Biology Seminar: Dr. Jingjing Sun

Adjacent progenitors can acquire distinct identities within minutes, yet how their molecular states resolve remains unclear. In the Drosophila posterior mesoderm, neighboring FoxL1- and HLH54F-associated progenitors separate during the final nuclear cycle before gastrulation. We genetically expanded these states and used stage-resolved single-embryo RNA-seq and ATAC-seq to reconstruct their divergence. Although initially related, their transcriptional and chromatin-accessibility profiles progressively separated through heterogeneous, partially uncoupled trajectories within a short interval. Accessibility models and genetic perturbations identified Runt as a regulator of the FoxL1-associated program and revealed stage-dependent responses to sustained Tailless expression. Loss of Runt shifted expression and accessibility away from the Cic-intact state. Conversely, elevated Runt in Cic-deficient embryos shifted marker expression and accessibility at substantial fractions of both opening and closing regions toward the Cic-intact state. Thus, adjacent states resolve yet retain regulatory plasticity, allowing altered regulator dosage to provide a partial alternative route toward a related chromatin landscape.