport by P-170 in KB-V1 plasma membrane vesicles

Purified plasma membrane vesicles isolated from multidrug-resistant human KB-V1 cells accumulate [3H]vinblastine in an energy-dependent manner. The accumulation of [3H]vinblastine in the presence of ATP is a saturable process. ATP can be replaced by other purine nucleotide triphosphates, of which GTP is the most efficient.

Mapping of a region of dengue virus type-2 glycoprotein required for binding by a neutralizing monoclonal antibody

Envelope glycoprotein E of flaviviruses is exposed at the surface of the virion, and is responsible for eliciting a neutralizing antibody (Ab) response, as well as protective immunity in the host. In this report, we describe a method for the fine mapping of a linear sequence of the E protein of dengue virus type-2 (DEN-2), recognized by a type-specific and neutralizing monoclonal Ab (mAb), 3H5. First, an Escherichia coli expression vector containing a heat-inducible lambda pL promoter was used to synthesize several truncated, and near-full length E polypeptides. Reactivities of these polypeptides with polyclonal mouse hyperimmune sera, as well as the 3H5 mAb revealed the location of the 3H5-binding site to be within a region of 166 amino acids (aa) between aa 255 and 422. For fine mapping, a series of targeted deletions were made inframe within this region using the polymerase chain reaction (PCR). The hydrophilicity pattern of this region was used as a guide to systematically delete the regions encoding the various groups of surface aa residues within the context of a near-full-length E polypeptide by using PCR. The 3H5-binding site was thus precisely mapped to a region encoding 12 aa (between aa 386 and 397). A synthetic peptide containing this sequence was able to bind to the 3H5 mAb specifically, as shown by enzyme-linked immunosorbent assay. In addition, we show that rabbit Abs raised against the synthetic peptide of 12 aa were able to bind to the authentic E protein, and to neutralize DEN-2 virus in a plaque reduction assay.

Detection of stable secondary structure at the 3' terminus of dengue virus type 2 RNA

The 3'-terminal sequences of flavivirus genomes within approx. 100 nucleotides (nt) have been suggested to have a highly conserved secondary structure, as based on the known nt sequence data and free-energy calculations using computer programs. To test the existence of a secondary structure in solution, we devised a strategy to generate truncated RNA molecules from about 0.3-1.4 kb in length, having the same polarity and nt sequence as dengue virus type 2 (DEN-2) RNA (New Guinea-C strain). When these labeled RNA molecules were digested by RNase A, and analyzed by denaturing polyacrylamide-gel electrophoresis, three resistant fragments of 16, 20 and 23 nt in length were reproducibly obtained. To examine whether these RNase A-resistant (RNaseR) fragments emerged from a stable secondary structure formed in solution consisting of 3'-terminal sequences, hybridization of the RNaseR fragments to four chemically synthesized oligodeoxyribonucleotides (oligos), complementary to nt 1-24, 25-48, 49-72, and 73-96 from the 3' terminus of DEN-2 RNA, followed by RNase H digestion were carried out. Oligos complementary to nt 25-48 and 49-72 from the 3' end of DEN-2 RNA were sufficient to render all three RNaseR fragments susceptible to RNase H digestion. These data indicate that a stable secondary structure is formed in solution involving nt 18-67 from the 3' terminus. The potential use of these unique transcripts to identify the viral and/or host proteins which might interact at the 3' terminus of DEN-2 RNA during initiation of replication is discussed.

Three basic regions in adenovirus DNA polymerase interact differentially depending on the protein context to function as bipartite nuclear localization signals

Adenovirus DNA polymerase (AdPol) contains three clusters of basic amino acids within the N-terminal 48 amino acids: RARR, which begins at amino acid 8, RRRVR, which begins at amino acid 25, and RARRRR, which begins at amino acid 41. These clusters are designated BS I, BS II, and BS III, respectively. (The amino acid codes are: R, arginine; A, alanine; V, valine.) Mutational analysis of these noncontiguous clusters showed that AdPol contains a novel organization of bipartite nuclear localization signals (NLS) that interact differentially to serve in the nuclear targeting of AdPol or of chimeric proteins in which AdPol is linked to Escherichia coli beta-galactosidase (beta-gal). The region containing BS I and BS II functioned interdependently as an NLS for the nuclear targeting of AdPol, for which BS III was dispensible. However, the region containing BS II and BS III constituted a second and more efficient bipartite NLS for the nuclear targeting of the AdPol-E. coli beta-gal fusion protein. Moreover, deletion or limited insertion of amino acids in the spacer region between BS II and BS III did not affect their nuclear targeting function for these fusion proteins. Chou-Fasman predictive analysis of protein secondary structure in the vicinity of the bipartite NLS sequences supports a model in which protein conformation in the spacer region may play an important role in bringing these clusters of basic amino acids into close proximity, allowing them to function as nuclear targeting signals for this class of nuclear proteins.

Laser scanning and confocal microscopy of daunorubicin, doxorubicin, and rhodamine 123 in multidrug-resistant cells

The multidrug-resistant gene (MDR1) encodes an energy-dependent drug efflux pump (P-glycoprotein) for many anti-cancer drugs. We have studied the intracellular distribution of rhodamine 123 (R123), daunorubicin (DN), and doxorubicin (DOX) in cells expressing a human MDR1 gene. The distribution of these fluorescent drugs was measured by laser scanning microscopy and confocal microscopy. We devised a new method for analysis of fluorescence line scan data to determine the intracellular distribution of fluorescent probes. This method and confocal microscopy showed that R123, DN, and DOX are localized to both plasma membrane and intracellular compartments in multidrug-resistant cells. When the cells are treated with verapamil, an inhibitor of the multidrug transporter, the amount of DOX, DN, and R123 associated with the cell rises. After inhibition, the relative distribution of DOX and DN between the cell surface and intracellular structures does not change dramatically. However, R123 tends to relocalize to intracellular sites from predominantly plasma membrane sites, indicating that this dye behaves differently than the anti-cancer drugs. These results show the subcellular distributions of R123, DN, and DOX in plasma membrane, cytoplasm, and intracellular membrane systems, but do not allow definitive distinctions among existing models of how P-glycoprotein affects the distribution of drugs.

Overproduction of adenovirus DNA polymerase and preterminal protein in HeLa cells

Adenovirus (Ad) DNA polymerase (AdPol) and the preterminal protein (pTP) form a complex that is involved in the in vitro initiation of Ad DNA replication. Recombinant vaccinia viruses (vv) were constructed in which the genes encoding AdPol and pTP were cloned into a vaccinia/T7 hybrid expression-based vector downstream from the T7 promoter (pT7)/encephalomyocarditis virus (EMCV) 5'-untranslated region (UTR). HeLa cells infected with the recombinant vv-AdPol or vv-pTP or a mixture of both, together with the vv expressing T7 RNA polymerase produced significant levels of pTP and AdPol which were biologically active in the in vitro initiation of Ad DNA replication. These amounts of pTP and AdPol were only about two-fold less than the levels produced in insect cells infected with the recombinant baculovirus constructs expressing AdPol and pTP.

Magnetic-affinity cell sorting of human multidrug-resistant cells

We have developed a method for isolating multidrug-resistant cells from a heterogeneous cell population using the magnetic-affinity cell-sorting system. Human KB carcinoma cell lines expressing different amounts of P-glycoprotein have been selected by use of the monoclonal antibody MRK-16 coupled to magnetic particles. This specific, rapid, and sensitive method allows the selection of viable and clonable drug-resistant cells from various drug-resistant human and murine cell populations. This method may prove useful in isolating drug-resistant cells from tumors with heterogeneous P-glycoprotein expression for further analysis.

Synthesis of biologically active adenovirus preterminal protein in insect cells using a baculovirus vector

A DNA fragment encoding the polyhedrin promoter of Autographa californica multiple nuclear polyhedrosis virus (AcMNPV strain) was constructed using overlapping oligodeoxyribonucleotides (oligos), which included the 5'-untranslated leader sequence of the polyhedrin-encoding gene. This DNA fragment was cloned into an intermediate transfer vector (pKX105) providing a unique BamHI site for the insertion of foreign genes. The Escherichia coli lacZ gene was first cloned at the BamHI site of pKX105 and the XhoI-KpnI fragment containing the lacZ gene was transferred to another plasmid vector (pEI) consisting of flanking AcMNPV sequences (pEI-lacZ). The E. coli beta-galactosidase that was produced in the infected insect cells using the recombinant virus constituted about 10% of the total cytoplasmic proteins. The pKX105 plasmid was also modified to give rise to pTT-lacZ which consisted of the lacZ gene under the control of the Rous sarcoma virus long terminal repeat promoter to facilitate rapid screening of the baculoviral recombinants in which the gene of interest was cloned under the control of the polyhedrin promoter. The efficiency of these transfer vectors was verified by obtaining high levels of expression of the adenovirus(Ad)-encoded preterminal protein (pTP) which is involved as a protein primer in the initiation of Ad DNA replication. The baculovirus-produced pTP was immunoprecipitable using rabbit polyclonal antibodies raised against a hydrophilic domain of pTP. The pTP protein was localized in the nucleus of the infected insect cells, and was biologically active in the in vitro Ad type 2 (Ad2) replication initiation assay.

Mutational analysis of single-stranded DNA templates active in the in vitro initiation assay for adenovirus DNA replication

Three distinct domains, A, the minimal origin, as well as B and C, the binding sites for the host nuclear factors, are required for efficient initiation of adenovirus (Ad) DNA replication at the termini. The initiation reaction was examined using partially purified nuclear extracts and various single-stranded oligomers as DNA templates. We observed that single-stranded oligomers containing Ad2 minimal origin (Ori) sequences (bp 1-18) from the I-strand of the Ad2 genome supported preterminal protein-dCMP complex formation in vitro. Using oligomers containing point mutations in the Ad2 minimal Ori sequence, six positions were identified as important to the function of the Ad2 minimal Ori sequence. Point mutations at position 7, 8, or 11 virtually abolished the ability of the oligomer to support the initiation reaction. Point mutations at position 4, 9, or 17 were found to decrease the ability of the oligomers to support the initiation reaction to 33, 67, and 58% of control, respectively. An oligomer complementary to the I-strand of the Ad2 minimal Ori was found to block initiation on minimal Ori template. A number of randomly selected nonspecific oligomers did not, in general, serve as templates for initiation with the exception of two oligomers, one of which was found to be about threefold more active than the control minimal Ori template. The biological significance of the in vitro initiation of Ad2 DNA replication on single-stranded DNA templates is discussed.

Electron-microscopic studies on the pathogenesis of exencephaly and cranioschisis induced in the rat after neural tube closure: role of the neuroepithelium and choroid plexus

Exencephaly was induced in Wistar rat fetuses by the administration of a single dose of cyclophosphamide (15 mg/kg) in saline, after neural tube closure. The neuroepithelium (NE) and the choroid plexus were studied electron-microscopically in sections taken from a few hours after treatment to day 19 of gestation. The reduction in polyribosomes and condensation of the nucleus and cytoplasm were followed by cell death and fragmentation in the NE. Such cellular debris were phagocytosed and digested by the apparently normal neuroblasts. Cell proliferation was inhibited. The progressive loss of cells and lack of neuropil arborisation resulted in the expansion of the extracellular space and reduced intercellular contacts. The internal and external limiting membranes became weak. The vascular endothelium was attenuated. There were no obvious discontinuities of endothelium, but clusters of extravascular red blood cells, particularly in the vicinity of capillaries, in the cavitations in the NE and in the ventricular lumen were prominent by day 15. Subsequently, the cavities in the NE frankly communicated with the ventricle internally and subcutaneous blebs externally. The choroid plexus of exencephalic embryos was more extensive than that of the age-matched controls. Hydropic vacuoles, dense bodies, distended mitochondria, clusters of vesicles in basal cytoplasm and lakes of monoparticulate glycogen progressively increased in the plexus cells. Pericapillary oedema was obvious in the core of the plexus. These observations suggest that, in addition to cell death and reduced cell proliferation, haemorrhage, oedema and enhanced cerebrospinal fluid production contribute to reopening of the closed neural tube in this model.

Scanning-electron-microscopic studies on the pathogenesis of exencephaly and cranioschisis induced in the rat after neural tube closure

Following a single-dose (15 mg/kg) administration of cyclophosphamide on day 12 of gestation to Wistar rats, fetuses were collected at various intervals of time and studied under the scanning electron microscope. Comparisons were made with age-matched controls. Disorganization of the neuro-epithelium (NE) was characterized by expansion of the intercellular space (ICS), appearance of abundant cellular debris, extravascular red blood cells and formation of haemorrhagic cysts in the subependymal zone. Proliferation of the choroid plexus and its surface modifications parallelled the changes in the NE. The ventricular system dilated progressively. Supra-ependymal elements appeared earlier and in greater abundance in the experimental than in the control embryos. The mesenchymal cells of the cyclophosphamide-treated embryos were scanty, poorly organized, had less numerous cytoplasmic processes than the corresponding controls and failed to develop into the primordium of the skull vault. Degenerative changes in the NE, ventricular dilatation and the absence of a supporting skull vault primordium appeared to underlie the reopening of the closed neural tube.

Characteristics of the limb malformations induced by maternal exposure to cadmium in the mouse

Single doses of 2,3,4,6,8,10, and 15 mg/kg of cadmium chloride were administered (SC) to groups of MF1 mice on one of days 7 to 12 of gestation. Fetuses collected on day 18 were observed for limb malformations, and alizarin red-S stained skeletons were examined for their skeletal bases. Ectrodactyly, postaxial polydactyly, syndactyly, brachydactyly, adactyly, phocomelia, meromelia, and malrotation of the limbs were detected in a significant number of fetuses. Days 7 to 10 were greatly susceptible for induction of these malformations. Postaxial ectrodactyly was more frequent in the forepaws, and sidedness was not significant. Preaxial ectrodactyly preferentially affected the left hindpaws in the 9th-day treatment group. Postaxial polydactyly was predominently right sided and mostly involved the forepaws. Day 8 was particularly susceptible for induction of adactyly. Malrotation of the limbs together with edema and caudal narrowing resulted in a 'penguin-like' appearance. Ossification of the long bones, the carpals, tarsals, and phalanges were affected. Even those limbs that were not externally malformed had skeletal dysgenesis. Limb buds examined histologically at midgestation showed scanty and poorly organized mesenchyme, extensive elaboration of marginal sinsus, reduced thickness of the apical ectodermal ridge (AER), and discontinuous basement membrane. It is speculated that such histologic alterations at early stages of development could have contributed to the defective morphogenesis of limbs in this animal model.

Sequence analysis of cloned dengue virus type 2 genome (New Guinea-C strain)

Sequences totalling 5472 nucleotides (nt) from four complementary DNA (cDNA) clones of the dengue virus type 2 (DEN-2) RNA (New Guinea strain, NGS-C) have been reported previously [Yaegashi et al., Gene 46 (1986) 257-267; Putnak et al., Virology 163 (1988) 93-103]. This report describes the complete nucleotide sequence, with the exception of about 7 nt at the 5'-noncoding region, of this RNA genome derived from several cDNA clones. It is 10,723 nt in length and contains a single long open reading frame of 10,173 nt, encoding a polyprotein of 3391 amino acids. The genomic organization is similar to that of other flaviviruses that have recently been reported. Among the three DEN-2 strains - the Jamaica genotype (DEN-2JAM), the DEN-2NGS-C, and the S1 candidate vaccine strain derived from Puerto Rico (PR)-159 isolate (DEN-2S1) - which have been sequenced to date, the amino acid sequences of the polyproteins bear 94%-99% similarity. When the amino acid sequences of DEN-2NGS-C are compared with those of the other two strains, the variations are greater in the DEN-2S1 than in the DEN-2JAM. When DEN-2 and DEN-4 are compared, the overall amino acid identities range from 30% to 80% in both the structural and nonstructural proteins; whereas between DEN-2 and DEN-1, they range from 68% to 79% in the region encoding the structural proteins and the nonstructural protein NS1.

Nuclear transport of adenovirus DNA polymerase is facilitated by interaction with preterminal protein

The mRNAs for the 80 kd adenovirus preterminal protein (pTP) and the 140 kd DNA polymerase (AdPol) contain several exons spliced to the main open reading frames (m-ORFs) located in the early transcription unit E2B. These proteins were transiently expressed in monkey kidney cells (CV1) utilizing the first ATG (pTP1 and AdPol1) or the ATG of a linker inserted at the beginning of the m-ORFs (pTP2 and AdPol2). Only pTP2 and AdPol2 were functionally active in an in vitro replication initiation assay. Both pTP1 and pTP2 were transported to the nucleus. The sequence RLPV(R)6VP, which is present in both pTPs, is identified as their nuclear localization signal. In contrast, AdPol1 was cytoplasmically localized, whereas AdPol2 was distributed in both compartments, suggesting that the nuclear localization signal for AdPol is within the first 139 amino acids. Interestingly, when AdPol1 and pTP1 or AdPol2 and pTP2 were coexpressed in the transfected cells, the nuclear distribution of AdPol1 or AdPol2 was significantly increased. We demonstrate that the nuclear transport of AdPol is facilitated, irrespective of the presence of its nuclear localization signal, by interaction with pTP.

Effects of acute doses of ethanol administered at pre-implantation stages on fetal development in the mouse

The objective of the present study was to investigate the effects of maternal administration of acute doses of alcohol at preimplantation stages of pregnancy on the fetus and fetal membranes. Single doses of 0.02 ml and 0.03 ml/g body wt. of 25% v/v of absolute alcohol in saline were administered to groups of MF1 mice on one of days 1-6 of gestation. Controls were either pair-fed and pair-watered or saline-treated. Fetuses and placentae were collected on day 15. Resorption and fetal death were increased in most of the alcohol treatment groups. The reduction in fetal body weight was significant in the 0.03 ml group. Compared to the saline controls, most experimental groups exhibited a rise in placental weight. The reduction in cord length was significant in comparison to untreated controls. Craniofacial and systemic abnormalities appeared to correlate with retardation of fetal growth. Hence, following treatment of 0.03 ml/g body wt. of alcohol solution on days 2 and 6, fetuses were collected on days 14, 16 and 18. Most fetuses were found to recover gradually from anomalies associated with growth retardation but the 'catch up' growth was not adequate enough to compensate for the reduction in body weight. These observations indicate that the pre-implantation stage of mouse embryo development is susceptible to the deleterious effects (fetal death and intrauterine growth retardation) of acute doses of alcohol.

Purification of transiently transfected cells by magnetic affinity cell sorting

A method was developed to purify transiently transfected HeLa cells or African green monkey kidney CV-1 cells by magnetic affinity cell sorting. Monolayer cultures were transfected with mammalian expression vectors coding for either of two novel cell surface antigens, the Tac subunit of the human IL-2 receptor or vesicular stomatitis virus G protein. During the transient expression phase, cell populations were placed in suspension and mixed with monoclonal-antibody-coated magnetic particles in the presence of a sorting solution designed to minimize nonspecific cell/cell and cell/particle interactions. Transfected cells expressing the vector-encoded cell surface antigen were then isolated by application of a magnetic field. Reconstruction experiments indicated that IL-2 receptor-positive cells were bound about 100-fold more efficiently than receptor-negative cells. In transient transfection experiments, populations of greater than 90% antigen-positive cells were reproducibly obtained.

Detection of dengue virus type 2 in Aedes albopictus by nucleic acid hybridization with strand-specific RNA probes

A molecular hybridization technique with radiolabeled, strand-specific RNA probes was developed to detect dengue virus type 2 RNA in pools of infected Aedes albopictus mosquitoes. One infected mosquito in a pool of 25 could be detected, corresponding to a dengue virus type 2 titer of 2.75 log10 50% tissue culture infectious doses.

Functional and antigenic domains of the dengue-2 virus nonstructural glycoprotein NS-1

The gene coding for the nonstructural glycoprotein of dengue-2 virus was cloned, sequenced, and expressed in Escherichia coli. There was about 70% conservation at the amino acid level with dengue serotypes 1 and 4 suggesting an important common function for this protein. Conserved hydrophobic domains were found both before the amino-terminus and at the carboxy-terminus, consistent with transmembrane roles. Evidence for at least partial translocation of NS-1 through the inner membrane of E. coli was found. Also conserved were two signals for N-linked glycosylation located near the middle of NS-1. Various regions of NS-1 were tested for antigenicity with mouse and rabbit polyclonal and mouse monoclonal antibodies. The mouse polyclonal antibodies, made against a crude dengue-infected mouse brain immunogen, reacted most strongly with N-terminal regions of NS-1, whereas, the rabbit antiserum, made against purified NS-1 protein, reacted strongest with C-terminal regions. These findings suggest that immunogen presentation or species differences could be important. Although most of the monoclonals appeared to be unreactive in Western blots with expressed NS-1 proteins, two appeared to react strongly; the region from amino acid (a.a.) 273 to a.a. 346 was required for antibody binding. This region, located adjacent to the two conserved C-terminal hydrophobic domains, is highly charged and contains 5 of the 10 conserved cysteine residues of NS-1.

Light microscopic studies on the pathogenesis of exencephaly and cranioschisis induced in the rat after neural tube closure

Administration of a single dose of cyclophosphamide (20 mg/kg) to Charles Foster (CF) rats on day 12 of gestation (i.e., well after neural tube closure) results in exencephaly in almost 100% of living fetuses at term (Padmanabhan, '84). Following the same treatment, embryos/fetuses were collected at various intervals of time (from 8 hr to day 19 of gestation) and studied histologically. At 10 hr after treatment, the neuroepithelium (NE) of the brain vesicles and the neural crest-derived ganglia exhibited pronounced cell death. By day 13, cell death appeared to be more intense and extensive in the NE; the mesenchyme (ME) was less proliferative and was loosely organized. In the following days, the NE presented vacuolizations which coalesced into cavities; these cavities were often bilaterally symmetrical, contained free neuroblasts and erythrocytes, and subsequently opened into the ventricles. The choroid plexus hypertrophied, the ventricles distended, and the NE gradually became very thin. The hypertrophied capillaries of the ME cleaved through the NE, thus delaminating an outer stratum. Subcutaneous blebs developed over the brain vesicles and communicated with the cavities in the brain. Thus the ventricles and the blebs came into direct communication. The ME dorsal and lateral to the brain was loose, and at no site was it organized into the skull primordium. By day 19, there were clear and multiple discontinuities in the walls of the brain. Initial cell death and vacuolization in the NE, inhibition of ME proliferation followed by hypertrophy of the choroid plexus, and possibly enhanced intraventricular pressure and hemorrhage and edema of the ME seem to underlie this process of reopening of the closed neural tube.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological analysis of 140-kDa adenovirus-encoded DNA polymerase in adenovirus type 2-infected HeLa cells using antibodies raised against the protein expressed in Escherichia coli

The E2B region of adenovirus genome contains a long open reading frame (ORF) extending from 24 to 14.2 map units which encodes most of the 140-kDa DNA polymerase. It was cloned at the polylinker region of pUC18 vector with Escherichia coli JM109 as the host. A clone was serendipitously isolated that expressed in E. coli a protein of approximately 120 kDa in size at high levels. DNA sequence analysis of this clone showed the presence of an in-frame fusion of a region, encoding 13 amino acids located upstream, to the first ATG of the ORF. Polyclonal antibodies raised against this protein purified from E. coli were used for immunological analysis. The antibodies were able to detect a 140- and a 66-kDa polypeptide from the adenovirus type 2-infected HeLa cells on Western blots. In addition, the antibodies showed evidence of cross-reactivity with partially purified DNA polymerase alpha from uninfected HeLa cells. The subcellular localization of the viral polymerase in the infected HeLa cells by using indirect immunofluorescence showed that the viral protein is associated with globular structures in the nucleus. The replicating viral DNA and the polymerase were colocalized in these globular sites. Furthermore, HeLa cells infected with Ad5ts149, a temperature-sensitive mutant defective in DNA replication, showed the presence of these globular sites only at the permissive temperature, suggesting that these sites are probably involved in viral DNA replication.

Specific growth inhibitory sequences in genomic DNA from quiescent human embryo fibroblasts

We used HeLa cells as recipients in a gene transfer assay to characterize DNA sequences that negatively regulate mammalian cell growth. In this assay, genomic DNA from quiescent human embryo fibroblasts was more inhibitory for HeLa replication than was DNA from either Escherichia coli or HeLa cells. Surprisingly, growth inhibitory activity depended on the growth state of the cells from which genomic DNA was prepared; it was strongest in DNA prepared from serum-deprived, quiescent embryo fibroblasts. This latter observation implies a role for DNA modification(s) in regulating the activity of the inhibitory sequences detected in our assay. The level of the observed growth inhibitory activity was sometimes high, suggesting that the relevant sequences may be abundantly represented in the mammalian genome. We speculate that these findings may provide new insights into the molecular mechanisms involved in cellular quiescence and in vitro senescence.

Detection of dengue virus RNA using nucleic acid hybridization

Conditions for using slot-blot nucleic acid hybridization to quantitatively detect dengue-2 virus using a radiolabelled cDNA probe, pVV17, were determined. As little as 11 plaque-forming units of virus were detected using a hybridization mixture without formamide and performing the test at 70 degrees C. While predominantly serotype-specific using stringent (65 degrees C) washing conditions, the probe detected all four dengue virus serotypes using astringent (28 degrees C) washing conditions. No significant qualitative differences were detected using Thai dengue-2 viruses isolated over a 10-year period. High titered, anti-flavivirus antibodies blocked virus detection by an antigen capture, enzyme-linked, immunosorbent assay or by intrathoracic inoculation of Toxorhyncites mosquitoes, but not by nucleic acid hybridization. The appearance of virus-specified RNA coincided with the detection of antigen in infected C6/36 (Aedes albopictus) cells by immunofluorescence, or in cell culture supernatants by the antigen capture method. The method has potential as a diagnostic tool for identifying dengue viruses in clinical and field specimens.

Abnormalities of the ear associated with exencephaly in mouse fetuses induced by maternal exposure to cadmium

Exencephaly was induced in mouse fetuses by maternal injection of cadmium chloride (CdCl2) on day 7 of gestation. The heads of exencephalic, nonexencephalic experimental, and control fetuses were embedded in paraffin and sections were stained with hematoxylin and eosin. Compared to those of controls, the ears of the exencephalic fetuses were smaller (microtia) and low set. The meatal plug representing the external auditory canal was thick, variously branched, and often directed inferiorly. Usually, there were just two ossicles. The stapedial artery, facial nerve, and stapedius muscle were hypoplastic; the tensor tympani was small or absent. There were 1.0 to 2.0 turns of the cochlea in contrast to 2.5 turns in the controls. The organ of Corti was underdifferentiated; the spiral ganglion had fewer cells. In the control, the long axes of the anterior and posterior semicircular ducts were at right angles to each other and in vertical planes, but in the exencephalics, they tended more laterally towards the horizontal plane. The differentiation of the cristae ampullares and maculae was also severely affected. In several specimens, the entire membranous labyrinth had been distended; these labyrinths also had unusual epithelial infoldings. In cadmium-treated nonexencephalic fetuses, the external ears were normal and appropriate to the body size; five of them were examined histologically; in all, the five middle ear contents were hypoplastic; in three, the cochlea had a maximum of two turns and the organ of Corti, crista ampullaris, and macula were hypoplastic. By an analogy to abnormalities of mutants with neural tube defects, it is suggested that the exencephaly induced by cadmium might affect the differentiation of the ear. Partial involvement of the ear in nonexencephalic experimental embryos may be the result of direct action of cadmium during critical stages of development.

Congenital malformations and intrauterine growth retardation in streptozotocin induced diabetes during gestation in the rat

Diabetes was induced in Wistar rats by single intraperitoneal injections of streptozotocin (STZ) (50 mg/kg, in citrate buffer pH 4.7) at both preimplantation and organogenetic stages. The controls were either buffer treated or, following STZ administration, injected intraperitoneally with 2 to 6 IU of insulin daily until term. Fetuses collected on day 20 were found to have several malformations. Major abnormalities included gastroschisis and evisceration, maxillary hypoplasia and interatrial, and interventricular septal defects. Intrauterine growth retardation was present in most of the diabetic groups. Heavier placentae and shorter umbilical cords were also observed. Malformations and intrauterine growth retardation were numerous and severe in the preimplantation treatment groups. Insulin administration significantly improved the fetal body weight but did not change the malformation rate in the group made diabetic during organogenesis. It appears that the duration of hyperglycemic state plays a crucial role in malformation and growth retardation, and meticulous control of blood sugar from early stages has significant beneficial effects on fetal development.

Sequence analysis in the E1 region of adenovirus type 4 DNA

Adenovirus type 4 (Ad4) is the sole member of adenovirus group E based on overall DNA sequence homology, restriction endonuclease cleavage patterns, and the size of capsid proteins. We cloned the BamHI-F fragment from the left end of Ad4 in pUC13-1 between the SalI and BamHI sites in order to carry out the structural analysis of the E1A region of Ad4. The complete sequence of the BamHI-F fragment (2042 bp) has been determined. From the DNA sequence, the splice sites for the putative 12 S and 13 S mRNAs, encoded by the E1A region of Ad4 were deduced. If protein synthesis initiates at the first available AUG triplet (position 575), these 12 S and 13 S mRNAs would code for polypeptides containing 226 and 257 amino acids, respectively. Comparison of Ad4- and Ad7-13 S mRNA-coded polypeptides indicates that there is 57% homology, whereas the homology is only 38% with Ad12 and 31% with Ad2-13 S mRNA-coded polypeptides. The structural analysis in the E1 region of Ad4 also includes the coding region for the E1B 19-kDa protein. Ad4 and Ad7 shows 65% homology in the coding regions for E1B 19-kDa protein. Comparison of the DNA sequence of Ad4 with those of Ad2, Ad7, and Ad12 by using a dot matrix computer program and by Southern hybridization revealed that Ad4 bears a stronger homology with Ad7 than with Ad2 and Ad12 in this region. Hydropathy plots and alignments of the putative polypeptides coded by this region in Ad4 with those from the corresponding regions of different serotypes to reveal the highly conserved domains also support the above conclusion.

MDBK nuclear factor-binding site of various serotypes of adenovirus DNA

A fraction with the ability to bind the terminal fragment of equine adenovirus (EAd) DNA was prepared from MDBK cell nuclei. The fraction (MDBK nuclear factor) bound to the terminal fragment of all human and animal adenovirus DNAs examined except avian adenovirus EDS-76. However, the terminal fragments of two animal adenoviruses, EAd and bovine adenovirus type 3 (BAd3), showed higher affinity for the nuclear factor than the others. The MDBK nuclear factor-binding site determined by footprinting analysis was the sequence located between nucleotides 22 and 46 in EAd, between 36 and 53 in canine adenovirus type 2, and between 20 and 46 in BAd3, counting from the terminus. The respective binding site contained a sequence resembling the consensus sequence. The binding site of Ad4 DNA was not within the inverted terminal repetition, but was located at least 550 base pairs apart from the terminus.

Generation of packaging-defective DNA molecules of equine adenovirus

Equine adenovirus (EAd) DNA prepared from infected bovine kidney (MDBK) cells contained additional sequences of about 100 to 700 bp at the left-hand end of the genome. These aberrant viral genomes were produced even after the first passage of the wild type EAd in MDBK cells and their relative amounts did not change significantly during serial passage. The left terminal fragments of two defective viral DNAs were cloned into the plasmid vector pBR322 and the nucleotide sequences of their terminal regions were analyzed. The data indicate that one viral DNA contained a duplication of the inverted terminal repetition (ITR) and the other contained 270 bp of additional sequences derived from the right-terminal region of EAd genome added to the left-terminal, ITR. While the former DNA was packaged into virions, the latter was not, presumable due to the alteration of the distance from the left terminus to the putative DNA packaging signal, reported to be located between 290 and 390 bp (Hammarskjold and Winberg, 1980). The possible mechanism for the generation of these defective DNAs is discussed.

Primary rat embryo cells transformed by one or two oncogenes show different metastatic potentials

Second-passage rat embryo cells were transfected with a neomycin resistance gene and the activated form of the c-Ha-ras I gene, or with these two genes plus the adenovirus type 2 E1a gene. Foci of morphologically transformed cells were observed in both cases; however, the frequency of transformation was at least ten times higher with two oncogenes than with the ras gene alone. All the transformed cell lines gave rise to rapidly growing tumors when injected subcutaneously into nude mice. All but one of the cell lines transformed by the ras oncogene alone formed metastatic nodules in the lungs of animals that had been injected subcutaneously with transformed cells. When transformed cells were injected intravenously, all the ras single-gene transformants gave rise to many metastatic lung nodules. In contrast, cell lines transformed with ras and E1a did not generate metastases after subcutaneous injection and gave rise to very few metastatic lung nodules after intravenous injection. These data demonstrate that a fully malignant cell with metastatic potential, as measured in an immunodeficient animal, can be obtained from early passage embryo cells by the transfection of the ras oncogene alone.

The 5'-flanking sequences of human globin genes contribute to tissue specific expression

The specificity of expression of the isolated 5'-flanking sequences of the human beta- and epsilon-globin genes was examined in the K562 human erythroleukemia cell line, the murine erythroleukemia (MEL) cell, and in nonerythroid cell lines CV-1, HeLa-S3, and WI-38. Globin flanking sequences were active only in the erythroid K562 and MEL cell lines. Furthermore, the upstream sequence of the adult, beta-globin gene was active in MEL cells which express adult globin and not in K562 cells which express embryonic and fetal globins suggesting that tissue specificity resides in these upstream sequences. No expression was observed in K562 cells which have an embryonic-fetal hemoglobin phenotype.

Partial sequence analysis of cloned dengue virus type 2 genome

Dengue virus (DEN) is a member of flaviviruses and contains a single, (+)-strand RNA of approx. 11 kb. Complementary DNA copy of the RNA was synthesized using reverse transcriptase and oligo(dT) as primer. The double-stranded DNA copy was cloned at the PstI site of pUC13'-1 vector and was used to transform Escherichia coli JM83. Eleven transfomants were found to contain DEN insert as screened by colony hybridization. Three clones were chosen for further characterization by nucleotide (nt), sequence analysis. Two of these clones overlapped by 470 bp. Sequences of these three clones totalling about 4.6 kb were obtained. Translation of this DNA in all possible reading frames revealed the presence of long open reading frames spanning the entire length of the cDNA clones. The putative polypeptides derived from the nt sequence are 885 and 643 amino acids in length and show homology to the region of polyprotein coded by the yellow fever virus genome corresponding to the non-structural proteins [Rice et al., Science 229 (1985) 726-733]. The significant homology between these two viruses in the regions coding for the non-structural proteins NS3 and NS5 suggests an important role for these two proteins in the life cycle of these viruses.