Repression of retrotransposal elements in mouse embryonic stem cells is primarily mediated by a DNA methylation-independent mechanism.
In defense of deleterious retrotransposition of intracisternal A particle (IAP) elements, IAP loci are heavily methylated and silenced in mouse somatic cells. To determine whether IAP is also repressed in pluripotent stem cells by DNA methylation, we examined IAP expression in demethylated mouse embryonic stem cells (mESCs) and epiblast-derived stem cells. Surprisingly, in demethylated ESC cultures carrying mutations of DNA methyltransferase I (Dnmt1), no IAP transcripts and proteins are detectable in undifferentiated Oct4(+) ESCs. In contrast, approximately 3.6% of IAP-positive cells are detected in Oct4(-) Dnmt1(-/-) cells, suggesting that the previously observed increase in IAP transcripts in the population of Dnmt1(-/-) ESCs could be accounted for by this subset of Oct4(-) Dnmt1(-/-) ESCs undergoing spontaneous differentiation. Consistent with this possibility, a dramatic increase of IAP mRNA (>100-fold) and protein expression was observed in Dnmt1(-/-) ESC cultures upon induction of differentiation through the withdrawal of leukemia-inhibitory factor for 6 or more days. Interestingly, both mRNAs and proteins of IAP can be readily detected in demethylated Oct4(+) epiblast-derived stem cells as well as differentiated mouse embryo fibroblasts, neurons, and glia upon conditional Dnmt1 gene deletion. These data suggest that mESCs are a unique stem cell type possessing a DNA methylation-independent IAP repression mechanism. This methylation-independent mechanism does not involve Dicer-mediated action of microRNAs or RNA interference because IAP expression remains repressed in Dnmt1(-/-); Dicer(-/-) double mutant ESCs. We suggest that mESCs possess a unique DNA methylation-independent mechanism to silence retrotransposons to safeguard genome stability while undergoing rapid cell proliferation for self-renewal.
Hutnick
Leah K
LK
Department of Human Genetics, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA.
Huang
Xinhua
X
Loo
Tao-Chuan
TC
Ma
Zhicheng
Z
Fan
Guoping
G
D000818:Animals; D015152:Blotting, Northern; D001921:Brain / Q000502:physiology; D018929:Cell Culture Techniques; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D019175:DNA Methylation; D053595:Embryonic Stem Cells / Q000166:cytology / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D017353:Gene Deletion; D015683:Gene Products, gag / Q000235:genetics; D017403:In Situ Hybridization; D051034:Inhibitor of Apoptosis Proteins / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009447:Neuroblastoma / Q000235:genetics / Q000503:physiopathology; D039904:Pluripotent Stem Cells / Q000166:cytology / Q000502:physiology; D012097:Repressor Proteins / Q000172:deficiency / Q000235:genetics; D018626:Retroelements / Q000502:physiology*
C485852:Dmap1 protein, mouse; D015683:Gene Products, gag; D051034:Inhibitor of Apoptosis Proteins; D012097:Repressor Proteins; D018626:Retroelements; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619381:Dnmt1 protein, mouse
Mol Cell Biol. 1996 Aug;16(8):4495-503
8754850
Nat Rev Genet. 2002 Sep;3(9):662-73
12209141
Proc Natl Acad Sci U S A. 1994 Feb 15;91(4):1337-41
8108413
Proc Natl Acad Sci U S A. 2008 Mar 25;105(12):4709-14
18339804
Hum Mol Genet. 2009 Aug 1;18(15):2875-88
19433415
Pediatr Res. 2007 May;61(5 Pt 2):58R-63R
17413844
Nature. 2010 Jan 14;463(7278):237-40
20075919
Nat Genet. 2001 Jan;27(1):31-9
11137995
Hum Mol Genet. 2000 Oct;9(16):2395-402
11005794
J Neurosci. 2001 Feb 1;21(3):788-97
11157065
Development. 1996 Oct;122(10):3195-205
8898232
Reprod Biol Endocrinol. 2006 Nov 08;4:55
17090336
Nature. 2007 Jul 12;448(7150):191-5
17597762
Gene. 2004 Aug 4;337:91-103
15276205
Genesis. 2003 Feb;35(2):88-93
12533790
Dev Biol. 1991 Feb;143(2):271-81
1899404
Nat Genet. 2004 May;36(5):534-9
15107856
J Virol. 1987 Oct;61(10):3020-9
3041022
J Virol. 1980 Mar;33(3):1211-4
7365876
Trends Biochem Sci. 2006 Feb;31(2):89-97
16403636
Nature. 2007 Jul 12;448(7150):196-9
17597760
Genomics. 2007 Jun;89(6):687-96
17418524
Nat Genet. 2001 Apr;27(4):361-5
11279513
Nature. 2010 Apr 8;464(7290):927-31
20164836
Nat Rev Genet. 2000 Oct;1(1):11-9
11262868
Mol Cell Biol. 2004 Feb;24(4):1640-8
14749379
Mol Cell Biol. 2002 Apr;22(7):2124-35
11884600
Cell. 1991 Jan 11;64(1):159-70
1846087
Cell. 2007 Feb 23;128(4):735-45
17320510
Nat Genet. 2003 Mar;33 Suppl:245-54
12610534
Nat Genet. 1998 Oct;20(2):116-7
9771701
Mol Carcinog. 2003 Jun;37(2):110-9
12766910
Mol Cell Biol. 1985 Mar;5(3):474-83
2859519
Nat Genet. 1999 Jan;21(1):70-1
9916792
Development. 2005 Aug;132(15):3345-56
16014513
Nucleic Acids Res. 2005 Oct 13;33(18):5868-77
16224102
J Virol. 1999 Jun;73(6):5166-71
10233982
Genomics. 2003 Aug;82(2):230-7
12837272
Methods. 2001 Dec;25(4):402-8
11846609
Genes Dev. 2005 Feb 15;19(4):489-501
15713842
Annu Rev Biochem. 2005;74:481-514
15952895
Cancer Res. 1968 Oct;28(10):2137-48
5696942
Cell. 2006 Dec 29;127(7):1375-88
17190601
Intervirology. 1979;11(6):321-5
227808
Proc Natl Acad Sci U S A. 2005 Aug 23;102(34):12135-40
16099834