View Program - 63rd Annual Drosophila Research Conference

Multicellular organisms are made up of numerous differentiated cell types that perform unique functions. Beginning from a single cell, organisms undergo a journey of differentiation, resulting in the formation of this variety of unique cell types. Because these cells all possess the same genome, distinct cell types are not due to differences in genotype, but rather differences in gene expression. Transcription factors bind DNA and drive this differential gene expression. However, compacted chromatin structure can act as a barrier to transcription-factor binding. Specialized transcription factors, known as pioneer transcription factors, can overcome this barrier by binding to condensed chromatin and increasing chromatin accessibility at previously inaccessible loci. While pioneer factors share the ability to bind condensed chromatin, the exact mechanisms are not understood as these factors all act through divergent DNA-binding domains. Grainy head (GRH) is an essential pioneer factor that drives epithelial cell fate and when misexpressed, can lead to cancer. It is conserved across species ranging from worms to humans and binds the same canonical DNA sequence in all species studied. These features make GRH a great candidate to elucidate the basic mechanisms by which pioneer factors engage the genome and their role in shaping cellular identity. Furthermore, while mammals have three GRH-like proteins, Drosophila encode GRH from a single gene, simplifying functional studies. To understand the properties of GRH that allow it to access compacted chromatin, we used in vitro studies to show that GRH can bind DNA in the context of nucleosomes. Using structural analysis, we identified mutations in the DNA-binding domain that mediate either sequence-specific or non-specific interactions and confirmed these properties in vitro. We are using these mutants to determine how this conserved protein interacts with DNA through its DNA-binding domain. We have further developed a tissue-culture system to investigate these mechanisms in vivo. Together our data will determine how GRH scans the genome and recognizes its motifs within inaccessible chromatin.

Uncovering how the pioneer transcription factor Grainy head binds and opens chromatin