TESK1 is a dual-specificity serine/threonine protein kinase that plays a central role in regulating actin cytoskeleton dynamics and cellular spreading 1. The kinase exhibits testis-specific expression during spermatogenesis, with mRNA predominantly expressed in round spermatids after postnatal day 18 in mice 1. TESK1 regulates actin cytoskeletal reorganization by phosphorylating cofilin, which stabilizes F-actin stress fibers and promotes integrin-mediated cell spreading on fibronectin 2. The kinase activity is regulated through interaction with 14-3-3β, which binds to phosphorylated Ser-439 and inhibits TESK1 kinase activity 3. During cell spreading on fibronectin, dissociation of the TESK1/14-3-3β complex correlates with increased kinase activity 3. TESK1 also functions as part of a regulatory network linking microtubule and actin cytoskeleton dynamics through inhibitory interactions with MARKK/TAO1, preventing microtubule breakdown while maintaining actin fiber stability 4. Additionally, actopaxin directly binds to TESK1's C-terminus and inhibits its kinase activity, with this interaction being negatively regulated by fibronectin adhesion 2. These regulatory mechanisms position TESK1 as a key coordinator of cytoskeletal dynamics during cell adhesion and spreading processes.