“Shock and awe” may be a good strategy if you’re planning an attack on ne’er-do-wells, but it really is a terrible strategy if you’re fine-tuning a nervous system. Instead the nervous system uses diplomacy in its refinement, and a recent paper describes a savvy signaling pathway that does the job.
During development, the nervous system refines its connections through removal of neuronal processes and elimination of excess neurons. Neuron removal takes place through apoptosis, or programmed cell death, and depends on signaling by the JNK pathway. JNK signaling, however, also functions in the growth and homeostasis of neurons. A recent paper describes how neurons can translate these opposing JNK signals. A kinase protein called DLK is able to induce neuron degeneration and apoptosis through JNK signaling, without affecting the other roles of JNK. The images above show neurons from mouse embryos cultured two different ways (top, bottom). Neuron growth was robust after the addition of growth factor (left). When the growth factor was taken away in control cases (middle), axons degenerated. Without DLK (right), neurons were protected from degeneration.
Sengupta Ghosh, A., Wang, B., Pozniak, C., Chen, M., Watts, R., & Lewcock, J. (2011). DLK induces developmental neuronal degeneration via selective regulation of proapoptotic JNK activity originally published in The Journal of Cell Biology, 194 (5), 751-764 DOI: 10.1083/jcb.201103153