Effect of thymosin β15 on the branching of developing neurons

The thymosin βs (Tβs) are polypeptide regulators of actin dynamics that are critical for the growth and branching of neurites in developing neurons. We found that mRNAs for Tβ4, Tβ10, and Tβ15 were highly expressed in the developing rat brain during neuritogenesis, supporting a role for the Tβs in this process. Overexpression of the Tβs increased the number of neurite branches per neuron in cultured hippocampal and cerebral cortex neurons, and Tβ15 had the greatest effect. Actin binding activity appears to be essential for the branch-promoting activity of Tβs because two mutants of Tβ15 lacking monomeric actin binding activity failed to stimulate branch formation. We also found that transfection of siRNA against Tβ15 reduced branching. Taken together, these data suggest that the three Tβs, and especially Tβ15, stimulate neurite branching during brain development.