Disease relevance of Dnmt3b

• We also show that hypermethylation of genomic DNA by Dnmt3a and Dnmt3b is necessary for ES cells to form teratomas in nude mice [1].
• 2) Dnmt3b-deficient MEF cells showed aneuploidy and polyploidy, chromosomal breaks, and fusions [2].
• Interestingly, many large adenomas showed regions with Dnmt3b inactivation, indicating that Dnmt3b is required for initial outgrowth of macroscopic adenomas but is not required for their maintenance [3].

High impact information on Dnmt3b

• Finally, we show that hypomethylation is associated with reduced levels of the de novo DNA methyltransferases Dnmt3a and Dnmt3b and that ectopic expression of these factors restores global methylation levels [4].
• Inactivation of both Dnmt3a and Dnmt3b, DNA methyltransferases essential for the initiation of de novo DNA methylation, abolished the establishment of DNA methylation and the silencing of Rhox cluster genes in the embryo proper [5].
• The PWWP domain is a weakly conserved sequence motif found in > 60 eukaryotic proteins, including the mammalian DNA methyltransferases Dnmt3a and Dnmt3b [6].
• We also show that recombinant Dnmt3b2 protein (a splice variant of Dnmt3b) and two N-terminal deletion mutants (Delta218 and Delta369) have approximately equal methyl transfer activity on unmethylated and hemimethylated CpG-containing oligonucleotides [6].
• Neither the wild type nor the catalytic site mutant of Dnmt3a or Dnmt3b was sensitive to 5-aza-CdR-mediated degradation [7].

Biological context of Dnmt3b

• To elucidate how DNA methyltransferases (Dnmts) participate in methylation of the genomic components, we investigated the genome-wide DNA methylation pattern of the T-DMRs with Dnmt1-, Dnmt3a-, and/or Dnmt3b-deficient ES cells by restriction landmark genomic scanning (RLGS) [8].
• Dnmt3L, an isoform of Dnmt3a and Dnmt3b, but lacking enzymatic activity, interacts with Dnmt2a and Dnmt3b and is required for spermatogenesis [9].
• Inactivation of both Dnmt3a and Dnmt3b in embryonic stem (ES) cells results in progressive loss of methylation in various repeats and single-copy genes [1].
• The DNA methyltransferases (MTases) Dnmt3a and Dnmt3b are thought to be the sole de novo MTases in the mammalian genome [10].
• To investigate the function of Dnmt3b in mouse development and to create animal models for ICF syndrome, we have generated three mutant alleles of Dnmt3b in mice: one carrying a deletion of the catalytic domain (null allele) and two carrying ICF-like missense mutations in the catalytic domain [11].

Anatomical context of Dnmt3b

• Establishment and maintenance of genomic methylation patterns in mouse embryonic stem cells by Dnmt3a and Dnmt3b [1].
• We have previously shown that the DNA methyltransferases Dnmt3a and Dnmt3b carry out de novo methylation of the mouse genome during early postimplantation development and of maternally imprinted genes in the oocyte [1].
• Inactivation of Dnmt3b in mouse embryonic fibroblasts results in DNA hypomethylation, chromosomal instability, and spontaneous immortalization [2].
• Use of an alternative promoter at the Dnmt3a locus produces the shorter Dnmt3a2 transcript in the germ line and postimplantation embryo only, whereas alternative splicing of the Dnmt3b transcript ensures that Dnmt3b1 is absent in the male prospermatogonia [12].
• Dnmt3a2 and Dnmt3b transcripts were at their highest levels in type A spermatogonia, decreased dramatically in type B spermatogonia and preleptotene spermatocytes and rose again in leptotene/zygotene spermatocytes, while Dnmt3a expression was mostly constant, except in type B spermatogonia where it increased [13].

Associations of Dnmt3b with chemical compounds

• De novo DNA methyltransferases Dnmt3a and Dnmt3b primarily mediate the cytotoxic effect of 5-aza-2'-deoxycytidine [14].
• DNA methyltransferases Dnmt1, Dnmt3a and Dnmt3b cooperatively regulate cytosine methylation in CpG dinucleotides in mammalian genomes, providing an epigenetic basis for gene silencing and maintenance of genome integrity [15].
• Dnmt3a purified through glycerol gradient centrifugation was also associated with a histone H3 methyltransferase (HMTase) activity whereas purified Dnmt3b/Dnmt1 was devoid of any HMTase activity [16].
• Quantitative analysis of genomic cytosine methylation levels demonstrated a robust Dnmt activity for the de novo methyltransferases Dnmt3a and Dnmt3b [17].
• MNB clones overexpressing Dnmt3a or Dnmt3b proteins were resistant to cisplatin treatment (10(-6) M) [18].

Physical interactions of Dnmt3b

• This is the first report on the identification of a few key co-repressors associated with endogenous Dnmt3a and of a complex containing Dnmt3b and a minor form of Dnmt1 following extensive biochemical fractionation [16].

Regulatory relationships of Dnmt3b

• Dnmt3a is expressed in postmitotic young neurons following the Dnmt3b expression [19].

Other interactions of Dnmt3b

• In particular, there are compensatory and cooperative roles between Dnmt3a and Dnmt3b [20].
• 4) The G(1) to S-phase checkpoint was intact in primary and spontaneously immortalized Dnmt3b-deficient MEFs because the p53 protein was inducible by DNA damage [2].
• Interestingly, protein levels of the cyclindependent kinase inhibitor p21 were increased in immortalized Dnmt3b-deficient MEFs even in the absence of p53 induction [2].
• The Dnmt3b null allele results in embryonic lethality from E14.5 to E16.5 with multiple tissue defects, including liver hypotrophy, ventricular septal defect and haemorrhage [11].
• These findings suggest that Dnmtases are differentially expressed in drug resistant murine neuroblastoma cells and overexpression of Dnmtl and Dnmt3b may contribute towards loss of function of the growth regulatory or tumor suppressor genes by methylation of their 'CpG' region and subsequently silencing of their expression [21].

Analytical, diagnostic and therapeutic context of Dnmt3b

• Results of the Western blot, immunofluorescence microscopy, RT-PCR, and quantitative real time RT-PCR analysis demonstrated that Dnmt1 and Dnmt3b expression increased significantly (P < 0.001) in drug resistant cells when compared with wild type cells [21].
• Increased expression of Dnmt3b was observed at days 5 and 14, followed by increased expression of Dnmt1 and Dnmt3a at day 30, as evaluated by real-time RT-PCR [22].
• Complete sequence analysis of the clone demonstrated that Dnmt3b consists of at least 24 exons and spans 38 kilobases [23].
• Assignment of cytosine-5 DNA methyltransferases Dnmt3a and Dnmt3b to mouse chromosome bands 12A2-A3 and 2H1 by in situ hybridization [24].

References