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Home    Ρύθμιση της μετα- μεταφραστικής τροποποίησης και σταθερότητας bHLH μεταγραφικών παραγόντων μέσω αλληλεπιδράσεων μεταξύ τους  

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Identifier 000376409
Title Ρύθμιση της μετα- μεταφραστικής τροποποίησης και σταθερότητας bHLH μεταγραφικών παραγόντων μέσω αλληλεπιδράσεων μεταξύ τους
Alternative Title Regulation of post- translational modifications an stability of bHLH transcription factors via mutual interactions.
Author Κηπαράκη, Μαριάνθη
Thesis advisor Δελιδάκης, Χρήστος
Reviewer Αλεξανδράκη, Δέσποινα
Ταλιανίδης, Ιωάννης
Abstract In neural fate assignment throughout the animal kingdom, three classes of bHLH transcription factors play crucial roles. Class II bHLH activators [such as Scute (Sc) in Drosophila] heterodimerize with a class I bHLH protein [Daughterless (Da)] and promote neural fate; they are therefore called proneural proteins. Neural fate is suppressed by transcriptional repressors that belong to class VI bHLH-Orange proteins [such as Enhancer of split, E(spl)]. Previous work, both from our lab and others, has shown that E(spl) and proneural proteins antagonize each other by various mechanisms, that include transcriptional regulation of the same target genes, either through binding to different DNA binding sites within the same cisregulatory modules or/and by recruitment of E(spl) to proneural target genes via interaction with the Da/Sc complex. In this study we examined cis elements of the Scute protein that affect its stability and function when the protein is expressed without or with its partner, Da. We found that Sc is a labile phosphorylated protein and has two types of degradation signals (degrons I , II) depending on its dimerization status; both degrons lead Scute to proteasome. In the absence of Da, the major Sc degron (degron I) is its transcriptional activation domain (TAD), which can promote degradation off DNA and does not require Sc phosphorylation. The second degron (type II) is activated when Sc is heterodimerized with Da, while at the same time degron I is inactivated. Degron II is a composite degron and has three prerequisites. The Da/Sc heterodimer must be able to bind DNA, the two Da TADs must be present and Sc must be phosporylated on its major phosphorylation motif, S268PTS. Despite the fact that half of these elements belong to the Da partner (the two TADs and half of the basic DNA binding domain), Da itself is a very stable protein. In parallel to the above analysis we found a new way of antagonism between proneural proteins and E(spl) proteins, which is mutual protein degradation upon interaction. By using different mutant forms of the proteins we conclude that the two events (Da/Sc degradation by E(spl) vs E(spl) degradation by Da/Sc) use two different mechanisms that have similarities and differences. In both types of degradation the proteins must be able to interact with each other and E(spl)m7 DNA binding is dispensable. Degradation of E(spl)m7 by the Da/Sc complex is favoured if Da/Sc is able to bind onto DNA. Degradation of Da/Sc complex by E(spl)m7 does not need DNA binding of either transcription factor, but depends on recruitment of the corepressor Groucho. Additionally Scute has to be phosphorylated on the S268PTS motif in order to be degraded by m7. These results indicate that the Da/Sc/m7 complex recruits different degradation factors (e.g. E3 ligases) that specifically target the different components of the complex. An intriguing observation in the process of these studies is that Da induces a significant increase in the MW of both Sc and E(spl)m7 upon complex formation. This effect can be mimicked by proteasome inhibition suggesting that this modified fraction of Sc or m7 is rather unstable. Although both Sc and E(spl)m7 display mono- and poly- ubiquitylation, as well as other high MW modifications, we have no conclusive evidence regarding the molecular nature of the Da-induced MW shift.
Language Greek
Subject Degradation signal
Drosophila
Enhancer of split
Groucho corepressor
Proneural proteins
Αποκοδομητικά σινιάλα
Δροσόφιλα
Προνευρικές πρωτεϊνες
Συγκαταστολέας Groucho
Issue date 2012-11-01
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Doctoral theses
  Type of Work--Doctoral theses
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