The SRA domain of UHRF1 flips 5-methylcytosine out of the DNA helix.

Maintenance methylation of hemimethylated CpG dinucleotides at DNA replication forks is the key to faithful mitotic inheritance of genomic methylation patterns. UHRF1 (ubiquitin-like, containing PHD and RING finger domains 1) is required for maintenance methylation by interacting with DNA nucleotide methyltransferase 1 (DNMT1), the maintenance methyltransferase, and with hemimethylated CpG, the substrate for DNMT1 (refs 1 and 2). Here we present the crystal structure of the SET and RING-associated (SRA) domain of mouse UHRF1 in complex with DNA containing a hemimethylated CpG site. The DNA is contacted in both the major and minor grooves by two loops that penetrate into the middle of the DNA helix. The 5-methylcytosine has flipped completely out of the DNA helix and is positioned in a binding pocket with planar stacking contacts, Watson-Crick polar hydrogen bonds and van der Waals interactions specific for 5-methylcytosine. Hence, UHRF1 contains a previously unknown DNA-binding module and is the first example of a non-enzymatic, sequence-specific DNA-binding protein domain to use the base flipping mechanism to interact with DNA.

Conservation and divergence of methylation patterning in plants and animals.

Cytosine DNA methylation is a heritable epigenetic mark present in many eukaryotic organisms. Although DNA methylation likely has a conserved role in gene silencing, the levels and patterns of DNA methylation appear to vary drastically among different organisms. Here we used shotgun genomic bisulfite sequencing (BS-Seq) to compare DNA methylation in eight diverse plant and animal genomes. We found that patterns of methylation are very similar in flowering plants with methylated cytosines detected in all sequence contexts, whereas CG methylation predominates in animals. Vertebrates have methylation throughout the genome except for CpG islands. Gene body methylation is conserved with clear preference for exons in most organisms. Furthermore, genes appear to be the major target of methylation in Ciona and honey bee. Among the eight organisms, the green alga Chlamydomonas has the most unusual pattern of methylation, having non-CG methylation enriched in exons of genes rather than in repeats and transposons. In addition, the Dnmt1 cofactor Uhrf1 has a conserved function in maintaining CG methylation in both transposons and gene bodies in the mouse, Arabidopsis, and zebrafish genomes.

Bulk Sequencing from mRNA with UMI for Evaluation of B-Cell Isotype and Clonal Evolution: A Method by the AIRR Community.

During the course of an immune response to a virus such as influenza, B cells undergo activation, clonal expansion, isotype switching, and somatic hypermutation (SHM). Members of an antigen-experienced B-cell clone can have different sequence features including SHM in the immunoglobulin heavy-chain V (IGHV) gene and can use the same IGVH gene in combination with different constant regions or isotypes (e.g., IgM, IgG, IgA). To study these features of expanded clones in an immune response by AIRR-seq, we provide a bulk RNA-based sequencing experimental procedure with unique molecular identifiers (UMIs) and the accompanying bioinformatics analytical workflow.

AIRR Community Guide to Planning and Performing AIRR-Seq Experiments.

The development of high-throughput sequencing of adaptive immune receptor repertoires (AIRR-seq of IG and TR rearrangements) has provided a new frontier for in-depth analysis of the immune system. The last decade has witnessed an explosion in protocols, experimental methodologies, and computational tools. In this chapter, we discuss the major considerations in planning a successful AIRR-seq experiment together with basic strategies for controlling and evaluating the outcome of the experiment. Members of the AIRR Community have authored several chapters in this edition, which cover step-by-step instructions to successfully conduct, analyze, and share an AIRR-seq project.

AXR1-ECR1 and AXL1-ECR1 heterodimeric RUB-activating enzymes diverge in function in Arabidopsis thaliana.

RELATED TO UBIQUITIN (RUB) modification of CULLIN (CUL) subunits of the CUL-RING ubiquitin E3 ligase (CRL) superfamily regulates CRL ubiquitylation activity. RUB modification requires E1 and E2 enzymes that are analogous to, but distinct from, those activities required for UBIQUITIN (UBQ) attachment. Gene duplications are widespread in angiosperms, and in line with this observation, components of the RUB conjugation pathway are found in multiples in Arabidopsis. To further examine the extent of redundancy within the RUB pathway, we undertook biochemical and genetic characterizations of one such duplication event- the duplication of the genes encoding a subunit of the RUB E1 into AUXIN RESISTANT1 (AXR1) and AXR1-LIKE1 (AXL1). In vitro, the two proteins have similar abilities to function with E1 C-TERMINAL-RELATED1 (ECR1) in catalyzing RUB1 activation and RUB1-ECR1 thioester formation. Using mass spectrometry, endogenous AXR1 and AXL1 proteins were found in complex with 3HA-RUB1, suggesting that AXR1 and AXL1 exist in parallel RUB E1 complexes in Arabidopsis. In contrast, AXR1 and AXL1 differ in ability to correct phenotypic defects in axr1-30, a severe loss-of-function AXR1 mutant, when the respective coding sequences are expressed from the same promoter, suggesting differential in vivo functions. These results suggest that while both proteins function in the RUB pathway and are biochemically similar in RUB-ECR1 thioester formation, they are not functionally equivalent.

Biological controls for standardization and interpretation of adaptive immune receptor repertoire profiling.

Use of adaptive immune receptor repertoire sequencing (AIRR-seq) has become widespread, providing new insights into the immune system with potential broad clinical and diagnostic applications. However, like many high-throughput technologies, it comes with several problems, and the AIRR Community was established to understand and help solve them. We, the AIRR Community's Biological Resources Working Group, have surveyed scientists about the need for standards and controls in generating and annotating AIRR-seq data. Here, we review the current status of AIRR-seq, provide the results of our survey, and based on them, offer recommendations for developing AIRR-seq standards and controls, including future work.

The SRA methyl-cytosine-binding domain links DNA and histone methylation.

Epigenetic gene silencing suppresses transposon activity and is critical for normal development . Two common epigenetic gene-silencing marks are DNA methylation and histone H3 lysine 9 dimethylation (H3K9me2). In Arabidopsis thaliana, H3K9me2, catalyzed by the methyltransferase KRYPTONITE (KYP/SUVH4), is required for maintenance of DNA methylation outside of the standard CG sequence context. Additionally, loss of DNA methylation in the met1 mutant correlates with a loss of H3K9me2. Here we show that KYP-dependent H3K9me2 is found at non-CG methylation sites in addition to those rich in CG methylation. Furthermore, we show that the SRA domain of KYP binds directly to methylated DNA, and SRA domains with missense mutations found in loss-of-function kyp mutants have reduced binding to methylated DNA in vitro. These data suggest that DNA methylation is required for the recruitment or activity of KYP and suggest a self-reinforcing loop between histone and DNA methylation. Lastly, we found that SRA domains from two Arabidopsis SRA-RING proteins also bind methylated DNA and that the SRA domains from KYP and SRA-RING proteins prefer methylcytosines in different sequence contexts. Hence, unlike the methyl-binding domain (MBD), which binds only methylated-CpG sequences, the SRA domain is a versatile new methyl-DNA-binding motif.

ORTH/VIM proteins that regulate DNA methylation are functional ubiquitin E3 ligases.

Appropriate methylation of genomes is essential for gene regulation. Here, we describe the six-member ORTHRUS (ORTH) gene family of Arabidopsis thaliana that plays a role in DNA methylation in vivo. ORTH1- ORTH5 are predicted to encode proteins that contain one plant homeodomain (PHD), two really interesting new gene (RING) domains, and one set ring associated (SRA) domain, whereas ORTHlike-1 encodes a protein with only one RING and SRA domain. cDNAs for ORTH1, ORTH2, ORTH5 and ORTHlike-1 were isolated, and when expressed as glutathione-S-transferase (GST) fusion proteins, were capable of promoting ubiquitylation in vitro with the E2 AtUBC11. ORTH1 promotes ubiquitylation when paired with additional AtUBC8 family members. ORTH1 proteins with substitutions in metal-ligand binding residues in each ORTH1 RING domain individually, and ORTH1 truncation derivatives lacking one or both RING domains, were tested for their ability to catalyze ubiquitylation in vitro. In these assays, either ORTH1 RING domain is capable of promoting ubiquitylation. The PHD alone is not active as an E3 ligase, nor is it required for ligase activity. GFP-ORTH1 and GFP-ORTH2 are nuclear-localized in transgenic Arabidopsis plants. Overexpression of ORTH1 or ORTH2 in Arabidopsis leads to an altered flowering time. Inspection of DNA methylation at FWA and Cen180 repeats revealed hypomethylation when ORTH proteins were overexpressed. Once initiated, a late-flowering phenotype persisted in the absence of the ORTH transgene, consistent with epigenetic effects at FWA. We conclude that ORTH proteins are E3 ligases mediating DNA methylation status in vivo.

High-throughput chromatin accessibility profiling at single-cell resolution.

Here we develop a high-throughput single-cell ATAC-seq (assay for transposition of accessible chromatin) method to measure physical access to DNA in whole cells. Our approach integrates fluorescence imaging and addressable reagent deposition across a massively parallel (5184) nano-well array, yielding a nearly 20-fold improvement in throughput (up to ~1800 cells/chip, 4-5 h on-chip processing time) and library preparation cost (~81¢ per cell) compared to prior microfluidic implementations. We apply this method to measure regulatory variation in peripheral blood mononuclear cells (PBMCs) and show robust, de novo clustering of single cells by hematopoietic cell type.

Strand-Specific Transcriptome Sequencing Using SMART Technology.

Next-generation sequencing is empowering a deeper understanding of biology by enabling RNA expression analysis over the entire transcriptome with high sensitivity and a wide dynamic range. One powerful application within this field is stranded RNA sequencing (RNA-seq), which is necessary to distinguish overlapping genes and to conduct comprehensive annotation and quantification of long non-coding RNAs. Commonly used methods for generating strand-specific RNA-seq libraries are often complicated by protocols that require several rounds of enzymatic treatments and clean-up steps, making them time-intensive, insensitive, and unsuitable for processing several samples simultaneously. An additional challenge in the generation of RNA-seq libraries from total RNA involves the high amount of ribosomal RNA (rRNA) in the starting material. This unit presents streamlined workflows for generating strand-specific RNA-seq libraries from 10 ng to 1 µg total RNA, representing a minimum of 1000 cells, in less than 7 hr with minimal carryover rRNA. These methods allow scientists to evaluate the expression of all transcripts, including non-polyadenylated long non-coding RNAs, even in limited biological samples. Combination of the RNase H-based RiboGone rRNA removal system and SMARTer Stranded RNA-seq technology enables depletion of over 95% of rRNA from mammalian samples, and direct production of Illumina-ready libraries that maintain strand-of-origin information. An alternate method for low input of highly degraded samples is also presented. © 2016 by John Wiley & Sons, Inc.

Transcriptome Analysis at the Single-Cell Level Using SMART Technology.

RNA sequencing (RNA-seq) is a powerful method for analyzing cell state, with minimal bias, and has broad applications within the biological sciences. However, transcriptome analysis of seemingly homogenous cell populations may in fact overlook significant heterogeneity that can be uncovered at the single-cell level. The ultra-low amount of RNA contained in a single cell requires extraordinarily sensitive and reproducible transcriptome analysis methods. As next-generation sequencing (NGS) technologies mature, transcriptome profiling by RNA-seq is increasingly being used to decipher the molecular signature of individual cells. This unit describes an ultra-sensitive and reproducible protocol to generate cDNA and sequencing libraries directly from single cells or RNA inputs ranging from 10 pg to 10 ng. Important considerations for working with minute RNA inputs are given. © 2016 by John Wiley & Sons, Inc.

Saccharomyces cerevisiae ubiquitin-like protein Rub1 conjugates to cullin proteins Rtt101 and Cul3 in vivo.

In Saccharomyces cerevisiae, the ubiquitin-like protein Rub1p (related to ubiquitin 1 protein) covalently attaches to the cullin protein Cdc53p (cell division cycle 53 protein), a subunit of a class of ubiquitin E3 ligases named SCF (Skp1-Cdc53-F-box protein) complex. We identified Rtt101p (regulator of Ty transposition 101 protein, where Ty stands for transposon of yeast), initially found during a screen for proteins to confer retrotransposition suppression, and Cul3p (cullin 3 protein), a protein encoded by the previously uncharacterized open reading frame YGR003w, as two new in vivo targets for Rub1p conjugation. These proteins show significant identity with Cdc53p and, therefore, are cullin proteins. Modification of Cul3p is eliminated by deletion of the Rub1p pathway through disruption of either RUB1 or its activating enzyme ENR2 / ULA1. The same disruptions in the Rub pathway decreased the percentage of total Rtt101p that is modified from approx. 60 to 30%. This suggests that Rtt101p has an additional RUB1 - and ENR2 -independent modification. All modified forms of Rtt101p and Cul3p were lost when a single lysine residue in a conserved region near the C-terminus was replaced by an arginine residue. These results suggest that this lysine residue is the site of Rub1p-dependent and -independent modifications in Rtt101p and of Rub1p-dependent modification in Cul3p. An rtt101 Delta strain was hypersensitive to thiabendazole, isopropyl ( N -3-chlorophenyl) carbamate and methyl methanesulphonate, but rub1 Delta strains were not. Whereas rtt101 Delta strains exhibited a 14-fold increase in Ty1 transposition, isogenic rub1 Delta strains did not show statistically significant increases. Rtt101K791Rp, which cannot be modified, complemented for Rtt101p function in a transposition assay. Altogether, these results suggest that neither the RUB1 -dependent nor the RUB1 -independent form of Rtt101p is required for Rtt101p function. The identification of additional Rub1p targets in S. cerevisiae suggests an expanded role for Rub in this organism.

UHRF1 plays a role in maintaining DNA methylation in mammalian cells.

Epigenetic inheritance in mammals relies in part on robust propagation of DNA methylation patterns throughout development. We show that the protein UHRF1 (ubiquitin-like, containing PHD and RING finger domains 1), also known as NP95 in mouse and ICBP90 in human, is required for maintaining DNA methylation. UHRF1 colocalizes with the maintenance DNA methyltransferase protein DNMT1 throughout S phase. UHRF1 appears to tether DNMT1 to chromatin through its direct interaction with DNMT1. Furthermore UHRF1 contains a methyl DNA binding domain, the SRA (SET and RING associated) domain, that shows strong preferential binding to hemimethylated CG sites, the physiological substrate for DNMT1. These data suggest that UHRF1 may help recruit DNMT1 to hemimethylated DNA to facilitate faithful maintenance of DNA methylation.

Arabidopsis has two redundant Cullin3 proteins that are essential for embryo development and that interact with RBX1 and BTB proteins to form multisubunit E3 ubiquitin ligase complexes in vivo.

Cullin-based E3 ubiquitin ligases play important roles in the regulation of diverse developmental processes and environmental responses in eukaryotic organisms. Recently, it was shown in Schizosaccharomyces pombe, Caenorhabditis elegans, and mammals that Cullin3 (CUL3) directly associates with RBX1 and BTB domain proteins in vivo to form a new family of E3 ligases, with the BTB protein subunit functioning in substrate recognition. Here, we demonstrate that Arabidopsis thaliana has two redundant CUL3 (AtCUL3) genes that are essential for embryo development. Besides supporting anticipated specific AtCUL3 interactions with the RING protein AtRBX1 and representative Arabidopsis proteins containing a BTB domain in vitro, we show that AtCUL3 cofractionates and specifically associates with AtRBX1 and a representative BTB protein in vivo. Similar to the AtCUL1 subunit of the SKP1-CUL1-F-box protein-type E3 ligases, the AtCUL3 subunit of the BTB-containing E3 ligase complexes is subjected to modification and possible regulation by the ubiquitin-like protein Related to Ubiquitin in vivo. Together with the presence of large numbers of BTB proteins with diverse structural features and expression patterns, our data suggest that Arabidopsis has conserved AtCUL3-RBX1-BTB protein E3 ubiquitin ligases to target diverse protein substrates for degradation by the ubiquitin/proteasome pathway.

Related to ubiquitin 1 and 2 are redundant and essential and regulate vegetative growth, auxin signaling, and ethylene production in Arabidopsis.

Related to Ubiquitin (RUB)/Nedd8 is a ubiquitin-like protein that covalently attaches to cullins, a subunit of the SCF (for Skp, Cdc53p/Cul1, and F-box protein) complex, an E3 ubiquitin ligase, and has been shown to be required for robust function of the complex. The effects of reducing protein levels for two Rub proteins, RUB1 and RUB2, were characterized in Arabidopsis thaliana. T-DNA insertional null lines homozygous at a single RUB-encoding locus were analyzed and found to have a wild-type phenotype. A double mutant was never recovered. More than one-quarter of the progeny from the self-fertilization of plants with a single functional RUB-encoding gene died as embryos at the two-cell stage. Outcrosses demonstrated reduced inheritance of the null allele from both the male and female parent. Hemigglutinin-tagged forms of RUB1 and RUB2 conjugate to the same cullin protein, CUL1, and produce the same conjugation pattern. To further understand the function of the RUB proteins, a construct designed to produce a double-stranded RUB1 mRNA was introduced into plants, and three lines with reduced levels of RUB1- and RUB2-encoding mRNA and RUB1/2 protein content were analyzed in detail. Mature plants were severely dwarfed, seedlings were insensitive to auxin in root assays, and dark-grown seedlings had a partial triple-response phenotype that was suppressed when seedlings were grown on ethylene perception or synthesis inhibitors. The dsrub lines produced threefold to fivefold more ethylene than the wild type. This study illustrates that RUB1 and RUB2 are genetically and biochemically redundant and demonstrates that RUB1/2 proteins are essential for early embryonic cell divisions and that they regulate diverse processes.