Analysis of Pir Gene Expression Across the Plasmodium Life Cycle

Abstract

Background Plasmodium interspersed repeat ( pir ) is the largest multigene family in the genomes of most Plasmodium species. A variety of functions for the PIR proteins which they encode have been proposed, including antigenic variation, immune evasion, sequestration and rosetting. However, direct evidence for these is lacking. The repetitive nature of the family has made it difficult to determine function experimentally. However, there has been some success in using gene expression studies to suggest roles for some members in virulence and chronic infection. Methods Here we examined pir gene expression across the life cycle of P. berghei using publicly available RNAseq data-sets, and at high resolution in the intraerythrocytic development cycle using new data from P. chabaudi . Results Expression of pir genes is greatest in stages of the parasite which invade and reside in red blood cells. The marked exception is that liver merozoites and male gametocytes produce a very large number of pir gene transcripts, notably compared to female gametocytes, which produce relatively few. Within the asexual blood stages different subfamilies peak at different times, suggesting further functional distinctions. Representing a subfamily of its own, the highly conserved ancestral pir gene warrants further investigation due to its potential tractability for functional investigation. It is highly transcribed in multiple life cycle stages and across most studied Plasmodium species and thus is likely to play an important role in parasite biology. Conclusions By identifying distinct expression patterns for different pir genes and subfamilies we hope to provide a basis for the design of future experiments to uncover their function.

Development and Optimization of a Selective Whole-Genome Amplification To Study Plasmodium ovale Spp.

“…scales, we first determined P. ovale wallikeri orthologous protein-coding genes that were still to be characterized ( 13 ). We first excluded the 1,742 pir proteins from the PocGH01 reference proteome ( 13 ), which are encoded by a multigenic family with numerous amino acid sequence variations, similarly to var genes in P. falciparum ( 26 ). By aligning P. ovale curtisi on P. ovale wallikeri protein sequences with BLAST+ ( 27 ), we identified 4,420 proteins with a high sequence similarity.…”