The COP9 signalosome of Aspergillus nidulans

Abstract

The COP9 signalosome (CSN) is a conserved eukaryotic multiprotein complex, playing a multifaceted role in the regulation of protein degradation by the ubiquitin system. The primary function of CSN is the removal of the ubiquitin-like Nedd8 moiety from the cullin subunits of SCF ubiquitin ligases, termed deneddylation. A complete conserved CSN was previously isolated in the model filamentous fungus Aspergillus nidulans, where it is necessary for sexual fruit body formation and establishment of developmental balance, but not essential for survival, providing an opportunity to study the functions of this complex in a genetically amenable organism.In the course of this work I have investigated the mechanism of CSN action during A. nidulans development using two complementary approaches: mutagenic analysis of the deneddylase-bearing CsnE subunit and transcriptome profiling of a csnE deletion strain.Mutagenesis of the JAMM metalloprotease motif reveals that it is primarily responsible for the csn deletion phenotype and therefore the deneddylase activity is probably essential for A. nidulans sexual development. Mutated CsnE is still able to interact with CsnF, another CSN subunit, indicating that the phenotype is not caused by impaired complex formation. We additionally show that rubA, a close homologue of mammalian Nedd8 is essential for A. nidulans growth.The results of the genome-wide transcriptome profiling of a csnE deletion strain show that the fungal CSN affects the regulation of many groups of genes across development. Differentially expressed genes include oxidoreductases, genes involved in cell wall degradation and membrane transport as well as a putative cluster of secondary metabolite biosynthesis genes. CSN is required for developmentally induced expression of brlA, the central regulator of asexual sporulation and the hormone synthesis oxygenase ppoC involved in regulation of developmental balance. It is also necessary for developmentally induced beta-glucanase activity, which might be prerequisite for fruit body formation. Analysis of cis-regulating sequences upstream of regulated genes suggests a possibility of crosstalk between the sexual and asexual signalling pathways. The results obtained in this work provide a basis for further elucidating transcriptional networks acting in A. nidulans developmental signalling and afford for insights into downstream targets of CSN in eukaryotes.The COP9 signalosome (CSN) is a conserved eukaryotic multiprotein complex, playing a multifaceted role in the regulation of protein degradation by the ubiquitin system. The primary function of CSN is the removal of the ubiquitin-like Nedd8 moiety from the cullin subunits of SCF ubiquitin ligases, termed deneddylation. A complete conserved CSN was previously isolated in the model filamentous fungus Aspergillus nidulans, where it is necessary for sexual fruit body formation and establishment of developmental balance, but not essential for survival, providing an opportunity to study the functions of this complex in a genetically amenable organism.In the course of this work I have investigated the mechanism of CSN action during A. nidulans development using two complementary approaches: mutagenic analysis of the deneddylase-bearing CsnE subunit and transcriptome profiling of a csnE deletion strain.Mutagenesis of the JAMM metalloprotease motif reveals that it is primarily responsible for the csn deletion phenotype and therefore the deneddylase activity is probably essential for A. nidulans sexual development. Mutated CsnE is still able to interact with CsnF, another CSN subunit, indicating that the phenotype is not caused by impaired complex formation. We additionally show that rubA, a close homologue of mammalian Nedd8 is essential for A. nidulans growth.The results of the genome-wide transcriptome profiling of a csnE deletion strain show that the fungal CSN affects the regulation of many groups of genes across development. Differentially expressed genes include oxidoreductases, genes involved in cell wall degradation and membrane transport as well as a putative cluster of secondary metabolite biosynthesis genes. CSN is required for developmentally induced expression of brlA, the central regulator of asexual sporulation and the hormone synthesis oxygenase ppoC involved in regulation of developmental balance. It is also necessary for developmentally induced beta-glucanase activity, which might be prerequisite for fruit body formation. Analysis of cis-regulating sequences upstream of regulated genes suggests a possibility of crosstalk between the sexual and asexual signalling pathways. The results obtained in this work provide a basis for further elucidating transcriptional networks acting in A. nidulans developmental signalling and afford for insights into downstream targets of CSN in eukaryotes.