Talin is required to increase stiffness of focal molecular complex in its early formation process

For cellular adaptation in mechanical environments, it is important to consider transmission of forces from the outside to the inside of cells via a focal molecular complex. The focal molecular complex, which consists of integrin, talin, vinculin and actin, is known to form in response to a force applied via the extra-cellular matrix (ECM). In the early formation process of the complex, the complex-actin connection is reinforced. These structural changes of the nascent complex result in an increase in its mechanical integrity and overall stiffness, possibly leading to the maturation of the nascent complex by enhancing force transmission. In this study, we hypothesized that the complex component talin is a crucial factor in increasing the stiffness of the nascent complex. To test the hypothesis, we used atomic force microscopy (AFM) to measure the stiffness of the nascent complex using a probe coated with fibronectin. Stiffness measurements were conducted for intact and talin knocked-down cells. Our results demonstrated that talin was required to increase the stiffness of the nascent complex, which could be caused by the reinforced connection between the complex and actin filaments mediated by talin.