A migration assay is a standard laboratory tool used in cellular biology to measure and analyze how cells move in a controlled environment. Cell movement, or motility, is a tightly regulated process fundamental to both normal development and disease progression. By quantifying the direction and speed of movement, researchers gain insight into the mechanisms that govern cell behavior, providing a window into complex biological events from healing to disease spread.
The Core Concept of Cell Movement
Cell movement is an active, highly regulated process essential for the function and survival of multicellular organisms. During embryonic development, cells migrate to specific locations to form tissues and organs. In adults, this movement is constantly at work in processes like tissue repair and the immune response.
When a wound occurs, connective tissue cells (fibroblasts) travel to the injury site to remodel the damaged structure. Immune cells, such as neutrophils and macrophages, migrate toward sites of infection. This directed movement is guided by external signals, where cells sense and respond to chemical gradients—a process known as chemotaxis. The physical movement is driven internally by the cell’s cytoskeleton, a dynamic network of proteins like actin and myosin that allows the cell to crawl across a surface.
Understanding the Goals of Measurement
Scientists use migration assays to understand the type and direction of cell movement in response to specific stimuli, not just the speed. A key distinction in these measurements is between migration and invasion. Migration refers to movement across a two-dimensional surface or through an open, porous barrier.
Invasion is a specialized form of movement that requires cells to actively penetrate a physical, three-dimensional barrier, such as the extracellular matrix surrounding tissues. This distinction is relevant in cancer research, as tumor cells must secrete enzymes to degrade this matrix barrier before they can spread (metastasis). Another goal is quantifying chemotaxis—the cell’s directional response to a chemical signal concentration gradient. Researchers determine if a cell exhibits positive chemotaxis (moving toward the signal) or negative chemotaxis (moving away from it).
Key Techniques for Assessing Migration
The two most common methods used to assess cell migration in the laboratory are the Scratch Assay and the Transwell Chamber system.
Scratch Assay
The Scratch Assay (or Wound Healing Assay) measures the ability of a cell population to migrate into an open space, simulating the closing of a wound. Researchers first grow a layer of cells until they form a dense, continuous sheet, known as a monolayer. A small, cell-free gap is then physically created in the monolayer, often using a pipette tip.
The cells bordering the scratch are monitored over a period of 12 to 48 hours using microscopy to track how quickly they move to close the gap. The rate of closure is quantified to determine the migration capacity of the cell line under specific experimental conditions.
Transwell Assay
The Transwell Assay (or Boyden Chamber Assay) measures directional migration through a physical barrier, making it ideal for studying chemotaxis. This system uses a small insert—a plastic cylinder with a porous membrane filter—suspended over a larger well. Cells are placed in the upper chamber, and a potential chemoattractant (e.g., a growth factor or cytokine) is placed in the lower chamber, establishing a chemical gradient.
Cells that migrate move through the membrane pores (3 to 8 micrometers in diameter) to reach the lower chamber. After incubation, the cells that successfully migrated to the underside of the filter are stained and counted, providing a quantitative measure of responsiveness to the chemical signal. When the membrane is coated with a protein mixture that mimics the extracellular matrix (like Matrigel), the assay converts to an invasion assay, requiring cells to actively degrade the matrix to pass through.
Real-World Applications in Health
The data gathered from migration assays translates into practical insights for developing new treatments and understanding disease progression. In oncology, these assays are routinely used to study cancer metastasis by measuring the invasive potential of tumor cells. By testing compounds, researchers identify potential drug candidates that inhibit cancer cells from degrading the extracellular matrix and invading surrounding tissue.
Migration assays are also fundamental to immunology, helping illuminate how immune cells navigate the body to fight infection. Researchers use these assays to test how effectively white blood cells migrate toward chemical signals released by damaged or infected tissues. In drug development, these assays screen pharmacological agents to see if a drug promotes or inhibits cell movement, which is relevant for conditions from wound healing disorders to chronic inflammatory diseases.