1.
Rac negative feedback links local PIP3 rate-of-change to dynamic control of neutrophil guidance.
Abstract:
To migrate efficiently, neutrophils must polarize their cytoskeletal regulators along a single axis of motion. This polarization process is thought to be mediated through local positive feedback that amplifies leading edge signals and global negative feedback that enables sites of positive feedback to compete for dominance. Though this two-component model efficiently establishes cell polarity, it has potential limitations, including a tendency to “lock” onto a particular direction, limiting the ability of cells to reorient. We use spatially-defined optogenetic control of a leading edge organizer (PI3K) to probe how cells balance “decisiveness” needed to polarize in a single direction with the flexibility needed to respond to new cues. Underlying this balancing act is a local Rac inhibitor that destabilizes the leading edge to promote exploration. We show that this local inhibitor enables cells to process input signal dynamics, linking front stability and orientation to local temporal increases in input signals.
2.
mTORC2 coordinates the leading and trailing edge cytoskeletal programs during neutrophil migration.
Abstract:
By acting both upstream and downstream of biochemical organizers of the cytoskeleton, physical forces function as central integrators of cell shape and movement. Here we use a combination of genetic, pharmacological, and optogenetic perturbations to probe the role of the conserved mechanoresponsive mTORC2 program in neutrophil polarity and motility. We find that the tension-based inhibition of leading edge signals (Rac, F-actin) that underlies protrusion competition is gated by the kinase-independent role of the complex, whereas the mTORC2 kinase arm is essential for regulation of Rho activity and Myosin II-based contraction at the trailing edge. Cells required mTORC2 for spatial and temporal coordination between the front and back polarity programs and persistent migration under confinement. mTORC2 is in a mechanosensory cascade, but membrane stretch did not suffice to stimulate mTORC2 unless the co-input PIP3 was also present. Our work suggests that different signalling arms of mTORC2 regulate spatially and molecularly divergent cytoskeletal programs allowing efficient coordination of neutrophil shape and movement.
