Quantitative Analysis of Cell Edge Dynamics during Cell Spreading

Summary

In this protocol, we present the experimental procedures of a cell spreading assay that is based on live-cell microscopy. We provide an open-source computational tool for the unbiased segmentation of fluorescently labeled cells and quantitative analysis of lamellipodia dynamics during cell spreading.

Abstract

Cell spreading is a dynamic process in which a cell suspended in media attaches to a substrate and flattens itself from a rounded to a thin and spread-out shape. Following the cell-substrate attachment, the cell forms a thin sheet of lamellipodia emanating from the cell body. In the lamellipodia, globular actin (G-actin) monomers polymerize into a dense filamentous actin (F-actin) meshwork that pushes against the plasma membrane, thereby providing the mechanical forces required for the cell to spread. Notably, the molecular players that control the actin polymerization in lamellipodia are essential for many other cellular processes, such as cell migration and endocytosis.

Since spreading cells form continuous lamellipodia that span the entire cell periphery and persistently expand outward, cell spreading assays have become an efficient tool to assess the kinetics of lamellipodial protrusions. Although several technical implementations of the cell spreading assay have been developed, a detailed description of the workflow, which would include both a step-by-step protocol and computational tools for data analysis, is currently lacking. Here, we describe the experimental procedures of the cell spreading assay and present an open-source tool for quantitative and unbiased analysis of cell edge dynamics during spreading. When combined with pharmacological manipulations and/or gene-silencing techniques, this protocol is amenable to a large-scale screen of molecular players regulating lamellipodial protrusions.

Introduction

Lamellipodial protrusions are prominent cytoskeletal structures formed at the front of a migrating cell. In lamellipodia, polymerization of actin with the aid of the Arp2/3 complex and formins creates a fast-growing branched actin meshwork that pushes against the plasma membrane^1,2. The pushing force generated by the actin meshwork physically propels the cell forward^1,3,4,5. Depletion of the Arp2/3 complex or disruption of signaling pathways essential for lamellipodial protrusio....

Protocol

1. Cell Seeding

NOTE: The described cell spreading protocol was performed using mouse embryonic fibroblasts (MEFs) expressing PH-Akt-GFP (a fluorescent marker for PIP₃/PI(3,4)P₂). This cell line was generated by genomically integrating an expression construct for PH-Akt-GFP (Addgene #21218) by CRISPR-mediated gene editing. However, other fluorescent markers that are expressed transiently or integrated in the genome can also be used in this assay. For optimal image segmentat.......

Discussion

The described cell spreading assay allows for the continuous tracking of morphological changes (e.g., cell size and shape) and cell edge movements (i.e., protrusion speed and retraction frequency), which are features missing in most cell spreading protocols^19,24. While commonly used end-point cell spreading assays allow for the determination of cell spreading speed, these assays fail to resolve the temporal dynamics of cell edge movements. The l.......

Materials

Name	Company	Catalog Number	Comments
0.05% Trypsin (0.05%), 0.53 mM EDTA	Wisent Bioproducts	325-042-CL
10.0 cm Petri Dish, Polystyrene, TC Treated, Vented	Starstedt	83.3902
15 mL High Clarity PP Centrifuge Tube, Conical Bottom, with Dome Seal Screw Cap, Sterile	Falcon	352097
1-Well Chamlide CMS for 22 mm x 22 mm Coverslip	Quorum Technologies	CM-S22-1
35 mm TC-treated Easy-Grip Style Cell Culture Dish	Falcon	353001
50 mL Centrifuge Tube, Transparent, Plug Seal	Nest	602002
6.0 cm Cell Culture Dishes Treated for Increased Cell Attachment, Sterile	VWR	10861-658
Arp2/3 Complex Inhibitor I, CK-666	Millipore Sigma	182515
Camera, Prime 95B-25MM	Photometrics
Dimethyl Sulfoxide, Sterile	BioShop	DMS666
DMEM, 1x, 4.5 g/L Glucose, with L-Glutamine, Sodium Pyruvate and Phenol Red	Wisent Bioproducts	319-005 CL
DMEM/F-12, HEPES, No Phenol Red	Gibco	11039021
D-PBS, 1X	Wisent Bioproducts	311-425 CL
Fetal Bovine Serum	Wisent Bioproducts	080-110
Fiji Software	ImageJ
HEPES (1 M)	Gibco	15630080
Human Plasma Fibronectin Purified Protein 1 mg	Millipore Sigma	FC010
Immersion Oil	Cargille	16241
L-Glutamine Solution (200 mM)	Wisent Bioproducts	609-065-EL
MEM Non-Essential Amino Acids Solution (100X)	Gibco	11140050
Micro Cover Glasses, Square, No. 11/2 22 x 22 mm	VWR	CA48366-227-1
Microscope Body, Eclipse Ti2-E	Nikon
Objective, CFI Plan Apo Lambda 60X Oil	Nikon	MRD01605
Penicillin-Streptomycin	Sigma	P4333
Spinning Disk, Crest Light V2	CrestOptics
Spyder	Anaconda
Stage top incubator	Tokai Hit
Statistics Software, Prism	GraphPad
Tweezers, Style 2	Electron Microscopy Sciences	78326-42