Cryptosporidium reuses its entry organelle to build a host-cell interface
A peer-reviewed study tracked how the diarrhoea-causing parasite Cryptosporidium parvum enters intestinal cells and establishes its connection with the host. Live imaging and detailed microscopy point to a continuing role for one secretory organelle after its first discharge. Experiments in cultured cells and mouse tissue support a model of sequential protein delivery.
Science··Morning
The parasite’s entry unfolds in minutes
A secretory organelle has several jobs as Cryptosporidium parvum settles into an intestinal cell. This single-celled parasite is associated with severe diarrhoea, particularly in young children and people whose immunity is impaired. In a peer-reviewed investigation, researchers watched 27 invasions unfold in living cells. The parasite took about five minutes to assume its rounded intracellular form. They also examined infected mouse tissue and human intestinal cells grown in culture, using electron microscopy and expansion microscopy alongside the live observations.[1]
Secretion starts before the host membrane closes
The organelle, called the rhoptry, releases its own contents first. Host-cell actin accumulated before dense granules moved to the parasite’s tip and discharged their cargo. That secretion took place before host membrane had fully enclosed the parasite. Expansion microscopy and electron microscopy revealed a membrane-bound compartment at the tip, connected to a channel opening towards the host cell.[1]
The organelle’s membrane persists at the interface
Two proteins marking rhoptry membrane remained around the compartment after the initial discharge. A small-granule protein later appeared at the same interface. In mature parasites, rhoptry membrane markers coincided with the feeder organelle separating parasite and host. These observations support a model in which the organelle serves successive roles in entry and protein transfer. Chemical fixation may affect high-resolution images; the channel’s molecular composition and how granules join it remain unknown.[1]
