Identification and functional analysis of an essential daughter bud assembly complex in Toxoplasma gondii

Toxoplasma gondii is a single-celled obligate intracellular parasite which is estimated to infect 30% of the global human population. While T. gondii infections are typically asymptomatic in healthy individuals, they can cause life-threatening complications in immunocompromised individuals and congenitally infected neonates. As current treatments are toxic and do not clear the lifelong chronic infection, a deeper understanding of parasite biology is needed to identify novel targets for therapeutic intervention. As a member of the phylum Apicomplexa, T. gondii contains several unique organelles which play critical roles in facilitating the parasite’s lytic cycle, which causes the acute phase of disease. One of these unique apicomplexan organelles is the inner membrane complex (IMC), which lies directly underneath the parasite’s plasma membrane and is composed of a series of flattened vesicles supported by an underlying cytoskeletal network. The IMC plays essential roles throughout the T. gondii lytic cycle by serving as the platform for the molecular machinery that controls parasite motility, stabilizing the apical complex which facilitates host cell invasion, and acting as a scaffold for developing daughter cells during parasite replication.T. gondii replicates using a unique form of internal budding called endodyogeny, in which two daughter buds are formed within the cytoplasm of a single maternal cell. Endodyogeny can be divided into four steps: bud initiation, elongation, constriction, and maturation. During this process, IMC components are added to the developing daughter cell scaffold in a tightly regulated, sequential manner. While many of the components of the IMC are known to be important for parasite fitness, most are maintained in mature parasites and play critical roles in other phases of the lytic cycle besides replication. Several IMC proteins have been identified which are found only in the IMC of daughter buds, but most are dispensable or have only mo