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Genetic relatedness of Plasmodium falciparum isolates and the origin of allelic diversity at the merozoite surface protein-1 (MSP-1) locus in Brazil and Vietnam.

Hoffmann EH, Ribolla PE, Ferreira MU - Malar. J. (2003)

Bottom Line: At least one epidemic clone propagating in Brazil remained relatively unchanged over more than one decade.Moreover, we found no evidence that rearrangements of MSP-1 repeats, putatively created by mitotic recombination events, generated new alleles within clonal lineages of parasites in either country.Identical MSP-1 alleles originated from co-ancestry in both populations, whereas nearly identical MSP-1 alleles have probably appeared independently in unrelated parasite lineages.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas da Universidade de São Paulo, Brazil. hoffmann@usp.br

ABSTRACT

Background: Despite the extensive polymorphism at the merozoite surface protein-1 (MSP-1) locus of Plasmodium falciparum, that encodes a major repetitive malaria vaccine candidate antigen, identical and nearly identical alleles frequently occur in sympatric parasites. Here we used microsatellite haplotyping to estimate the genetic distance between isolates carrying identical and nearly identical MSP-1 alleles.

Methods: We analyzed 28 isolates from hypoendemic areas in north-western Brazil, collected between 1985 and 1998, and 23 isolates obtained in mesoendemic southern Vietnam in 1996. MSP-1 alleles were characterized by combining PCR typing with allele-specific primers and partial DNA sequencing. The following single-copy microsatellite markers were typed : Polyalpha, TA42 (only for Brazilian samples), TA81, TA1, TA87, TA109 (only for Brazilian samples), 2490, ARAII, PfG377, PfPK2, and TA60.

Results: The low pair-wise average genetic distance between microsatellite haplotypes of isolates sharing identical MSP-1 alleles indicates that epidemic propagation of discrete parasite clones originated most identical MSP-1 alleles in parasite populations from Brazil and Vietnam. At least one epidemic clone propagating in Brazil remained relatively unchanged over more than one decade. Moreover, we found no evidence that rearrangements of MSP-1 repeats, putatively created by mitotic recombination events, generated new alleles within clonal lineages of parasites in either country.

Conclusion: Identical MSP-1 alleles originated from co-ancestry in both populations, whereas nearly identical MSP-1 alleles have probably appeared independently in unrelated parasite lineages.

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Diversity in the MSP-1 gene of Plasmodium falciparum. In A, conserved, semiconserved and variable blocks of the MSP-1 gene are represented as open, hatched and filled boxes, respectively. The location and orientation of primers used for typing and sequencing this locus are also shown. Procedures are described elsewhere [5]. In B, the 27 different MSP-1 alleles found in the analysed sample set from Brazil and Vietnam are represented. Alleles were defined as unique combinations of: (a) allelic types in non-repetitive parts of blocks 2, 4 and 6–16, as determined by PCR typing; (b) repeat haplotypes in K1-type and MAD20-type block 2, as determined by DNA sequencing; and (c) nucleotide polymorphisms in blocks 1, 3 and 17, as determined by DNA sequencing. Alleles and repeat haplotypes were numbered according to Ferreira and colleagues [5]. K1-type repeat haplotypes differ in the number and arrangement of SGT and SGP motifs, while MAD20-type repeat haplotypes differ in the number and arrangement of SGG, SVA, SVT and SKG motifs. Codon numbers are given according to Miller and colleagues [13].
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Figure 1: Diversity in the MSP-1 gene of Plasmodium falciparum. In A, conserved, semiconserved and variable blocks of the MSP-1 gene are represented as open, hatched and filled boxes, respectively. The location and orientation of primers used for typing and sequencing this locus are also shown. Procedures are described elsewhere [5]. In B, the 27 different MSP-1 alleles found in the analysed sample set from Brazil and Vietnam are represented. Alleles were defined as unique combinations of: (a) allelic types in non-repetitive parts of blocks 2, 4 and 6–16, as determined by PCR typing; (b) repeat haplotypes in K1-type and MAD20-type block 2, as determined by DNA sequencing; and (c) nucleotide polymorphisms in blocks 1, 3 and 17, as determined by DNA sequencing. Alleles and repeat haplotypes were numbered according to Ferreira and colleagues [5]. K1-type repeat haplotypes differ in the number and arrangement of SGT and SGP motifs, while MAD20-type repeat haplotypes differ in the number and arrangement of SGG, SVA, SVT and SKG motifs. Codon numbers are given according to Miller and colleagues [13].

Mentions: The merozoite surface protein-1 (MSP-1) of P. falciparum is a prime malaria vaccine candidate antigen. Its coding sequence may be divided into 17 blocks, according to the levels of inter-allele divergence (Figure 1A). Most variation is dimorphic: sequences may be grouped into one of two allelic families (K1 and MAD20). Block 2 represents an exception to dimorphism, since in addition to K1-type and MAD20-type sequences, that contain degenerate tripeptide repeats, an apparently non-repetitive allele known as RO33 is commonly found. Genetic diversity at the MSP-1 locus may be generated by exchanging blocks of sequences during sexual (meiotic) recombination [4] and by putative strand-slippage events during the asexual (mitotic) replication of parasites leading to rearrangements of block 2 tripeptide repeats [5], but the relative contribution of each recombination mechanism remains unknown. High meiotic recombination rates within MSP-1 have been estimated for parasites in areas of intense malaria transmission in Africa, where most human infections consist of mixtures of genetically distinct clones [6]; most new MSP-1 alleles, therefore, originate from cross-mating followed by meiotic recombination. Mitotic recombination events may be important in generating new MSP-1 alleles in areas of low to intermediate levels of malaria transmission outside Africa, where meiotic recombination rates at the MSP-1 locus are substantially lower [5,7].


Genetic relatedness of Plasmodium falciparum isolates and the origin of allelic diversity at the merozoite surface protein-1 (MSP-1) locus in Brazil and Vietnam.

Hoffmann EH, Ribolla PE, Ferreira MU - Malar. J. (2003)

Diversity in the MSP-1 gene of Plasmodium falciparum. In A, conserved, semiconserved and variable blocks of the MSP-1 gene are represented as open, hatched and filled boxes, respectively. The location and orientation of primers used for typing and sequencing this locus are also shown. Procedures are described elsewhere [5]. In B, the 27 different MSP-1 alleles found in the analysed sample set from Brazil and Vietnam are represented. Alleles were defined as unique combinations of: (a) allelic types in non-repetitive parts of blocks 2, 4 and 6–16, as determined by PCR typing; (b) repeat haplotypes in K1-type and MAD20-type block 2, as determined by DNA sequencing; and (c) nucleotide polymorphisms in blocks 1, 3 and 17, as determined by DNA sequencing. Alleles and repeat haplotypes were numbered according to Ferreira and colleagues [5]. K1-type repeat haplotypes differ in the number and arrangement of SGT and SGP motifs, while MAD20-type repeat haplotypes differ in the number and arrangement of SGG, SVA, SVT and SKG motifs. Codon numbers are given according to Miller and colleagues [13].
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC184523&req=5

Figure 1: Diversity in the MSP-1 gene of Plasmodium falciparum. In A, conserved, semiconserved and variable blocks of the MSP-1 gene are represented as open, hatched and filled boxes, respectively. The location and orientation of primers used for typing and sequencing this locus are also shown. Procedures are described elsewhere [5]. In B, the 27 different MSP-1 alleles found in the analysed sample set from Brazil and Vietnam are represented. Alleles were defined as unique combinations of: (a) allelic types in non-repetitive parts of blocks 2, 4 and 6–16, as determined by PCR typing; (b) repeat haplotypes in K1-type and MAD20-type block 2, as determined by DNA sequencing; and (c) nucleotide polymorphisms in blocks 1, 3 and 17, as determined by DNA sequencing. Alleles and repeat haplotypes were numbered according to Ferreira and colleagues [5]. K1-type repeat haplotypes differ in the number and arrangement of SGT and SGP motifs, while MAD20-type repeat haplotypes differ in the number and arrangement of SGG, SVA, SVT and SKG motifs. Codon numbers are given according to Miller and colleagues [13].
Mentions: The merozoite surface protein-1 (MSP-1) of P. falciparum is a prime malaria vaccine candidate antigen. Its coding sequence may be divided into 17 blocks, according to the levels of inter-allele divergence (Figure 1A). Most variation is dimorphic: sequences may be grouped into one of two allelic families (K1 and MAD20). Block 2 represents an exception to dimorphism, since in addition to K1-type and MAD20-type sequences, that contain degenerate tripeptide repeats, an apparently non-repetitive allele known as RO33 is commonly found. Genetic diversity at the MSP-1 locus may be generated by exchanging blocks of sequences during sexual (meiotic) recombination [4] and by putative strand-slippage events during the asexual (mitotic) replication of parasites leading to rearrangements of block 2 tripeptide repeats [5], but the relative contribution of each recombination mechanism remains unknown. High meiotic recombination rates within MSP-1 have been estimated for parasites in areas of intense malaria transmission in Africa, where most human infections consist of mixtures of genetically distinct clones [6]; most new MSP-1 alleles, therefore, originate from cross-mating followed by meiotic recombination. Mitotic recombination events may be important in generating new MSP-1 alleles in areas of low to intermediate levels of malaria transmission outside Africa, where meiotic recombination rates at the MSP-1 locus are substantially lower [5,7].

Bottom Line: At least one epidemic clone propagating in Brazil remained relatively unchanged over more than one decade.Moreover, we found no evidence that rearrangements of MSP-1 repeats, putatively created by mitotic recombination events, generated new alleles within clonal lineages of parasites in either country.Identical MSP-1 alleles originated from co-ancestry in both populations, whereas nearly identical MSP-1 alleles have probably appeared independently in unrelated parasite lineages.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas da Universidade de São Paulo, Brazil. hoffmann@usp.br

ABSTRACT

Background: Despite the extensive polymorphism at the merozoite surface protein-1 (MSP-1) locus of Plasmodium falciparum, that encodes a major repetitive malaria vaccine candidate antigen, identical and nearly identical alleles frequently occur in sympatric parasites. Here we used microsatellite haplotyping to estimate the genetic distance between isolates carrying identical and nearly identical MSP-1 alleles.

Methods: We analyzed 28 isolates from hypoendemic areas in north-western Brazil, collected between 1985 and 1998, and 23 isolates obtained in mesoendemic southern Vietnam in 1996. MSP-1 alleles were characterized by combining PCR typing with allele-specific primers and partial DNA sequencing. The following single-copy microsatellite markers were typed : Polyalpha, TA42 (only for Brazilian samples), TA81, TA1, TA87, TA109 (only for Brazilian samples), 2490, ARAII, PfG377, PfPK2, and TA60.

Results: The low pair-wise average genetic distance between microsatellite haplotypes of isolates sharing identical MSP-1 alleles indicates that epidemic propagation of discrete parasite clones originated most identical MSP-1 alleles in parasite populations from Brazil and Vietnam. At least one epidemic clone propagating in Brazil remained relatively unchanged over more than one decade. Moreover, we found no evidence that rearrangements of MSP-1 repeats, putatively created by mitotic recombination events, generated new alleles within clonal lineages of parasites in either country.

Conclusion: Identical MSP-1 alleles originated from co-ancestry in both populations, whereas nearly identical MSP-1 alleles have probably appeared independently in unrelated parasite lineages.

Show MeSH