TFAP2E and retinoblastoma: The trend towards mutual exclusion of AP-2ε and AP-2γ RNAs in different retinoblastoma cell lines also supports the idea that retinoblastoma tumors are derived from different amacrine subtypes, in keeping with the low level of overlap between AP-2ε- and AP-2γ-expressing amacrine cells at early stage of retinal differentiation in mouse.