|Ph.D Student||Nachman Atalya|
|Subject||Spatial and Temporal Regulation Cell Adhesion is Mediated|
by Discrete Regulatory Elements in the Delilah
|Department||Department of Medicine||Supervisor||Professor Adi Salzberg|
|Full Thesis text|
Cellular adhesion is a fundamental process involved in normal development and function of different cell types, but also in pathological situations such as cancer, making the regulation on cellular adhesion a tightly controlled process, not yet fully understood. In Drosophila, one mechanism for regulation on cell adhesion is mediated by Delilah, a bHLH transcription factor that works as a "binary switch" by activating the expression of the adhesion molecule β integrin in each cell type that requires adhesion to endure strong mechanical forces during the fly life cycle. Delilah is dynamically expressed during fly development in different cell types, including the embryonic muscle and tendon cells, the embryonic chordotonal organs (specialized organs that sense proprioception) and the pupal wing and eye. Indeed, alteration in Delilah normal expression is manifested in different cell types at different developmental stages and can even results in lethality. Therefore, in order to guarantee the correct spatiotemporal expression of Delilah in a variety of cell types during development, the gene's regulatory apparatus must be able to respond to different genetic milieus in changing developing environment. At present, almost nothing is known about the molecular mechanism underlying Delilah expression. In this work, the delilah locus was analyzed by a deletion analysis approach based on evolutionary conservation and using in-vivo lacZ reporter assays in transgenic flies. This approach revealed a modular organization of the delilah locus whereby several independent cis regulatory modules are responsible for different aspects of Delilah expression pattern. Each of these modules responds to different signaling pathways: Drosophila Serum Response Factor in the pupal wing, Drosophila Myocyte Enhancer Factor 2 in the embryonic muscle cells and Stripe (the Drosophila homolog of the vertebrate Early Growth Response factor) in the embryonic tendon cells and the chordotonal organs attachment cells. The latter regulatory module was further demonstrated by site-directed mutagenesis to contain Stripe binding sites necessary for normal expression in the tendon cells and the chordotonal organ cap-attachment cells. In addition, two cell types exhibited a biphasic regulation on Delilah, namely the muscle cells and the chordotonal organ cap-attachment cells. In each of these cell types, two different regulatory modules induced a temporally distinct expression that demonstrated transcription factor specificity coinciding with the changing differentiation state of the cells. In this way, delilah cis regulatory modules orchestrate the interplay between the different upstream signaling pathways to ensure correct spatiotemporal expression of Delilah during fly development.