Figure 9.

Zyxin-null cells fail to augment actin stress fibers in response to jasplakinolide. Wild-type (A) and zyxin-null (B) fibroblasts were treated with vehicle or jasplakinolide and then fixed and stained by phalloidin. Jasplakinolide induced thick actin stress fibers in wild-type cells (C), but noticeably thinner and less robust actin in zyxin−/− cells (D). A method to quantitate an SFTI was developed using a computer algorithm based on erosion filtering (E), as described in Materials and methods. 20 images of phalloidin-stained cells were randomly recorded, and the average of SFTI was compared using analysis of variance between groups. (F) No difference between wild-type and zyxin−/− actin filaments was detected in untreated controls, but a statistically significant difference between jasplakinolide-treated wild-type and zyxin−/− fibroblasts was observed. A population of jasplakinolide-treated zyxin-null fibroblasts, some of which were expressing GFP-zyxin (G), was stained with phalloidin (H). More robust actin stress fibers were observed in the null cells that expressed GFP-zyxin. (I) SFTI analysis confirmed that reintroduced zyxin enhanced the actin filaments in zyxin-null cells. Data represent the mean ± SEM of 33 measurements. **, P < 0.005.