The mechanisms that govern pattern formation within the cell are poorly understood. Ciliates carry on their surface an elaborate pattern of cortical organelles that are arranged along the anteroposterior and circumferential axes by largely unknown mechanisms. Ciliates divide by tandem duplication: the cortex of the pre-division cell is remodeled into two similarly-sized and complete daughters. In the conditional cdaI-1 mutant of Tetrahymena thermophile, the division plane migrates from its initially correct equatorial position toward the cell’s anterior, resulting in unequal cell division, and defects in nuclear divisions and cytokinesis. We used comparative whole genome sequencing, to identify the cause of cdaI-1 as a mutation in a Hippo/Mst kinase. CdaI is a cortical protein with a cell cycle-dependent, highly polarized localization. Early in cell division, CdaI marks the anterior half of the cell, and later concentrates at the posterior end of the emerging anterior daughter. Despite the strong association of CdaI with the new posterior cell end, the cdaI-1 mutation does not affect the patterning of the new posterior cortical organelles. We conclude that in Tetrahymena, the Hippo pathway maintains an equatorial position of the fission zone and by this activity specifies the relative dimensions of the anterior and posterior daughter cell.
- Received February 1, 2017.
- Accepted March 29, 2017.
- Copyright © 2017, The Genetics Society of America