A2 gene of Old World cutaneous Leishmania is a single highly conserved functional gene

Abstract

BackgroundLeishmaniases are among the most proteiform parasitic infections in humans ranging from unapparent to cutaneous, mucocutaneous or visceral diseases. The various clinical issues depend on complex and still poorly understood mechanisms where both host and parasite factors are interacting. Among the candidate factors of parasite virulence are the A2 genes, a family of multiple genes that are developmentally expressed in species of the Leishmania donovani group responsible for visceral diseases (VL). By contrast, in L. major determining cutaneous infections (CL) we showed that A2 genes are present in a truncated form only. Furthermore, the A2 genomic sequences of L. major were considered subsequently to represent non-expressed pseudogenes [1]. Consequently, it was suggested that the structural and functional properties of A2 genes could play a role in the differential tropism of CL and VL leishmanias. On this basis, it was of importance to determine whether the observed structural/functional particularities of the L. major A2 genes were shared by other CL Leishmania, therefore representing a proper characteristic of CL A2 genes as opposed to those of VL isolates.MethodsIn the present study we amplified by PCR and sequenced the A2 genes from genomic DNA and from clonal libraries of the four Old World CL species comparatively to a clonal population of L. infantum VL parasites. Using RT-PCR we also amplified and sequenced A2 mRNA transcripts from L. major.ResultsA unique A2 sequence was identified in Old World cutaneous Leishmania by sequencing. The shared sequence was highly conserved among the various CL strains and species analysed, showing a single polymorphism C/G at position 58. The CL A2 gene was found to be functionally transcribed at both parasite stages.ConclusionThe present study shows that cutaneous strains of leishmania share a conserved functional A2 gene. As opposed to the multiple A2 genes described in VL isolates, the CL A2 gene is unique, lacking most of the nucleotide repeats that constitute the variable region at the 5'end of the VL A2 sequences. As the variable region of the VL A2 gene has been shown to correspond to a portion of the protein which is highly immunogenic, the present results support the hypothesis of a possible role of the A2 gene in the differential tropism of CL and VL leishmania parasites.

Cross-species genetic exchange between visceral and cutaneous strains of Leishmania in the sand fly vector

“…In these species, multiple copies of the A2 genes are arranged in tandem on Chr 22, whereas in L. major, the corresponding sequences have been found functionally expressed as a single copy gene (24). Amplification of these sequences in Li and Lm confirmed a full-length and truncated copy of the A2 gene(s), respectively, and revealed that each of the hybrids had inherited at least one A2 locus from each parent (Fig.…”

Whole genome sequencing of multiple Leishmania donovani clinical isolates provides insights into population structure and mechanisms of drug resistance

“…The A2 protein plays a role in promastigote-amastigote differentiation (Alcolea et al 2010) and is expressed solely during amastigote-stage host infection in L. donovani (Ghedin et al 1998;Zhang and Matlashewski 2001) but not L. major, and has been associated with the differing disease tropisms between the two species (Zhang et al 2003). In contrast to the conserved A2 locus in L. major (Garin et al 2005), functional CNVs have been previously observed in the L. donovani species complex, and we see significant sequence diversity and structural variation at this region even between our related lines. Whereas 39 and 59 A2-related genes possessed nine high-frequency protein-level SNPs, genes on the rest of that chromosome had only a total of four, suggesting a possible role for variability at this locus in A2 gene expression (Zhang et al 2003).…”

Evaluation of Leishmania Species Reactivity in Human Serologic Diagnosis of Leishmaniasis

“…For example, the amastigote stage specific A2 protein in CL isolates was lacking most of the nucleotide repeats that constitute the variable region at the 5′ end of the A2 sequences in VL that are responsible for its immunogenicity. 20 Further studies using a higher number of cutaneous disease patients and Leishmania species are needed to explore the lack of species-specific diagnosis in CL .…”