What is the core of microvilli?

• A. Microtubules
• B. Intermediate filaments
• C. Actin
• D. Keratin

Answer: (C)

A bundle of actin filaments forms the structural core of microvilli. This actin core provides the rigidity and length needed for the finger-like projections that dramatically increase the surface area of the cell’s apical surface, which is essential for efficient absorption. Actin filaments are tightly packed and cross-linked by proteins such as fimbrin and villin, helping maintain the uniform, dense core that supports the microvillus and keeps its shape as it interfaces with the surrounding membrane. The actin core extends into the terminal web, a network that anchors the microvilli to the apical cytoskeleton and helps stabilize the overall brush border. Interactions with membrane-associated proteins like myosin I enable coordinated movement and membrane dynamics during transport processes. In contrast, microtubules would not form the core of microvilli (they are the primary components of cilia and other cell extensions), and keratin is an intermediate filament involved in broader cellular integrity rather than the specialized core of microvilli.