Biology subjects

Scazzocchio, C.

Publications and source records attributed to Scazzocchio, C..

5 recordsLinked to original sources

bioRxiv2023

Neo-functionalization in Saccharomyces cerevisiae: A Novel Nrg1-Rtg3 chimeric transcriptional modulator is essential to maintain mitochondrial DNA integrity

In Saccharomyces cerevisiae, the transcriptional repressor Nrg1 (Negative Regulator of Glucose-repressed genes) and the b/Zip transcription factor Rtg3 (ReTroGrade regulation) mediate glucose repression and mitochondria to nucleus signaling, respectively. Here we show a novel function for these two proteins, in which alanine promotes the formation of a chimeric Nrg1/Rtg3 regulator that represses the ALT2 gene (encoding an alanine transaminase paralogue of unknown function) expression. A NRG1/NRG2 paralogous pair, resulting from a post-wide genome, small scale duplication event, is extant in the Saccharomyces genus. Neo-functionalization of only one paralogue resulted in Nrg1, able to interact with Rtg3. Either nrg1{Delta} or rtg3{Delta} single mutant strains are unable to utilize ethanol and show a typical petite (small) phenotype on glucose. Neither of the WT genes complemented the petite phenotype, suggesting irreversible mitochondrial DNA damage in these mutants. Neither nrg1{Delta} nor rtg3{Delta} mutant strains express genes encoded by any of five polycistronic units transcribed from mitochondrial DNA in S. cerevisiae. This, and the direct measure of the mitochondrial DNA gene complement confirms that irreversible damage of the mitochondrial DNA occurred in both mutant strains and is consistent with an essential role of the chimeric Nrg1/Rtg3 regulator in mitochondrial DNA maintenance.

microbiology↗

bioRxiv2021

Nicotinate degradation in a microbial eukaryote: a novel, complete pathway extant in Aspergillus nidulans

Several strikingly different aerobic and anaerobic pathways of nicotinate utilization had been described in bacteria. No similar work is extant in any eukaryote. Here we elucidate a complete eukaryotic nicotinate utilization pathway, by constructing single or multiple gene deleted strains and identifying metabolic intermediates by ultra-high performance liquid chromatography - high-resolution mass spectrometry. Enzymes catalyzing each step and all intermediate metabolites were identified. We previously established that the cognate eleven genes organized in three clusters constitute a regulon, strictly dependent on HxnR, a pathway-specific transcription factor. The first step, hydroxylation of nicotinic acid to 6-hydroxynicotinic acid is analogous to that occurring in bacterial pathways and is catalyzed by an independently evolved molybdenum-containing hydroxylase. The following enzymatic steps have no prokaryotic equivalents: 6-hydroxynicotinic acid is converted to 2,3,6-trihydroxypyridine through 2,5-dihydroxypiridine and the trihydroxylated pyridine ring is then saturated to 5,6-dihydroxypiperidine-2-one followed by the oxidation of the C6 hydroxyl group resulting in 3-hydroxypiperidine-2,6-dione. The latter two heterocyclic compounds are newly identified cellular metabolites, while 5,6-dihydroxypiperidine-2-one is a completely new chemical compound. Ring opening between C and N results in -hydroxyglutaramate, an unprecedented compound in prokaryotic nicotinate catabolic routes. The pathway extant in A. nidulans, and in many other ascomycetes, is different from any other previously analyzed in bacteria. Our earlier phylogenetic analysis of Hxn proteins together with the complete novel biochemical pathway we now describe further illustrates the convergent evolution of catabolic pathways between fungi and bacteria. Significance StatementThis eukaryotic nicotinate catabolic pathway illustrates the convergent evolution of prokaryotic and microbial eukaryotic metabolism. It brings to light newly identified metabolites and step processing enzymes. The identification of hitherto undescribed metabolites - which could serve as precursor biosynthetic molecules - is potentially relevant to both pharmaceutical and agrochemical industries.

microbiology↗

bioRxiv2021

Genome organisation and evolution of a eukaryotic nicotinate co-inducible pathway

In Aspergillus nidulans a regulon including 11 hxn genes (hxnS, T, R, P, Y, Z, X, W, V, M and N) is inducible by a nicotinate metabolic derivative, repressible by ammonium and under stringent control of the nitrogen-state sensitive GATA factor AreA and the specific transcription factor HxnR. This is the first report in a eukaryote of the genomic organisation of a possibly complete pathway of nicotinate utilisation. In A. nidulans the regulon is organised in three distinct clusters, this organisation is variable in the Ascomycota. In some Pezizomycotina species all the 11 genes map in a single cluster, in other in two clusters. This variable organisation sheds light on cluster evolution. Instances of gene duplication, followed by, or simultaneous with, integration in the cluster; partial or total cluster loss; horizontal gene transfer of several genes, including an example of whole cluster re-acquisition in Aspergillus of section Flavi were detected, together with the incorporation in some clusters of genes not found in the A. nidulans co-regulated regulon, which underlie both the plasticity and the reticulate character of metabolic cluster evolution. This study provides a comprehensive phylogeny of six members of the cluster across representatives of all Ascomycota classes.

microbiology↗

bioRxiv2021

De novo germline mutation in the Dual Specificity Phosphatase 10 gene accelerates autoimmune diabetes in Non-Obese Diabetic (NOD) mice

Here we report the isolation by selective breeding of two sublines of Non-Obese Diabetic (NOD) mice exhibiting a significant difference in the incidence of autoimmune type 1 diabetes (T1D). Whole genome sequencing of the NOD/NckH (high T1D incidence) and NOD/NckL (low T1D incidence) revealed the presence of a limited number of variants specific to each subline. Treating the age of T1D onset as a quantitative trait and using automated meiotic mapping (AMM), enhanced susceptibility in the NOD/NckH subline was unambiguously attributed to a recessive allele of Dusp10 which encodes a dual specificity phosphatase. The causative effect of the mutation was verified with a high level of confidence by targeting Dusp10 with CRISPR/Cas9 in NOD/NckL mice: in these animals a higher incidence of diabetes was observed. Expression of wild-type Dusp10 correlated with higher levels of surface PD-L1 in the islets of NOD/NckL mice.

immunology↗

bioRxiv2018

Reticulate evolution in eukaryotes: origin and evolution of the nitrate assimilation pathway

Genes and genomes can evolve through interchanging genetic material, this leading to reticular evolutionary patterns. However, the importance of reticulate evolution in eukaryotes, and in particular of horizontal gene transfer (HGT), remains controversial. Given that metabolic pathways with taxonomically-patchy distributions can be indicative of HGT events, the eukaryotic nitrate assimilation pathway is an ideal object of investigation, as previous results revealed a patchy distribution and suggested one crucial HGT event. We studied the evolution of this pathway through both multi-scale bioinformatic and experimental approaches. Our taxon-rich genomic screening shows this pathway to be present in more lineages than previously proposed and that nitrate assimilation is restricted to autotrophs and to distinct osmotrophic groups. Our phylogenies show a pervasive role of HGT, with three bacterial transfers contributing to the pathway origin, and at least seven well-supported transfers between eukaryotes. Our results, based on a larger dataset, differ from the previously proposed transfer of a nitrate assimilation cluster from Oomycota (Stramenopiles) to Dikarya (Fungi, Opisthokonta). We propose a complex HGT path involving at least two cluster transfers between Stramenopiles and Opisthokonta. We also found that gene fusion played an essential role in this evolutionary history, underlying the origin of the canonical eukaryotic nitrate reductase, and of a novel nitrate reductase in Ichthyosporea (Opisthokonta). We show that the ichthyosporean pathway, including this novel nitrate reductase, is physiologically active and transcriptionally co-regulated, responding to different nitrogen sources; similarly to distant eukaryotes with independent HGT-acquisitions of the pathway. This indicates that this pattern of transcriptional control evolved convergently in eukaryotes, favoring the proper integration of the pathway in the metabolic landscape. Our results highlight the importance of reticulate evolution in eukaryotes, by showing the crucial contribution of HGT and gene fusion in the evolutionary history of the nitrate assimilation pathway.

evolutionary biology↗