Myosin IIA drives membrane bleb retraction

Abstract

Membrane blebs are specialized cellular protrusions that play diverse roles in processes such as cell division and cell migration. Blebbing can be divided into three distinct phases: bleb nucleation, bleb growth, and bleb retraction. Following nucleation and bleb growth, the actin cortex, comprising actin, cross-linking proteins, and nonmuscle myosin II (MII), begins to reassemble on the membrane. MII then drives the final phase, bleb retraction, which results in reintegration of the bleb into the cellular cortex. There are three MII paralogues with distinct biophysical properties expressed in mammalian cells: MIIA, MIIB, and MIIC. Here we show that MIIA specifically drives bleb retraction during cytokinesis. The motor domain and regulation of the nonhelical tailpiece of MIIA both contribute to its ability to drive bleb retraction. These experiments have also revealed a relationship between faster turnover of MIIA at the cortex and its ability to drive bleb retraction.

Precise tuning of cortical contractility regulates cell shape during cytokinesis

“…8B). This role of MIIA in driving bleb retraction was consistent with our previous report (Taneja and Burnette, 2019).…”

“…The size of the bleb created immediately following ablation is positively correlated with the instantaneous intracellular pressure. Ablation of the metaphase cortex of Scr cells resulted in the creation of a bleb, which subsequently retracted over a period of 45-90 seconds, as has been reported previously (Charras et al, 2006;Taneja and Burnette, 2019). Since MIIA lo cells have lower cortex tension compared to Scr cells, we hypothesized that smaller blebs would be created in these cells.…”

“…Calibration of protein expression was performed using an immunofluorescence based approach as described previously ( Supplementary Fig. 7) (Taneja and Burnette, 2019). siRNA resistant MII was introduced into the knockdown cells using transient transfection, plated on glass coverslips, followed by fixation.…”

CLIC4 is a cytokinetic cleavage furrow protein that regulates cortical cytoskeleton stability during cell division

“…In contrast, shCLIC4 cells form much larger blebs, with many of them occurring at the furrow (Figure 3C, D, G), suggesting that CLIC4 may predominately function to regulate the cortex stiffness and inhibit blebbing at the furrow during its conversion to the stable intercellular bridge. Since NMYIIA/IIB were previously shown to regulate bleb formation [30][31][32]37 , we also examined the recruitment of NMYIIA /IIB in shCLIC4 cells. Consistent with the involvement of CLIC4 in the regulation of blebbing, loss of CLIC4 resulted in the decrease of the NMYIIA/IIB at the furrow cortex in late anaphase ( Figure 5).…”

“…Thus, we decided to identify the mechanisms that require CLIC4 during anaphase-to-telophase transition. Recent studies identified several proteins involved in the regulation of mitotic blebbing process, namely the non-muscle myosins IIA (NMYIIA) and IIB (NMYIIB) [29][30][31] . Furthermore, NMYIIA and NMYIIB have previously been shown to be responsible for regulating cortical rigidity during anaphase and telophase 32 .…”