How to build a rib cage for a cell: the patterning, growth, and maturation of the cortical microtubules in Toxoplasma

Project Summary: The apicomplexans are unicellular parasites that infect a wide variety of vertebrates and invertebrates, and are the causative agents for many diseases (e.g., malaria, toxoplasmosis, and cryptosporidiosis) that impact the global population. Although differing greatly in host range and specificity, these parasites share similar major features in their cellular architectures, with species-specific modifications. For example, they all have an array of cortical (subpellicular) microtubules rooted in a ring-like structure (the apical polar ring), but the number of cortical microtubules varies widely (e.g., two to four in P. falciparum asexual blood-stage parasites vs. 22 in T. gondii). Chemical inhibition of microtubule polymerization results in ill-formed daughter cortex and inviable progeny, indicating that the construction of the cortical microtubules is required for guiding the growth of the parasite cortex and proper packaging the daughter organelles. Although their importance to parasite replication has long been appreciated, the basic mechanism of patterning and development of the cortical microtubules remains unexplored. In the last few years, we discovered that the structure and activities for both the apical polar ring and the cortical microtubules are distinct in the mature vs. growing daughter parasites and can be separated genetically. We will take advantage of this unique launch pad and combine it with molecular genetic, microscopy, and comparative proteomics to explore the initiation of patterning (Aim 1), growth and maturation (Aim 2) of the microtubule array. This project will open new avenues for discovering new druggable, parasite- specific targets for treating toxoplasmosis, generate novel molecular and structural insights into the mechanism through which complex cytoskeletal frameworks are assembled, and enable comparative studies of the biogenesis of mcrotubule arrays in other apicomplexan parasites. When integrated with the naturally occurring variations among these relatives, this will help to reveal the molecular basis for divergence of apicomplexan cytoskeletal structures, an important part of the evolution of this group of parasites.