Martin Bachman

BACKGROUND: DNA methylation (5mC) plays important roles in epigenetic regulation of genome function. Recently, TET hydroxylases have been found to oxidise 5mC to hydroxymethylcytosine (5hmC), formylcytosine (5fC) and carboxylcytosine (5caC) in DNA. These derivatives have a role in demethylation of DNA but in addition may have epigenetic signaling functions in their own right. A recent study identified proteins which showed preferential binding to 5-methylcytosine (5mC) and its oxidised forms, where readers for 5mC and 5hmC showed little overlap, and proteins bound to further oxidation forms were enriched for repair proteins and transcription regulators. We extend this study by using promoter sequences as baits and compare protein binding patterns to unmodified or modified cytosine using DNA from mouse embryonic stem cell extracts. RESULTS: We compared protein enrichments from two DNA probes with different CpG composition and show that, whereas some of the enriched proteins show specificity to cytosine modifications, others are selective for both modification and target sequences. Only a few proteins were identified with a preference for 5hmC (such as RPL26, PRP8 and the DNA mismatch repair protein MHS6), but proteins with a strong preference for 5fC were more numerous, including transcriptional regulators (FOXK1, FOXK2, FOXP1, FOXP4 and FOXI3), DNA repair factors (TDG and MPG) and chromatin regulators (EHMT1, L3MBTL2 and all components of the NuRD complex). CONCLUSIONS: Our screen has identified novel proteins that bind to 5fC in genomic sequences with different CpG composition and suggests they regulate transcription and chromatin, hence opening up functional investigations of 5fC readers.

Phenotypic plasticity is important in adaptation and shapes the evolution of organisms. However, we understand little about what aspects of the genome are important in facilitating plasticity. Eusocial insect societies produce plastic phenotypes from the same genome, as reproductives (queens) and nonreproductives (workers). The greatest plasticity is found in the simple eusocial insect societies in which individuals retain the ability to switch between reproductive and nonreproductive phenotypes as adults. We lack comprehensive data on the molecular basis of plastic phenotypes. Here, we sequenced genomes, microRNAs (miRNAs), and multiple transcriptomes and methylomes from individual brains in a wasp (Polistes canadensis) and an ant (Dinoponera quadriceps) that live in simple eusocial societies. In both species, we found few differences between phenotypes at the transcriptional level, with little functional specialization, and no evidence that phenotype-specific gene expression is driven by DNA methylation or miRNAs. Instead, phenotypic differentiation was defined more subtly by nonrandom transcriptional network organization, with roles in these networks for both conserved and taxon-restricted genes. The general lack of highly methylated regions or methylome patterning in both species may be an important mechanism for achieving plasticity among phenotypes during adulthood. These findings define previously unidentified hypotheses on the genomic processes that facilitate plasticity and suggest that the molecular hallmarks of social behavior are likely to differ with the level of social complexity.