title: Cell-type specific utilization of multiple negative feedback loops generates developmental constancy.
abstract: Signaling pathways generally contain multiple negative regulators that are induced by the signal they repress, constructing negative feedback loops. Although such negative regulators are often expressed in a tissue- or cell-type specific manner during development, little is known about the significance of their differential expression patterns and possible interactions. We show the role and interplay of two cell-type specific negative feedback loops during specification of photoreceptor neurons in the Drosophila compound eye, a process that occurs via epidermal growth factor (EGF)-mediated sequential induction through the activation of the Ras/MAPK signaling pathway. Inducing cells secreting EGF express a negative regulator Sprouty (SPRY) that lowers Ras/MAPK signaling activity, and as a consequence reduces the signal-dependent expression of a secreted EGF inhibitor, Argos (AOS). Induced cells in turn express an orphan nuclear receptor Seven-up (SVP), which represses SPRY expression thereby allowing expression and secretion of AOS, preventing further induction. When this intricate system fails, as in spry mutants, sequential induction is no longer constant and the number of photoreceptor neurons becomes variable. Thus, cell-type specific utilization of multiple negative feedback loops not only confers developmental robustness through functional redundancy, but is a key component in generating consistent patterning.
authors.affiliation: Division of Developmental Genetics, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Iwanami
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Hiromi
authors.forename: Masataka
authors.initials: M
authors.lastname: Okabe
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000196:embryology* / Q000235:genetics*; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005123:Eye / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism; D025461:Feedback, Physiological; D018507:Gene Expression Regulation, Developmental; D011905:Genes, ras; D008565:Membrane Proteins / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000196:embryology* / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D005136:Eye Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011987:Receptors, Steroid; C110486:sty protein, Drosophila; C094295:svp protein, Drosophila; C075638:aos protein, Drosophila; D004815:Epidermal Growth Factor; D020928:Mitogen-Activated Protein Kinases