Conserved linkage groups associated with large-scale chromosomal rearrangements between Old World and New World Leishmania genomes

The genus Leishmania can be taxonomically separated into three main groups: the Old World subgenus L. (Leishmania), the New World subgenus L. (Leishma nia) and the New World subgenus L. (Viannia). The haploid genome of Old Wor ld Leishmania species has been shown to contain 36 chromosomes defined as p hysical linkage groups. the latter were found entirely conserved across spe cies. In the present study, we tried to verify whether this conservation of the genome structure extends to the New World species of Leishmania. 300 l oci were explored by hybridization on optimized pulsed field gel electropho resis separations of the chromosomes of polymorphic strains of the six main pathogenic Leishmania species of the New World. When comparing these New W orld karyotypes with their Old World counterparts, 32 out of 36 linkage gro ups were found conserved among all species. Four chromosomal rearrangements were found. All species belonging to the L. (Viannia) subgenus were charac terized by the presence (i) of a short sequence exchange between chromosome s 26 and 35, and (ii) more importantly, of a fused version of chromosomes 2 0 and 34 which are separated in all Old World species. 69 additional marker s were isolated from a plasmid library specifically constructed from the re arranged chromosomes 20 + 34 in an attempt to detect mechanisms other than a fusion or breakage: only two markers out of 40 did not belong to the link age groups 20 and 34. On the other hand, all strains belonging to the New W orld subgenus L. (Leishmania) were characterized by two different chromosom al rearrangements of the same type (fusion/breakage) as above as compared w ith Old World species: chromosomes 8 + 29 and 20 + 36. Consequently, these two groups of species have 35 and 34 heterologous chromosomes, respectively . Overall, these results show that large-scale chromosomal rearrangements o ccurred during the evolution of the genus Leishmania, and that the three ma in groups of pathogenic species are characterized by different chromosome n umbers. Nevertheless, translocations seem particularly rare, and the conser vation of the major linkage groups should be an essential feature for the c ompared genetics between species of this parasite. (C) 1998 Elsevier Scienc e B.V. All rights reserved.