Enzymes catalyzing CpG methylation in DNA, including DNMT1 and DNMT3A/B, are indispensable for mammalian tissue development and homeostasis 1-4. They are also implicated in human developmental disorders and cancers 5-8 , supporting a critical role of DNA methylation during cell fate specification and maintenance. Recent studies suggest that histone posttranslational modifications (PTMs) are involved in specifying patterns of DNMT localization and DNA methylation at promoters and actively transcribed gene bodies 9-11. However, mechanisms governing the establishment and maintenance of intergenic DNA methylation remain poorly understood. Germline mutations in DNMT3A define Tatton-Brown-Rahman syndrome (TBRS), a

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NRMT1 is an N-terminal methyltransferase that methylates histone CENP-A as well as nonhistone substrates. Here, we report the crystal structure of human NRMT1 bound to CENP-A peptide at 1.3 Å. NRMT1 adopts a core methyltransferase fold that resembles DOT1L and PRMT but not SET domain family histone methyltransferases. Key substrate recognition and catalytic residues were identified by mutagenesis studies. Histone peptide profiling revealed that human NRMT1 is highly selective to human CENP-A and fruit fly H2B, which share a common "X aaPro-Lys/Arg" motif. These results, along with a 1.5 Å costructure of human NRMT1 bound to the fruit fly H2B peptide, underscore the importance of the NRMT1 recognition motif.

Drosophila Dscam1 (Down Syndrome Cell Adhesion Molecules) and vertebrate clustered protocadherins (Pcdhs) are two classic examples of the extraordinary isoform diversity from a single genomic locus. Dscam1 encodes 38,016 distinct isoforms via mutually exclusive splicing in D. melanogaster, while the vertebrate clustered Pcdhs utilize alternative promoters to generate isoform diversity. Here we reveal a shortened Dscam gene family with tandemly arrayed 5′ cassettes in Chelicerata. These cassette repeats generally comprise two or four exons, corresponding to variable Immunoglobulin 7 (Ig7) or Ig7–8 domains of Drosophila Dscam1. Furthermore, extraordinary isoform diversity has been generated through a combination of alternating promoter and alternative splicing. These sDscams have a high sequence similarity with Drosophila Dscam1, and share striking organizational resemblance to the 5′ variable regions of vertebrate clustered Pcdhs. Hence, our findings have important implications for understanding the functional similarities between Drosophila Dscam1 and vertebrate Pcdhs, and may provide further mechanistic insights into the regulation of isoform diversity.

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Mutually exclusive splicing is an important means of increasing the protein repertoire, by which the Down's syndrome cell adhesion molecule (Dscam) gene potentially generates 38,016 different isoforms in Drosophila melanogaster. However, the regulatory mechanisms remain obscure due to the complexity of the Dscam exon cluster. Here, we reveal a molecular model for the regulation of the mutually exclusive splicing of the serpent pre-mRNA based on competition between upstream and downstream RNA pairings. Such dual RNA pairings confer fine tuning of the inclusion of alternative exons. Moreover, we demonstrate that the splicing outcome of alternative exons is mediated in relative pairing strength-correlated mode. Combined comparative genomics analysis and experimental evidence revealed similar bidirectional structural architectures in exon clusters 4 and 9 of the Dscam gene. Our findings provide a novel mechanistic framework for the regulation of mutually exclusive splicing and may offer potentially applicable insights into long-range RNA-RNA interactions in gene regulatory networks.

NF-κB is a key player in inflammatory diseases, including multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). However, the effects of NF-κB activation on oligodendrocytes in MS and EAE remain unknown. We generated a mouse model that expresses IκBαΔN, a super-suppressor of NF-κB, specifically in oligodendrocytes and demonstrated that IκBαΔN expression had no effect on oligodendrocytes under normal conditions (both sexes). Interestingly, we showed that oligodendrocyte-specific expression of IκBαΔN blocked NF-κB activation in oligodendrocytes and resulted in exacerbated oligodendrocyte death and hypomyelination in young, developing mice that express IFN-γ ectopically in the CNS (both sexes). We also showed that NF-κB inactivation in oligodendrocytes aggravated IFN-γ-induced remyelinating oligodendrocyte death and remyelination failure in the cuprizone model (male mice). Moreover, we found that NF-κB inactivation in oligodendrocytes increased the susceptibility of mice to EAE (female mice). These findings imply the cytoprotective effects of NF-κB activation on oligodendrocytes in MS and EAE. Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS. NF-κB is a major player in inflammatory diseases that acts by regulating inflammation and cell viability. Data indicate that NF-κB activation in inflammatory cells facilitates the development of MS. However, to date, attempts to understand the role of NF-κB activation in oligodendrocytes in MS have been unsuccessful. Herein, we generated a mouse model that allows for inactivation of NF-κB specifically in oligodendrocytes and then used this model to determine the precise role of NF-κB activation in oligodendrocytes in models of MS. The results presented in this study represent the first demonstration that NF-κB activation acts cell autonomously to protect oligodendrocytes against inflammation in animal models of MS.

A large amount of maternal RNA is deposited in oocytes and is reserved for later development. Control of maternal RNA translation during oocyte maturation has been extensively investigated and its regulatory mechanisms are well documented. However, translational regulation of maternal RNA in early oogenesis is largely unexplored. In this study, we generated zebrafish zar1 mutants that result in early oocyte apoptosis and fully penetrant male development. Loss of p53 suppresses the apoptosis in zar1 mutants and restores oocyte development. zar1 immature ovaries show upregulation of proteins implicated in endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). More importantly, loss of Zar1 causes marked upregulation of zona pellucida (ZP) family proteins, while overexpression of ZP proteins in oocytes causes upregulation of stress-related activating transcription factor 3 (atf3), arguing that tightly controlled translation of ZP proteins is essential for ER homeostasis during early oogenesis. Furthermore, Zar1 binds to ZP gene mRNAs and represses their translation. Together, our results indicate that regulation of translational repression and de-repression are essential for precisely controlling protein expression during early oogenesis.