Antigenic variation in Giardia lamblia is regulated by RNA interference

Area of Science:

• Parasitology
• Molecular Biology
• Immunology

Background:

• Giardia lamblia is a common human intestinal parasite.
• Antigenic variation allows Giardia to evade the host immune response, leading to chronic infections.
• Giardia expresses one variant-specific surface protein (VSP) at a time from a large gene repertoire, switching VSPs through unknown mechanisms.

Purpose of the Study:

• To elucidate the molecular mechanisms regulating VSP expression and antigenic variation in Giardia.
• To investigate the role of RNA interference (RNAi) pathway components in controlling VSP gene switching.

Main Methods:

• Analysis of VSP gene transcription and transcript accumulation in Giardia clones.
• Detection of antisense RNAs and small RNAs associated with VSP gene expression.
• Functional studies involving silencing of key RNAi pathway components (Dicer, RNA-dependent RNA polymerase).

Main Results:

• Giardia efficiently transcribes multiple VSP genes but accumulates transcripts for only the expressed VSP.
• Antisense RNAs are detected for silenced VSP genes, and small RNAs are found from silenced, but not expressed, VSP genes.
• Silencing Dicer or RNA-dependent RNA polymerase disrupts single VSP expression, leading to multiple VSP expression in individual parasites.

Conclusions:

• The RNA interference machinery, including Dicer and RNA-dependent RNA polymerase, plays a critical role in regulating VSP expression and antigenic variation in Giardia.
• This study implicates RNAi in the precise control of VSP switching, enabling parasite persistence.
• Understanding this mechanism offers potential targets for controlling Giardia infections.