Targeting specificity is an essential issue in the development of CRISPR-Cas technology. Using a luciferase activation assay, off-target cleavage activity of sgRNA was systematically investigated on single nucleotide-mismatched targets. In addition to confirming that PAM-proximal mismatches are less tolerated than PAM-distal mismatches, our study further identified a “core” sequence that is highly sensitive to target-mismatch. This sequence is of 4-nucleotide long, located at +4 to +7 position upstream of PAM, and positioned in a steric restriction region when assembled into Cas9 endonuclease. Our study also found that, single or multiple target mismatches at this region abolished off-target cleavage mediated by active sgRNAs, thus proposing a principle for gene-specific sgRNA design. Characterization of a mismatch sensitive “core” sequence not only enhances our understanding of how this elegant system functions, but also facilitates our efforts to improve targeting specificity of a sgRNA.

To explore the editing specificity of CRISPR/Cpf1 system, effects of target mutation were systematically examined using a reporter activation assay, with a set of single-nucleotide mutated target site. Consistent with our previous study performed with CRISPR/Cas9, a "core" sequence region that is highly sensitive to target mutation was characterized. The region is of 4-nucleotide long, located from +4 to +7 position of the target site, and positioned within a positively charged central channel when assembled into Cpf1 endonuclease. Single-nucleotide mutation at the core sequence could abolish gene editing mediated by a however active sgRNA. With a great majority of the target sites, a kind of 'super' off-target gene editing was observed with both CRISPR/Cpf1 and CRISPR/Cas9. For a given target site, mutation at certain positions led to greatly enhanced off-target gene editing efficacy, even up to 10-fold of that of the fully-matched target. Study further found that these effects were determined by the identity of target nucleotide, rather than the nucleotide of crRNA. This likely suggests that the interactions between target nucleotide and the endonuclease are involved in this process.

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As one of the most abundant DNA methylation form in prokaryotes, N 6-methyladenine nucleotide (6 mA) was however only recently identified in eukaryotic genomes. To explore the implications of N 6adenine methylation in adipogenesis, genomic N 6-adenine methylation was examined across adipocyte differentiation stages of 3T3-L1 cells. When the N 6-adenine methylation profiles were analyzed and compared with the levels of gene expression, a positive correlation between the density of promoter 6 mA and gene expression level was uncovered. By means of in vitro methylation and gene knockdown assay, METTL4, a homologue of Drosophila methylase CG14906 and C. elegans methylase DAMT-1, was demonstrated to be a mammalian N 6-adenine methylase that functions in adipogenesis. Knockdown of Mettl4 led to altered adipocyte differentiation, shown by defective gene regulation and impaired lipid production. We also found that the effects of N 6-adenine methylation on lipid production involved the regulation of INSR signaling pathway, which promotes glucose up-taking and lipid production in the terminal differentiation stage.

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During the development of primary Sjögren's syndrome (pSS), aberrant expression of autoantigen is a hallmark event. To explore the regulation of autoantigen tripartite motif containing 21 (Ro/SSA, TRIM21), microRNA profiling was performed in our previous study. In which, two TRIM21-targeting microRNAs were identified, namely miR-1207-5p and miR-4695-3p. To further pursue their roles in the development of pSS, assays were performed with cultured human submandibular gland (HSG) cells, and salivary gland tissues. Results showed that transfection of miR-1207-5p or miR-4695-3p mimics down-regulated not only the expression of TRIM21, but also the levels of proapoptotic genes B cell lymphoma 2 associated X (BAX), Caspase 9 (CASP-9) and Caspase 8 (CASP-8). This finally led to antiapoptotic phenotypes in HSG cells. Consistent with the antiapoptotic activity, transfection of microRNA inhibitors up-regulated the expression of TRIM21 and led to a pro-apoptotic phenotype. These therefore propose miR-1207-5p and miR-4695-3p as two antiapoptotic microRNAs functioning through apoptosis pathway. Supporting this speculation, assays performed with salivary gland tissues revealed down-regulation of miR-1207-5p and miR-4695-3p, as well as up-regulation of TRIM21 and pro-apoptotic CASP-8 gene in pSS samples. Significance of the study: For pSS patients, apoptosis of acinar and ductal epithelial cells has been proposed to be a potential mechanism that impairs the secretion of salivary glands. In our study, two autoantigen-targeting microRNAs were characterized as antiapoptotic microRNAs functioning through apoptosis pathway, which may be potential targets for the treatment of pSS. K E Y W O R D S caspase 8, cell apoptosis, miR-1207-5p, miR-4695-3p, primary Sjögren's syndrome (pSS) 1 | INTRODUCTION Primary Sjögren's syndrome is a chronic inflammatory autoimmune disease, that is, characterized by lymphocytic infiltration of salivary and lachrymal glands. During the development of the disease, aberrant activation of immune system is a hallmark event. 1-3 This often leads to hypergammaglobulinemia in pSS patients, showing by increased circulating autoantibodies. 4 Among them, anti-Ro/SSA (TRIM21) and anti-La/SSB antibodies are the two most representative molecules. 2 Being an major index in disease diagnosis, 5 production of autoantibodies is proposed to be an antigen-driven event. 3 Another hallmark in pSS development is the leukocytes infiltration of the exocrine glands. This leads to abnormal apoptosis of tissue cells and end up with autoimmune lesions. 6-8 Apoptosis is a mechanism of programmed cell death and featured by distinct morphological changes and gene regulation profile. 9 In which process, two major apoptotic pathways have been characterized, namely extrinsic and intrinsic pathway. 10 In the extrinsic pathway, the assembly of Fas cell surface death receptor (FAS), FAS ligand (FASL), FASassociated death domain protein (FADD) and pro-caspase 8 leads to the

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