The GxcM-Fbp17/RacC-WASP signaling cascade regulates polarized cortex assembly in migrating cells

Abstract

The actin-rich cortex plays a fundamental role in many cellular processes. Its architecture and molecular composition vary across cell types and physiological states. The full complement of actin assembly factors driving cortex formation and how their activities are spatiotemporally regulated remain to be fully elucidated. Using Dictyostelium as a model for polarized and rapidly migrating cells, we show that GxcM, a RhoGEF localized specifically in the rear of migrating cells, functions together with F-BAR protein Fbp17, a small GTPase RacC, and the actin nucleation-promoting factor WASP to coordinately promote Arp2/3 complex-mediated cortical actin assembly. Over-activation of this signaling cascade leads to excessive actin polymerization in the rear cortex, whereas its disruption causes defects in cortical integrity and function. Therefore, different from its well-defined role in the formation of the front protrusions, the Arp2/3 complex-based actin carries out a previously unappreciated function in building the rear cortical subcompartment in rapidly migrating cells.

A transcription factor complex in Dictyostelium enables adaptive changes in macropinocytosis during the growth-to-development transition

“…PHcrac-GFP, LimEDcoil-GFP, GFP-Rab5A, GFP-Rab7A, TAPP1-RFP, GFP-23FYVE, GFP-RBD, and Flamindo2 were described previously. 34,37,[45][46][47] To make knockout constructs for gene deletion, 5' and 3' arms were PCR-amplified from genomic DNA and cloned upstream and downstream of a BSR cassette or a Hygromycin resistance cassette, 48 respectively. The resulting disruption cassette was PCR-amplified or digested from the knockout construct and electroporated into cells.…”

“…Random motility assay was performed as described previously. 46 In brief, vegetative cells were seeded in HL5 medium and allowed to adhere for 4 h. Before imaging, the medium was replaced with fresh HL5 medium. Images were acquired with phase illumination on a Zeiss 880 inverted microscope equipped with a 103/0.45 objective.…”