Cell Biology. In the article “Cell locomotion and focal adhesions are regulated by substrate flexibility” by Robert J. Pelham, Jr., and Yu-li Wang, which appeared in number 25, December 9, 1997, of Proc. Natl. Acad. Sci. USA (94, 13661–13665), the authors wish to publish the following corrections to Fig. 1. The y axis of Fig. 1B should be labeled with “0” at the origin and should cover a range of 0–80. The numbers placed along the y axis were misaligned with respect to the scale on the graph. Also, the unit should have been “10³ N/m²” instead of “N/m²” as originally indicated in the legend. The corrected figure and its legend are shown below.

Figure 1.

Mechanical characteristics of polyacrylamide substrates and effects on cell morphology. (A and B) identically sized strips of polyacrylamide with various acrylamide/bis-acrylamide ratios were fixed at one end and stretched at the other end with a downward force of 0.103 N. The dashed lines represent the amount of stretching caused by applied weight (A). The extent of stretching was then used for the calculation of Young’s modulus, expressed as 10³ N/m² (B). (C–F) Phase morphology of NRK (C and D) or 3T3 (E and F) cells plated on substrates containing 0.26% bis- (C and E) or 0.03% bis-acrylamide (D and F). NRK cells on the more flexible substrate are less well spread and contain irregular ruffles on the ventral surface (D, arrow), as determined by optical sectioning at a high magnification. Similarly, 3T3 cells on the substrate of high flexibility are typically less well spread and with a polarized morphology (F). Bar = 10 μm.