Isolation and characterization of the cDNA encoding human DNA methyltransferase

Abstract

We have cloned a series of overlapping cDNA clones encoding a 5194 bp transcript for human DNA methyltransferase (DNA MTase). This sequence potentially codes for a protein of 1495 amino acids with a predicted molecular weight of 169 kDa. The human DNA MTase cDNA has eighty percent homology at the nucleotide level, and the predicted protein has seventy-four percent identity at the amino acid level, to the DNA MTase cDNA cloned from mouse cells. Like the murine DNA MTase, the amino terminal two-thirds of the human protein contains a cysteine-rich region suggestive of a metal-binding domain. The carboxy terminal one-third of the protein shows considerable similarity to prokaryotic (cytosine-5)-methyltransferases. The arrangement of multiple motifs conserved in the prokaryotic genes is preserved in the human DNA MTase, including the relative position of a proline-cysteine dipeptide thought to be an essential catalytic site in all (cytosine-5)-methyltransferases. A single 5.2 kb transcript was detected in all human tissues tested, with the highest levels of expression observed in RNA from placenta, brain, heart and lung. DNA MTase cDNA clones were used to screen a chromosome 19 genomic cosmid library. The DNA MTase-positive cosmids which are estimated to span a genomic distance of 93 kb have been localized to 19p13.2-p13.3 by fluorescence in situ hybridization. Isolation of the cDNA for human DNA MTase will allow further study of the regulation of DNA MTase expression, and of the role of this enzyme in establishing DNA methylation patterns in both normal and neoplastic cells.

Selective epigenetic alteration of layer I GABAergic neurons isolated from prefrontal cortex of schizophrenia patients using laser-assisted microdissection

“…[3][4][5][6] However, previous studies have reported that adult mammalian brains, which mainly consist of postmitotic, terminally differentiated neurons and glial cells, express high levels of DNMT1 mRNA and enzyme activity. [7][8][9] In recent in situ and immunohistochemical studies of DNMT1 cellular localization in adult human brains, we provided evidence that DNMT1 is below the limit of detection in cortical pyramidal neurons and in glial cells, but is expressed at unexpectedly high levels in cortical GABAergic interneurons. 10,11 As cortical GABAergic neurons are postmitotic, terminally differentiated cells, the observation that these neurons express relatively high levels of DNMT1 mRNA and protein suggests that in these cells, DNMT1 possesses additional functions beyond the maintenance of DNA methylation at replication foci.…”

“…The human DNMT1 gene maps to chromosome 19p13.2 7 and linkage studies only weakly implicate markers spanning this chromosome region as susceptibility factors in schizophrenia vulnerability. 57 This, and the fact that in the cortex the overexpression of DNMT1 mRNA is restricted to only certain subsets of GABAergic neurons, makes a DNMT1 DNA sequence mutation as the cause of an alteration of DNMT1 transcription an unlikely possibility.…”

Involvement of DNMT3B in the pathogenesis of Hirschsprung disease and its possible role as a regulator of neurogenesis in the human enteric nervous system

“…For instance, failure to appropriately repress genes has been related to many human diseases, including neurodevelopmental disorders and cancer. 14,15 DNA methylation patterns are established by three independent DNA methyltransferases-DNMT1, DNMT3A, and DNMT3B 16,17 -known to be necessary during neural progenitor cell development. [18][19][20] DNMT1 is mainly implicated in Purpose: Hirschsprung disease (OMIM 142623) is a neurocristopathy attributed to a failure of cell proliferation or migration and/or failure of the enteric precursors along the gut to differentiate during embryonic development.…”

Human maintenance DNA (cytosine-5)-methyltransferase and p53 modulate expression of p53-repressed promoters

“…DNA methylation in the mammalian genome takes place exclusively at the cytosine bases in CpG dinucleotides. Three known classes of catalytically active DNA (cytosine-5)-methyltransferases (DNMTs), DNMT1, DNMT3a, and DNMT3b, have been cloned and characterized (1)(2)(3). DNMT1 methylates the daughter strands of newly replicated nuclear DNA to preserve the parental methylation pattern.…”