The Zic family homologue Odd-paired regulates Alk expression in Drosophila.

The Anaplastic Lymphoma Kinase (Alk) receptor tyrosine kinase (RTK) plays a critical role in the specification of founder cells (FCs) in the Drosophila visceral mesoderm (VM) during embryogenesis. Reporter gene and CRISPR/Cas9 deletion analysis reveals enhancer regions in and upstream of the Alk locus that influence tissue-specific expression in the amnioserosa (AS)， the VM and the epidermis. By performing high throughput yeast one-hybrid screens (Y1H) with a library of Drosophila transcription factors (TFs) we identify Odd-paired (Opa)， the Drosophila homologue of the vertebrate Zic family of TFs， as a novel regulator of embryonic Alk expression. Further characterization identifies evolutionarily conserved Opa-binding cis-regulatory motifs in one of the Alk associated enhancer elements. Employing Alk reporter lines as well as CRISPR/Cas9-mediated removal of regulatory elements in the Alk locus， we show modulation of Alk expression by Opa in the embryonic AS， epidermis and VM. In addition， we identify enhancer elements that integrate input from additional TFs， such as Binou (Bin) and Bagpipe (Bap)， to regulate VM expression of Alk in a combinatorial manner. Taken together， our data show that the Opa zinc finger TF is a novel regulator of embryonic Alk expression.