Structural organisation of microsatellite families in the Leishmania genome and polymorphisms at two (CA)n loci

In the present study, we have analysed the frequency and distribution of several microsatellite DNAs [(CA)n, (GGT)n and (GCA)n] in the genome of Leishmania. Hybridisation analysis on the molecular karyotypes of different Leishmania strains showed the presence of these three microsatellites on all chromosomes of the parasite. The number of microsatellite clusters appeared grossly similar among strains from different Old World complexes. However, these three microsatellite families showed an uneven distribution among heterologous chromosomes of the same strain. Moreover, restriction analysis of chromosome I in various strains of Leishmania infantum showed a strong clustering of these microsatellites in the same chromosomal region. A partial genomic library was screened with a (CA)n probe, and 21 positive clones were isolated. The sequencing of these clones confirmed the association of various microsatellites such as (CA)n, (CT)n, and (GCA)n. Finally, specific polymerase chain reaction amplification of two cloned (CA)n loci demonstrated allelic size polymorphisms among strains within L. infantum and Leishmania donovani. Most of the 34 strains analysed were found to be monoallelic, while two alleles were found in a small number of strains. The interest of these sequences for studies on ploidy and population genetics of the parasite is discussed.