Identification of Conserved Protein Kinase CK2 and 14-3-3 Target Sites In Neurogenic Transcriptional Regulators

In the decades following the identification of CK2 as the first \u27phosphotransferase\u27, a great deal has been learned regarding its biological importance. In one developmental context, CK2 regulates cell fate decisions during Drosophila neurogenesis by activating the E(spl)M8 repressor, a terminal effector of the Notch pathway. The finding that CK2 is intimately involved in retinal cell determination propelled a search for additional neurogenic factors regulated by CK2. Here, using bioinformatics and biochemical assays, the transcription factors E(spl)Mgamma, Extramacrochaetae, and Sine Oculis were identified and characterized as targets of CK2. Significantly, each of these factors is expressed at distinct time points of eye development and thereby adds to the participation of CK2 in neurogenesis. Furthermore, E(spl)M8, -M5, and -M7 phosphorylation studies revealed that specific residues in the C-terminal domain regulate these repressors. However, the sequence motifs present in the aforementioned are variable and not present in all E(spl) members, raising the possibility of divergent regulation. Interestingly, previous experiments suggested that the cofactor 14-3-3 formed complexes with most E(spl) proteins. Bioinformatics and genetic analyses revealed a conserved 14-3-3 interaction motif in E(spl)Mdelta and its mammalian homologs HES1 and HES4. These findings demonstrate a functional diversification among E(spl) repressors through disparate kinases and protein cofactors