A well-conserved Plasmodium falciparum var gene shows an unusual stage-specific transcript pattern

Area of Science:

• Malariology
• Molecular Parasitology
• Genomics

Background:

• The Plasmodium falciparum var gene family encodes PfEMP1 variant antigens, crucial for virulence via host receptor adhesion.
• PfEMP1 expression is regulated transcriptionally, with predominant single-type expression and switching to evade immunity.
• Conflicting data exist regarding var gene transcription timing, with RT-PCR suggesting later stages and Northern blots indicating earlier stages.

Purpose of the Study:

• To resolve discrepancies in var gene transcription timing.
• To investigate the expression patterns of diverse var gene transcripts.
• To examine the expression and function of the conserved varCSA transcript.

Main Methods:

• Northern blot analysis using probes for a diverse var gene repertoire.
• Investigation of var gene transcription across different developmental stages of Plasmodium falciparum.
• Correlation analysis between varCSA transcript presence and chondroitin sulfate A binding phenotype.

Main Results:

• Northern blot analysis confirmed that most var transcript types are predominantly detected in the ring stages.
• The well-conserved varCSA transcript was found to be constitutively expressed across different laboratory parasite lines.
• Constitutive expression of varCSA transcripts did not correlate with the chondroitin sulfate A (CSA)-binding phenotype.

Conclusions:

• Var gene transcription, in general, occurs predominantly in the early ring stages of Plasmodium falciparum.
• The varCSA transcript is constitutively expressed and may not undergo antigenic variation.
• The presence of full-length varCSA transcripts is not a reliable indicator of the CSA-binding phenotype.