Size-Dependent Expression of the Fission Yeast Cdc13 Cyclin is Conferred by Translational Regulation

Abstract

Two fission yeast mitotic activators, Cdc13 and Cdc25, have been shown to increase in concentration in correlation with cell size, and have been proposed to thereby regulate cell size at division. Here, we show that the expression of both Cdc13 and Cdc25 are, in fact, size dependent, as apposed to simply size-correlated due to time-dependent expression. However, we also find that their size dependence is regulated by different mechanisms. Cdc25 was known to be regulated transcriptionally. Here, we show that Cdc13 is regulated translationally. Its transcript is not expression is a size-dependent manner, rather a size-dependent concentration of protein is expressed from a size-independent concentration of mRNA. Moreover, the degradation rate of Cdc13 is not size dependent, implicating size-dependent translation in its regulation. We identify a 20-amino-acid motif, which includes the APC D-box degron, as necessary and sufficient for size-dependent expression, which allowed us to construct a size-independent allele of cdc13. Using this allele, in combination with a size-independent allele of cdc25, expressed from a size-independent promoter, we show that size-dependent expression of neither Cdc13 nor Cdc25 is required for size control, nor are the redundantly required for size control.

Fission yeast obeys a linear size law under nutrient titration

“…In these experiments, cell mutants with different widths were studied in reference media, and a cryptic volume control was found. Other recent studies have proposed Cdc25 and/or Cdc13 as reporters of cell volume (Keifenheim et al, 2017;Curran et al, 2022;Miller et al, 2022;Bashir et al, 2023). We speculate that the observed volume scaling with nutrient titration (panel D) may be regulated by Cdc25 and Cdc13 rather than Cdr2 that senses cell surface.…”

pomBseen: An automated pipeline for analysis of fission yeast images

“…The four images analyzed here were taken of yFS1136 (h- leu1::pFS531 (cdc25-NeonGreen leu1) ura4-D18 wee1::pWAU-50 (P(adh1):wee1-50ts) or yFS1078 (h- leu1::pFS461(P(adh1):ZEV leu1) ura4-D18 ade6-216 P(ZE3V):wee1 (kanMX) cdc25-NeonGreen (hygMX) nph6-mCherry (ura4)) and cells [ 17 ] grown in YES medium to mid log phase. To obtain different sized cells for the analysis in Fig 2C–2E , cells were grown in presence of different levels of beta-estradiol [ 15 ], as indicated in the figure legend.…”