The Role of Broad in Regulating Border Cell Migration During Drosophila Oogenesis

Drosophila development is a highly regulated process governed by the precise timing and spatial cues of hormones and signaling pathways. The follicular epithelium of the Drosophila egg chamber has been a well-studied model system for identifying key molecular regulators of morphological changes and cell migration. Broad (Br), a zinc finger transcription factor, is a well-known early response gene of the steroid hormone ecdysone, which is essential for the initiation of metamorphosis. Our previous findings have shown that Br is a target of Notch signaling, and its suppression is required for proper epithelial cell cuboidal-to-squamous transition during Drosophila oogenesis. Here, we report that proper border cell (BC) migration requires the suppression of Br expression during Drosophila oogenesis. Br expression can be induced by Notch signaling as early as stage 4, but its expression decreases in BCs during cell migration at stage 9. Further findings revealed that JAK/ STAT and ecdysone signaling are highly active during the onset of BC migration and contribute to Br suppression. We demonstrated that JAK/ STAT suppresses Br expression to facilitate proper BC migration. In addition, we analyzed single-cell RNA sequencing data to highlight the shift in gene expression while Br was suppressed and BCs became mobile. The analysis confirmed the high expression of known BC markers, including slbo and sn, and identified br as specifically repressed in BCs, supporting the quality of the dataset and our experimental findings. Gene Ontology enrichment analysis revealed significant overrepresentation of biological processes related to cell migration, morphogenesis, and cell junction assembly, all of which are important for BC morphological transition and migration.