The topological reorganization imposed on the chromatin during mitosis leads to a global shutdown of the gene expression. How then is the transcriptional program reestablished after division ? Previous work lacks the coupling between spatial and temporal resolution to assess in real-time the interplay between the transcriptional machinery and the physical properties of the chromatin. The goal of this project is to investigate gene regulation with high spatial and temporal resolution before, during and just after mitosis. Using quantitative imaging we will monitor enhancer-promoter contacts and continuously record transcriptional activity, particularly as cells undergo mitosis. Computational and statistical analyses as well as polymer models will be developed to quantify dynamic interactions and associate them to TF activity, mitotic progression and transcriptional outputs.
The image shows a Drosophila embryo 2 hr after fertilization, with nuclei at the surface fluorescently labeled for Bicoid protein (blue), Hunchback protein (green), and DNA (red). Using two-photon microscopy these embryos were imaged to quantitatively characterize the dynamics and precision of how morphogen molecules communicate positional information to individual nuclei. In this example, the shallow Bicoid gradient generates a sharp Hunchback boundary (enlarged in the background), partitioning the embryo in half. This input/output relationship is quantitatively represented in the foreground (yellow), where each dot specifies the Bicoid concentration (horizontal axis) and Hunchback concentration (vertical axis) measured in a single nucleus. The results indicate that the precision with which the embryo interprets and locates this boundary is very high, approaching limits set by simple physical principles.