A novel actin-related protein is associated with daughter cell formation in Toxoplasma

Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110

^* To whom correspondence should be addressed. Email: sibley{at}borcim.wustl.edu.

	Abstract

Cell division in Toxoplasma gondii occurs by an unusual budding mechanism termed endodyogeny, during which twin daughters are formed within the body of the mother cell. Cytokinesis begins with the coordinated assembly of the inner membrane complex (IMC), which surrounds the growing daughter cells. The IMC is compiled of both flattened membrane cisternae and subpellicular filaments composed of articulin-like proteins attached to underlying singlet microtubules. While proteins that comprise the elongating IMC have been described, little is known about its initial formation. Using Toxoplasma as a model system, we demonstrate that actin-like protein 1 (ALP1) is partially redistributed to the IMC at early stages in its formation. Immuno-EM localized ALP1 to a discrete region of the nuclear envelope, on transport vesicles, and on the nascent IMC of the daughter cells, prior to the arrival of proteins such as IMC-1. Over-expression of ALP1 under control of a strong constitutive promoter disrupted formation of the daughter cell IMC, leading to delayed growth and defects in nuclear and apicoplast segregation. Collectively, these data suggest that ALP1 participates in formation of daughter cell membranes during cell division in apicomplexan parasites.