Model of functional relationship between CSAR1 and ERK7. (A) Pseudo-timecourse of cell cycle using fixed confocal micrographs of CSAR1^3xHA(ERK7^AID) parasites grown in +IAA for 5 h. CSAR1 signal appears to build up first at the maternal and then at the daughter conoids just before the loss of the structures. Scale bar is 2 μm. (B) In normal parasites, ERK7 concentrates at the apical caps of both maternal and daughter parasites and drives CSAR1 to concentrate in the residual body (RB), possibly through ERK7 kinase activity. This protects the maternal and daughter apical complexes from degradation. When ERK7 is lost, CSAR1 is not retained in the residual body and concentrates at the apical tips of mother and daughter cells, leading to premature degradation of the conoids.