DscI is antagonized by CortI and IQGAP1, which serves as a negative regulator of CK mechanoresponsiveness. (A) Representative growth curves in suspension culture of WT (blue), dsc1 (red), and cortI (green) single mutants and cortI; dsc1 (brown) double mutant. Growth curve of cortI; dsc1 shows faster growth, as compared to the cortI single mutant. n = 3 per growth curve; bars represent SEM. (B) The quantified growth rates for the exponential growth phase for each cell line shown in A are presented. The average growth rate of cortI; dsc1 (0.051 h⁻¹) was significantly higher than that of cortI (0.026 h⁻¹) and was lower than dsc1 single mutants (0.059 h⁻¹). P values were calculated using ANOVA followed by Fisher’s LSD test. Number of samples analyzed, n = 6 from two independent experiments. (C) Representative images of DIC and nuclei show relative cell size and number of nuclei/cell between different cell lines. cortI single mutant displayed an enlarged cell size due to a higher degree of multinucleation. Cells were less multinucleated in the cortI; dsc1 double mutant strain. DIC and Hoescht images for WT are reproduced from Fig. 1 G. (D) Quantification of the number of nuclei/cell for WT, dsc1, cortI, and cortI;dsc1 after 2 d in suspension. The cortI mutant displayed a high number of multinucleated cells, especially in the 3–10 nuclei/cell range. Note that among these cell lines, only cortI accumulated >10 nuclei. The cortI; dsc1 double mutant was less multinucleated as compared to the cortI single mutant, with most cells having 1–2 nuclei/cell, similar to dsc1 single mutant cells. The data provided represent two replicates, with 90–115 cells per cell line for each replicate. P value was calculated using the Comparison of Proportions test. (**, P < 0.001; n.s, not significant). (E) Representative growth curves in suspension culture of WT (blue), dsc1 (red), and iqgap1 (orange) single mutant cells and the iqgap1; dsc1 double (black) mutant cells. Growth in suspension of iqgap1; dsc1 was faster than that of iqgap1 and slower than that of dsc1 single mutant cells. n = 6 per growth curve, bars represent SEM. (F) Growth rates of the exponential growth phase for each cell line. The average growth rate of iqgap1; dsc1 (0.041 h⁻¹) was higher than that of iqgap1 (0.026 hr⁻¹) and lower than dsc1 (0.048 h⁻¹). P values were derived using ANOVA followed by Fisher’s LSD test. Number of samples analyzed, n = 6 from two independent experiments. (G) Summary diagram shows the genetic relationship between DscI, CortI, and IQGAP1. While IQGAP1 is a known inhibitor of CortI, it also antagonizes DscI. On the other hand, DscI is also antagonized by CortI, whose roles are important for balanced cellular mechanics and cytokinesis regulation.