Thyroid hormone-regulated actin polymerization in brain.

Thyroid hormones play an important role in the growth and development of the brain. Central to the proper integration of neuronal circuitry is the ability of the growing neurite to interpret guidance cues during its migration. The action cytoskeleton is especially rich in the growth cone, and is a likely target for thyroid hormone regulation. This brief review summarizes work showing that thyroxine, but not T3, dynamically regulates the polymerization of the actin cytoskeleton in astrocytes. The ability of T4 to enhance actin polymerization, without directly affecting gene expression, has a profound effect on the ability of the cell to interact with laminin, the major extracellular matrix protein in the developing brain. T4 also regulates the formation of key cell contacts with extracellular matrix guidance cues. These processes are likely to participate in thyroid hormone's regulation of brain development.