Genetic Diversity and Protective Efficacy of the RTS,S/AS01 Malaria Vaccine

BACKGROUND

The RTS,S/AS01 vaccine targets the circumsporozoite protein of Plasmodium falciparum and has partial protective efficacy against clinical and severe malaria disease in infants and children. We investigated whether the vaccine efficacy was specific to certain parasite genotypes at the circumsporozoite protein locus.

METHODS

We used polymerase chain reaction-based next-generation sequencing of DNA extracted from samples from 4985 participants to survey circumsporozoite protein polymorphisms. We evaluated the effect that polymorphic positions and haplotypic regions within the circumsporozoite protein had on vaccine efficacy against first episodes of clinical malaria within 1 year after vaccination.

RESULTS

In the per-protocol group of 4577 RTS,S/AS01-vaccinated participants and 2335 control-vaccinated participants who were 5 to 17 months of age, the 1-year cumulative vaccine efficacy was 50.3% (95% confidence interval [CI], 34.6 to 62.3) against clinical malaria in which parasites matched the vaccine in the entire circumsporozoite protein C-terminal (139 infections), as compared with 33.4% (95% CI, 29.3 to 37.2) against mismatched malaria (1951 infections) (P=0.04 for differential vaccine efficacy). The vaccine efficacy based on the hazard ratio was 62.7% (95% CI, 51.6 to 71.3) against matched infections versus 54.2% (95% CI, 49.9 to 58.1) against mismatched infections (P=0.06). In the group of infants 6 to 12 weeks of age, there was no evidence of differential allele-specific vaccine efficacy.

CONCLUSIONS

These results suggest that among children 5 to 17 months of age, the RTS,S vaccine has greater activity against malaria parasites with the matched circumsporozoite protein allele than against mismatched malaria. The overall vaccine efficacy in this age category will depend on the proportion of matched alleles in the local parasite population; in this trial, less than 10% of parasites had matched alleles. (Funded by the National Institutes of Health and others.).

A phylogenetic analysis using full-length viral genomes of South American dengue serotype 3 in consecutive Venezuelan outbreaks reveals a novel NS5 mutation

Dengue virus currently causes 50-100 million infections annually. Comprehensive knowledge about the evolution of Dengue in response to selection pressure is currently unavailable, but would greatly enhance vaccine design efforts. In the current study, we sequenced 187 new dengue virus serotype 3 (DENV-3) genotype III whole genomes isolated from Asia and the Americas. We analyzed them together with previously-sequenced isolates to gain a more detailed understanding of the evolutionary adaptations existing in this prevalent American serotype. In order to analyze the phylogenetic dynamics of DENV-3 during outbreak periods; we incorporated datasets of 48 and 11 sequences spanning two major outbreaks in Venezuela during 2001 and 2007-2008, respectively. Our phylogenetic analysis of newly sequenced viruses shows that subsets of genomes cluster primarily by geographic location, and secondarily by time of virus isolation. DENV-3 genotype III sequences from Asia are significantly divergent from those from the Americas due to their geographical separation and subsequent speciation. We measured amino acid variation for the E protein by calculating the Shannon entropy at each position between Asian and American genomes. We found a cluster of seven amino acid substitutions having high variability within E protein domain III, which has previously been implicated in serotype-specific neutralization escape mutants. No novel mutations were found in the E protein of sequences isolated during either Venezuelan outbreak. Shannon entropy analysis of the NS5 polymerase mature protein revealed that a G374E mutation, in a region that contributes to interferon resistance in other flaviviruses by interfering with JAK-STAT signaling was present in both the Asian and American sequences from the 2007-2008 Venezuelan outbreak, but was absent in the sequences from the 2001 Venezuelan outbreak. In addition to E, several NS5 amino acid changes were unique to the 2007-2008 epidemic in Venezuela and may give additional insight into the adaptive response of DENV-3 at the population level.

Human genome anatomy: BACs integrating the genetic and cytogenetic maps for bridging genome and biomedicine

Human genome sequencing is accelerating rapidly. Multiple genome maps link this sequence to problems in biology and clinical medicine. Because each map represents a different aspect of the structure, content, and behavior of human chromosomes, these fundamental properties must be integrated with the genome to understand disease genes, cancer instability, and human evolution. Cytogenetic maps use 400-850 visible band landmarks and are the primary means for defining prenatal defects and novel cancer breakpoints, thereby providing simultaneous examination of the entire genome. Recent genetic, physical, and transcript maps use PCR-based landmarks called sequence-tagged sites (STSs). We have integrated these genome maps by anchoring the human cytogenetic to the STS-based genetic and physical maps with 1021 STS-BAC pairs at an average spacing of approximately 1 per 3 Mb. These integration points are represented by 872 unique STSs, including 642 polymorphic markers and 957 bacterial artificial chromosomes (BACs), each of which was localized on high resolution fluorescent banded chromosomes. These BACs constitute a resource that bridges map levels and provides the tools to seamlessly translate questions raised by genomic change seen at the chromosomal level into answers based at the molecular level. We show how the BACs provide molecular links for understanding human genomic duplications, meiosis, and evolution, as well as reagents for conducting genome-wide prenatal diagnosis at the molecular level and for detecting gene candidates associated with novel cancer breakpoints.

A novel member of the F-box/WD40 gene family, encoding dactylin, is disrupted in the mouse dactylaplasia mutant

Early outgrowth of the vertebrate embryonic limb requires signalling by the apical ectodermal ridge (AER) to the progress zone (PZ), which in response proliferates and lays down the pattern of the presumptive limb in a proximal to distal progression. Signals from the PZ maintain the AER until the anlagen for the distal phalanges have been formed. The semidominant mouse mutant dactylaplasia (Dac) disrupts the maintenance of the AER, leading to truncation of distal structures of the developing footplate, or autopod. Adult Dac homozygotes thus lack hands and feet except for malformed single digits, whereas heterozygotes lack phalanges of the three middle digits. Dac resembles the human autosomal dominant split hand/foot malformation (SHFM) diseases. One of these, SHFM3, maps to chromosome 10q24 (Refs 6,7), which is syntenic to the Dac region on chromosome 19, and may disrupt the orthologue of Dac. We report here the positional cloning of Dac and show that it belongs to the F-box/WD40 gene family, which encodes adapters that target specific proteins for destruction by presenting them to the ubiquitination machinery. In conjuction with recent biochemical studies, this report demonstrates the importance of this gene family in vertebrate embryonic development.

A YAC-based physical map of the mouse genome

A physical map of the mouse genome is an essential tool for both positional cloning and genomic sequencing in this key model system for biomedical research. Indeed, the construction of a mouse physical map with markers spaced at an average interval of 300 kb is one of the stated goals of the Human Genome Project. Here we report the results of a project at the Whitehead Institute/MIT Center for Genome Research to construct such a physical map of the mouse. We built the map by screening sequenced-tagged sites (STSs) against a large-insert yeast artificial chromosome (YAC) library and then integrating the STS-content information with a dense genetic map. The integrated map shows the location of 9,787 loci, providing landmarks with an average spacing of approximately 300 kb and affording YAC coverage of approximately 92% of the mouse genome. We also report the results of a project at the MRC UK Mouse Genome Centre targeted at chromosome X. The project produced a YAC-based map containing 619 loci (with 121 loci in common with the Whitehead map and 498 additional loci), providing especially dense coverage of this sex chromosome. The YAC-based physical map directly facilitates positional cloning of mouse mutations by providing ready access to most of the genome. More generally, use of this map in addition to a newly constructed radiation hybrid (RH) map provides a comprehensive framework for mouse genomic studies.

Mouse molecular cytogenetic resource: 157 BACs link the chromosomal and genetic maps

We have established a collection of strong molecular cytogenetic markers that span the mouse autosomes and X chromosome at an average spacing of one per 19 Mb and identify 127 distinct band landmarks. In addition, this Mouse Molecular Cytogenetic Resource relates the ends of the genetic maps to their chromosomal locations. The resource consists of 157 bacterial artificial chromosome (BAC) clones, each of which identifies specific mouse chromosome bands or band borders, and 42 of which are linked to genetic markers that define the centromeric and telomeric ends of the Whitehead/MIT recombinational maps. In addition, 108 randomly selected and 6 STS-linked BACs have been assigned to single chromosome bands. We have also developed a high-resolution fluorescent reverse-banding technique for mouse chromosomes that allows simultaneous localization of probes by fluorescence in situ hybridization (FISH) with respect to the cytogenetic landmarks. This approach integrates studies of the entire mouse genome. Moreover, these reagents will simplify gene mapping and analyses of genomic fragments in fetal and adult mouse models. As shown with the MMU16 telomeric marker for the trisomy 16 mouse model of Down syndrome, these clones can obviate the need for metaphase analyses. The potential contribution of this resource and associated methods extends well beyond mapping and includes clues to understanding mouse chromosomes and their rearrangements in cancers and evolution. Finally it will facilitate the development of an integrated view of the mouse genome by providing anchor points from the genetic to the cytogenetic and functional maps of the mouse as we attempt to understand mutations, their biological consequences, and gene function.

The mouse pudgy mutation disrupts Delta homologue Dll3 and initiation of early somite boundaries

Pudgy (pu) homozygous mice exhibit clear patterning defects at the earliest stages of somitogenesis, resulting in adult mice with severe vertebral and rib deformities. By positional cloning and complementation, we have determined that the pu phenotype is caused by a mutation in the delta-like 3 gene (Dll3), which is homologous to the Notch-ligand Delta in Drosophila. Histological and molecular marker analyses show that the pu mutation disrupts the proper formation of morphological borders in early somite formation and of rostral-caudal compartment boundaries within somites. Viability analysis also indicates an important role in early development. The results point to a key role for a Notch-signalling pathway in the initiation of patterning of vertebrate paraxial mesoderm.

Serrate2 is disrupted in the mouse limb-development mutant syndactylism

The mouse syndactylism (sm) mutation impairs some of the earliest aspects of limb development and leads to subsequent abnormalities in digit formation. In sm homozygotes, the apical ectodermal ridge (AER) is hyperplastic by embryonic day 10.5, leading to abnormal dorsoventral thickening of the limb bud, subsequent merging of the skeletal condensations that give rise to cartilage and bone in the digits, and eventual fusion of digits. The AER hyperplasia and its effect on early digital patterning distinguish sm from many other syndactylies that result from later failure of cell death in the interdigital areas. Here we use positional cloning to show that the gene mutated in sm mice encodes the putative Notch ligand Serrate. The results provide direct evidence that a Notch signalling pathway is involved in the earliest stages of limb-bud patterning and support the idea that an ancient genetic mechanism underlies both AER formation in vertebrates and wing-margin formation in flies. In addition to cloning the sm gene, we have mapped three modifiers of sm, for which we suggest possible candidate genes.

A bacterial artificial chromosome-based framework contig map of human chromosome 22q

We have constructed a physical map of human chromosome 22q using bacterial artificial chromosome (BAC) clones. The map consists of 613 chromosome 22-specific BAC clones that have been localized and assembled into contigs using 452 landmarks, 346 of which were previously ordered and mapped to specific regions of the q arm of the chromosome by means of chromosome 22-specific yeast artificial chromosome clones. The BAC-based map provides immediate access to clones that are stable and convenient for direct genome analysis. The approach to rapidly developing marker-specific BAC contigs is relatively straightforward and can be extended to generate scaffold BAC contig maps of the rest of the chromosomes. These contigs will provide substrates for sequencing the entire human genome. We discuss how to efficiently close contig gaps using the end sequences of BAC clone inserts.

Construction and characterization of a human bacterial artificial chromosome library

We have constructed an arrayed human genomic BAC library with approximately 4x coverage that is represented by 96,000 BAC clones with average insert size of nearly 140 kb. A new BAC vector that allows color-based positive screening to identify transformants with inserts has increased BAC cloning efficiency. The library was gridded onto hybridization filters at high density for efficient identification of BAC clones by colony hybridization. The library was also formulated into characteristic DNA pools to allow for PCR screening of the library for STS content. We have characterized the library mainly by screening with more than 300 different landmarks that include cDNA, STSs, and cosmid clones. We describe methods for using BAC clones and discuss the implications for genome characterization, mapping, and sequencing.

A human chromosome 22 fosmid resource: mapping and analysis of 96 clones

We have created a resource for chromosome 22 consisting of 96 unique, well-characterized Fosmids. The Fosmid vector permits efficient cloning of DNA fragments averaging 40 kb in a single-copy vector based on the F factor of Escherichia coli. We have found that Fosmid clones from human chromosome 22 show remarkable stability and are useful for a wide variety of applications in genome analysis. These 96 clones have been localized by FISH, using high-resolution fluorescent banding and multicolor mapping techniques, and their position on the chromosome was correlated with their content of a number of common repeated sequence elements. We identified a subset of clones likely to contain genes by restriction analysis using the enzymes NotI, MluI, SacII, and BssHII. This collection of cytogenetically anchored clones, representing nearly 7% of the chromosome, is of immediate value for detecting chromosomal rearrangements, for use in gene isolation, and as a framework for physical mapping.

Disruption of the nuclear hormone receptor RORalpha in staggerer mice

Homozygous staggerer (sg) mice show a characteristic severe cerebellar ataxia due to a cell-autonomous defect in the development of Purkinje cells. These cells show immature morphology, synaptic arrangement, biochemical properties and gene expression, and are reduced in numbers. In addition, sg heterozygotes show accelerated dendritic atrophy and cell loss, suggesting that sg has a role in mature Purkinje cells. Effects of this mutation on cerebellar development have been studied for 25 years, but its molecular basis has remained unknown. We have genetically mapped staggerer to an interval of 160 kilobases on mouse chromosome 9 which was found to contain the gene encoding RORalpha, a member of the nuclear hormone-receptor superfamily. Staggerer mice were found to carry a deletion within the RORalpha gene that prevents translation of the ligand-binding homology domain. We propose a model based on these results, in which RORalpha interacts with the thyroid hormone signalling pathway to induce Purkinje-cell maturation.

An STS-based map of the human genome

A physical map has been constructed of the human genome containing 15,086 sequence-tagged sites (STSs), with an average spacing of 199 kilobases. The project involved assembly of a radiation hybrid map of the human genome containing 6193 loci and incorporated a genetic linkage map of the human genome containing 5264 loci. This information was combined with the results of STS-content screening of 10,850 loci against a yeast artificial chromosome library to produce an integrated map, anchored by the radiation hybrid and genetic maps. The map provides radiation hybrid coverage of 99 percent and physical coverage of 94 percent of the human genome. The map also represents an early step in an international project to generate a transcript map of the human genome, with more than 3235 expressed sequences localized. The STSs in the map provide a scaffold for initiating large-scale sequencing of the human genome.

Use of secondary pulsed field gel electrophoresis in separation of large DNA

It has been reported that secondary pulsed field gel (SPFG) electrophoresis can dramatically increase the speed of separation of large DNA molecules without a decrease in resolution (Zhang, T. Y., Smith, C. L., and Cantor, C. R. (1991) Nucleic Acids Res. 19, 1291-1296). However, our attempts to duplicate previous SPFG conditions were unsuccessful. We therefore sought to more precisely define the effects of secondary pulsing on the separation of large DNA and to determine the value of the technique in separating molecules up to 1100 kb. Here we report on two of the key SPFG parameters, namely the frequency and duration of the secondary pulse on the migration and resolution of DNA in SPFG. We found that the size range of separation is determined by the sum of the duration of the primary and secondary pulses. Under optimal conditions, a 25-70% increase in velocity can be achieved without loss in resolution.

The basis of high resolution separation of small DNAs by asymmetric-voltage field inversion electrophoresis and its application to DNA sequencing gels

We have previously shown that asymmetric-voltage field inversion electrophoresis produces more uniform separation for fragments between 1 and 50 kilobases (kb) than other modes of pulsed field gel electrophoresis. We now report on the basis of this phenomenon. As in conventional electrophoresis, the pulsed field mobility of DNAs between 1 and 50 kb varies with voltage in a size dependent manner. The complex migration pattern obtained with asymmetric-voltage field inversion electrophoresis reflects the difference between the mobilities of each sized fragment under the conditions used for the forward and reverse fields. We have applied this technique to DNA sequencing gels and find improvement in resolution for single-stranded fragments in polyacrylamide gels.

Pulsed field gel electrophoresis: studies of DNA migration made with the programmable, autonomously-controlled electrode electrophoresis system

We have studied the migration of DNA in pulsed field agarose gels under a variety of electrophoresis conditions. We have made use of an instrument which can generate electric fields of any orientation, magnitude, or duration to compare different separation techniques for DNA molecules of from 1 to several thousand kilobase pairs. We discuss the capabilities of the system and present results of gel runs in which electrophoresis conditions were changed individually or in combination. The mobility of DNA in pulsed field gels is shown to reflect a number of interdependent physical parameters.

Pulsed field gel electrophoresis techniques for separating 1- to 50-kilobase DNA fragments

Conventional agarose gel electrophoresis separates DNA using a static electric field. The maximum size limit for separation of DNA by this method is about 20 kilobase pairs (kb). A number of new electrophoretic techniques which employ periodic reorientation of electric fields permit separation of DNA well beyond this size limit. We sought to determine whether the use of very fast (millisecond) field switching could improve separation of DNA in the size range of 1 to 50 kb. Additionally, we have compared the resolution obtained with each of the different field switching regimens for DNA in this size range. Switching intervals of from 0.2 to 900 ms were used with unidirectional pulsing of a single electric field, with pulsed field gels, and with field inversion gel electrophoresis. Plotting the mobility of DNA as a function of size demonstrates that under the conditions used, each of these techniques offers comparable resolution. We also have examined the separation obtained when field inversion gels are run with forward and reverse fields of equal voltage and different durations, versus using fields of equal duration and different voltages. Field inversion which uses forward and reverse fields of different voltages yields resolution which is superior to the other methods examined.

Relaxation intervals alter the mobility of large DNA molecules in pulsed field gel electrophoresis

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A novel instrument for separating large DNA molecules with pulsed homogeneous electric fields

A new instrument has been developed for the electrophoretic separation of large DNA molecules that can independently regulate the voltage of each of 24 electrodes and allow the magnitude, orientation, homogeneity, and duration of the electric field to be precisely controlled. Each parameter can be varied at any time during the electrophoretic process. Thus distinct sets of conditions can be combined to optimize the separation of various fragment sizes in a single run. Independent control of electrode voltage allows all of the fields to be generated with electrodes arranged in a closed contour, independent of a particular geometry. This device increases both the resolution in any size range and the speed of separation, especially for DNA molecules larger than 3 megabases.

Optimized conditions for pulsed field gel electrophoretic separations of DNA

Quantitative measurement of DNA migration in gel electrophoresis requires precisely controlled homogeneous electric fields. A new electrophoresis system has allowed us to explore several parameters governing DNA migration during homogeneous field pulsed field gel (PFG) electrophoresis. Migration was measured at different switch times, temperatures, agarose concentrations, and voltage gradients. Conditions which increase DNA velocities permit separation over a wider size range, but reduce resolution. We have also varied the angle between the alternating electric fields. Reorientation angles between 105 degrees and 165 degrees give equivalent resolution, despite significant differences in DNA velocity. Separation of DNA fragments from 50 to greater than 7000 kilobases (Kb) can easily be optimized for speed and resolution based on conditions we describe.

Butyrate-induced changes in nuclease sensitivity of chromatin cannot be correlated with transcriptional activation

We examined in the H4IIE rat hepatoma cell line the relationship between butyrate-induced changes in the nuclease sensitivity of chromatin and changes in transcriptional activity of specific genes. The butyrate-inducible metallothionein I (MT-I) gene underwent a dramatic increase in DNase I sensitivity after 3 h of butyrate treatment. However, genes not transcribed in H4IIE cells underwent the same changes in DNase I sensitivity. Thus, butyrate-induced increases in DNase I sensitivity are not sufficient for the transcriptional activation of a gene. Butyrate treatment has also been reported to alter the sensitivity of sequences to micrococcal nuclease (MNase) in a manner reflecting their tissue-specific expression. Butyrate exposure caused increased digestion of the MT-I gene by MNase. However, butyrate-induced MNase sensitivity also occurred for genes which are neither transcribed in untreated cells nor butyrate inducible. Moreover, cadmium, a potent transcriptional activator of the MT-I gene, does not alter the sensitivity of the MT-I gene to MNase. Thus, the butyrate-induced alterations in MNase sensitivity are neither sufficient for, necessary for, nor indicative of transcriptional activation.

Distinct forms of the beta subunit of GTP-binding regulatory proteins identified by molecular cloning

Two distinct beta subunits of guanine nucleotide-binding regulatory proteins have been identified by cDNA cloning and are referred to as beta 1 and beta 2 subunits. The bovine transducin beta subunit (beta 1) has been cloned previously. We have now isolated and analyzed cDNA clones that encode the beta 2 subunit from bovine adrenal, bovine brain, and a human myeloid leukemia cell line, HL-60. The 340-residue Mr 37,329 beta 2 protein is 90% identical with beta 1 in predicted amino acid sequence, and it is also organized as a series of repetitive homologous segments. The major mRNA that encodes the bovine beta 2 subunit is 1.7 kilobases in length. It is expressed at lower levels than beta 1 subunit mRNA in all tissues examined. The beta 1 and beta 2 messages are expressed in cloned human cell lines. Hybridization of cDNA probes to bovine DNA showed that beta 1 and beta 2 are encoded by separate genes. The amino acid sequences for the bovine and human beta 2 subunit are identical, as are the amino acid sequences for the bovine and human beta 1 subunit. This evolutionary conservation suggests that the two beta subunits have different roles in the signal transduction process.

Regulation of the rat metallothionein-I gene by sodium butyrate

Sodium butyrate selectively induces accumulation of metallothionein-I (MT-I) RNA in H4IIE rat hepatoma cells. The induction is rapid; significant elevation in cytoplasmic MT-I RNA can be observed within three hours after exposure to 5 mM butyrate. Maximal levels of MT-I RNA are obtained after eight hours. Butyrate stimulates MT RNA accumulation in the absence of de novo protein synthesis, indicating that MT induction by butyrate is not a distal step in a cascade of gene activation events. Butyrate blocks the induction of tyrosine amino transferase by dexamethasone. In contrast, butyrate and dexamethasone induced MT RNA elevations are additive. Butyrate induced MT-I RNA transcripts initiate at the correct start site. Measurements of the transcriptional activity of the MT-I gene indicate that butyrate stimulates MT-I transcription. The rapid, direct nature of the induction of MT-I by butyrate, combined with the extensive characterization of the metallothionein gene, provide an excellent system in which to study the effects of butyrate on a small, well-defined, responsive region of chromatin.

Rat metallothionein-1 structural gene and three pseudogenes, one of which contains 5'-regulatory sequences

As shown by Southern blot analysis, the metallothionein-1 (MT-1) genes in rats comprise a multigene family. We present the sequence of the MT-1 structural gene and compare its features with other metallothionein genes. Three MT-1 pseudogenes which we sequenced apparently arose by reverse transcription of processed mRNA transcripts. Two of these, MT-1 psi a and MT-1 psi c, are retrogenes which derive from the MT-1 mRNA, having diverged from the MT-1 gene 6.9 and 2.6 million years ago, respectively. The third, MT-1 psi b, differs from the MT-1 cDNA by only three nucleotide alterations. Surprisingly, MT-1 psi b also preserves sequence homology for 142 base pairs 5' to the transcription initiation site of the parent gene; it contains a promoter sequence sufficient for specifying metal ion induction. We identified, by S1 nuclease mapping, an RNA polymerase II initiation site 432 base pairs 5' of the MT-1 transcription initiation site of the MT-1 structural gene which could explain the formation of the mRNA precursor to this pseudogene. We were unable to detect MT-1 psi b transcripts, either in liver tissue or after transfection. We conclude that the absence of detectable transcripts from this pseudogene is due to either a reduced level of transcription or the formation of unstable transcripts as a consequence of the lack of a consensus sequence normally found 3' of transcription termination in the MT-1 structural gene.

The hormonal regulation of gene expression of glial markers: glutamine synthetase and glycerol phosphate dehydrogenase in primary cultures of rat brain and in C6 cell line

Increases in the mRNA levels of two neuroglial markers, glutamine synthetase (EC 6.3.1.2; GS) and glycerolphosphate dehydrogenase (EC 1.1.1.8; GPDH), were observed in hydrocortisone-treated cultures of astrocytes and oligodendrocytes, respectively, and in C6 cells by Northern blot analysis and in situ hybridization. In vitro transcription assays demonstrated increased GS transcription in isolated nuclei from hydrocortisone (HC)-treated primary cultures of astrocytes and C6 cells, relative to untreated cells. This increased transcription is reflected in increased GS mRNA levels in the cytoplasm and increased levels of GS protein synthesis. Sodium butyrate (NaB) blocked the glucocorticoid-mediated increase in GS transcription in the primary cultures of astrocytes but not in C6 cells. From our earlier observations (Kumar et al: J Neurochem 43:1455-1463, 1984) we found NaB in combination with HC to increase the levels of GS mRNA and GS protein synthesis (Weingarten et al: FEBS Lett 126:289-291, 1981). We now report that NaB, alone or in combination with HC, does not increase the rate of transcription, suggesting that NaB plays a role in post-transcriptional regulation of GS in C6. In addition, we report the presence of two distinct sizes of GS mRNA, 2.9 and 1.8 kb, in the primary cultures of astrocytes and C6 cells.

Mutations affecting the regulation of transcription of the cytochrome P1-450 gene in the mouse Hepa-1 cell line

The cytochrome P1-450-dependent activity, aryl hydrocarbon hydroxylase, and cytochrome P1-450 messenger RNA levels were studied in wild-type Hepa1c1c7 cells and in aryl hydrocarbon hydroxylase-deficient mutants derived from this line. Tetrachlorodibenzo-p-dioxin (TCDD) induced both parameters approximately 50-fold in Hepa1c1c7 cells. Mutants in genes B and C that are affected in the functioning of the Ah receptor required for hydroxylase induction and dominant mutants had nondetectable or much reduced P1-450 mRNA levels and hydroxylase activities after TCDD treatment. Hybrids between wild-type cells and the dominant mutants were also deficient in these parameters. The dominant mutants therefore appear to express a trans-acting repressor of cytochrome P1-450 transcription. Mutants in gene A were heterogenous. Some lacked the mRNA completely; others were inducible for it; while still others (subgroup IV) had high levels even when they were grown without TCDD. These results suggest strongly that gene A is the structural gene for cytochrome P1-450. When subgroup IV mutants were cultured together with wild-type cells, they failed to express P1-450 mRNA in the absence of TCDD treatment. These cells probably accumulate an inducer that can be metabolized by aryl hydrocarbon hydroxylase. The inducer did not appear to be a component of the medium and therefore may be an endogenous ligand of the Ah receptor.

Metallothionein synthesis in foetal, neonatal and maternal rat liver

The synthesis of hepatic metallothionein relative to other cytosol proteins was measured by [35S]cysteine incorporation in foetal, neonatal and pregnant rats. The relative rate of hepatic metallothionein synthesis reached a maximum in foetal liver on days 18-21 of gestation. Metallothionein synthesis then declined until weaning, when adult levels were established. The rate of metallothionein synthesis was greater in pregnant rats at term than in nulliparous rats. To determine if circulating inducing agents could play a role in the regulation of metallothionein synthesis in foetal liver we treated pregnant rats with inducers at a time prior to the normal rise in foetal liver metallothionein synthesis. Injections of copper, cadmium or hydrocortisone to 17-day-pregnant dams failed to induce foetal metallothionein synthesis. In contrast, zinc injection to the dam was an effective inducer in the foetuses. Maternal laparotomy (performed to expose the foetus for direct injection of inducers) induced foetal metallothionein synthesis. Metallothionein synthesis in the livers of 17-day-gestation dams was induced by all metal injections and laparotomy but, surprisingly, not by hydrocortisone injection. Maternal adrenalectomy did not influence the subsequent normal elevation in foetal or maternal metallothionein synthesis. These results, in conjunction with previous reports, suggest that mobilization of zinc in serum during late gestation may regulate foetal and maternal changes in metallothionein synthesis.

Levels of metallothionein messenger RNA in foetal, neonatal and maternal rat liver

We have used translation in vitro of hepatic polyadenylated RNA to characterize the levels of metallothionein mRNA in foetal, neonatal, pregnant and nulliparous rats. The translation products of foetal hepatic metallothionein mRNA increased relative to other mRNA translation products from day 18 of gestation to birth and attained a maximum, maintained throughout suckling, which is tenfold above 17-day foetal hepatic levels and fourfold above adult levels. Maternal liver metallothionein mRNA decreased fivefold between 17 days and 20 days of gestation, rose sharply immediately before birth, and was low throughout lactation.

Molecular cloning of the rat metallothionein 1 (MT-1) mRNA sequence

Starting with liver mRNA from cadmium chloride-treated rats, we constructed a cDNA library. A mouse metallothionein 1 (MT-1) cDNA restriction fragment (Durnam et al. 1980) was used as a hybridization probe to isolate from this library a cDNA (p2A10) which is a nearly complete copy of the rat MT-1 mRNA sequence. Southern analysis of rat DNA, using p2A10 as a probe, together with the screening of a rat genomic library, reveal that the rat MT-1 gene belongs to a family of related sequences. The rat MT-1 gene is inducible both by glucocorticoids and by metals.