The Mute button: Turning down the volume of histone expression

PROJECT SUMMARY
During DNA replication, a cell must replicate not only its DNA, but also the nucleosomes that
package its genome. To meet this extremely high demand for rapid histone protein biosynthesis,
all eukaryotes coordinate high expression of replication-dependent (RD) histone gene clusters
during S-phase of the cell division cycle. Regulating the level of expression of RD-histone genes
during S-phase is important for maintaining genomic integrity and normal cell cycle progression,
as too many or too few histones lead to toxic effects such as enhanced DNA damage sensitivity
or cell cycle arrest. While the transcriptional activation of RD-histone genes has been
characterized, little is known about the negative regulation that occurs as cells exit S-phase or
the modulation of transcription that occurs during S-phase. My preliminary research has shown
the Drosophila protein Mute (a homologue of human Yarp/Gon4L) is a prime candidate for a
negative transcriptional regulator of RD-histone genes. I have found that loss of Mute uncouples
expression of RD-histone genes from S-phase in Drosophila embryos. I hypothesize Mute is both
restricting RD-histone expression to S-phase as well as regulating levels of expression during S-
phase. This proposal seeks to uncover the mechanisms through which Mute represses RD-
histone genes and how this repression is connected to the cell cycle. Using an interdisciplinary
approach, the mechanisms of Mute’s repression at both the cellular and molecular levels will be
explored using a combination of genomic, fluorescent imaging, genetic, and proteomic techniques
in the Drosophila model system. This project will enhance our understanding of the role of histone
gene regulation in metazoans and provide insight into the mechanisms that govern the regulation
of this highly conserved cellular process.