Monoallelic methylation of the promoter of the somatic (long) isoform of DNMT1 (DNA
(cytosine-5-)-methyltransferase 1) has been repeatedly
detected in human placentas (Yuen RK et al,
2011; Novakovic B et al, 2010; Das R et al, 2013).
Das R et al (2013) used bisulphite
sequencing to confirm allele-specific methylation (mostly) in three placentas and in one case the
methylated allele was found to be maternal (Figure 3). Oocytes show methylation and sperm do not
show methylation at this promoter (Okae H et
al, 2014). Using triploid and molar placentas Yuen RK et al (2011) showed results
consistent with maternal methylation. Previously Novakovic B et al (2010) detected examples of
both methylated and unmethylated maternal and paternal alleles in several heterozygous samples and
concluded that DNMT1 was not imprinted, but in a subsequent publication refer to DNMT1 as being
imprinted (Novakovic B & Saffery R, 2013).
Das R et al (2013) reported monoallelic
expression in all 8 informative placentas and paternal expression confirmed in all 4 informative
cases. Yuen RK et al (2011) showed
monoallelic paternal in one informative case.