No abstract

Gene expression is generally regulated by recruitment of transcription factors and RNA polymerase II (RNAP II) to specific sequences in the gene promoter region. The Integrator complex mediates processing of small nuclear RNAs (snRNAs) as well as the initiation and release of paused RNAP II at specific genes in response to growth factors. Here we show that in C . elegans , disruption of the Integrator complex leads to transcription of genes located downstream of the snRNA loci via a non-conventional transcription mechanism based on the lack of processing of the snRNAs. RNAP II read-through generates long chimeric RNAs containing snRNA, the intergenic region and the mature mRNA of the downstream gene located in sense . These chimeric sn-mRNAs remain as untranslated long non-coding RNAs, in the case of U1- and U2-derived sn-mRNAs, but can be translated to proteins in the case of SL-derived sn-mRNAs. The transcriptional effect caused by disruption of the Integrator complex is not restricted to genes located downstream of the snRNA loci but also affects key regulators of signal transduction such as kinases and phosphatases. Our findings highlight that these transcriptional alterations may be behind the correlation between mutations in the Integrator complex and tumor transformation.

The transcriptomes of model organisms have been defined under specific laboratory growth conditions. The standard protocol for Caenorhabditis elegans growth and maintenance is 20°C on an Escherichia coli diet. Temperatures ranging from 15°C to 25°C or feeding with other species of bacteria are considered physiological conditions, but the effect of these conditions on the worm transcriptome has not been well characterized. Here, we compare the global gene expression profile for the reference Caenorhabditis elegans strain (N2) grown at 15°C, 20°C, and 25°C on two different diets, Escherichia coli and Bacillus subtilis. When C. elegans were fed E. coli and the growth temperature was increased, we observed an enhancement of defense response pathways and down-regulation of genes associated with metabolic functions. However, when C. elegans were fed B. subtilis and the growth temperature was increased, the nematodes exhibited a decrease in defense response pathways and an enhancement of expression of genes associated with metabolic functions. Our results show that C. elegans undergo significant metabolic and defense response changes when the maintenance temperature fluctuates within the physiological range and that the degree of pathogenicity of the bacterial diet can further alter the worm transcriptome.

Under non-stressed conditions, the redox status of the different subcellular compartments is tightly controlled . Hence, the cytoplasm has a reducing environment that favours cysteine protein residues in their dithiol form while the endoplasmic reticulum environment is oxidizing to facilitate the formation of disulfide bonds for protein folding . This situation is reversed in the presence of aggregation-prone proteins, as both com partments undergo a dramatic shift in their respective redox status, with the cytoplasm becoming more oxidized and the endoplasmic reticulum more reducing [1]. However, whether changes in the cellular redox status affect protein aggregation has not yet been addressed .We approached this hypothesis by using a C. elegans mutant strain lacking the gsr-1 gene, encoding glutathione reductase, the enzyme responsible for recycling oxidized glutathione (GSSG) and thus maintenance of glutathione redox homeostasis (2]. We found that gsr-1 deficiency enhances the deleterious phenotypes of worm di sea se models ca u sed by aggregating proteins like human b-amyloid peptide, a-synuclein or polyglutamine repeats containing proteins. lmportantly, gsr-1 dependent proteostatic disruption is also found in C. elegans strains expressing endogenous UNC-52 and LET-60 aggregate-prone metastable proteins. This deleterious effect is largely phenocopied by the GSH depleting agent diethyl ma leate [3].Protein aggregates can be disposed by autophagy and consistent with a role of GSR-1 in this process, gsr-1 mutants abolish nuclear translocation of the TFEB/HLH-30 transcription factor (a key mediator of autophagy induction) and strongly impair the degradation of the autophagy substrate p62/SQST -1 ::GFP. In agreement, genetic disruption of autophagy in gsr-1 mutants expressing aggregation prone proteins resulted in strong synthetic developmental phenotypes and in sorne cases lethality. Downregulation of glutathione reductase and GSH levels in both yeast and mammalian cell models also caused phenotypes associated to protein aggregation and impaired TFEB nuclear translocation [3]. Together, this study demonstrates a novel, evolutionarily conserved role of glutathione redox homeostasis in proteostasis maintenance through autophagy regulation . {1] Kirstein J, et al. (2015) Proteotoxtc stress and aqeinq triqqers the loss of redox homeostasis across ce/fular compartments. EMBO J. 34: 2334-49. {2] Mora-Larca JA et al. (20 16) Glutathione reductase qsr-1 is an essenttal gene required for Caenorhabditis eleqans earlv embryomc development. Free Radie Biol Med. 96:446-61 . {3] Guerrero-Gómez O, et al. (2019) Loss of qlutathtone redox homeostasis impairs proteostasis bv inhibitinq autophaqy-dependent protein deqradation. Ce// Oeath Oiffer. m press. 9

28• C. elegans gsr-1 gene encodes cytoplasmic and mitochondria isoforms of glutathione reductase. 30• gsr-1 is essential for C. elegans embryonic development. 32• The lethality of gsr-1 mutants is due to a specific requirement of GSR-1 protein in the cytoplasm. 34• gsr-1 embryos have a progressive cell division delay and an aberrant distribution of interphasic 35 chromatin. 37• gsr-1 worms with maternally contributed GSR-1 are able to reach adulthood but display