Laser ablation reveals the impact of Cdc15p on the stiffness of the contractile ring

Abstract

The mechanics that govern the constriction of the contractile ring remain poorly understood yet are critical to understanding the forces that drive cytokinesis. We used laser ablation in fission yeast cells to unravel these mechanics focusing on the role of Cdc15p as a putative anchoring protein. Our work shows that the severed constricting contractile ring recoils to a finite point leaving a gap that can heal if less than ∼1 µm. Severed contractile rings in Cdc15p-depleted cells exhibit an exaggerated recoil, which suggests that the recoil is limited by the anchoring of the ring to the plasma membrane. Based on a physical model of the severed contractile ring, we propose that Cdc15p impacts the stiffness of the contractile ring more than the viscous drag.

Cooperation between Imp2p and Cdc15p imparts stiffness to the constricting contractile ring in fission yeast

“…To determine the impact of Imp2p on the mechanical properties of the contractile ring, we tracked the position of the severed tips during the recoil phase and calculated the recoil displacement as the distance of the severed tips from their initial position immediately after the cut over time. The recoil displacements of the severed tips in both wild-type and Δimp2 cells followed an exponential profile as expected for a material with viscoelastic properties (Figure 1F) (Moshtohry et al ., 2022) (Kumar et al ., 2006; Colombelli et al ., 2009; Silva et al ., 2016; Roca-Cusachs et al ., 2017). The mean recoil displacement of the severed tips Δ L fits to a single exponential, .…”

“…We recently described the contribution of Cdc15p to the stiffness of the constricting contractile ring (Moshtohry et al ., 2022). Laser ablation of the contractile ring can reveal otherwise undetectable features about the structure including its mechanical properties (Silva et al ., 2016; Moshtohry et al ., 2022). We hypothesized that Imp2p may impact the mechanical properties of the ring in a distinct manner that would reveal specific functions in cytokinesis.…”

“…We hypothesized that Imp2p may impact the mechanical properties of the ring in a distinct manner that would reveal specific functions in cytokinesis. We used laser ablation to sever constricting contractile rings in wild-type and Δ imp2 cells expressing mEGFP-Myp2p to highlight the bundle of actin filaments in the ring (Supplemental Figure 1A and Methods) (Moshtohry et al ., 2022). We focused on contractile rings that were 20-50% constricted to avoid confounding results with non-constricting contractile rings that may have distinct mechanical properties.…”

“…After laser ablation of the constricting contractile ring in wild-type cells, the severed tips recoiled away from each other revealing a growing gap in the ring (Moshtohry et al ., 2022). We interpreted this response as the local release of tension present in the constricting contractile ring prior to ablation (McDargh et al ., 2021).…”

“…We calculated the impact of Imp2p on the effective stiffness k eff and effective viscous drag η eff of the contractile ring based on our framework for the contractile ring as a viscoelastic material under tension T 0 (McDargh et al ., 2021; Moshtohry et al ., 2022). Both A and τ describe the displacement profile of the severed tips and are influenced by the mechanical properties of the contractile ring as A = T 0 / k eff and τ = η eff / k eff (Figure 1F).…”