Cells within the body do not exist in isolation; they are organized into tissues and organs with specialized functions. This arrangement relies on cells recognizing and adhering, forming stable connections. Specialized proteins on the cell surface facilitate this process, and cadherins play a central role in cell-to-cell adhesion.
The Building Blocks of Connection
Cadherins are transmembrane proteins located on the cell surface. Each cadherin has three main parts: an extracellular domain (outside the cell), a transmembrane domain (within the cell membrane), and an intracellular domain (inside the cell). The extracellular domain binds to other cells, while the intracellular domain connects to the cell’s internal cytoskeleton.
Cadherin function depends on calcium ions. Calcium ions are essential for cadherins to adopt the correct shape, enabling them to connect with other cadherin molecules on neighboring cells. Without sufficient calcium, cadherins cannot form stable connections, which is important for cellular organization. This calcium-dependent binding allows cadherins to act as molecular “glue,” holding cells together.
How Cells Stick Together
The primary mechanism by which cadherins mediate cell adhesion is through a process called homophilic binding. This means that a cadherin molecule on one cell typically binds specifically to an identical type of cadherin molecule on an adjacent cell. For instance, an E-cadherin on one cell will bind to another E-cadherin on a neighboring cell, rather than to a different type of cadherin. This precise recognition ensures that cells with similar identities can selectively associate.
These homophilic interactions lead to the formation of strong cell-to-cell junctions, effectively gluing cells together to create cohesive tissues. The connections formed by cadherins are not static; they are dynamic and can be regulated by the cell. This allows tissues to adapt and remodel as needed, for example, during development or in response to injury. The ability to form and break these connections in a controlled manner is crucial for many biological processes.
Different Types, Different Roles
The cadherin family is diverse, comprising numerous members, each with specific roles and distributions throughout the body. Among the most studied are the “classical cadherins,” which include E-cadherin, N-cadherin, and P-cadherin. These different types are expressed in a tissue-specific manner, meaning certain cadherins are found predominantly in particular tissues, contributing to their unique structures and functions.
E-cadherin, for example, is primarily found in epithelial cells, which form protective linings and coverings throughout the body, such as in the skin and the lining of the gut. N-cadherin is prevalent in nerve cells and muscle cells, playing a role in the formation and function of the nervous system and muscle tissue. P-cadherin is expressed in the placenta and in certain skin cells, contributing to the specialized structures found in these areas. This tissue-specific expression helps cells recognize and sort themselves during development, ensuring that different cell types organize into their correct locations to form functional tissues and organs.
Cadherins and Body Health
Cadherins are fundamental to many essential biological processes, underscoring their importance for overall body health. During embryonic development, they guide cells to migrate and assemble correctly, shaping the intricate tissues and organs that make up an organism. In adult life, cadherins are continuously involved in maintaining the structural integrity of tissues, such as the robust barrier formed by skin and the lining of the digestive tract.
They also play a role in wound healing, where cells need to move and re-establish connections to repair damaged tissue. When cadherin function is disrupted, either through genetic changes or environmental factors, it can impact cell behavior. Such alterations might lead to cells losing their normal adhesive properties or changing their ability to move, potentially affecting the orderly arrangement and function of tissues.