Open Access Open Badges Research article

Stage-specific expression of protease genes in the apicomplexan parasite, Eimeria tenella

Marilyn Katrib1, Rowan J Ikin1, Fabien Brossier3, Michelle Robinson1, Iveta Slapetova1, Philippa A Sharman2, Robert A Walker2, Sabina I Belli1, Fiona M Tomley4 and Nicholas C Smith2*

Author Affiliations

1 Institute for the Biotechnology of Infectious Diseases, University of Technology, 2007, Sydney, Broadway, N.S.W., Australia

2 Queensland Tropical Health Alliance Research Laboratory, Faculty of Medicine, Health and Molecular Sciences, James Cook University, Cairns Campus, McGregor Road, 4878, Smithfield, QLD, Australia

3 INRA UR1282, Equipe Pathogenèse des Coccidioses, Infectiologie Animale et Santé Publique, 37380, Nouzilly, France

4 Royal Veterinary College, Hawkshead Lane, North Mymms, AL9 7TA, Hatfield, Hertfordshire, UK

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BMC Genomics 2012, 13:685  doi:10.1186/1471-2164-13-685

Published: 7 December 2012



Proteases regulate pathogenesis in apicomplexan parasites but investigations of proteases have been largely confined to the asexual stages of Plasmodium falciparum and Toxoplasma gondii. Thus, little is known about proteases in other Apicomplexa, particularly in the sexual stages. We screened the Eimeria tenella genome database for proteases, classified these into families and determined their stage specific expression.


Over forty protease genes were identified in the E. tenella genome. These were distributed across aspartic (three genes), cysteine (sixteen), metallo (fourteen) and serine (twelve) proteases. Expression of at least fifteen protease genes was upregulated in merozoites including homologs of genes known to be important in host cell invasion, remodelling and egress in P. falciparum and/or T. gondii. Thirteen protease genes were specifically expressed or upregulated in gametocytes; five of these were in two families of serine proteases (S1 and S8) that are over-represented in the coccidian parasites, E. tenella and T. gondii, distinctive within the Apicomplexa because of their hard-walled oocysts. Serine protease inhibitors prevented processing of EtGAM56, a protein from E. tenella gametocytes that gives rise to tyrosine-rich peptides that are incorporated into the oocyst wall.


Eimeria tenella possesses a large number of protease genes. Expression of many of these genes is upregulated in asexual stages. However, expression of almost one-third of protease genes is upregulated in, or confined to gametocytes; some of these appear to be unique to the Coccidia and may play key roles in the formation of the oocyst wall, a defining feature of this group of parasites.

Eimeria; Apicomplexa; Protease; Protease inhibitors; Gametocyte; Oocyst wall