Cell cycle timings and zygotic gene activation (ZGA) are controlled by the ratio of nuclear content to cytoplasmic volume (N/C ratio). Some genes, called N/C ratio-dependent genes, are directly regulated by the N/C ratio via one of three overlapping modes: changing the timing of nascent RNA output (changes in cell cycle duration), the rate at which transcription occurs (kinetics of expression), or the probability of transcription initiation. In eukaryotes, genes are regulated by noncoding regions of DNA, such as enhancers and promoters. These sequences bind to proteins called transcription factors (TFs) that in turn regulate whether a gene is expressed and how. While ZGA is controlled by the N/C ratio, whether this regulation acts through enhancers remains unexplored.

This project aims to identify new N/C ratio-dependent genes (as well as their modes of regulation), to learn more about the underlying mechanism of expression for these genes in embryos with various N/C ratios, and to examine the role of enhancers in sensing changes in the N/C ratio. We do this via the MS2/MCP visualization system in genetically engineered Drosophila embryos. Currently, we are analyzing gene expression via a reporter system, where MS2 sequence repeats are inserted into the regulatory region of the target gene rather than at the endogenous locus. In the future, we hope to study expression directly at the endogenous locus rather than using indirect methods and to perform more experiments to uncover the underlying mechanisms behind enhancer-mediated expression.