Dear Editor,
Mammalian central nervous system neurons show asymmetry during early brain development that defines the elaborate function of neural circuitry (Kriegstein and Noctor, 2004). Many intracellular signaling pathways, which are important for the transition to the polarized state and the development of axons and dendrites, have been identified (Barnes and Polleux, 2009). How these pathways are initiated during neuronal development in vivo remained elusive until Yi et al. (2010) found that transforming growth factor-β (TGF-β) is essential for the differentiation and growth of axons. JNK is also crucial for neuronal polarity and axon formation (Oliva et al., 2006). However, whether and how JNK is activated by TGF-β signaling during brain development is not clear.
