Chunk #14 — RESULTS — Differential expression of cell adhesion molecules and carbohydrate modifying enzymes suggests large capacity for cell surface and extracellular matrix labels
Each GABAergic neuron receives inputs from and extends output to diverse pre- and postsynaptic neurons, respectively (Figure 3A). The cell adhesion molecules (CAMs) that regulate their morphology, connectivity, synaptic transmission and plasticity are largely unknown. Our computational screen identified multiple CAM families that effectively discriminate PCPs (Figure 3B–E). Based on broadly annotated HGNC families and the literature (de Wit and Ghosh, 2016; Kolodkin and Tessier-Lavigne, 2011; Takahashi and Craig, 2013), we selected ~275 genes encoding all major neuronal CAMs and organized them into 12 adhesion groups according to sequence homology and receptor-ligand relationships (Figure 3B; Table S4). Nearly all major groups of neuronal CAMs implicated in different aspects of neural development are expressed in PCPs, and each PCP expresses ~200 CAM genes (Figure 3C). This was an underestimate of CAM diversity as our RNAseq method does not detect splicing variants. Among the ~275 CAM genes, 130 show highly distinct subpopulation profiles (Figure 3E, Table S6). Strikingly, multiple CAM families each manifests differential expression among PCPs (Figure 3F, Figure S3A–D). For example, UNC5 members and their ligand netrin1 are differentially expressed; UNC5b is highly specific to CHCs (Figure S2B, S3C); these receptor-ligand pairs might mediate cell-cell recognition (Figure S3A).
