Inga R, De Doncker S, Gomez J, Lopez M, Garcia R, Le Ray D, Arevalo J, Dujardin J C
Department of Physiological Sciences and Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru.
Mol Biochem Parasitol. 1998 May 1;92(2):219-28. doi: 10.1016/s0166-6851(98)00009-7.
Chromosomal size polymorphism in Leishmania of subgenus Viannia has been correlated with eco-geography. The sizes of chromosomes bearing rDNA genes were determined in 69 isolates. A considerable size-variation was observed, ranging from 1100 to 1500 kb. Chromosomes of L.(V.). braziliensis, L.(V.)guyanensis and L.(V.) peruviana from northern Peru were significantly larger (200 kb) than those of L.(V.) peruviana from southern Peru. In addition, 31 out of 69 isolates presented each two different-sized homologues of the rDNA chromosome. Long range restriction mapping of three different-sized rDNA chromosomes from L.(V.)braziliensis M2903 and L.(V.)peruviana HB31 (north) and LC106 (south) each revealed three fragments delimited by PmeI restriction sites: two constant in size (the centre and one extremity of the chromosome) and one variable (the other extremity, containing a single cluster of rDNA genes). Further analysis of the M2903 rDNA chromosome allowed the localization of its 140 kb rDNA cluster at 85 kb from the telomeric end. Two arguments indicated that size-variation of the rDNA chromosome is partially due to amplification/deletion of the clustered rDNA genes: (i) size-variation of the cluster-containing fragment was proportional to the size-variation of the whole chromosome, and (ii) hybridization signal intensity of the rDNA chromosome with a small subunit rDNA probe strongly correlated with chromosomal size. Nevertheless, DNA sequences present between the rDNA cluster and the telomere might also play a role in chromosomal size polymorphism. In addition, our data suggest that rDNA gene copy number (20-40 copies cell(-1) under a diploid hypothesis) in subgenus Viannia is lower than reported previously.
维安亚属利什曼原虫的染色体大小多态性与生态地理学相关。在69个分离株中测定了携带rDNA基因的染色体大小。观察到相当大的大小变异，范围从1100至1500 kb。来自秘鲁北部的巴西利什曼原虫（维安亚属）、圭亚那利什曼原虫（维安亚属）和秘鲁利什曼原虫（维安亚属）的染色体明显比来自秘鲁南部的秘鲁利什曼原虫（维安亚属）的染色体大（200 kb）。此外，69个分离株中有31个呈现出rDNA染色体的每两个不同大小的同源物。对来自巴西利什曼原虫M2903、秘鲁利什曼原虫HB31（北部）和LC106（南部）的三种不同大小的rDNA染色体进行的长距离限制性图谱分析，各自揭示了由PmeI限制性位点界定的三个片段：两个大小恒定（染色体的中心和一个末端）和一个可变（另一个末端，包含单个rDNA基因簇）。对M2903 rDNA染色体的进一步分析允许将其140 kb的rDNA簇定位在距端粒末端85 kb处。有两个论据表明rDNA染色体的大小变异部分归因于成簇rDNA基因的扩增/缺失：（i）含簇片段的大小变异与整个染色体的大小变异成比例，并且（ii）rDNA染色体与小亚基rDNA探针的杂交信号强度与染色体大小密切相关。然而，rDNA簇和端粒之间存在的DNA序列也可能在染色体大小多态性中起作用。此外,我们的数据表明，维安亚属中的rDNA基因拷贝数（在二倍体假设下为20 - 40个拷贝/细胞）低于先前报道的数值。
