Conserved location of genes on polymorphic chromosomes of four species of malaria parasites.

The number of chromosomes and the chromosomal location and linkage of more than 50 probes, mainly of genes, have been established in four species of Plasmodium which infect African murine rodents. We expected that the location and linkage of genes would not be conserved between these species of malaria parasites since extensive inter- and intraspecific size differences of the chromosomes existed and large scale internal rearrangements and chromosome translocations in parasites from laboratory lines had been reported. Our study showed that all four species contained 14 chromosomes, ranging in size between 0.

Differential expression in blood stages of the gene coding for the 21-kilodalton surface protein of ookinetes of Plasmodium berghei as detected by RNA in situ hybridisation.

The developmentally regulated transcription of the gene encoding the ookinete surface protein, Pbs21, has been investigated in the rodent malaria parasite, Plasmodium berghei, by RNA in situ hybridisation using fluorescently labelled DNA probes. We used a procedure that will allow the visualisation of cytoplasmic mRNA in the parasite and of high copy DNA repeats in the nucleus. Specific hybridisation to Pbs21 mRNA occurred in the cytoplasm of female gametocytes, zygotes and ookinetes, while asexual blood stages, male gametocytes and gametes showed no fluorescence.

The effect of (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl) adenine on nuclear and organellar DNA synthesis in erythrocytic schizogony in malaria.

The very effective (ID50 = 47 nM) and selective antimalarial compound (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl) adenine (HPMPA) abruptly arrests Plasmodium falciparum-cultured schizonts at concentrations between 1 and 10 x ID50 as soon as their DNA content reaches 8 times that of the haploid ringform stage. Even very high HPMPA concentrations do not inhibit the first 2-3 rounds of schizogonic DNA replication. Also, in the presence of HPMPA, replication of the 6-kb mitochondrial and 35-kb chloroplast-like DNA proceeds normally and in close concert with each other, both to a 16-fold amount within 5 h during the trophozoite stage.

Comparison of in vivo and in vitro antimalarial activity of artemisinin, dihydroartemisinin and sodium artesunate in the Plasmodium berghei-rodent model.

The in vitro and in vivo antimalarial activity of artemisinin, artesunate and dihydroartemisinin has been compared using the Plasmodium berghei-rodent model. Drugs were added to synchronized short-term in vitro cultures of the erythrocytic stages and inhibition of parasite development was determined by measuring DNA synthesis by flow cytometry. Dihydroartemisinin was the most effective drug.

Genome organization, chromosome translocation and size polymorphism in rodent malaria parasites.

In our laboratory, rodent malaria models are used to investigate processes that underlie cell differentiation with specific emphasis on sexual development. The rodent parasite Plasmodium berghei is particularly suited for this research since the different sexual stages (from young gametocytes to mature ookinetes) can be obtained pure and in large numbers.

Factors regulating natural transmission of Plasmodium berghei to the mosquito vector, and the cloning of a transmission-blocking immunogen.

Naturally occurring factors that regulate the infectivity of P. berghei infected rodent hosts to the mosquito vector in vivo have been compared in T.O.

Structure and expression of a post-transcriptionally regulated malaria gene encoding a surface protein from the sexual stages of Plasmodium berghei.

The sexual stage-specific protein Pbs21 of the rodent malaria parasite Plasmodium berghei, expressed on the surface of zygotes and ookinetes, has been shown to induce an effective and long-lasting transmission blocking immunity. The gene encoding Pbs21 was cloned by screening a cDNA library prepared from enriched zygotes and ookinetes using the monoclonal antibody 13.1.

Flow cytometric screening of blood samples for malaria parasites.

An automated method for the detection and estimation of malaria parasites in blood samples using flow cytometry is presented. In a single-step procedure 50 microliters of blood sample was collected in 1 ml of lysis solution containing formaldehyde, causing red blood cells to lyse while parasites and white blood cells are preserved. Thus prepared, samples could be transported and remained stored in lysis solution until flow cytometric analysis was performed.

Serotonergic modulation of junctional conductance in an identified pair of neurons in the mollusc Lymnaea stagnalis.

Serotonin (5-HT) is shown to modulate electrotonic coupling between two giant peptidergic neurons in the CNS of Lymnaea stagnalis. The primary effect of 5-HT appears to be a rapid and reversible decrease in gap junctional conductance.

Chromosome translocation in Plasmodium berghei.

We describe a chromosome translocation in a karyotype mutant of the rodent malarial parasite Plasmodium berghei. In this mutant (named EP) a small chromosome (chromosome 7), which has exhibited a size range between 0.9 and 1.

Plasmodium berghei: in vivo generation and selection of karyotype mutants and non-gametocyte producer mutants.

We previously reported that karyotype and gametocyte-producer mutants spontaneously arose during in vivo asexual multiplication of Plasmodium berghei. Here we studied the rate of selection of these mutants in vivo. Gametocyte production and karyotype pattern were established at regular intervals during prolonged periods of asexual multiplication of clone 8417 of P.

Deletion, insertion and translocation of DNA sequences contribute to chromosome size polymorphism in Plasmodium berghei.

Extensive chromosome size polymorphism arises in Plasmodium berghei during in vivo mitotic multiplication. Size differences between homologous chromosomes mainly involve rearrangements in the subtelomeric regions while internal chromosomal regions are more conserved. Size differences are almost exclusively due to differences in the copy number of a 2.

The role of membrane properties, synaptic input and electrical junction in determination of spike output of a pair of peptidergic neurons in the mollusc Lymnaea stagnalis.

The two electrotonically coupled peptidergic neurons, VD1 and RPD2 show in the isolated central nervous system (CNS) a patterned activity. The cells fire in almost perfect synchrony in CNS's derived from animals of moderate age, while in old animals disturbances in synchrony are observed. The firing pattern varies from beating to bursting.

The role of pacemaker properties and synaptic input in generation and modulation of spiking activity in a pair of electrically coupled peptidergic neurons.

The origin of patterned electrical activity in two electronically coupled peptidergic neurons, VD1 and RPD2, in the CNS of Lymnaea stagnalis was investigated. VD1 proved to have intrinsic beating pacemaker properties. Hybrid current/voltage clamp experiments demonstrated that in the intact CNS generation of spike activity in the coupled cell system is dominated by VD1.

Age-related changes in junctional and non-junctional conductances in two electrically coupled peptidergic neurons of the mollusc Lymnaea stagnalis.

Age-related changes in electrotonic coupling ratio of two identified neurons in Lymnaea stagnalis were studied together with the underlying changes in the steady-state conductance properties of the network. Two phases were distinguished in the development of coupling ratio across lifespan. During the first phase (age of 3-13 months), coupling ratio decreased from decreased from 60% to 30%.

Detection of different developmental stages of malaria parasites by non-radioactive DNA in situ hybridization.

A highly sensitive non-radioactive DNA in situ hybridization procedure is described that enables detection and unequivocal identification of various developmental stages of human and rodent malaria parasites. Using biotinylated species-specific DNA probes, erythrocytic parasites can be specifically stained in blood smears. Similarly exoerythrocytic stages can be visualized in cell culture and in sections of paraffin-embedded liver.

Long insertions within telomeres contribute to chromosome size polymorphism in Plasmodium berghei.

During prolonged in vivo mitotic multiplication of a Plasmodium berghei ANKA clone (8417HP), parasites that contained an enlarged version of chromosome 4 were observed. Restriction mapping and hybridization results demonstrated that the extra DNA present in the enlarged chromosome consists of 2.3-kb tandem repeats, known to be normally located in subtelomeric position at several chromosomal ends but absent in the original chromosome.