Figure 4. A diagram representing the pigment biogenesis pathway in retinal pigment epithelium (RPE) cells. Mutations in genes that cause foveal hypoplasia are in denoted in red font. The nuclear MITF/PAX6 transcription factors directly regulate the downstream expression of TYR, TYRP1, DCT, and GPR143 genes. The red arrows show which part of the melanin pathway are affected by gene mutations in the melanosome. Some L-DOPA is secreted from the RPE cell and binds to the GPR143 receptor in the RPE membrane, resulting in pigment epithelial-derived factor (PEDF) secretion into the interphotoreceptor matrix. The GPR143 receptor is localized to both the RPE and melanosome membranes. PEDF binds to receptors on ganglion and photoreceptor cells in the retina, eliciting several neurodevelopmental processes including ganglion cell protection, photoreceptor neurogenesis, opsin synthesis and antiangiogenesis pathways.