Citrullination Was Introduced into Animals by Horizontal Gene Transfer from Cyanobacteria.

Protein posttranslational modifications add great sophistication to biological systems. Citrullination, a key regulatory mechanism in human physiology and pathophysiology, is enigmatic from an evolutionary perspective. Although the citrullinating enzymes peptidylarginine deiminases (PADIs) are ubiquitous across vertebrates, they are absent from yeast, worms, and flies. Based on this distribution PADIs were proposed to have been horizontally transferred, but this has been contested. Here, we map the evolutionary trajectory of PADIs into the animal lineage. We present strong phylogenetic support for a clade encompassing animal and cyanobacterial PADIs that excludes fungal and other bacterial homologs. The animal and cyanobacterial PADI proteins share functionally relevant primary and tertiary synapomorphic sequences that are distinct from a second PADI type present in fungi and actinobacteria. Molecular clock calculations and sequence divergence analyses using the fossil record estimate the last common ancestor of the cyanobacterial and animal PADIs to be less than 1 billion years old. Additionally, under an assumption of vertical descent, PADI sequence change during this evolutionary time frame is anachronistically low, even when compared with products of likely endosymbiont gene transfer, mitochondrial proteins, and some of the most highly conserved sequences in life. The consilience of evidence indicates that PADIs were introduced from cyanobacteria into animals by horizontal gene transfer (HGT). The ancestral cyanobacterial PADI is enzymatically active and can citrullinate eukaryotic proteins, suggesting that the PADI HGT event introduced a new catalytic capability into the regulatory repertoire of animals. This study reveals the unusual evolution of a pleiotropic protein modification.

Allele-specific suppression in Caenorhabditis elegans reveals details of EMS mutagenesis and a possible moonlighting interaction between the vesicular acetylcholine transporter and ERD2 receptors.

A missense mutant, unc-17(e245), which affects the Caenorhabditis elegans vesicular acetylcholine transporter UNC-17, has a severe uncoordinated phenotype, allowing efficient selection of dominant suppressors that revert this phenotype to wild-type. Such selections permitted isolation of numerous suppressors after EMS (ethyl methanesulfonate) mutagenesis, leading to demonstration of delays in mutation fixation after initial EMS treatment, as has been shown in T4 bacteriophage but not previously in eukaryotes. Three strong dominant extragenic suppressor loci have been defined, all of which act specifically on allele e245, which causes a G347R mutation in UNC-17. Two of the suppressors (sup-1 and sup-8/snb-1) have previously been shown to encode synaptic proteins able to interact directly with UNC-17. We found that the remaining suppressor, sup-2, corresponds to a mutation in erd-2.1, which encodes an endoplasmic reticulum retention protein; sup-2 causes a V186E missense mutation in transmembrane helix 7 of ERD-2.1. The same missense change introduced into the redundant paralogous gene erd-2.2 also suppressed unc-17(e245). Suppression presumably occurred by compensatory charge interactions between transmembrane helices of UNC-17 and ERD-2.1 or ERD-2.2, as previously proposed in work on suppression by SUP-1(G84E) or SUP-8(I97D)/synaptobrevin. erd-2.1(V186E) homozygotes were fully viable, but erd-2.1(V186E); erd-2.2(RNAi) exhibited synthetic lethality [like erd-2.1(RNAi); erd-2.2(RNAi)], indicating that the missense change in ERD-2.1 impairs its normal function in the secretory pathway but may allow it to adopt a novel moonlighting function as an unc-17 suppressor.

H3K27 modifiers regulate lifespan in C. elegans in a context-dependent manner.

BACKGROUND: Evidence of global heterochromatin decay and aberrant gene expression in models of physiological and premature ageing have long supported the "heterochromatin loss theory of ageing", which proposes that ageing is aetiologically linked to, and accompanied by, a progressive, generalised loss of repressive epigenetic signatures. However, the remarkable plasticity of chromatin conformation suggests that the re-establishment of such marks could potentially revert the transcriptomic architecture of animal cells to a "younger" state, promoting longevity and healthspan. To expand our understanding of the ageing process and its connection to chromatin biology, we screened an RNAi library of chromatin-associated factors for increased longevity phenotypes. RESULTS: We identified the lysine demethylases jmjd-3.2 and utx-1, as well as the lysine methyltransferase mes-2 as regulators of both lifespan and healthspan in C. elegans. Strikingly, we found that both overexpression and loss of function of jmjd-3.2 and utx-1 are all associated with enhanced longevity. Furthermore, we showed that the catalytic activity of UTX-1, but not JMJD-3.2, is critical for lifespan extension in the context of overexpression. In attempting to reconcile the improved longevity associated with both loss and gain of function of utx-1, we investigated the alternative lifespan pathways and tissue specificity of longevity outcomes. We demonstrated that lifespan extension caused by loss of utx-1 function is daf-16 dependent, while overexpression effects are partially independent of daf-16. In addition, lifespan extension was observed when utx-1 was knocked down or overexpressed in neurons and intestine, whereas in the epidermis, only knockdown of utx-1 conferred improved longevity. CONCLUSIONS: We show that the regulation of longevity by chromatin modifiers can be the result of the interaction between distinct factors, such as the level and tissue of expression. Overall, we suggest that the heterochromatin loss model of ageing may be too simplistic an explanation of organismal ageing when molecular and tissue-specific effects are taken into account.