Single nucleotide polymorphisms, putatively neutral DNA markers and population genetic parameters in Indian Plasmodium vivax isolates

Putative circumsporozoite protein (CSP) of Plasmodium vivax is considerably distinct from the well-known CSP and plays a role in the protein ubiquitination pathway

Amidst technical challenges which limit successful culture and genetic manipulation of P. vivax parasites, we used a computational approach to identify a critical target with evolutionary significance. The putative circumsporozoite protein on chromosome 13 of P. vivax (PvpuCSP)is distinct from the well-known vaccine candidate PfCSP. The aim of this study was to understand the role of PvpuCSP and its relatedness to the well-known CSP. The study revealed PvpuCSP as a membrane bound E3 ubiquitin ligase involved in ubiquitination. It has a species-specific tetra-peptide unit which is differentially repeated in various P. vivax strains. The PvpuCSP is different from CSP in terms of stage-specific expression and function. Since E3 ubiquitin ligases are known antimalarial drug targets targeting the proteasome pathway, PvpuCSP, with evolutionary connotation and a key role in orchestrating protein degradation in P. vivax, can be explored as a potential drug target.

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PvpuCSP is predicted as E3 ubiquitin ligase, a part of ubiquitination pathway.

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Tetra-peptide tandem repeat at C terminal of PvpuCSP is exclusive to P. vivax.

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Moderately expressed during all parasitic stages in host and vector

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Partially disordered protein with both structured domains and two distinct IDRs

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A transmembrane protein with highly conserved functional domain across Apicomplexa

Molecular evidence of Plasmodium vivax mono and mixed malaria parasite infections in Duffy-negative native Cameroonians

The malaria parasite Plasmodium vivax is known to be majorly endemic to Asian and Latin American countries with no or very few reports of Africans infected with this parasite. Since the human Duffy antigens act as receptors for P. vivax to invade human RBCs and Africans are generally Duffy-negative, non-endemicity of P. vivax in Africa has been attributed to this fact. However, recent reports describing P. vivax infections in Duffy-negative Africans from West and Central parts of Africa have been surfaced including a recent report on P. vivax infection in native Cameroonians. In order to know if Cameroonians living in the southern regions are also susceptible to P. vivax infection, we collected finger-prick blood samples from 485 malarial symptomatic patients in five locations and followed PCR diagnostic assays with DNA sequencing of the 18S ribosomal RNA gene. Out of the 201 malaria positive cases detected, 193 were pure P. falciparum, six pure P. vivax and two mixed parasite infections (P. falciparum + P. vivax). The eight P. vivax infected samples (six single + two mixed) were further subjected to DNA sequencing of the P. vivax multidrug resistance 1 (pvmdr1) and the P.vivax circumsporozoite (pvcsp) genes. Alignment of the eight Cameroonian pvmdr1 sequences with the reference sequence showed high sequence similarities, reconfirming P. vivax infection in all the eight patients. DNA sequencing of the pvcsp gene indicated all the eight P. vivax to be of VK247 type. Interestingly, DNA sequencing of a part of the human Duffy gene covering the promoter region in the eight P. vivax-infected Cameroonians to identify the T-33C mutation revealed all these patients as Duffy-negative. The results provide evidence of single P. vivax as well as mixed malaria parasite infection in native Cameroonians and add knowledge to the growing evidences of P. vivax infection in Duffy-negative Africans.

Genomics, population genetics and evolutionary history of Plasmodium vivax

Plasmodium vivax is part of a highly diverse clade that includes several Plasmodium species found in nonhuman primates from Southeast Asia. The diversity of primate malarias in Asia is staggering; nevertheless, their origin was relatively recent in the evolution of Plasmodium. We discuss how humans acquired the lineage leading to P. vivax from a nonhuman primate determined by the complex geological processes that took place in Southeast Asia during the last few million years. We conclude that widespread population genomic investigations are needed in order to understand the demographic processes involved in the expansion of P. vivax in the human populations. India represents one of the few countries with widespread vivax malaria. Earlier studies have indicated high genetic polymorphism at antigenic loci and no evidence for geographic structuring. However, new studies using genetic markers in selectively neutral genetic regions indicate that Indian P. vivax presents complex evolutionary history but possesses features consistent with being part of the ancestral distribution range of this species. Such studies are possible due to the availability of the first P. vivax genome sequences. Next generation sequencing technologies are now paving the way for the sequencing of more P. vivax genomes that will dramatically increase our understanding of the unique biology of this species.

Development of multilocus putatively neutral DNA markers in the X-chromosome for population genetic studies in humans

BACKGROUND

It has now been well documented that the type (coding, non-coding) and location (nuclear, mitochondrial etc.) of genetic markers heavily influence evolutionary inferences; realistic assumptions can be drawn if multiple putatively neutral DNA fragments spread across the genome are used.

AIM

To infer human population history, Single Nucleotide Polymorphisms (SNPs), located in the non-coding regions of different genes in the X-chromosome have been developed as 'putatively neutral markers'.

SUBJECTS AND METHODS

A population sample consisting of 16 male individuals from the western part of India was utilized for sequencing eight DNA fragments located in introns of three genes (Duchenne muscular dystrophy, Factor IX and Pyruvate dehydrogenase E1 sub-unit) on the human X-chromosome. PCR amplification and DNA sequencing confirmed the polymorphic status of all the fragments.

RESULTS

Twenty nine SNPs were found to be segregating in the Western Indian population samples. Using these SNPs the nucleotide diversity and demographic parameters of the Western Indian population were estimated. Several tests of neutrality ascertained that all eight fragments evolve putatively neutrally. Further, linkage disequilibrium analyses confirmed this fact.

CONCLUSION

All eight DNA fragments seem to bear the characteristics to be considered as 'putatively neutral genetic markers' and thus, could be utilized for inference of human population and demographic histories.