Chromosome size polymorphism and DNA rearrangements in plasmodium

Abstract

Protozoan parasites often follow a complex life cycle that features the display of many distinct developmental stages. The life cycle of many of these parasites takes place in two different hosts, Such organisms are therefore adapted to differentiate cyclically, growing and developing in very different environments. The malaria parasite is a good example of a unicellular parasite demonstrating complex differentiation pattems. Here short periods of rapid asexual proliferation are alternated with sexual differentiation. The haploid parasite sequentially multiplies by mitotic divisions in the liver and the blood of the vertebrate host, followed by sexual development in the midgut of mosquitoes and the production of infectious sporozoites in the salivary glands of the mosquitoes. Malaria parasites have a unique biology that enables them to complete the complex differentiation cycles necessary for survival in two different hosts. The question addressed here is whether the organization and molecular biology of the chromosomes of malaria parasites have similarly unique features that play a direct role in the progression of the parasite through its life cycle. Research on genome organization has revealed that malaria parasites apparently exhibit a remarkable plasticity of their genome, as shown by intra-specific size differences between homologous chromosomes. Based on the characterization of several mechanisms involved in the generation of chromosome size polymorphism in several Plasmodium species, the presence of unique molecular processes with specific functions has been the subject of speculation. It has been proposed that size polymorphism could be associated with programmed DNA rearrangements that are involved in the regulation of gene transcription or in generating diversity in