The Influence of the regulation of Toxoplasma gondii TgMIC2 transgene on host cell infection

Toxoplasma gondii microneme protein 2 (TgMIC2), an apically stored adhesin, was shown to be a key participant involved in the initial attachment and invasion to a host cell. In this study, we had established the clonal line of T. gondii tachyzoites which over-expressed TgMIC2 using the tetracycline repressor (TetR)-based inducible gene expression system. The TgMIC2 over-expression significantly reduced tachyzoite propagation in vitro (p < 0.002) and significantly reduced the parasite virulence in mice (p = 0.002). The over-expression of exogenous TgMIC2 caused the increase of mRNA expression level of endogenous TgMIC2. Wild type parasites mainly expressed TgMIC2115 protein, the microneme store and the surface form of TgMIC2. Over-expression of TgMIC2 induced production of TgMIC2110, the cell surface form of TgMIC2 produced by N-terminal proteolytic processing of TgMIC2115. Some of tachyzoites became spherical shape having disordered apical complex after TgMIC2 over-expression. TgMIC2 over-expression did not effect mRNA expression level of TgMIC2-associated protein (TgM2AP), but appeared to cause the aberrance of TgM2AP protein. In conclusion, our results reveal the novel findings on the importance of the regulation of TgMIC2 transgene expression on post-translational modification of TgMIC2 and TgM2AP, and parasite’s morphology and propagation, with all together impacting the outcome of infection