Genetic changes during laboratory propagation: Copy number At the reticulocyte-binding protein 1 locus of Plasmodium falciparum

Comparative genomic hybridization studies have revealed elevated copy number (CN) at the reticulocyte-binding protein 1 gene (PfRh1) in fast growing lab-adapted parasites, while genetic manipulation demonstrates a causal link between cell invasion and PfRh1 CN. We therefore examined PfRh1 copy number variation (CNV) in 202 single clone parasite isolates from four countries to quantify the extent of CNV within natural populations. Surprisingly, we found that no natural parasite infections showed elevated CN. In contrast, 4/28 independent laboratory reference strains show elevated CN. One possibility is that amplification of PfRh1 (or neighboring loci) is selected during laboratory culture. In the case of FCR3 group of parasites, clone trees show that PfRh1 amplification arose in laboratory lines following establishment in culture. These data show that CNV at PfRh1 is rare or non-existent in natural populations, but can arise during laboratory propagation. We conclude that PfRh1 CNV is not an important determinant of gene expression, cell invasion or growth rate in natural parasite populations.