UW Madison Genetic Colloquium - Eliana Torres Zelada

Eliana Torres Zelada presents her research on the pioneer factor Zelda in Drosophila. She begins by introducing the maternal-to-zygotic transition (MZT) and the role of Zelda as a key activator of the zygotic genome. Her work extends beyond the embryo to neural stem cells (neuroblasts) in the larval brain, where Zelda is expressed in type I and type II neuroblasts and is required for their self-renewal. Overexpression of Zelda in type II neuroblasts leads to an overproliferation phenotype, and expression in partially differentiated cells can reprogram them back to a stem cell fate, but this ability is limited by differentiation state. Using ChIP-seq, she shows that Zelda binding is tissue-specific, with shared and unique sites between embryo and neuroblasts. The unique sites in neuroblasts are not enriched for the canonical CAGGTAG motif, suggesting that binding is influenced by chromatin context. She identifies a specific zinc finger (zinc finger 2) that has opposing functions: in the embryo it inhibits Zelda’s role in zygotic genome activation, while in neuroblasts it is required for Zelda’s ability to promote stem cell fate. Using reporter assays and cell lines, she demonstrates that zinc finger 2 is necessary for binding to non-canonical sites and for pioneering activity at those sites. The work highlights how protein domains and cellular context shape pioneer factor binding and activity.