Figure 14. Comprehensive cross-species models for reciprocal regulation of genes during retinal pigment epithelium cell differentiation Models for regulatory regions, including promoters and first introns, of differentiated and undifferentiated gene clusters, were constructed as described in the text. transcription response elements (TREs) inclusion criteria indicated in these models are frequency ratio, evolutionary conservation factor, and RT–PCR detection of mRNA expression. Symbols representing TREs indicates passage of corresponding criteria filter, as indicated in key, by TRE, filled boxes signify that a TRE has passed all criteria filters.