Fig. 8. Functional mechanism of ISL1 and BRN3B in the development of RGCs. (A) Concurrent binding of ISL1 and BRN3B to RGC-specific promoters. Anti-BRN3B and anti-ISL1 antibodies but not IgG co-precipitate with the promoters of Brn3b, Shh, Brn3a and Isl2. Both antibodies do not precipitate with control Brn3b ORF. (B) Functional synergy of ISL1 and BRN3B on Brn3a luciferase reporter gene expression. Cells transfected with empty pcDNA expression vector and reporter are used as controls. Luciferase activity is determined by normalizing firefly activity with renilla activity. Then fold activation is calculated by dividing the luciferase activity of experimental groups with that of control. Each histogram represents the mean+s.d. (n=4). (C) The Math5-Brn3b/Isl1 pathway in the development of RGCs. Solid lines, direct regulation identified; broken lines, indirect or proposed regulation.