5-Hydroxymethylcytosine

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Contents

5-Hydroxymethylcytosine
Hydroxymethylcytosine.png
5-Hydroxymethylcytosine-3D-balls.png
Names
Preferred IUPAC name
4-Amino-5-(hydroxymethyl)pyrimidin-2(1H)-one
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
PubChem CID
UNII
  • InChI=1S/C5H7N3O2/c6-4-3(2-9)1-7-5(10)8-4/h1,9H,2H2,(H3,6,7,8,10) Yes check.svgY
    Key: RYVNIFSIEDRLSJ-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C5H7N3O2/c6-4-3(2-9)1-7-5(10)8-4/h1,9H,2H2,(H3,6,7,8,10)
    Key: RYVNIFSIEDRLSJ-UHFFFAOYAT
  • C1=NC(=O)NC(=C1CO)N
  • O=C1/N=C\C(=C(\N)N1)CO
Properties
C5H7N3O2
Molar mass 141.13 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

5-Hydroxymethylcytosine (5hmC) is a DNA pyrimidine nitrogen base derived from cytosine. It is potentially important in epigenetics, because the hydroxymethyl group on the cytosine can possibly switch a gene on and off. It was first seen in bacteriophages in 1952. [1] [2] However, in 2009 it was found to be abundant in human and mouse brains, [3] as well as in embryonic stem cells. [4] In mammals, it can be generated by oxidation of 5-methylcytosine, a reaction mediated by TET enzymes.

Localization

Every mammalian cell seems to contain 5-Hydroxymethylcytosine, but the levels vary significantly depending on the cell type. The highest levels are found in neuronal cells of the central nervous system. [5] [6] [7] The amount of hydroxymethylcytosine increases with age, as shown in mouse hippocampus and cerebellum. [5] [8]

Function

The exact function of this nitrogen base is still not fully elucidated, but it is thought that it may regulate gene expression or prompt DNA demethylation. This hypothesis is supported by the fact that artificial DNA that contains 5-hydroxymethylcytosines (5hmC) can be converted into unmodified cytosines once introduced into mammalian cells. [9] Moreover, 5hmC is highly enriched in primordial germ cells, where it apparently plays a role in global DNA demethylation. [10] Additionally, 5-Formylcytosine, an oxidation product of 5-Hydroxymethylcytosine and possible intermediate of an oxidative demethylation pathway was detected in DNA from embryonic stem cells, [11] although no significant amounts of these putative demethylation intermediates could be detected in mouse tissue. [7] 5-Hydroxymethylcytosine may be especially important in the central nervous system, as it is found in very high levels there. [7] Reduction in the 5-Hydroxymethylcytosine levels have been found associated with impaired self-renewal in embryonic stem cells. [12] 5-Hydroxymethylcytosine is also associated with labile, unstable nucleosomes which are frequently repositioned during cell differentiation. [13]

The accumulation of 5-hydroxymethylcytosine (5hmC) in post-mitotic neurons is associated with “functional demethylation” that facilitates transcription and gene expression. [14] The term “demethylation,” as applied to neurons, ordinarily refers to the replacement of 5-methylcytosine (5mC) by cytosine in DNA that can occur through a series of reactions involving a TET enzyme as well as enzymes of the DNA base excision repair pathway (see Epigenetics in learning and memory). “Demethylation” of 5mC in DNA most often results in the promotion of expression of genes with neuronal activities. “Functional demethylation” refers to the replacement of 5mC by 5hmC, ordinarily a single-step TET-mediated reaction, that also facilitates gene expression, an effect similar to that of “demethylation.”

Bacteria and phages

Phages probably evolved to use 5hmC to avoid recognition by most restriction enzymes in bacteria. The T4 phage uses 5hmC exclusively during replication, adding glycosylation to the hydroxyl group to further complicate the moiety. [15] Some bacteria have in turn evolved restriction enzymes specific for sites containing 5hmC. One prominent example is PvuRts1I, originally identified in 1994. [16]

5hmC in T4 is produced by genome protein 42, deoxycytidylate 5-hydroxymethyltransferase ( P08773 ; EC 2.1.2.8). The glycosylation reactions are known as EC 2.4.1.26, EC 2.4.1.27, and EC 2.4.1.28.

History

5-Hydroxymethylcytosine was observed by Skirmantas Kriaucionis, an associate at the Heintz lab, who was looking for levels of 5-methylcytosine in two different neuron types. He discovered a significant amount of an unknown substance instead, and after conducting several tests, identified it as being 5-hydroxymethylcytosine. [17]

The lab of L. Aravind used bioinformatic tools to predict that the Tet family of enzymes would likely oxidize 5-methylcytosine to 5-hydroxymethylcytosine. [18] This was demonstrated in vitro and in live human and mouse cells by scientists working in the labs of Anjana Rao and David R. Liu.

5-Hydroxymethylcytosine was originally observed in mammals in 1972 by R. Yura, [19] but this initial finding is dubious. Yura found 5-hmC present at extremely high levels in rat brain and liver, completely supplanting 5-methylcytosine. This contradicts all research conducted on mammalian DNA composition conducted before and since, including the Heintz and Rao papers, and another group was unable to reproduce Yura's result. [20]

With the discovery of 5-hydroxymethylcytosine some concerns have been raised regarding DNA methylation studies using the bisulfite sequencing technique. [21] 5-hydroxymethylcytosine has been shown to behave like its precursor, 5-methylcytosine, in bisulfite conversion experiments. [22] Therefore, bisulfite sequencing data may need to be revisited to verify whether the detected modified base is 5-methylcytosine or 5-hydroxymethylcytosine. In 2012 the lab of Chuan He discovered a method to solve the problems of 5-hydroxymethylcytosine being detected as 5-methylcytosine in normal bisulfite conversion experiments using the oxidative properties of the Tet-family of enzymes, this method has been termed TAB-seq. [23] [24]

In June 2020, Oxford Nanopore added a hydroxymethyl cytosine detection model to their research basecaller, rerio, allowing old signal-level data from any R9+ nanopore runs to be re-called to identify 5hmC. [25]

Related Research Articles

<span class="mw-page-title-main">Epigenetics</span> Study of DNA modifications that do not change its sequence

In biology, epigenetics is the study of heritable traits, or a stable change of cell function, that happen without changes to the DNA sequence. The Greek prefix epi- in epigenetics implies features that are "on top of" or "in addition to" the traditional genetic mechanism of inheritance. Epigenetics usually involves a change that is not erased by cell division, and affects the regulation of gene expression. Such effects on cellular and physiological phenotypic traits may result from environmental factors, or be part of normal development. Epigenetic factors can also lead to cancer.

<span class="mw-page-title-main">5-Methylcytosine</span> Chemical compound which is a modified DNA base

5-Methylcytosine is a methylated form of the DNA base cytosine (C) that regulates gene transcription and takes several other biological roles. When cytosine is methylated, the DNA maintains the same sequence, but the expression of methylated genes can be altered. 5-Methylcytosine is incorporated in the nucleoside 5-methylcytidine.

<span class="mw-page-title-main">CpG site</span> Region of often-methylated DNA with a cytosine followed by a guanine

The CpG sites or CG sites are regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases along its 5' → 3' direction. CpG sites occur with high frequency in genomic regions called CpG islands.

A regulatory sequence is a segment of a nucleic acid molecule which is capable of increasing or decreasing the expression of specific genes within an organism. Regulation of gene expression is an essential feature of all living organisms and viruses.

<span class="mw-page-title-main">DNA methyltransferase</span> Class of enzymes

In biochemistry, the DNA methyltransferase family of enzymes catalyze the transfer of a methyl group to DNA. DNA methylation serves a wide variety of biological functions. All the known DNA methyltransferases use S-adenosyl methionine (SAM) as the methyl donor.

<span class="mw-page-title-main">Germline</span> Population of a multicellular organisms cells that pass on their genetic material to the progeny

In biology and genetics, the germline is the population of a multicellular organism's cells that develop into germ cells. In other words, they are the cells that form gametes, which can come together to form a zygote. They differentiate in the gonads from primordial germ cells into gametogonia, which develop into gametocytes, which develop into the final gametes. This process is known as gametogenesis.

<span class="mw-page-title-main">DNA methylation</span> Biological process

DNA methylation is a biological process by which methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene promoter, DNA methylation typically acts to repress gene transcription. In mammals, DNA methylation is essential for normal development and is associated with a number of key processes including genomic imprinting, X-chromosome inactivation, repression of transposable elements, aging, and carcinogenesis.

In biology, reprogramming refers to erasure and remodeling of epigenetic marks, such as DNA methylation, during mammalian development or in cell culture. Such control is also often associated with alternative covalent modifications of histones.

DNA oxidation is the process of oxidative damage of deoxyribonucleic acid. As described in detail by Burrows et al., 8-oxo-2'-deoxyguanosine (8-oxo-dG) is the most common oxidative lesion observed in duplex DNA because guanine has a lower one-electron reduction potential than the other nucleosides in DNA. The one electron reduction potentials of the nucleosides are guanine 1.29, adenine 1.42, cytosine 1.6 and thymine 1.7. About 1 in 40,000 guanines in the genome are present as 8-oxo-dG under normal conditions. This means that >30,000 8-oxo-dGs may exist at any given time in the genome of a human cell. Another product of DNA oxidation is 8-oxo-dA. 8-oxo-dA occurs at about 1/10 the frequency of 8-oxo-dG. The reduction potential of guanine may be reduced by as much as 50%, depending on the particular neighboring nucleosides stacked next to it within DNA.

<span class="mw-page-title-main">Bisulfite sequencing</span> Lab procedure detecting 5-methylcytosines in DNA

Bisulfitesequencing (also known as bisulphite sequencing) is the use of bisulfite treatment of DNA before routine sequencing to determine the pattern of methylation. DNA methylation was the first discovered epigenetic mark, and remains the most studied. In animals it predominantly involves the addition of a methyl group to the carbon-5 position of cytosine residues of the dinucleotide CpG, and is implicated in repression of transcriptional activity.

<span class="mw-page-title-main">DNA demethylation</span> Removal of a methyl group from one or more nucleotides within a DNA molecule.

For molecular biology in mammals, DNA demethylation causes replacement of 5-methylcytosine (5mC) in a DNA sequence by cytosine (C). DNA demethylation can occur by an active process at the site of a 5mC in a DNA sequence or, in replicating cells, by preventing addition of methyl groups to DNA so that the replicated DNA will largely have cytosine in the DNA sequence.

<span class="mw-page-title-main">8-Oxo-2'-deoxyguanosine</span> Chemical compound

8-Oxo-2'-deoxyguanosine (8-oxo-dG) is an oxidized derivative of deoxyguanosine. 8-Oxo-dG is one of the major products of DNA oxidation. Concentrations of 8-oxo-dG within a cell are a measurement of oxidative stress.

While the cellular and molecular mechanisms of learning and memory have long been a central focus of neuroscience, it is only in recent years that attention has turned to the epigenetic mechanisms behind the dynamic changes in gene transcription responsible for memory formation and maintenance. Epigenetic gene regulation often involves the physical marking of DNA or associated proteins to cause or allow long-lasting changes in gene activity. Epigenetic mechanisms such as DNA methylation and histone modifications have been shown to play an important role in learning and memory.

<span class="mw-page-title-main">Tet methylcytosine dioxygenase 1</span> Mammalian protein found in Homo sapiens

Ten-eleven translocation methylcytosine dioxygenase 1 (TET1) is a member of the TET family of enzymes, in humans it is encoded by the TET1 gene. Its function, regulation, and utilizable pathways remain a matter of current research while it seems to be involved in DNA demethylation and therefore gene regulation.

<span class="mw-page-title-main">Tet methylcytosine dioxygenase 2</span> Human gene

Tet methylcytosine dioxygenase 2 (TET2) is a human gene. It resides at chromosome 4q24, in a region showing recurrent microdeletions and copy-neutral loss of heterozygosity (CN-LOH) in patients with diverse myeloid malignancies.

<span class="mw-page-title-main">Ventricular zone</span> Transient embryonic layer of tissue containing neural stem cells

In vertebrates, the ventricular zone (VZ) is a transient embryonic layer of tissue containing neural stem cells, principally radial glial cells, of the central nervous system (CNS). The VZ is so named because it lines the ventricular system, which contains cerebrospinal fluid (CSF). The embryonic ventricular system contains growth factors and other nutrients needed for the proper function of neural stem cells. Neurogenesis, or the generation of neurons, occurs in the VZ during embryonic and fetal development as a function of the Notch pathway, and the newborn neurons must migrate substantial distances to their final destination in the developing brain or spinal cord where they will establish neural circuits. A secondary proliferative zone, the subventricular zone (SVZ), lies adjacent to the VZ. In the embryonic cerebral cortex, the SVZ contains intermediate neuronal progenitors that continue to divide into post-mitotic neurons. Through the process of neurogenesis, the parent neural stem cell pool is depleted and the VZ disappears. The balance between the rates of stem cell proliferation and neurogenesis changes during development, and species from mouse to human show large differences in the number of cell cycles, cell cycle length, and other parameters, which is thought to give rise to the large diversity in brain size and structure.

<span class="mw-page-title-main">Whole genome bisulfite sequencing</span>

Whole genome bisulfite sequencing is a next-generation sequencing technology used to determine the DNA methylation status of single cytosines by treating the DNA with sodium bisulfite before high-throughput DNA sequencing. The DNA methylation status at various genes can reveal information regarding gene regulation and transcriptional activities. This technique was developed in 2009 along with reduced representation bisulfite sequencing after bisulfite sequencing became the gold standard for DNA methylation analysis.

<span class="mw-page-title-main">Tet methylcytosine dioxygenase 3</span> Protein-coding gene in the species Homo sapiens

Tet methylcytosine dioxygenase 3 is a protein that in humans is encoded by the TET3 gene.

<span class="mw-page-title-main">TET enzymes</span> Family of translocation methylcytosine dioxygenases

The TET enzymes are a family of ten-eleven translocation (TET) methylcytosine dioxygenases. They are instrumental in DNA demethylation. 5-Methylcytosine is a methylated form of the DNA base cytosine (C) that often regulates gene transcription and has several other functions in the genome.

<span class="mw-page-title-main">5-Formylcytosine</span> Chemical compound

5-Formylcytosine (5fC) is a pyrimidine nitrogen base derived from cytosine. In the context of nucleic acid chemistry and biology, it is regarded as an epigenetic marker. Discovered in 2011 in mammalian embryonic stem cells by Thomas Carell's research group the modified nucleoside was more recently confirmed to be relevant both as an intermediate in the active demethylation pathway and as a standalone epigenetic marker. In mammals, 5fC is formed by oxidation of 5-Hydroxymethylcytosine (5hmC) a reaction mediated by TET enzymes. Its molecular formula is C5H5N3O2.

References

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  5. 1 2 Münzel M, et al. (July 2010). "Quantification of the Sixth DNA Base Hydroxymethylcytosine in the Brain". Angew. Chem. Int. Ed. 49 (31): 5375–5377. doi:10.1002/anie.201002033. PMID   20583021.
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  11. ↑ Pfaffeneder T, Hackner B, Truss M, Münzel M, Müller M, Deiml CA, Hagemeier C, Carell T (30 June 2011). "The Discovery of 5-Formylcytosine in Embryonic Stem Cell DNA". Angew. Chem. Int. Ed. 50 (31): 7008–7012. doi:10.1002/anie.201103899. PMID   21721093.
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  22. ↑ Jin SG et al. (Jun 2010) "Examination of the specificity of DNA methylation profiling techniques towards 5-methylcytosine and 5-hydroxymethylcytosine." Nucleic Acids Res. 2010 Jun 1;38(11):e125
  23. ↑ Yu M, Hon GC, Szulwach KE, Song CX, Zhang L, Kim A, Li XK, Dai Q, Shen Y, Park B, Min JH, Jin P, Ren B, He C (June 2012). "Base-resolution analysis of 5-hydroxymethylcytosine in the mammalian genome". Cell. 149 (6): 1368–1380. doi:10.1016/j.cell.2012.04.027. PMC   3589129 . PMID   22608086.
  24. ↑ Song CX, Szulwach KE, Fu Y, Dai Q, Yi C, Li X, Li Y, Chen CH, Zhang W, Jian X, Wang J, Zhang L, Looney TJ, Zhang B, Godley LA, Hicks LM, Lahn BT, Jin P, He C (2011). "Selective chemical labeling reveals the genome-wide distribution of 5-hydroxymethylcytosine". Nat. Biotechnol. 29 (1): 68–72. doi:10.1038/nbt.1732. PMC   3107705 . PMID   21151123.
  25. ↑ "Added CpG (min, prom, and min 5mC+5hmC) models and some minor cleanup". nanoporetech / rerio. GitHub. Retrieved 18 June 2020.

See also

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