Invadopodia/Fluorescent Gelatin Degradation Assay

Reagents and chemicals

• Fluorescent gelatin is used as the degradable matrix substrate, and gelatin-coated coverslips provide a two-dimensional matrix surface for detecting localized degradation by attached cells^[1][2].

• Paraformaldehyde is used for fixation, Triton X-100 is used for permeabilization, and blocking buffer is used before antibody staining to reduce nonspecific immunofluorescence signal^[1][2].

Antibodies, probes, dyes, or kits

• Phalloidin is used to label F-actin-rich invadopodial structures, and antibodies against cortactin or TKS5 are used to identify invadopodia-associated protein enrichment^[1][2][3].

• DAPI or another nuclear dye is used to identify cells for per-cell normalization of degradation measurements^[1][2].

Equipment and instruments

• Glass coverslips or compatible imaging surfaces are used for substrate preparation and cell culture^[1][2].

• A fluorescence microscope or confocal microscope is used to acquire channels for fluorescent gelatin, invadopodia markers, and nuclei, and ImageJ/Fiji-based analysis can quantify degraded area, percentage of degrading cells, and marker colocalization^[1][2].

Preparation Steps

• Prepare fluorescent gelatin-coated coverslips before cell seeding, and use the same gelatin preparation, coating workflow, and imaging settings across experimental groups because matrix fluorescence uniformity is required for reliable degradation quantification^[1][2].

• Prepare actively growing cells and include matched control and experimental conditions, because invadopodia formation and matrix degradation can change after genetic knockdown, drug treatment, growth-factor stimulation, or altered signaling through Src, Arg, cortactin, TKS5, integrins, or MMP-related pathways^[3][4][5][6].

Operation Steps

• Seed cells on fluorescent gelatin-coated coverslips and incubate them long enough to attach, form invadopodia, and degrade the fluorescent substrate; published protocols use endpoint immunofluorescence to detect invadopodia formation and gelatin degradation in the same sample^[1][2].

• After incubation, fix cells, permeabilize them, stain F-actin and invadopodia markers such as cortactin or TKS5, counterstain nuclei, and image the fluorescent gelatin channel together with invadopodia-marker channels^[1][2][3].

• Avoid changing microscope exposure or thresholding rules between groups within an experiment, because the degradation readout depends on detecting loss of fluorescent gelatin signal relative to intact surrounding substrate^[1][2].

Data Acquisition and Analysis

• Quantify degradation as the area of lost gelatin fluorescence per cell, percentage of cells with degradation, or degraded area associated with invadopodia marker-positive structures^[1][2].

• Interpret mature invadopodia as marker-positive actin-rich structures associated with local matrix degradation, because precursor-like marker puncta without degradation do not necessarily indicate proteolytically active invadopodia^[1][3][4].

• Include negative controls expected to reduce invadopodia function, such as knockdown or inhibition of established invadopodia regulators, and include viability or cell-number normalization when testing treatments that may change cell survival or adhesion^[3][4][5][6].

Problem: Gelatin degradation is weak or absent.

• Possible Cause: Cells may form invadopodia precursors without maturation into degradation-competent invadopodia.
• Literature-supported Solution: Confirm colocalization of F-actin with cortactin or TKS5 and include a known degrading cell condition or regulator-dependent control to distinguish absent invadopodia from inactive invadopodia^[1][3][4].

Problem: Degradation is difficult to quantify because background fluorescence is uneven.

• Possible Cause: Nonuniform fluorescent gelatin coating affects threshold-based analysis.
• Literature-supported Solution: Standardize gelatin coating and imaging conditions across all samples and quantify degradation relative to adjacent intact matrix fluorescence^[1][2].

Problem: Marker-positive puncta do not overlap with degradation.

• Possible Cause: Invadopodia markers can identify immature or nondegrading structures, while degradation requires mature proteolytic activity.
• Literature-supported Solution: Score invadopodia formation and gelatin degradation as related but distinct readouts, and report both marker-positive structures and degraded gelatin area^[1][3][4].