In vivo expression and distribution of dense granule protein 7 (GRA7) in the exoenteric (tachyzoite, bradyzoite) and enteric (coccidian) forms of Toxoplasma gondii

The in vivo expression and distribution of the dense granule protein GRA7 w as examined in both the exoenteric (tachyzoite and bradyzoite) and enteric (coccidian) forms of Toxoplasma gondii by immunocytochemistry. There was st rong staining of GRA7 in granules within all the infectious stages (tachyzo ite, bradyzoite, merozoite and sporozoite). During tachyzoite development, GRA7 was secreted and was associated with the parasitophorous vacuole. In c ontrast, although there was staining of granules within the bradyzoites of more mature cysts, there appeared to be little staining of the tissue cyst wall or host cell. The apparent stage-specific variation in secretion of GR A7 between tachyzoites and bradyzoites was confirmed by double labelling us ing stage-specific markers (SAG1 and BAG1). In the enteric forms in the cat gut there was strong labelling of the PV containing early asexual and sexu al stages and staining of a few granules in the apical cytoplasm of the mer ozoite. The positive enteric staining pattern differentiates GRA7 from the other GRA proteins (GRA1-6) which were absent in the merozoites and enteric stages. The staining pattern of GRA7 with strong staining during tachyzoit e and enteric development and reduced staining in the tissue cysts is simil ar to that seen for NTPases. The function of GRA7 is unknown but it is uniq ue among the dense granule proteins in being expressed in all the infectiou s forms of T. gondii which would point to a basic role in the vacuolar adap tations required for active parasite development.