Correction: Single amino-acid mutation in a Drosoph ila melanogaster ribosomal protein: An insight in uL11 transcriptional activity.

[This corrects the article DOI: 10.1371/journal.pone.0273198.].

Single amino-acid mutation in a Drosoph ila melanogaster ribosomal protein: An insight in uL11 transcriptional activity.

The ribosomal protein uL11 is located at the basis of the ribosome P-stalk and plays a paramount role in translational efficiency. In addition, no mutant for uL11 is available suggesting that this gene is haplo-insufficient as many other Ribosomal Protein Genes (RPGs). We have previously shown that overexpression of Drosophila melanogaster uL11 enhances the transcription of many RPGs and Ribosomal Biogenesis genes (RiBis) suggesting that uL11 might globally regulate the level of translation through its transcriptional activity. Moreover, uL11 trimethylated on lysine 3 (uL11K3me3) interacts with the chromodomain of the Enhancer of Polycomb and Trithorax Corto, and both proteins co-localize with RNA Polymerase II at many sites on polytene chromosomes. These data have led to the hypothesis that the N-terminal end of uL11, and more particularly the trimethylation of lysine 3, supports the extra-ribosomal activity of uL11 in transcription. To address this question, we mutated the lysine 3 codon using a CRISPR/Cas9 strategy and obtained several lysine 3 mutants. We describe here the first mutants of D. melanogaster uL11. Unexpectedly, the uL11K3A mutant, in which the lysine 3 codon is replaced by an alanine, displays a genuine Minute phenotype known to be characteristic of RPG deletions (longer development, low fertility, high lethality, thin and short bristles) whereas the uL11K3Y mutant, in which the lysine 3 codon is replaced by a tyrosine, is unaffected. In agreement, the rate of translation decreases in uL11K3A but not in uL11K3Y. Co-immunoprecipitation experiments show that the interaction between uL11 and the Corto chromodomain is impaired by both mutations. However, Histone Association Assays indicate that the mutant proteins still bind chromatin. RNA-seq analyses from wing imaginal discs show that Corto represses RPG expression whereas very few genes are deregulated in uL11 mutants. We propose that Corto, by repressing RPG expression, ensures that all ribosomal proteins are present at the correct stoichiometry, and that uL11 fine-tunes its transcriptional regulation of RPGs.

Altering the Temporal Regulation of One Transcription Factor Drives Evolutionary Trade-Offs between Head Sensory Organs.

Size trade-offs of visual versus olfactory organs is a pervasive feature of animal evolution. This could result from genetic or functional constraints. We demonstrate that head sensory organ size trade-offs in Drosophila are genetically encoded and arise through differential subdivision of the head primordium into visual versus non-visual fields. We discover that changes in the temporal regulation of the highly conserved eyeless/Pax6 gene expression during development is a conserved mechanism for sensory trade-offs within and between Drosophila species. We identify a natural single nucleotide polymorphism in the cis-regulatory region of eyeless in a binding site of its repressor Cut that is sufficient to alter its temporal regulation and eye size. Because eyeless/Pax6 is a conserved regulator of head sensory placode subdivision, we propose that its temporal regulation is key to define the relative size of head sensory organs.

Cyclin G and the Polycomb Repressive complexes PRC1 and PR-DUB cooperate for developmental stability.

In Drosophila, ubiquitous expression of a short Cyclin G isoform generates extreme developmental noise estimated by fluctuating asymmetry (FA), providing a model to tackle developmental stability. This transcriptional cyclin interacts with chromatin regulators of the Enhancer of Trithorax and Polycomb (ETP) and Polycomb families. This led us to investigate the importance of these interactions in developmental stability. Deregulation of Cyclin G highlights an organ intrinsic control of developmental noise, linked to the ETP-interacting domain, and enhanced by mutations in genes encoding members of the Polycomb Repressive complexes PRC1 and PR-DUB. Deep-sequencing of wing imaginal discs deregulating CycG reveals that high developmental noise correlates with up-regulation of genes involved in translation and down-regulation of genes involved in energy production. Most Cyclin G direct transcriptional targets are also direct targets of PRC1 and RNAPolII in the developing wing. Altogether, our results suggest that Cyclin G, PRC1 and PR-DUB cooperate for developmental stability.

Drosophila Cyclin G and epigenetic maintenance of gene expression during development.

BACKGROUND: Cyclins and cyclin-dependent kinases (CDKs) are essential for cell cycle regulation and are functionally associated with proteins involved in epigenetic maintenance of transcriptional patterns in various developmental or cellular contexts. Epigenetic maintenance of transcription patterns, notably of Hox genes, requires the conserved Polycomb-group (PcG), Trithorax-group (TrxG), and Enhancer of Trithorax and Polycomb (ETP) proteins, particularly well studied in Drosophila. These proteins form large multimeric complexes that bind chromatin and appose or recognize histone post-translational modifications. PcG genes act as repressors, counteracted by trxG genes that maintain gene activation, while ETPs interact with both, behaving alternatively as repressors or activators. Drosophila Cyclin G negatively regulates cell growth and cell cycle progression, binds and co-localizes with the ETP Corto on chromatin, and participates with Corto in Abdominal-B Hox gene regulation. Here, we address further implications of Cyclin G in epigenetic maintenance of gene expression. RESULTS: We show that Cyclin G physically interacts and extensively co-localizes on chromatin with the conserved ETP Additional sex combs (ASX), belonging to the repressive PR-DUB complex that participates in H2A deubiquitination and Hox gene silencing. Furthermore, Cyclin G mainly co-localizes with RNA polymerase II phosphorylated on serine 2 that is specific to productive transcription. CycG interacts with Asx, PcG, and trxG genes in Hox gene maintenance, and behaves as a PcG gene. These interactions correlate with modified ectopic Hox protein domains in imaginal discs, consistent with a role for Cyclin G in PcG-mediated Hox gene repression. CONCLUSIONS: We show here that Drosophila CycG is a Polycomb-group gene enhancer, acting in epigenetic maintenance of the Hox genes Sex combs reduced (Scr) and Ultrabithorax (Ubx). However, our data suggest that Cyclin G acts alternatively as a transcriptional activator or repressor depending on the developmental stage, the tissue or the target gene. Interestingly, since Cyclin G interacts with several CDKs, Cyclin G binding to the ETPs ASX or Corto suggests that their activity could depend on Cyclin G-mediated phosphorylation. We discuss whether Cyclin G fine-tunes transcription by controlling H2A ubiquitination and transcriptional elongation via interaction with the ASX subunit of PR-DUB.

Drosophila melanogaster Cyclin G coordinates cell growth and cell proliferation.

Mammalian Cyclins G1 and G2 are unconventional cyclins whose role in regulating the cell cycle is ambiguous. Cyclin G1 promotes G2/M cell cycle arrest in response to DNA damage whereas ectopic expression of CCNG2, that encodes Cyclin G2, induces G1/S cell cycle arrest. The only Drosophila Cyclin G was previously shown to be a transcriptional regulator that interacts with the chromatin factor Corto and controls expression of the homeotic gene Abdominal B. It is very close to mammalian Cyclin G1 and G2 except in its N-terminal region, that interacts with Corto, and that seems to have been acquired in dipterans. Ubiquitous misregulation of Cyclin G (CycG) using transgenic lines lengthens development and induces phenotypes suggesting growth or proliferation defects. Using tissue-specific misregulation of CycG and FACS, we show that overproduction of Cyclin G produces small cells whereas shortage produces large cells, suggesting that Cyclin G negatively regulates cell growth. Furthermore, overexpression of CycG lengthens the cell cycle, with a prominent effect on G1 and S phases. Genetic interactions with Cyclin E suggest that Cyclin G prevents G1 to S transition and delays S phase progression. Control of cell growth and cell cycle by Cyclin G might be achieved via interaction with a network of partners, notably the cyclin-dependent kinases CDK4 and CDK2.