The Leishmania Genome Comprises 36 Chromosomes Conserved Across Widely Divergent Human Pathogenic Species

Abstract

All the physical linkage groups constituting the genome of Leishmania infantum have been identified for the first time by hybridization of specific DNA probes to pulsed field gradient-separated chromosomes. The numerous co-migrating chromosomes were individualised using the distinctive size polymorphisms which occur among strains of the L. infantum/L. donovani complex as a tool. A total of 244 probes, consisting of 41 known genes, 66 expressed sequence tags (ESTs) and 137 anonymous DNA sequences, were assigned to a specific linkage group. We show that this genome comprises 36 chromosomes ranging in size from 0.35 to -3 Mb. This information enabled us to compare the genome structure of L. infantum with those of the three other main Leishmania species that infect man in the Old World, L. major, L. tropica and L. aethiopica. The linkage groups were consistently conserved in all species examined. This result is in striking contrast to the large genetic distances that separate these species and suggests that conservation of the chromosome structure may be critical for this human pathogen. Finally, the high density of markers obtained during the present study (with a mean of 1 marker/130 kb) will speed up the construction of a detailed physical map that would facilitate the genetic analysis of this parasite, for which no classical genetics is available.

Adaptive mechanisms in pathogens: universal aneuploidy in Leishmania

“…Old World Leishmania species (L. donovani/infantum, L. major, and L. tarentolae) have 36 chromosomes, whereas 35 are present in L. braziliensis, and 34 in L. mexicana, as result of unique chromosome fusion events [15,[18][19][20]. Gene content and synteny are remarkably well conserved across the species in comparison to other microbes, despite an estimated divergence time of 20-100 million years [15].…”

Genomic rearrangements in trypanosomatids: an alternative to the "one gene" evolutionary hypotheses?

“…Phylogenetic reconstruction based on glucose transporters was in agreement with the monophyly of genus Trypanosoma and the early separation of T. vivax from the other Salivarian trypanosomes. Another example concerns the α-and β-tubulin genes which are linked and organised in alternated tandem repeats in T. cruzi (Maingon et al 1988, Cano et al 1995 and T. brucei (Tomashow et al 1983), while they are unlinked in Leishmania and Sauroleishmania (Dujardin 1995, Wincker et al 1996, Britto et al 1998 Wincker et al 1996, Britto et al 1998, and (ii) 4 chromosomes (1,8,21, and 32 in subgenus Viannia, or NWV; Dujardin 1995, Britto et al 1998. As globins in mammals (Dover et al 1982, Jeffreys 1982, it is likely that tubulin genes arose from a single copy gene that duplicated, diverged towards α-and β-tubulin genes, and then began to spread differentially among the genome of the different trypanosomatids.…”

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

“…The Leishmania genome is organized in 36 chromosomes for the Old World species, such as L. major, L. donovani, and Leishmania infantum, and in 35 and 34 for the New World species Leishmania braziliensis and Leishmania mexicana, respectively (4,5). Although approximately a diploid organism, aneuploidy, including mosaic aneuploidy, is now known to be widespread (6-10); we refer to the nearly diploid state as "2n" here.…”