Angelike M. Stathopoulos
In the Stathopoulos lab, we are working to define the gene network controlling gastrulation in Drosophila. To this end, we are identifying and characterizing target genes of the Dorsal transcription factor which is present in a nuclear gradient along the dorsoventral axis of Drosophila embryos. Dorsal is a maternally deposited rel-containing transcription factor that is present in a nuclear gradient within the early Drosophila embryo. High levels of nuclear Dorsal are present in ventral regions with lower levels in more dorsal regions. In the past 10 years, about 16 direct Dorsal target genes have been identified. These genes encode transcription factors and components of signaling pathways. High levels of nuclear Dorsal present in ventral regions activate the expression of genes required for mesoderm formation like twist and snail, which encode bHLH and zinc-finger domain containing transcription factors, respectively. Lower levels of nuclear Dorsal in lateral regions activate the expression of genes that specify the neurogenic ectoderm like rhomboid and short-gastrulation (sog), which encode an EGFR ligand processing protease and extracellular TGF-? inhibitor, respectively. Dorsal can also work as a repressor of transcription and limits the expression of certain genes to dorsal regions of the embryo where no nuclear Dorsal is present as for the expression of the morphogen Dpp and homeodomain transcription factor Zerknult (Zen).
Study of the Dorsal gene network has the potential to provide insights into a vast array of different cellular processes. One can follow how changes in gene expression affect signaling to control cell movements and differentiation. For this reason, our work has focused on taking a whole-genome approach towards characterizing Dorsal target genes in order to get a better understanding of the gene networks established by this transcription factor. We conducted a micorarray screen that identified over 300 genes upregulated in one of three mutant backgrounds containing either high, intermediate, or no nuclear Dorsal. We have limited our studies initially to genes expressed to levels comparable to known Dorsal targets and found many previously uncharacterized genes including receptor ligands, metalloproteases, and transcription factors. Those expressed in the presumptive mesoderm we named Mes1 through Mes5, those in the neurogenic ectoderm Neu1 through Neu5, and those in the dorsal ectoderm Ect1 through Ect5.
The long-term goal of my future research is to determine how the Dorsal transcription factor generates multiple outputs of gene expression to control gastrulation in the Drosophila melanogaster early embryo. There are three projects that I want to continue in my laboratory that will increase our understanding of the molecular mechanisms by which gastrulation proceeds.
The first project will involve study of two very interesting Dorsal target genes isolated from our microarray screen, pyramus (pyr) and thisbe (ths), that encode a pair of FGF-like ligands (below in blue and red, respectively). We will study how pyr and ths control the many mesoderm migrations throughout embryogenesis including those during gastrulation. We have found that these genes are also expressed later in embryogenesis and throughout development. In vertebrates, FGF-ligands are known to control a variety of important processes from brain morphogenesis to limb development. We will use the Drosophila model system to further understand how FGF-ligands function to control development and specifically why they often function in pairs.
The second is to study additional target genes isolated from our microarray screen which identified over 300 genes that exhibit changes of expression in a Dorsal-dependent manner. We will analyze their expression patterns, mutant phenotypes, and Dorsal-dependent enhancers.
The third project involves the isolation and study of the transcription factors that function together with Dorsal to specify distinct outputs of gene expression. To identify binding sites for these transcription factors, bioinformatic and classical approaches will be used to isolate conserved cis-regulatory motifs from co-regulated enhancers.