Indiana University-Purdue University Indianapolis (IUPUI) / Toxoplasma gondii is a ubiquitous, protozoan parasite contributing
significantly to global human and animal health. In the host, this obligate
intracellular parasite converts into a latent tissue cyst form known as the
bradyzoite, which is impervious to the immune response. The tissue cysts
facilitate wide-spread transmission through the food chain and give rise to
chronic toxoplasmosis in immune compromised patients. In addition, they may
reactivate into replicating tachyzoites which cause tissue damage and
disseminated disease. Current available drugs do not appear to have appreciable
activity against latent bradyzoites. Therefore, a better understanding of the
molecular mechanisms that drive interconversion between tachyzoite and
bradyzoite forms is required to manage transmission and pathogenesis of
Toxoplasma.
Conversion to the bradyzoite is accompanied by an altered transcriptome,
but the molecular players directing this process are largely uncharacterized.
Studies of stage-specific promoters revealed that conventional cis-acting
mechanisms operate to regulate developmental gene expression during tissue
cyst formation. The major class of transcription factor likely to work through these
cis-regulatory elements appears to be related to the Apetala-2 (AP2) family in
plants. The Toxoplasma genome contains nearly 70 proteins harboring at least one predicted AP2 domain, but to date only three of these T. gondii AP2 proteins
have been linked to bradyzoite development.
We show that the putative T. gondii transcription factor, AP2IX-4, is
localized to the parasite nucleus and exclusively expressed in tachyzoites and
bradyzoites undergoing division. Knockout of AP2IX-4 had negligible effect on
tachyzoite replication, but resulted in a reduced frequency of bradyzoite cysts in
response to alkaline stress induction – a defect that is reversible by
complementation. Microarray analyses revealed an enhanced activation of
bradyzoite-associated genes in the AP2IX-4 knockout during alkaline conditions.
In mice, the loss of AP2IX-4 resulted in a modest virulence defect and reduced
brain cyst burden. Complementation of the AP2IX-4 knockout restored cyst
counts to wild-type levels. These findings illustrate the complex role of AP2IX-4 in
bradyzoite development and that certain transcriptional mechanisms responsible
for tissue cyst development operate across parasite division.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/12538 |
| Date | 10 January 2017 |
| Creators | Huang, Sherri Y. |
| Contributors | Arrizabalaga, Gustavo, Sullivan, William J., Jr., Lu, Tao, Takagi, Yuichiro, Zhang, Jian-Ting |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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