The molecular determinants that direct these specificities remain to be identified

r could have several markers, e.g., Nts, Il31ra and Htr1f for C2 and Cadps2, Baiap2l1 and Necab2 for C9. The subclusters C1-1 and C1-2 are marked by Gal together with Cldn9 and Asic3, and Gal combined with Zcchc12 and Sstr2, respectively. C2-2 is separated from C2-1 by the expression of Pvalb and S100b. Both Mrgpra3 and Mrgprb4 are combined markers for C4-2, whereas Mrgpra3 alone is a marker for C4-1. Mrgprd is expressed highly in C5 and moderately in C6. In Mrgprd-marked C5 neurons, the presence of Gal, Sstr2, Zcchc12, Asic3 and Gfra3 distinguishe C5-1 from C5-2 neurons. C6 neurons are distinguished from C5 by their expression of Cpne6 and S100b. C6-1 contain Gal, whereas C6-2 GW 501516 express Prkcq and Lpar3 at high levels. Notably, abundant Gal expression is also found in C5-1 and C6-1 neurons. C5-1 differ from Galmarked C1 by the expression of Mrgprd, whereas C6-1 is differentiated by Mrgprd and high levels of Cpne6 and S100b expression. For large DRG neurons, Nxph1, Trappc3l and Cadps2 are markers for C7, C8 and C9, respectively. C8-1 express high levels of Ntrk3 and Htr1d, whereas C8-2 contain high levels of Ntrk1 and Htr3a. C9-2 is distinguished from C9-1 by higher levels of Asic3 and Cgnl1. The large neurons of C10 express Gal, Th, Rspo1 and Kcnk2. Traditional markers of neuronal subsets, such as Tac1 and Calca for the PEP subset, IB4 for the NP subset and Nehf for large neurons, are observed in multiple clusters. IB4 labels C4 and C5 neurons as well as some neurons in C1 and C6. Some IB4-positive neurons in C4 and C5 also express Tac1 and Calca. Moreover, many recently suggested marker genes, such as Cntnap2 , are also found in multiple clusters. The growth factor receptors Ntrk and Gfra are also not restricted to a single neuron cluster. However, differential combinations of Ntrk and Gfra are consistent with the clustering of DRG neurons. Ntrk1 and Gfra3 are present in C1, C10 and C2 neurons; Ntrk1 and Gfra1 in C4 neurons; Gfra2 and low levels of Gfra1 expression in C5 neurons; Gfra1 and high levels of Ntrk3 expression in C8-1 neurons; Ntrk1 and low levels of Ntrk3 expres- npg Types of primary sensory neurons 92 Chang-Lin Li et al. npg 93 sion in C8-2 neurons, and Ntrk2 and low levels of Ntrk3 expression in C9 neurons. Double fluorescent ISH was used to examine the distribution of the markers. Il31ra is co-expressed with Nppb but not Gal in small neurons. Almost all Th-positive neurons express Fam19a4 and Fxyd6, but not Gal and Nppb. Mrgpra3 is not co-expressed with Nppb or Gfra2. Mrgprd is not co-expressed with Il31ra in DRG neurons. S100b is not expressed in Th-positive neurons, PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19822663 and Pvalb and Th are absent from Ntrk2-positive large neurons. Thus, markers identified in this study can be used to identify neuron types in DRG tissue. Functional phenotypes of neuron clusters We next asked whether neuron clusters represent neurons of different sensory modalities. A heterogeneity analysis of signaling molecules in neuron clusters as well as previous reports implies the functionalities of these neuron clusters. TRP channels are involved in temperature sensing. Trpv1 is expressed strongly in C1-1 and moderately in C1-2 and C2-1. Trpv2 is expressed in almost all clusters but at a low level in C8, whereas Trpv4 is present in some C3 neurons. Trpm8 is expressed in some neurons in C1-2, C6-1 and C8-2, whereas Trpa1 is expressed in C1-2, C4-2, C5-2, C6-2 and C10. Ano1 is present in C2-2 and C7. Thus, several neuron clusters are likely to be differ