| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2004: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2003: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
1.Genetic diversity of Plasmodiumfalciparum
Since surface antigen genes of the human malaria parasite, Plasmodium falciparum, show extensive polymorphism, a rapid evolution of their polymorphism is presumed. However, little is known about frequency of the generation of novel polymorphisms. We are interested in P.falciparum populations in Vanuatu, in the southwestern Pacific, where the malaria epidemiological settings are suitable to test whether novel antigen polymorphism evolves rapidly because infections of mixed gentoypes are rare. We analyzed single nucleotidfe polymorphisms (SNPs) and repeat-length polymorphisms in three major surface antigens, msp1,msp2 and csp, in populations from 7 islands of Vanuatu in 1996 to 2002. We also sequenced simple repeat-length polymorphisms at three microsatellite loci, serca second intron, TA4O and TA 101. Analysis of more than one million bases revealed no de novo SNPs in the three antigen genes in Vanuatu. In contrast, repeat length polymorphism e
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volved rapidly. Analysis of ‘linkage disequilibrium' between pairs of loci revealed a spectrum of population genetic structure, suggesting that some of old antigen alleles have persisted through meiotic shuffling of chromosomes after the appearance of chloroquine resistance in Vanuatu. We argue that SNPs in P.falciparum antigen genes are substantially stable in isolated populations.
2.Estimation of TMRCA of Plasmodium falciparum.
The estimation of the time to the most recent common ancestor (TMRCA) of the extant populations of Plasmodium falciparuim is crucial for understanding the genetic diversity of the parasite. To estimate TMRCA, we obtained full-length sequences of two housekeeping genes, sarcoplasmic and endoplasmic reticulum Ca^<2+>-ATPase (serca) and lactate dehydrogenase (ldh), from 11 isolates of P.falciparum and one isolate of P.reichenowi, a chimpanzee malaria parasite closely related to P.falciparum. Interspecific genetic distance between the two species and intraspecific genetic distance within P.falciparum were 0.0672±0.0088 and 0.00 11±0.0007, respectively. Based on the ratio of interspecific distance to intraspecific distance, TMRCA of P.falciparum was estimated to be (8.30±5.40) x 10^4 and (11.62±7.56) x 10^4 years ago, assuming the divergence time of the two parasite species to be 5 and 7 million years ago, respectively. Less
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