title: The Neurospora photoreceptor VIVID exerts negative and positive control on light sensing to achieve adaptation.
abstract: The light response in Neurospora is mediated by the photoreceptor and circadian transcription factor White Collar Complex (WCC). The expression rate of the WCC target genes adapts in daylight and remains refractory to moonlight, despite the extraordinary light sensitivity of the WCC. To explain this photoadaptation, feedback inhibition by the WCC interaction partner VIVID (VVD) has been invoked. Here we show through data-driven mathematical modeling that VVD allows Neurospora to detect relative changes in light intensity. To achieve this behavior, VVD acts as an inhibitor of WCC-driven gene expression and, at the same time, as a positive regulator that maintains the responsiveness of the photosystem. Our data indicate that this paradoxical function is realized by a futile cycle that involves the light-induced sequestration of active WCC by VVD and the replenishment of the activatable WCC pool through the decay of the photoactivated state. Our quantitative study uncovers a novel network motif for achieving sensory adaptation and defines a core input module of the circadian clock in Neurospora.
authors.affiliation: Division of Theoretical Systems Biology, German Cancer Research Center-DKFZ, Heidelberg, Germany.
authors.forename: Elan
authors.initials: E
authors.lastname: Gin
authors.forename: Axel C R
authors.initials: AC
authors.lastname: Diernfellner
authors.forename: Michael
authors.initials: M
authors.lastname: Brunner
authors.forename: Thomas
authors.initials: T
authors.lastname: Höfer
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D057906:Circadian Clocks / Q000235:genetics* / Q000528:radiation effects; D002940:Circadian Rhythm / Q000235:genetics / Q000528:radiation effects; D003198:Computer Simulation; D025461:Feedback, Physiological / Q000528:radiation effects; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000528:radiation effects*; D008027:Light; D008957:Models, Genetic; D009492:Neurospora crassa / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D020283:Photoreceptors, Microbial / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D020283:Photoreceptors, Microbial; D014157:Transcription Factors; C423283:VVD protein, Neurospora crassa