title: R7 Photoreceptor Specification in the Developing Drosophila Eye: The Role of the Transcription Factor Deadpan.
abstract: As cells proceed along their developmental pathways they make a series of sequential cell fate decisions. Each of those decisions needs to be made in a robust manner so there is no ambiguity in the state of the cell as it proceeds to the next stage. Here we examine the decision made by the Drosophila R7 precursor cell to become a photoreceptor and ask how the robustness of that decision is achieved. The transcription factor Tramtrack (Ttk) inhibits photoreceptor assignment, and previous studies found that the RTK-induced degradation of Ttk was critically required for R7 specification. Here we find that the transcription factor Deadpan (Dpn) is also required; it is needed to silence ttk transcription, and only when Ttk protein degradation and transcriptional silencing occur together is the photoreceptor fate robustly achieved. Dpn expression needs to be tightly restricted to R7 precursors, and we describe the role played by Ttk in repressing dpn transcription. Thus, Dpn and Ttk act as mutually repressive transcription factors, with Dpn acting to ensure that Ttk is effectively removed from R7, and Ttk acting to prevent Dpn expression in other cells. Furthermore, we find that N activity is required to promote dpn transcription, and only in R7 precursors does the removal of Ttk coincide with high N activity, and only in this cell does Dpn expression result.
authors.affiliation: Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America.
authors.forename: Yannis Emmanuel
authors.initials: YE
authors.lastname: Mavromatakis
authors.affiliation: Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, New York, United States of America.
authors.forename: Andrew
authors.initials: A
authors.lastname: Tomlinson
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D019070:Cell Lineage; D003433:Crosses, Genetic; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology*; D005786:Gene Expression Regulation; D018507:Gene Expression Regulation, Developmental; D009687:Nuclear Proteins / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D034622:RNA Interference; D051880:Receptors, Notch / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D019076:Transgenes
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D051880:Receptors, Notch; D012097:Repressor Proteins; C497759:N protein, Drosophila; C096356:trk protein, Drosophila; C075878:ttk protein, Drosophila; C078020:Dpn protein, Drosophila