PbSR is synthesized in macrogametocytes and involved in formation of the malaria crystalloids

Area of Science:

• Malariology
• Cell Biology
• Parasitology

Background:

• Crystalloids are transient organelles in malaria ookinetes with unknown origins and functions.
• The Plasmodium berghei scavenger receptor-like protein (PbSR) is vital for parasite transmission from mosquito to host.
• PbSR knockout parasites exhibit normal oocyst numbers but lack sporozoites, indicating a role in oocyst sporogony.

Purpose of the Study:

• To investigate the role of PbSR in malaria parasite development, specifically its involvement with crystalloids.
• To elucidate the synthesis, targeting, and function of PbSR during the parasite lifecycle.

Main Methods:

• Fluorescent protein tagging was employed to track PbSR localization.
• Targeted gene disruption (knockout) was used to assess PbSR function.
• Oocyst sporulation rates were analyzed in both infected mosquitoes and in vitro conditions.

Main Results:

• PbSR is synthesized in macrogametocytes and targeted to crystalloids in developing ookinetes, contributing to their formation.
• PbSR knockout parasites show significantly reduced oocyst sporulation rates in infected mosquitoes.
• In vitro sporulation rates of PbSR knockout parasites were unaffected, suggesting mosquito-specific factors influence the phenotype.

Conclusions:

• PbSR is the first identified parasite protein associated with the crystalloid organelle.
• PbSR plays a critical role in crystalloid formation and subsequent sporozoite development within the oocyst.
• A novel protein-trafficking mechanism for delivering PbSR to oocysts is suggested, potentially influenced by mosquito factors.