cysts by ciliated protozoa and confirmation of predation of Cryptosporidium spp. The deduced calpain-like protein sequence does not display the calcium-binding domain of conventional calpains it belongs to a diverging phylogenetic cluster that includes Aspergillus palB, a protein which is involved in a signal transduction pathway that is sensitive to ambient pH.įirst report of predation of Giardia sp. The deduced cathepsin L-like protein sequence displays the structural signatures and phylogenetic relationships of cathepsin H, a protein that is known only in plants and animals and that is involved in the degradation of extracellular matrix components in cancer diseases.

histriomuscorum cathepsin B is closely related to its Giardia homologues, which take part in the cyst wall breakdown process. A phylogenetic analysis showed for the first time that the cathepsin B tree is paraphyletic and that the diverging S. Reverse transcription-PCR experiments showed that both genes display differential expression between the cyst and the vegetative cells. Excystation was selectively inhibited at a precise differentiating stage by cysteine proteases inhibitors, suggesting that these proteins are specifically required during the excystment process. While studying the nature of the genes involved in this process, we isolated three different cysteine proteases genes, namely, a cathepsin B gene, a cathepsin L-like gene, and a calpain-like gene.

The process of excystment of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) leads in a few hours, through a massive influx of water and the resorption of the cyst wall, from an undifferentiated resting cyst to a highly differentiated and dividing vegetative cell. Villalobo, Eduardo Moch, Clara Fryd-Versavel, Ghislaine Fleury-Aubusson, Anne Morin, LoÃ¯c Cysteine proteases and cell differentiation: excystment of the ciliated protist Sterkiella histriomuscorum.

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