View Program - 63rd Annual Drosophila Research Conference

Polycomb group (PcG) proteins repress transcription and maintain a molecular memory of gene inactivity that is important for embryonic patterning and cell differentiation. Where and when Polycomb silencing initiates is therefore critical for producing correct gene expression patterns during later development. While biochemical and genetic approaches have identified many PcG proteins, how these proteins collaborate to correctly initiate silencing in genomic space and developmental time and poorly understood. We developed a new model system to study Polycomb silencing initiation. We recently discovered that nurse cells in the Drosophila ovary initiate Polycomb silencing on common target genes similarly to somatic cells in the early embryo. During silencing initiation, accessory proteins remodel PRC2 mobility across the transcriptionally inactive B-compartment. Faster migrating PRC2 complexes methylate and silence most inactive regions and slower migrating complexes focus PRC2 activity on traditional Polycomb target genes. By combining genetics and live imaging, we determined how individual PcG proteins contribute to this transition. A single protein, Scm, is critical for establishing high concentrations of PcG proteins on target genes during the initiation step. We will present our recent findings for how Scm is developmentally regulated and how it contributes to the site-specificity of PcG protein targeting. We will also present our ongoing efforts to use single molecule tracking to measure the kinetic properties of PcG protein complexes before and after silencing initiation.

Reguation of Polycomb silencing initiation during nurse cell development