Studies carried out in cultured cells have implicated modifiers of epigenetic 
reprogramming in the regulation of telomere length, reporting elongation in 
cells that were null 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.