Somatosensory neurons detect mechanical, thermal, and chemical stimuli, which is crucial for animals to sense their environment and respond appropriately. Many studies have suggested that the interactions between somatosensory neurons and skin cells not only play an important role during development but also may be critical for neuron function. Thus, we have undertaken a genomic approach to investigate the interactions between touch-sensing neurons and skin cells.
Peripheral axons of somatosensory neurons first arborize between the two epithelial layers (periderm and basal cells) that compose larval zebrafish skin, starting at the ~18 somite stage. Electron microscopy has revealed that the free endings of somatosensory axons become ensheathed by basal cells between 54 and 78 hours post fertilization (hpf). To identify genes that may be involved in axon/skin interactions, we examined the gene expression profiles of skin cells in zebrafish at three different stages: 20 hpf, 52 hpf, and 72 hpf. To accomplish this goal, periderm cells, basal cells, and non-skin cells were purified with fluorescent activated cell sorting of krt4:DsRed krt5:GFP transgenic fish that express DsRed in both epithelial layers, but only express GFP in periderm cells. mRNAs isolated from these cells were used for RNA-Seq. This method provides comprehensive and quantitative gene expression data. RNA-Seq was also performed on skin cells in wildtype fish as well as fish lacking somatosensory neurons to gain a genomic view of transcriptional changes in skin cells as they respond to axon innervation.
Currently, we are using molecular and cellular methods to verify the expression pattern of genes that are enriched in a specific skin layer and/or at a specific developmental stage. Loss-of-function studies will be conducted to unveil the functions of these genes.