| Visual information is conveyed from the retina to the brain through axons of retinal ganglion cells (RGCs). There are >20 different subtypes of RGCs, each of which detects specific features. Classification of RGC subtypes is thus essential for us to understand how visual information is processed and delivered to the brain.;Here I reported my efforts in classifying different subtypes of RGCs, using morphological, physiological and molecular criteria. A combination of these criteria allowed me to successfully identify subtypes from alpha RGCs, Foxp2-positive RGCs (F-RGCs) and RGCs labeled in a transgenic mouse line W3.;First, I presented studies of classifying subtypes of alpha RGCs. Cell attached recording followed by morphology reconstruction revealed four subtypes of alpha-like RGCs: Off-sustained, Off-transient, On-sustained, On-transient subtypes, each of which has distinct morphological properties. In addition, we found osteopontin (OPN) as a molecular marker for all alpha RGCs. Following this discovery, we studied the role of OPN in alpha RGCs, Analysis showed that alpha RGCs preferentially survive and regenerate compared with other RGCs, leading us to test whether OPN can promote axon regeneration. Indeed, by combining OPN with growth factors, we were able to promote axon regenerations of RGCs.;Second, I presented work in classifying subtypes of F-RGCs, which are recognized by expressing a transcription factor, Foxp2. Combinatory expression of Foxp2 with other transcriptional factors divides F-RGCs into four subtypes, which form two pairs differing in their dendritic field sizes. Cell attached recording showed that one pair, F-minion and F-mini off RGCs, are direction-selective, while the other pair, F-midi on and F-midioff RGCs, are not. Thus, we identified four new subtypes of RGCs labeled by transcriptional factor Foxp2.;Third, I described initial efforts in classifying subtypes of RGCs labeled in the transgenic mouse line W3. W3 RGCs can be separated into two group based on their expression levels of fluorescent proteins, with the dimly labeled RGCs (W3D) remained uncharacterized. Initial analysis showed W3D RGCs include at least five subtypes of RGCs, which are different in their structures and physiological properties.;Lastly, I described my work in developing a molecular tool for mapping electrical synaptic connections from genetically defined neurons or neuronal subtypes, making use of a dipeptide transporter, Pept2. Cells expressing Pept2 (in a Cre-dependent way) take up a gap junction permeable fluorescent dipeptide, which then diffuses and labels the coupled cells. We tested this method in cultured cells and validated it in mouse retina using AAV carrying Cre-dependent Pept2. I applied this method to one subtype of RGCs, J-RGCs, to label their coupling partners. |
