by Catherine Shaffer
There are four main classes of cell migration assay: chemotaxis, haptotaxis, transmigration, and wound healing. Chemotaxis measures migration of cells based on a chemical environment; haptotaxis measures cell migration within a gradient of chemoattractants; transmigration is the movement of cells through the vascular endothelium; and wound healing addresses the migration of cells into a wound to close the gap. Different types of cell migration assays have different benefits and liabilities in terms of the information that can be obtained. Standard methods for studying cell migration, such as Boyden chambers, tend to be cumbersome, and labeling methods may interfere with the results of the experiment. Novel strategies have resulted in more advanced cell migration assays that are more accurate, more sensitive, and more convenient, especially in the wound healing space, where previous assay methods have been unsatisfactory.
Cell Biolabs offers assays for all of the above types of cell migration. One of their most unique products is the CytoSelect™ Wound Healing Assay. A conventional wound healing assay involves making a scratch across a monolayer of cells, then measuring the time required for surrounding cells to fill in the gap. This assay is notoriously inconsistent because of variation in the size of the scratch and other characteristics of the assay. Cells can also be damaged along the edge of the scratch area, which can prevent the migration of healthy cells across the gap. The CytoSelect™ Wound Healing Assay was designed to be a truly scientific assay for cell migration in wound healing. Ken Rosser, director of marketing and sales, explains: "This product was years in the making because we wanted to engineer accuracy, consistency, and reliability into the assay." The assay is performed in a 24-well plate with custom-designed precision molded plastic inserts that create a consistently defined 0.9 mm gap across the diameter of the well. When cells are added, they form a monolayer across the well. After the insert is removed, cells can migrate across the gap, healing the "wound," which can be accurately monitored over time using a microscope. The advantages of the assay include prevention of cell damage that occurs in a scratch assay, and a clean, consistent gap with no inhibitory chemical residues from the insert.
Other cell migration assays from Cell Biolabs include the CytoSelect™ Chemotaxis Assays, which use a traditional Boyden chamber in a 24-well or 96-well configuration; the CytoSelect™ Cell Haptotaxis Assays, which are similar to the chemotaxis assays except that the underside of the membrane insert is coated with Collagen I or Fibronectin; and the CytoSelect™ Transmigration Assays, in which the inserts are coated with endothelial cells.
Another wound healing alternative assay comes from Platypus Technologies. The Oris™ Cell Migration Assay was developed to provide a more reproducible alternative to the scratch assay for wound healing studies, and a less cumbersome method than Boyden chamber devices for cell migration assays. The assay uses cell seeding stoppers made of medical grade silicone that fit into each well of a 96-well plate. The 96-well assay plate is coated with collagen I, fibronectin, or another tissue culture treated surface. Visualization of cell movement by microscopy is achieved by pre-staining cells with a dye, use of a GFP expressed protein, or post-migration cytostaining. Cell migration can be quickly quantified using a microplate reader when the Oris™ Detection Mask is attached to the bottom of the plate.
The Oris™ Cell Migration Assay permits image analysis and microplate analysis all in the same well without having to transfer samples between plates. A typical Boyden chamber device uses a transmembrane with a cell culture insert in each well. The cells move from the top to bottom chamber through a membrane, to be detected with a microplate reader. The membrane prevents real-time imaging of cell movement using a high content screening system or microscope unless the insert is removed.
Says Maria Perr, director of marketing for Platypus Technologies: "The Oris™ Universal and FLEX Cell Migration Assembly kits provide the ultimate in adherent cell migration assay design, since the Oris™ Cell Seeding Stoppers are packaged separately from the plates. This allows the researcher to coat the Oris™-compatible microplate with any extracellular matrix protein of their choice before inserting the Oris™ stoppers into each well. Researchers can design 2-D wound closure assays, cell migration assays, or even 3-D cell invasion assays."
These new technologies offer a simpler, cleaner assay for cell migration (over older methods), particularly for wound healing, with greater accuracy, sensitivity, and reliability.