Cdc24 interacts with septins to create a positive feedback loop during bud site assembly in yeast

Abstract

Yeast cells select the position of their new bud at the beginning of each cell cycle. The recruitment of the septins to this prospective bud site is one of the critical events in a complex assembly pathway that culminates in the outgrowth of a new daughter cell. Hereby, the septin-rods follow the high concentration of Cdc42GTP that is generated by the focused localization of its GEF Cdc24. We show that shortly before budding Cdc24 not only activates Cdc42 but also transiently interacts with Cdc11, the septin subunit that caps both ends of the septin rods. Mutations in Cdc24 reducing the affinity to Cdc11 impair septin recruitment and decrease the stability of the polarity patch. The interaction between septins and Cdc24 thus reinforces bud assembly at sites where septin structures are formed. Once the septins polymerize into the ring, Cdc24 is found at the cortex of the bud and directs its further outgrowth from this position.

A time-resolved interaction analysis of Bem1 reconstructs the flow of Cdc42 during polar growth

“…The interaction signal between Bem1CRU and N ub -Cdc11 was lost upon removal of PB1 Bem1 ( Fig 1 ). Cdc11 interacts directly with Cdc24 ( Chollet et al, 2020 ). We conclude that the interaction between Cdc11 and Bem1 occurs most likely through Cdc24 in a Bem1-Cdc24-Cdc11 complex.…”

“…Epo1 binds to the same site of Boi1 as Nba1 or Fir1 but at a different cell cycle phase. *The time point of interaction between Bem1-Cdc24-Cdc11 was obtained from a previous study ( Chollet et al, 2020 ). **The time point of Fir1- and Gps1 binding to Bem1 were indirectly derived through their effects on Bem1 localization ( Fig 7 ).…”

Masters of asymmetry – lessons and perspectives from 50 years of septins

“…Prior to budding, a regulatory interplay between septins and the Rho family small GTPase Cdc42 enables yeast cells to polarize growth at a single site. GTP-bound Cdc42 initially recruits septins to a cloudy patch (Gladfelter et al, 2002), where a transient direct interaction between the septin Cdc11 and Cdc24, a GEF for Cdc42, creates a short-term positive feedback loop to reinforce septin recruitment and Cdc42 activation (Chollet et al, 2020). Targeted delivery of Cdc42-containing but septin-free vesicles to the center of the septin patch transforms it into a ring (Gladfelter et al, 2002;Okada et al, 2013).…”

A Cdc42-Borg4-Septin 7 axis regulates HSCs polarity and function

“…Pharmacological attenuation of the aging-related increase in the activity of Cdc42 by a specific small molecule inhibitor of Cdc42 activity termed CASIN resets the frequency of polar HSCs back to level reported for young HSCs and rejuvenates the function of chronologically aged HSC. Cdc42 activity is thus a critical regulator of HSC polarity and aging (Florian et al, 2020).While there is information on polarity regulation pathways orchestrated by Cdc42 activity in yeast (Okada et al, 2013;Chollet et al, 2020), the mechanisms by which Cdc42 controls polarity and especially how elevated activity of Cdc42 result in loss of polarity in HSCs are not understood.…”

“…Cdc42 activity is thus a critical regulator of HSC polarity and aging (Florian et al , 2020). While there is information on polarity regulation pathways orchestrated by Cdc42 activity in yeast (Okada et al , 2013; Chollet et al , 2020), the mechanisms by which Cdc42 controls polarity and especially how elevated activity of Cdc42 result in loss of polarity in HSCs are not understood.…”