Analyzing somatosensory axon projections with the sensory neuron-specific Advillin gene

Peripheral sensory neurons detect diverse physical stimuli and transmit the information into the CNS. At present, the genetic tools for specifically studying the development, plasticity, and regeneration of the sensory axon projections are limited. We found that the gene encoding Advillin, an actin binding protein that belongs to the gelsolin superfamily, is expressed almost exclusively in peripheral sensory neurons. We next generated a line of knock-in mice in which the start codon of the Advillin is replaced by the gene encoding human placenta alkaline phosphatase (Avil-hPLAP mice). In heterozygous Avil-hPLAP mice, sensory axons, the exquisite sensory endings, as well as the fine central axonal collaterals can be clearly visualized with a simple alkaline phosphatase staining. Using this mouse line, we found that the development of peripheral target innervation and sensory ending formation is an ordered process with specific timing depending on sensory modalities. This is also true for the in-growth of central axonal collaterals into the brainstem and the spinal cord. Our results demonstrate that Avil-hPLAP mouse is a valuable tool for specifically studying peripheral sensory neurons. Functionally, we found that the regenerative axon growth of Advillin-null sensory neurons is significantly shortened and that deletion of Advillin reduces the plasticity of whisker-related barrelettes patterns in the hindbrain.