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Chromosome size variation occurs in cloned Plasmodium falciparum on in vitro cultivationt

Thomas E. Wellems^I; Ayo M.J. Oduola^II; Brian Fenton^III; Robert Desjardins^IV; Lindsey J. Panton^I; Virgilio E. do Rosario^V

^ILaboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA. Send correspondence to T.E.W.
^IIExperimental Therapeutics, Department of Parasitology, Walter Reed Army Institute, Silver Spring, MD 20910, USA
^IIIDepartment of Genetics, University of Edinburgh, Edinburgh, Scotland, UK
^IVAmerican Cyanamid, Lederle Laboratories, Pearl River, NY 10965, USA
^VBiomedical Research Institute, Rockville, MD 20852, USA

ABSTRACT

Chromosome size variations occurred in parasite lines derived from a clone of Plasmodium falciparum. These variations developed over periods of many months in haploid erythrocyte-stage parasites maintained in vitro. Chromosome size variations were more numerous in parasite populations made mefloquine resistant by cultivation under drug pressure than in control parasites maintained in culture medium alone. In some cases, the changes in size were sufficiently large to alter the relative order of chromosome DNA bands in pulsed-field gradient gel electrophoresis separations. Subtelomeric regions of the chromosomes are especially active regions involved in rearrangements responsible for the size changes. The biological role of these rearrangements is not known. However, their occurrence in control experiments along with their frequent appearance under conditions of mefloquine pressure suggests that they may reflect generalized modifications of genomic structure in response to environmental conditions.

Keywords: chromosome; variation; Plasmodium falciparum ; cultivationt.

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