Genetic and phenotypic analysis of CREB-binding protein and Pointed during oogenesis in Drosophila melanogaster

To investigate the mechanisms by which intercellular signaling directs pattern formation, I have focused on the development of the dorsal-ventral (DV) axis during oogenesis in Drosophila melanogaster. Establishment and patterning of the DV axis during oogenesis is the result of signaling through the Epidermal Growth Factor Receptor (EGFR) pathway. Proper patterning gives rise to two dorsal respiratory appendages on the eggshell, or chorion. The current model for epithelial patterning involves autoregulation of the EGFR pathway through activation of the downstream target genes rhomboid (rho) and argos (aos). EGFR signaling in the dorsal follicular epithelium, initiated by the EGFR ligand Gurken, leads to the expression of rho. Rho leads to the local activation of the ligand Spitz which further amplifies EGFR activity within the epithelium. Maximal levels of EGFR signaling result in expression of aos in the midline. Aos inhibits EGFR locally thereby bisecting its activity profile into two dorsal lateral patches, which will produce the two dorsal appendages via expression of Broad-Complex (BR-C). The interaction between these EGFR signaling components is well characterized; however, their regulation at the transcriptional level remains largely unknown. I have identified nejire ( nej), which encodes the Drosophila homolog of CREB-Binding Protein (dCBP), as a component of DV patterning and EGFR signaling. CBP is a transcriptional co-regulator involved in many signaling networks, and has been implicated in cancer and neurodegenerative diseases. I have determined that nej loss-of-function mutations alter patterning of the chorion, affecting only a subset of EGFR dependent processes in this context. Comparison of the effects of nej on targets of EGFR signaling, suggests that dCBP is necessary for autoregulation of EGFR signaling during dorsal patterning. Furthermore, I present genetic and biochemical evidence that CBP functions with the ETS domain-containing transcription factor Pointed (Pnt) in epithelial patterning. Finally, I present evidence overturning the current paradigm of Aos mediated epithelial patterning. My work represents the first link between EGFR signaling and CBP activity in a developmental context and suggests that distinct transcriptional responses to EGFR signaling are likely to be mediated in part through the actions of CBP.