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Table 1 Functions and expression of human and murine proteins involved in the cytosine methylation/demethylation cycle

From: TET proteins and the control of cytosine demethylation in cancer

Proteins

Functions

Expression levels during development and in embryonic stem cells

Expression levels in adult tissues

Expression levels in adult hematopoiesis

TET1

Oxidization of 5-mC

High in mES cells, low in oocytes and zygotes [2,30,31]

Variable expression [56]

Low [83]

TET2

Oxidization of 5-mC

High in mES cells, low in oocytes and zygotes [2,30,31]

Widely expressed [56]

High [83]

TET3

Oxidization of 5-mC

Low in mES cells, high in oocytes and zygotes [2,30,31]

Limited expression in colon, stomach, adrenal glands and peripheral blood cells [56]

Low [83]

DNMT1

Methylation maintenance during DNA replication

High in early embryonic stages [129]

Ubiquitous [130,131]

Uniform but low in neutrophils [132]

DNMT3A

De novo methylation

High in early embryonic stages [129]

Ubiquitous [130,131]

Uniform but high in T lymphocytes and neutrophils [132]

DNMT3B

De novo methylation

High in later embryonic stages and differentiated cells [129]

Low levels except testis, thyroid and bone marrow [130,131]

Low expression except in human CD34+ cells [132]

AID

Cytidine deamination

High in immature B cells from fetal bone marrow and liver [133]

High in lymph nodes and moderated in spleen and bone marrow [134]

Mainly in activated mature B cells [134]

TDG

Glycosylation and deamination

Ubiquitous from ED 7.5 to 13.5 in mouse, high in central and peripheral nervous system, thymus, lung, liver, kidney, adrenal glands and intestine at ED 14.5 [135]

Mouse aorta [98]

Not reported

IDH1

Isocitrate decarboxylation of citric acid cycle

Not reported

Cytoplasm [92,103]

Not reported

IDH2

Isocitrate decarboxylation of citric acid cycle

Not reported

Mitochondria [92,103]

Not reported

FH

Hydration of fumarate of citric acid cycle

Not reported

Mitochondria [136]

Mature erythrocytes [136]

SDH

Oxidation of succinate of citric acid cycle

Not reported

Mitochondria [136]

Not reported

  1. References listed in this table are based on mouse model studies, except for [56,103,83,130-133]. 5-mC, 5-methylcytosine; AID, activation-induced deaminase; DNMT, DNA methyltransferase; ED, embryonic day; FH, fumarate hydratase; IDH, isocitrate dehydrogenase; mES, murine embryonic stem; SDH, succinate dehydrogenase; TDG, thymine DNA glycosylase; TET, ten-eleven translocation.