NCK is critical for the development of deleted in colorectal cancer (DCC) sensitive spinal circuits

As our understanding of motor circuit function increases, our need to understand how circuits form to ensure proper function becomes increasingly important. Recently, deleted in colorectal cancer (DCC) has been shown to be important in the development of spinal circuits necessary for gait. Importantly, humans with mutation in DCC show mirror movement disorders pointing to the significance of DCC in the development of spinal circuits for coordinated movement. Although DCC binds a number of ligands, the intracellular signaling cascade leading to the aberrant spinal circuits remains unknown. Here, we show that the non-catalytic region of tyrosine kinase adaptor (NCK) proteins 1 and 2 are distributed in the developing spinal cord. Using dissociated dorsal spinal neuron cultures we show that NCK proteins are necessary for the outgrowth and growth cone architecture of DCC(+ve) dorsal spinal neurons. Consistent with a role for NCK in DCC signaling, we show that loss of NCK proteins leads to a reduction in the thickness of TAG1(+ve) commissural bundles in the floor plate and loss of DCC mRNA in vivo. We suggest that DCC signaling functions through NCK1 and NCK2 and that both proteins are necessary for the establishment of normal spinal circuits necessary for gait. Reduction in NCK proteins in the developing CNS leads to a reduction in TAG1(+ve) commissural tract thickness, a reduction in growth cone complexity of DCC(+ve) spinal interneurons, and a reduction in DCC mRNA. These are consistent with an in vivo role for NCK in the development of critical DCC spinal circuits, and may be important for the normal development of spinal circuits critical for walking.