Transgenic mice with elevated level of CuZnSOD are highly susceptible to malaria infection.

Copper/zinc superoxide dismutase (CuZnSOD) catalyses the conversion of O2.- into H2O2. Constitutive overexpression of CuZnSOD in cells and animals creates an indigenous oxidative stress that predisposes them to added insults. In this study, we used transgenic CuZnSOD (Tg-CuZnSOD) mice with elevated levels of CuZnSOD to determine whether overexpression of CuZnSOD affected the susceptibility of these mice to plasmodium infection. Acute malaria is associated with oxidative stress, mediated by redox-active iron released from the infected RBC. Two independently derived Tg-CuZnSOD lines showed higher sensitivity than control mice to infection by Plasmodium berghei (P. berghei), reflected by an earlier onset and increased rate of mortality. Nevertheless, while Tg-CuZnSOD mice were more vulnerable than control mice, the levels of parasitemia were comparable in both strains. Moreover, treatment of infected red blood cells (RBC) with oxidative stress inducers, such as ascorbate or paraquat, reduced the viability of parasites equally in both transgenic and control RBC. This further confirms that increased CuZnSOD does not support plasmodia development. The data are consistent with the possibility that the combination of increased redox-active iron and elevated H2O2 in the plasmodium-infected Tg-CuZnSOD mice, led to an enhanced Fenton's reaction-mediated HO. production, and the resulting oxidative injury renders the transgenic mice more vulnerable to parasite infection.

Metabolic profile of fetal dopamine neurons transplanted to the adult rat striatum.

In the present study, we have examined the expression and distribution of the metabolic marker neuron-specific enolase (NSE) in solid-tissue transplants of fetal substantia nigra (SN) to the striatum of intact and 6-hydroxydopamine lesioned mature rats. Immunocytochemistry was applied to label NSE and tyrosine hydroxylase (TH) respectively. Cellular content of NSE is indicative of metabolic activity as well as synaptogenesis/maturation. Three months after implantation, the fetal grafts exhibited intensely TH-immunoreactive neurons, typically organized in elongated clusters, especially along the graft-host border and along blood vessels penetrating into the graft interior. Moderate to high metabolic activity as indicated by NSE immunoreactivity was observed in neuronal perikarya, principally in non-TH immunoreactive areas. In contrast to these immunohistochemical findings, in situ hybridization for TH mRNA, carried out exclusively on grafts into the intact striatum, demonstrated DA cell bodies both at the graft-host interface and, significantly, throughout the graft interior. The number of transcripts per cell, moreover, did not differ significantly in these two locations. We propose that conditions at the graft-host border promote tissue-specific regulation of nigral DA neurons, and that this regulation occurs post-transcriptionally. Thus, DA neurons relatively distant from the host parenchyma are underregulated, resulting in a higher level of metabolic activity and an increased turnover of TH in the grafted neurons.

Detection of Plasmodium falciparum in blood using DNA hybridization.

A rapid and simple assay for detecting Plasmodium falciparum in human blood was developed. The assay is based on DNA-DNA spot hybridization, using radiolabeled P. falciparum DNA as a probe and finger prick blood as the assay sample. It is very sensitive, able to detect parasitemia levels of 0.0001% in 10 microliter of blood. The assay can be quantified and used to estimate parasitemia levels. Several hundred blood samples can be processed simultaneously, and the entire procedure is completed within 24 hr. This assay can be useful for epidemiological surveys, for screening of blood by blood banks and for health authorities examining immigrants and tourists coming from malaria infested areas.

Prenatal ontogeny of tyrosine hydroxylase gene expression in the rat ventral mesencephalon.

We have examined the development of dopaminergic (DA) neurons in the embryonic mesencephalon with regard to the expression of the gene coding for tyrosine hydroxylase (TH). Mesencephalic DA neurons from rat embryos aged E13 to E21 were analyzed using a quantitative in situ hybridization protocol featuring a 35S-labeled RNA probe complimentary to TH mRNA. In the early-to-mid stage embryonic brains, the expression of the TH gene was examined relative to the position of individual, migrating DA cells in the caudal-rostral and dorsal-ventral axes of the mesencephalon. In the later embryonic subjects, neurons were analyzed according to their position in one of the midbrain DA nuclei. The ontogeny of TH gene expression in the rat mesencephalon exhibited two phases: during the early phase (E13-E15), we observed major fluctuations in the level of TH gene expression accompanying the differentiation and maturation processes of the DA cells. Later, in the mid-to-late gestation fetus (E18-E21), TH gene expression generally stabilized as TH mRNA-expressing neurons reached their final anatomical positions within the mesencephalic DA complex. Our data demonstrate the complex dynamics which characterize the ontogeny of TH gene expression in the prenatally developing mesencephalon, and suggest a connection between the maturational level of DA neurons and the expression of the key gene regulating their principle neurotransmitter.

Expression of tyrosine hydroxylase mRNA in transplanted fetal dopamine neurons.

Expression of genes coding for synthesis of secretory products has been shown to be an important index of neuronal activity. Gene expression in transplanted fetal substantia nigra (SN) was examined for the first time, utilizing in situ hybridization with a probe for tyrosine hydroxylase mRNA. Three months after implantation, the grafts contained many labeled neurons. Compared to host SN neurons, the grafted dopaminergic cells expressed more message for the enzyme, while they showed lower amounts of the enzyme itself. This result suggests that a molecular approach applied to neural transplantation can detect important if subtle differences in graft cell activity.

The effect of ascaridole on the in vitro development of Plasmodium falciparum.

Ascaridole is a terpene isolated from the plant Chenopodium ambrosioides (American wormseed); it is one of the few naturally occurring endoperoxidases. Artemisinin, which also belongs to this group, is a potent antimalarial. We therefore undertook a study to determine the effect of ascaridole, a known anthelmintic, on the in vitro development of Plasmodium falciparum. Ascaridole was found to be a potent inhibitor of plasmodial growth; after 3 days, development was arrested by a drug concentration of 0.05 microM, and at 0.1 microM no parasites were visible in the culture. At lower concentrations the effect was observed mainly at the trophozoite stage, whereas the ring stage was marginally affected. However, even at these lower concentrations, the ring culture could not continue normal development and ceased to grow at a later stage. The peroxide group is essential for the antimalarial activity of ascaridole, as judged from the fact that cineol, which bears an epoxide group instead of the peroxide group found in ascaridole, was totally inactive at identical concentrations.

Plasmodium falciparum: evidence for a DNA methylation pattern.

The methylation status of the adenine and cytosine residues in the genome of Plasmodium falciparum was studied using restriction enzymes exhibiting differential activity dependent on the methylation state of these residues in their recognition site. The gene coding for the enzyme dihydrofolate reductase-thymidylate synthase was studied for that purpose. No methylated adenine residues were observed in this gene in four strains tested. However, partial methylation of cytosine residues was observed in all strains. This methylation occurred at a specific site of the gene and was of the eukaryotic type, namely at a CpG sequence.

Differential expression of tyrosine hydroxylase mRNA in the developing rat mesencephalon.

1. With respect to the mesostriatal projection, the mesencephalon is composed of two dopaminergic (DA) cell populations, called dorsal tier and ventral tier. Strong evidence suggests differences in both the spatial and the temporal sequence of the innervation of the striatum between the two groups, with the ventral tier neurons innervating striatal patches prenatally and dorsal tier cells innervating striatal matrix postnatally. 2. Using in situ hybridization, we have examined the expression of the gene coding for tyrosine hydroxylase (TH) in mesencephalic DA neurons with respect to their postnatal development. Two ontogenic patterns of expression were observed: (a) dorsal tier neurons of the medial mesencephalon exhibited a sharp increase in expression beginning after birth, peaking on day 14, then decreasing and, finally, stabilizing; and (b) ventral tier neurons and dorsal tier cells from the lateral and the medial-dorsal mesencephalon showed only a slight increase in TH mRNA, reaching a plateau at P10. 3. The time course of the observed increase in TH gene expression in the first group, generally parallels the innervation of their target cells in the striatal matrix, suggesting that TH gene expression in these cells may be influenced by their postsynaptic cells or by the innervation process.

Methylation of foreign DNA sequences in eukaryotic cells.

The herpesvirus thymidine kinase gene has been used to introduce foreign DNA sequences into mouse L cells by DNA-mediated gene transfer. These inserted genes were then assayed for methylation at the specific sequence C-C-G-G by using the restriction enzyme isoschizomers Hpa II and Msp I. Despite the fact that 70% of the cellular C-C-G-G sites are methylated, herpesvirus sequences, plasmid DNA, and growth hormone gene DNA were found to remain unmethylated in 90% of the clones that contain these genes. DNA that had been methylated in vitro with Hpa II methylase was also inserted into L cells. The presence of this modification in the vector DNA did not, however, guarantee that these sequences remained methylated in the recipient clones. Only 10% of all transformed clones were found to contain methylated C-C-G-G sequences in the vector DNA, and these modifications were stable for 25-50 generations. Hha I and Mbo I were used to probe for methyl groups at these restriction sites, but none of the inserted sequences acquired these modifications. These results are discussed in relation to various models put forth to explain the process of methylation in eukaryotic cells.

Impaired kinetic properties of hypoxanthine-guanine phosphoribosyl transferase as a cause of uric acid nephropathy in early infancy.

A 6-month-old infant presented with failure to thrive, hyperuricaemia and renal insufficiency. The hyperuricaemia was due to uric acid over-production. The level of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity was found to be normal. However, a two-fold increase in the Km of the enzyme to hypoxanthine as well as in the Vmax values was observed. It seems therefore, that in cases of uric acid over-production, screening tests of HGPRT activity may be insufficient and additional kinetic properties of the enzyme should be tested.

Detection of mycoplasmas infecting cell cultures by DNA hybridization.

Infection of cell cultures by mycoplasmas can be detected and the mycoplasma identified by Southern blot hybridization of the Eco RI-digested DNA of the suspected cell cultures with a nick-translated probe consisting of cloned ribosomal RNA genes of Mycoplasma capricolum. The probe does not hybridize with eukaryotic DNA. The hybridization pattern with mycoplasmal DNA is species specific, enabling the identification of the four most prevalent mycoplasma contaminants, Mycoplasma orale, Mycoplasma hyorhinis, Mycoplasma arginini, and Acholeplasma laidlawii. The test is also very sensitive and can detect as little as 1 ng of mycoplasmal DNA, roughly equivalent to the DNA content of 10(5) mycoplasmas.

Plasmodium falciparum: expression of the adenine phosphoribosyltransferase gene in mouse L cells.

Genomic libraries of Plasmodium falciparum were constructed in the pBR322 plasmid. Using the DNA-mediated gene transfer technique, the genomic libraries were introduced into tissue-cultured mouse cells lacking the enzyme adenine phosphoribosyltransferase. Following selection for the adenine phosphoribosyltransferse phenotype, several colonies were isolated. All clones were shown to possess adenine phosphoribosyltransferase activity and pBR322 sequences. In addition, the Km value of adenine phosphoribosyltransferase (for adenine) from a transformant was found to be identical to that from P. falciparum. These results indicate that the adenine phosphoribosyltransferase gene of P. falciparum was successfully cloned and expressed in a mammalian system.

Methylation pattern of mouse mitochondrial DNA.

The pattern of methylation of mouse mitochondrial DNA (mtDNA) was studied using several techniques. By employing a sensitive analytical procedure it was possible to show that this DNA contains the modified base 5-methylcytosine (m5Cyt). This residue occurred exclusively at the dinucleotide sequence CpG at a frequency of 3 to 5%. The pattern of methylation was further investigated by determining the state of methylation of several MspI (HpaII) sites. Different sites were found to be methylated to a different extent, implying that methylation of mtDNA is nonrandom. Based on the known base composition and nucleotide sequence of mouse mtDNA, the dinucleotide sequence CpG was found to be underrepresented in this DNA. The features of mtDNA methylation (CpG methylation, partial methylation of specific sites and CpG underrepresentation) are also characteristic of vertebrate nuclear DNA. This resemblance may reflect functional relationship between the mitochondrial and nuclear genomes.

Clonal inheritance of the pattern of DNA methylation in mouse cells.

DNA-mediated gene transfer was used to investigate the mode of inheritance of 5-methylcytosine in mouse L cells. Unmethylated phi X174 replicative form DNA remains unmethylated after its introduction and integration into these cells. On the other hand, phi X174 replicative form DNA that was methylated in vitro at its C-C-G-G residues retains these methylations as shown by restriction enzyme analysis with Hpa II and Msp I to detect methylation at this specific site. Although these unselected methylated vectors are prone to lose 30-40% of their methyl moieties upon transfection, this demethylation appears to be random. Once established, the resulting methylation pattern is stable for at least 100 cell generations. In order to examine the specificity of methylation inheritance, fully hemimethylated duplex phi X174 DNA was synthesized in vitro from primed single-strand phi X174 DNA by using 5-methyl deoxycytidine 5'-triphosphate. This molecule was inserted into mouse L cells by cotransformation and subsequently was analyzed by a series of restriction enzymes. Only methylations located at C-G residues were conserved after many generations of cell growth. The results suggest that the inheritance of the cellular DNA methylation pattern is based on a C-G-specific methylase that operates on newly replicated hemimethylated DNA.

The genome of Plasmodium falciparum. I: DNA base composition.

Some structural properties of the DNA of Plasmodium falciparum were studied thoroughly using several techniques. Its G+C content was found to be extremely low (17-19%), the lowest reported for a living organism. The DNA seems to be composed only of the four major bases as no methylated bases were detected. This DNA had a Tm value of 62.5 degrees C and its denaturation profile showed no marked intramolecular heterogeneity.

Studies on the biological role of dna methylation; IV. Mode of methylation of DNA in E. coli cells.

Two pairs of restriction enzyme isoschizomers were used to study in vivo methylation of E. coli and extrachromosomal DNA. By use of the restriction enzymes MboI (which cleaves only the unmethylated GATC sequence) and its isoschizomer Sau3A (indifferent to methylated adenine at this sequence), we found that all the GATC sites in E. coli and in extrachromosomal DNAs are symmetrically methylated on both strands. The calculated number of GATC sites in E. coli DNA can account for all its m6Ade residues. Foreign DNA, like mouse mtDNA, which is not methylated at GATC sites became fully methylated at these sequences when introduced by transfection into E. coli cells. This experiment provides the first evidence for the operation of a de novo methylation mechanism for E. coli methylases not involved in restriction modification. When the two restriction enzyme isoschizomers, EcoRII and ApyI, were used to analyze the methylation pattern of CCTAGG sequences in E. coli C and phi X174 DNA, it was found that all these sites are methylated. The number of CCTAGG sites in E. coli C DNA does not account for all m5Cyt residues.

Cytoplasmic inheritance in mammalian tissue culture cells.

A series of intraspecific, interspecific and interorder somatic cell cybrids and hybrids have been prepared by fusions in which one of the parents contained the cytoplasmically inherited marker for chloramphenicol (CAP) resistance. A clear relationship has been established between the expression of the CAP-resistant (CAP-R) determinants in the fusion products and the genetic homology of the parents. With increased genetic divergence, the acceptability of the CAP-R mitochondria decreased. Intraspecific cybrids and hybrids of the same strain were stable for the CAP-R marker, while those between strains were stable only in CAP. Intergeneric mouse-hamster cybrids occurred at a high frequency but were unstable in CAP, while CAP suppressed hybrid formation 100-fold. Interorder cybrids (CAP-R human X CAP-S mouse) occurred either at a moderate frequency and were stable at a low frequency and were unstable in CAP. Interorder hybrids could only be formed by challenging HAT-selected hybrids with CAP or by direct selection in ouabain and CAP. Reciprocal interorder crosses between CAP-R mouse and CAP-S human cells were unsuccessful. Interspecific cybrids contain only the chromosomes of the CAP-S parent. Interspecific hybrids selected directly in CAP segregated the chromosomes of the CAP-S parent, while hybrids selected in HAT and then CAP segregated those of the CAP-R parent. The mitochondrial DNA(mtDNA) of all mouse-human cybrids and most HAT and then CAP-selected hybrids contain only the mtDNA of the CAP-S mouse parent. However, preliminary evidence suggests that one of these hybrids contains both mouse and human mtDNA sequences.

Breast biopsy nuclear pellets are a convenient source of DNA for routine determination of Her-2/neu gene amplification.

Cell nuclei from breast biopsies are a byproduct of routine hormone receptor determination and are usually discarded. We report here that DNA purified from this source is suitable for use in conventional Southern blot or Polymerase Chain Reaction (PCR) techniques to screen for Her-2/neu amplification, enabling efficient use of limited biopsy material.