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Reduced dosage of the modifiers of epigenetic reprogramming Dnmt1, Dnmt3L, SmcHD1 and Foxo3a has no detectable effect on mouse telomere length in vivo.

Roberts AR, Blewitt ME, Youngson NA, Whitelaw E, Chong S - Chromosoma (2011)

Bottom Line: Studies carried out in cultured cells have implicated modifiers of epigenetic reprogramming in the regulation of telomere length, reporting elongation in cells that were for DNA methyltransferase DNA methyltransferase 1 (Dnmt1), both de novo DNA methyltransferases, Dnmt3a and Dnmt3b or various histone methyltransferases.Terminal restriction fragment analysis was used to compare telomere length in homozygous mutants, heterozygous mutants and wild-type littermates.Contrary to expectation, we did not detect overall lengthening in the mutants, raising questions about the role of epigenetic processes in telomere length in vivo.

View Article: PubMed Central - PubMed

Affiliation: Epigenetics Laboratory, Queensland Institute of Medical Research, Herston, QLD, Australia.

ABSTRACT
Studies carried out in cultured cells have implicated modifiers of epigenetic reprogramming in the regulation of telomere length, reporting elongation in cells that were for DNA methyltransferase DNA methyltransferase 1 (Dnmt1), both de novo DNA methyltransferases, Dnmt3a and Dnmt3b or various histone methyltransferases. To investigate this further, we assayed telomere length in whole embryos or adult tissue from mice carrying mutations in four different modifiers of epigenetic reprogramming: Dnmt1, DNA methyltransferase 3-like, structural maintenance of chromosomes hinge domain containing 1, and forkhead box O3a. Terminal restriction fragment analysis was used to compare telomere length in homozygous mutants, heterozygous mutants and wild-type littermates. Contrary to expectation, we did not detect overall lengthening in the mutants, raising questions about the role of epigenetic processes in telomere length in vivo.

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Telomere length in adult spleen cells deficient for Dnmt3L. TRF results are shown for Dnmt3L+/+, Dnmt3L+/− and Dnmt3L−/− spleen cells from male and female mice, 4 to 5 months of age. Individual variation in telomere length is evident from the high molecular weight bands that vary in size between each mouse
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Fig2: Telomere length in adult spleen cells deficient for Dnmt3L. TRF results are shown for Dnmt3L+/+, Dnmt3L+/− and Dnmt3L−/− spleen cells from male and female mice, 4 to 5 months of age. Individual variation in telomere length is evident from the high molecular weight bands that vary in size between each mouse

Mentions: Dnmt3L is a homolog of Dnmt3a and Dnmt3b that lacks catalytic activity; is highly expressed in the early embryo, ES cells and gametes and is known to have a critical role in imprinting. It is thought to function as a co-regulator of both Dnmt3a and Dnmt3b (Hata et al. 2002). The combined loss of Dnmt3a and Dnmt3b has been reported to lead to telomere elongation in cultured cells (Gonzalo et al. 2006), and we tested whether Dnmt3L deficiency affects overall telomere length in vivo. Complete loss of Dnmt3L is embryonic viable. However, the progeny of homozygous mutant females fail to develop beyond 9.5 days p.c., and homozygous mutant males are sterile (Bourc’his et al. 2001; Hata et al. 2002; Bourc’his and Bestor 2004). An independently produced knockout allele of Dnmt3L that displays identical phenotypes to those described above was used in our study (Webster et al. 2005). Dnmt3L−/− male germ cells (from both knockout lines) have been shown to be hypomethylated at repeats leading to widespread transcriptional reactivation and meiotic failure (Webster et al. 2005; Bourc'his and Bestor 2004). TRF analysis of spleen from Dnmt3L−/− mice revealed no shift in overall telomere length in mutants compared to wild types (Fig. 2). We used adult spleen, as opposed to embryos, because Dnmt3L−/− mice from a heterozygous intercross survive to adulthood, and TRF length in spleen tissue represents that of the whole animal (see below). Heterogeneous high molecular weight TRFs were detected in Dnmt3L−/− mice, but these were also present in samples from wild-type littermates (Fig. 2). Such heterogeneous bands were first reported more than 20 years ago (Kipling and Cooke 1990; Starling et al. 1990), but it is worth highlighting that they represent a forgotten genetic heterogeneity between individuals within an inbred (often termed isogenic) colony. They are not the result of incomplete digestion, as the same TRF patterns were reproduced in independent experiments using samples from the same individuals (Online Resource 1). Family studies support the idea that these bands are not always directly inherited across generations (Fig. 3a) and that their length is established very early in development (Graakjaer et al. 2004), as the same pattern is seen in tissues representative of all three germ layers and in mature gametes (Fig. 3b; Kipling and Cooke 1990). While these findings are not novel, they do rule out the need to carry out the TRF analysis in a range of different tissue types from inbred mice.Fig. 2


Reduced dosage of the modifiers of epigenetic reprogramming Dnmt1, Dnmt3L, SmcHD1 and Foxo3a has no detectable effect on mouse telomere length in vivo.

Roberts AR, Blewitt ME, Youngson NA, Whitelaw E, Chong S - Chromosoma (2011)

Telomere length in adult spleen cells deficient for Dnmt3L. TRF results are shown for Dnmt3L+/+, Dnmt3L+/− and Dnmt3L−/− spleen cells from male and female mice, 4 to 5 months of age. Individual variation in telomere length is evident from the high molecular weight bands that vary in size between each mouse
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3140923&req=5

Fig2: Telomere length in adult spleen cells deficient for Dnmt3L. TRF results are shown for Dnmt3L+/+, Dnmt3L+/− and Dnmt3L−/− spleen cells from male and female mice, 4 to 5 months of age. Individual variation in telomere length is evident from the high molecular weight bands that vary in size between each mouse
Mentions: Dnmt3L is a homolog of Dnmt3a and Dnmt3b that lacks catalytic activity; is highly expressed in the early embryo, ES cells and gametes and is known to have a critical role in imprinting. It is thought to function as a co-regulator of both Dnmt3a and Dnmt3b (Hata et al. 2002). The combined loss of Dnmt3a and Dnmt3b has been reported to lead to telomere elongation in cultured cells (Gonzalo et al. 2006), and we tested whether Dnmt3L deficiency affects overall telomere length in vivo. Complete loss of Dnmt3L is embryonic viable. However, the progeny of homozygous mutant females fail to develop beyond 9.5 days p.c., and homozygous mutant males are sterile (Bourc’his et al. 2001; Hata et al. 2002; Bourc’his and Bestor 2004). An independently produced knockout allele of Dnmt3L that displays identical phenotypes to those described above was used in our study (Webster et al. 2005). Dnmt3L−/− male germ cells (from both knockout lines) have been shown to be hypomethylated at repeats leading to widespread transcriptional reactivation and meiotic failure (Webster et al. 2005; Bourc'his and Bestor 2004). TRF analysis of spleen from Dnmt3L−/− mice revealed no shift in overall telomere length in mutants compared to wild types (Fig. 2). We used adult spleen, as opposed to embryos, because Dnmt3L−/− mice from a heterozygous intercross survive to adulthood, and TRF length in spleen tissue represents that of the whole animal (see below). Heterogeneous high molecular weight TRFs were detected in Dnmt3L−/− mice, but these were also present in samples from wild-type littermates (Fig. 2). Such heterogeneous bands were first reported more than 20 years ago (Kipling and Cooke 1990; Starling et al. 1990), but it is worth highlighting that they represent a forgotten genetic heterogeneity between individuals within an inbred (often termed isogenic) colony. They are not the result of incomplete digestion, as the same TRF patterns were reproduced in independent experiments using samples from the same individuals (Online Resource 1). Family studies support the idea that these bands are not always directly inherited across generations (Fig. 3a) and that their length is established very early in development (Graakjaer et al. 2004), as the same pattern is seen in tissues representative of all three germ layers and in mature gametes (Fig. 3b; Kipling and Cooke 1990). While these findings are not novel, they do rule out the need to carry out the TRF analysis in a range of different tissue types from inbred mice.Fig. 2

Bottom Line: Studies carried out in cultured cells have implicated modifiers of epigenetic reprogramming in the regulation of telomere length, reporting elongation in cells that were for DNA methyltransferase DNA methyltransferase 1 (Dnmt1), both de novo DNA methyltransferases, Dnmt3a and Dnmt3b or various histone methyltransferases.Terminal restriction fragment analysis was used to compare telomere length in homozygous mutants, heterozygous mutants and wild-type littermates.Contrary to expectation, we did not detect overall lengthening in the mutants, raising questions about the role of epigenetic processes in telomere length in vivo.

View Article: PubMed Central - PubMed

Affiliation: Epigenetics Laboratory, Queensland Institute of Medical Research, Herston, QLD, Australia.

ABSTRACT
Studies carried out in cultured cells have implicated modifiers of epigenetic reprogramming in the regulation of telomere length, reporting elongation in cells that were for DNA methyltransferase DNA methyltransferase 1 (Dnmt1), both de novo DNA methyltransferases, Dnmt3a and Dnmt3b or various histone methyltransferases. To investigate this further, we assayed telomere length in whole embryos or adult tissue from mice carrying mutations in four different modifiers of epigenetic reprogramming: Dnmt1, DNA methyltransferase 3-like, structural maintenance of chromosomes hinge domain containing 1, and forkhead box O3a. Terminal restriction fragment analysis was used to compare telomere length in homozygous mutants, heterozygous mutants and wild-type littermates. Contrary to expectation, we did not detect overall lengthening in the mutants, raising questions about the role of epigenetic processes in telomere length in vivo.

Show MeSH