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Biomedical subjects

A A Sultan

Publications and source records attributed to A A Sultan.

18 recordsLinked to original sources
PubMed2001

Complementation of Plasmodium berghei TRAP knockout parasites using human dihydrofolate reductase gene as a selectable marker.

Previously we have used the Plasmodium dihydrofolate reductase thymidylate synthase (DHFR-TS) selectable marker to generate Plasmodium berghei TRAP null mutant parasites. These TRAP null mutants do not glide and they showed a great reduction in their ability to infect mosquito salivary glands and the hepatocytes of the vertebrate host. Thus far, complementation of these knockout parasites was not possible due to the lack of additional selectable markers. Recently, a new selectable marker, based on the human dihydrofolate reductase (hDHFR) gene, has been developed which confers resistance to the antifolate drug WR99210. This drug has been found to be highly active against pyrimethamine-sensitive and -resistant strains of P. berghei. In this study, we have used the hDHFR gene as a second selectable marker for the complementation of P. berghei TRAP null mutant parasites. Restoration of the TRAP null mutant parasites to the wild-type phenotype was achieved in this study via autonomously replicating episomes bearing a wild-type copy of the TRAP gene. This is the first report of complementation of a mutant phenotype in malaria parasites.

Animals↗
PubMed1999

Green fluorescent protein as a marker in Plasmodium berghei transformation.

We present a new marker that confers both resistance to pyrimethamine and green fluorescent protein-based fluorescence on the malarial parasite Plasmodium berghei. A single copy of the cassette integrated into the genome is sufficient to direct fluorescence in parasites throughout the life cycle, in both its mosquito and vertebrate hosts. Erythrocyte stages of the parasite that express the marker can be sorted from control parasites by flow cytometry. Pyrimethamine pressure is not necessary for maintaining the cassette in transformed parasites during their sporogonic cycle in mosquitoes, including when it is borne by a plasmid. This tool should thus prove useful in molecular studies of P. berghei, both for generating parasite variants and monitoring their behavior.

Animals↗
PubMed1999

Subtle mutagenesis by ends-in recombination in malaria parasites.

The recent advent of gene-targeting techniques in malaria (Plasmodium) parasites provides the means for introducing subtle mutations into their genome. Here, we used the TRAP gene of Plasmodium berghei as a target to test whether an ends-in strategy, i.e., targeting plasmids of the insertion type, may be suitable for subtle mutagenesis. We analyzed the recombinant loci generated by insertion of linear plasmids containing either base-pair substitutions, insertions, or deletions in their targeting sequence. We show that plasmid integration occurs via a double-strand gap repair mechanism. Although sequence heterologies located close (less than 450 bp) to the initial double-strand break (DSB) were often lost during plasmid integration, mutations located 600 bp and farther from the DSB were frequently maintained in the recombinant loci. The short lengths of gene conversion tracts associated with plasmid integration into TRAP suggests that an ends-in strategy may be widely applicable to modify plasmodial genes and perform structure-function analyses of their important products.

Animals↗
PubMed1999

Molecular mechanisms of malaria sporozoite motility and invasion of host cells.

Malaria sporozoites have the unique capacity to invade two entirely different types of target cell in the mosquito vector and the vertebrate host during the course of the parasite's life cycle. Although little is known about the specific interaction of the sporozoite with its target cells, two sporozoite proteins, circumsporozoite (CS) and thrombospondin-related adhesive protein (TRAP), have been shown to play important roles in the invasion of both cell types. CS protein is a multifunctional protein involved in sporogony, invasion of the salivary glands, the specific arrest of sporozoites in the liver sinusoid, gliding motility of the sporozoite, and hepatocyte recognition and entry. TRAP has been shown to be critical for sporozoite infection of the mosquito salivary glands and liver cells, and is essential for sporozoite gliding motility. This review will focus on the involvement of these molecules in sporozoite motility and the invasion of host cells.

Amino Acid Sequence↗
PubMed1997

TRAP is necessary for gliding motility and infectivity of plasmodium sporozoites.

Many protozoans of the phylum Apicomplexa are invasive parasites that exhibit a substrate-dependent gliding motility. Plasmodium (malaria) sporozoites, the stage of the parasite that invades the salivary glands of the mosquito vector and the liver of the vertebrate host, express a surface protein called thrombospondin-related anonymous protein (TRAP) that has homologs in other Apicomplexa. By gene targeting in a rodent Plasmodium, we demonstrate that TRAP is critical for sporozoite infection of the mosquito salivary glands and the rat liver, and is essential for sporozoite gliding motility in vitro. This suggests that in Plasmodium sporozoites, and likely in other Apicomplexa, gliding locomotion and cell invasion have a common molecular basis.

Animals↗
PubMed1997

Circumsporozoite protein is required for development of malaria sporozoites in mosquitoes.

Malaria parasites undergo a sporogonic cycle in the mosquito vector. Sporozoites, the form of the parasite injected into the host during a bloodmeal, develop inside oocysts in the insect midgut, then migrate to and eventually invade the salivary glands. The circumsporozoite protein (CS), one of the major proteins synthesized by salivary gland sporozoites, is a surface-associated molecule which is important in sporozoite infectivity to the host. Here, by gene targeting, we created Plasmodium berghei lines in which the single-copy CS gene was disrupted. The CS(-) and wild-type parasites produced similar numbers of oocysts of comparable size in the mosquito midgut. In the CS(-) oocysts, however, sporozoite formation was profoundly inhibited. CS therefore appears to have a pleiotropic role and to be vital for malaria parasites in both the vector and the host: in mosquitoes, CS is essential for sporozoite development within oocysts, and in the vertebrate host it promotes sporozoite attachment to hepatocytes.

Animals↗
PubMed1996

Detection of Herpes Simplex Virus and candida infection with special emphasis on their possible role in human Squamous Cell Carcinoma and its variants.

Sixty seven cases of human oral S.C.C. with its intra oral variances were investigated microbiologically, histopathologically, histochemically and immunologically. Yeasts were isolated from 85% of examined cases. "Candifast test" showed that Candida albicans was the commonest form of the detected fungi, followed by C. parapsilosis and C. tropicalis, while the least in frequency was the Torulopsis glabrata. Yeasts were more detected in females, elders and tobacco smokers. Two cases of well differentiated S.C.C. were surprisingly detected, and for the first time in literature, associated with a specific granulomatous reaction and showed positively impregnated fungi. While negative reactions for fungi were noticed in all lymphoepitheliomas, almost all the verrucous carcinoma were positive. Viral inclusion bodies were demonstrated for the first time by MT. This method was rapid, economic and could be used as a pilot study before applying the more specific monoclonal antibody techniques or in-situ hybridization methods. Comparing the results of HSV hybridization with that of candida infection we found that both could be detected in some cases. The results indicate that viral and fungal factors may be synergetic in the development of oral carcinomas.

Adult↗
PubMed1994

Cloning and characterisation of a Plasmodium falciparum homologue of the Ran/TC4 signal transducing GTPase involved in cell cycle control.

On the basis of conserved sequences characteristic of the Ran/TC4 subfamily of the GTPase superfamily, a fragment of the gene encoding a Plasmodium falciparum Ran/TC4 homologue was amplified in the polymerase chain reaction. The fragment was used to screen a cDNA library to obtain clones which allowed determination of the complete gene sequence. The gene, designated pfran (Plasmodium falciparum ras-like nuclear protein), has around 70% amino acid identity with previously characterised Ran/TC4 proteins. Like other malarial mRNAs, the pfran mRNA contains a long (at least 679 bp) 5' untranslated region. Southern blotting experiments show that pfran is a single copy gene located on chromosome 11. RNA hybridisation experiments indicate that pfran mRNA is abundant in late trophozoite and schizont stages, but present at very low levels in gametocytes and early asexual stages.

Amino Acid Sequence↗
PubMed1994

MVR-PCR analysis of hypervariable DNA sequence variation.

Techniques for accurate marking of infectious microbial agents circulating in populations would be very useful to epidemiologists. In this article, David Arnot, Cally Roper and Ali Sultan review recent progress in transferring MVR-PCR DNA finger-printing techniques from human forensic medicine to parasitology.

Journal Article↗
PubMed1989

Schistosomal versus nonschistosomal variceal bleeders. Do they respond differently to selective shunt (DSRS)?

The distal splenorenal shunt (DSRS) was performed in 125 consecutive variceal bleeders. To date, no patients have been lost to follow-up (mean of 79 +/- 20 months). Liver pathology was documented in 85 patients: 45 patients had schistosomal hepatic fibrosis, 17 had nonalcoholic cirrhosis, and 23 had mixed pattern (hepatic fibrosis and cirrhosis). The preoperative data base for these three groups was matched (p greater than 0.05), with a mean follow-up of 79 +/- 20, 70 +/- 14, and 77 +/- 22 months for each population, respectively. The results showed low operative mortality (4.8%), high cumulative patency rate (94.8%) and low recurrent variceal hemorrhage (5.6%). The biochemical data showed significant increase in serum bilirubin (p less than 0.001) and aspartate transaminase (AST) (p less than 0.05) in the nonschistosomal patients. Chronic hyperbilirubinemia was found in 33% of the schistosomal group. Prograde portal perfusion was detected in 94% of the patients, with development of collaterals in 91%. The angiographic pattern of these collaterals was 50% pancreatic, 45% gastric, and 26% colosplenic. Patients with mixed liver disease had a high incidence of Grade III portal perfusion (57%) and more common pancreatic and gastric collaterals (71%). The cumulative survival for all patients was 74.1%, with hepatic cell failure being the leading cause of death (13 patients, 50% of all deaths). The schistosomal patients had a 91.6% incidence, whereas the cirrhotic and mixed groups had survival rates of 75.6% and 65.2%, respectively. Also, of a 15% total incidence of encephalopathy, 4.4% was related to the schistosomal patients, 23.5% to the cirrhotics, and 21.7% to the mixed population. Statistically, the survival rate was significantly better (p less than 0.05) and encephalopathy was significantly lower (p less than 0.05) in the schistosomal population. In conclusion, this data shows that: 1) DSRS has a high patency rate and a low variceal hemorrhage recurrence rate; 2) it maintains some degree of portal perfusion in patients with different nonalcoholic liver diseases, despite development of collaterals; and 3) the schistosomal patients have a better survival rate, with a low incidence of encephalopathy after DSRS, compared with the cirrhotic and mixed populations.

Actuarial Analysis↗
PubMedDate not supplied

Drug response and genetic characterization of Plasmodium falciparum clones recently isolated from a Sudanese village.

We have isolated 20 clones of Plasmodium falciparum from isolates from patients attending a village clinic in Sudan during 10 d in October-November 1989. The clones were genetically diverse, having highly variable molecular karyotypes and a wide range of drug responses. Chloroquine-sensitive (50% inhibitory concentration [IC50] in the 4-15 nM range) and chloroquine-resistant clones (IC50 in the 40-95 nM range) co-existed in the population, but no obvious amplification of the P-glycoprotein homologue gene, Pgh1 (previously known as the multi-drug resistance gene, mdr1) marked the chloroquine-resistant clones. Chloroquine resistance was reversible by verapamil in these clones, although they varied in their susceptibility to verapamil alone. These observations indicate that the biochemical characteristics of the Sudanese chloroquine-resistant P. falciparum are similar to those reported from south-east Asian and Latin American isolates, which is consistent with there being a similar molecular basis for this phenomenon.

Animals↗