Figure 4. RT–PCR analysis of GPR109A expression in transformed retinal cell lines. A: RT–PCR of RNA samples collected from rat Müller (rMC-1) and rat ganglion (RGC-5) cells using PCR primers specific for rat GPR109A did not detect the presence of mRNA transcripts encoding GPR109A. 18S rRNA was used as an internal control. B: RT–PCR of RNA samples collected from ARPE-19 cells, using primer pairs specific for human GPR109A and GPR109B respectively, detected the presence of mRNA transcripts for both isoforms.