Protein kinase which regulates actin filament dynamics. Phosphorylates and inactivates the actin binding/depolymerizing factor cofilin, thereby stabilizing the actin cytoskeleton. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Expressed in the early cleavage stages of the embryo. Expression decreases at the gastrula stage and subsequently reappears at the neurula stage, and continues to increase from this point on. In post neurula stages, expressed predominantly in the anterior region of the embryo, including the developing brain and sensory organs. Belongs to the protein kinase superfamily. TKL Ser/Thr protein kinase family.