The hippo pathway maintains the equatorial division plane in the ciliate tetrahymena
Jiang YY, Maier W, Baumeister R, Minevich G, Joachimiak E, Ruan Z, Kannan N, Clarke D, Frankel J, Gaertig J
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 dupliclation: the cortex of the predivision cell is remodeled into two similarly sized and complete daughters. In the conditional cdal-1 mutant of Tetrahymena thermophila, 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 dcal-1 as a mutation in a Hippo/Mst kinase. Cdal is a cortical protein with a cell cycle-dependent, highly polarized localization. Early in cell division, Cdal marks the the anterior half of the cell, and later concentrates at the posterior end of the emerging anterior daughter. Despite the strong association of Cdal with the new posterior cell end, the cdal-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.
