title: Stage-specific expression of protease genes in the apicomplexan parasite, Eimeria tenella.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute for the Biotechnology of Infectious Diseases, University of Technology, Sydney, Broadway, N.S.W. 2007, Australia.
authors.forename: Marilyn
authors.initials: M
authors.lastname: Katrib
authors.forename: Rowan J
authors.initials: RJ
authors.lastname: Ikin
authors.forename: Fabien
authors.initials: F
authors.lastname: Brossier
authors.forename: Michelle
authors.initials: M
authors.lastname: Robinson
authors.forename: Iveta
authors.initials: I
authors.lastname: Slapetova
authors.forename: Philippa A
authors.initials: PA
authors.lastname: Sharman
authors.forename: Robert A
authors.initials: RA
authors.lastname: Walker
authors.forename: Sabina I
authors.initials: SI
authors.lastname: Belli
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Tomley
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Smith
mesh_terms: D000818:Animals; D002432:Cecum / Q000469:parasitology; D002645:Chickens / Q000469:parasitology; D003048:Coccidiosis / Q000469:parasitology; D016786:Eimeria tenella / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D005786:Gene Expression Regulation; D018503:Genome, Protozoan; D015698:Genomic Library; D052940:Merozoites / Q000378:metabolism; D033661:Oocysts / Q000378:metabolism; D010447:Peptide Hydrolases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
chemical_list: D010447:Peptide Hydrolases