Dynamics of the Toxoplasma gondii inner membrane complex

Abstract

Unlike most cells, protozoa in the phylum apicomplexa divide by a distinctive process in which multiple daughters are assembled within the mother (schizogony, endodyogeny), using scaffolding known as the Inner Membrane Complex. The ‘IMC’ underlies the plasma membrane during interphase, but new daughters develop in the cytoplasm, as cytoskeletal filaments associate with flattened membrane cisternae (alveolae), which elongate rapidly to encapsulate subcellular organelles. Newly assembled daughters acquire their plasma membrane as they emerge from the mother, leaving behind vestiges of the maternal cell. While the maternal plasma membrane remains intact throughout this process, the maternal IMC disappears – is it degraded, or recycled to form the daughter IMC? Exploiting fluorescently tagged IMC markers, we have used live cell imaging, fluorescence photobleaching-recovery, and mEos2 photoactivation to monitor the dynamics of IMC biogenesis and turnover during Toxoplasma gondii tachyzoite replication. These studies reveal that formation of the T. gondii IMC involves two distinct steps: de novo assembly during daughter IMC elongation within the mother cell, followed by recycling of maternal IMC membranes after the emergence of daughters from the mother cell.