Blocked transcription through KvDMR1 results in absence of methylation and gene silencing resembling Beckwith-Wiedemann syndrome

Abstract

The maternally methylated KvDMR1 ICR regulates imprinted expression of a cluster of maternally expressed genes on human chromosome 11p15.5. Disruption of imprinting leads to BeckwithWiedemann syndrome (BWS), an overgrowth and cancer predisposition condition. In the majority of individuals with BWS, maternal-specific methylation at KvDMR1 is absent and genes under its control are repressed. We analyzed a mouse model carrying a poly(A) truncation cassette inserted to prevent RNA transcripts from elongation through KvDMR1. Maternal inheritance of this mutation resulted in absence of DNA methylation at KvDMR1, which led to biallelic expression of Kcnq1ot1 and suppression of maternally expressed genes. This study provides further evidence that transcription is required for establishment of methylation at maternal gametic DMRs. More importantly, this mouse model recapitulates the molecular phenotypic characteristics of the most common form of BWS, including loss of methylation at KvDMR1 and biallelic repression of Cdkn1c, suggesting that deficiency of maternal transcription through KvDMR1 may be an underlying cause of some BWS cases.

Transcription-dependent DNA methylation at the imprintedZrsr1-DMR

“…The results of this study indicate that transcription through the Zrsr1-DMR is essential for the establishment of methylation at the DMR in the growing oocyte, as reported for four other imprinted loci (Chotalia et al, 2009, Singh et al, 2017, Veselovska et al, 2015. Our results also indicate that transcription-dependent methylation in the Zrsr1-DMR does not occur after fertilization, which suggests that the mechanism of de novo methylation of the Zrsr1-DMR is oocyte-specific.…”

“…oogenesis. The results indicate that transcription through the Zrsr1-DMR is essential for the establishment of methylation at the DMR in the growing oocyte, as reported for four other imprinted loci (Chotalia et al, 2009, Singh et al, 2017, Veselovska et al, 2015.…”

“…This was based on the findings that most maternal gDMRs are located in actively transcribed regions (Chotalia, Smallwood et al, 2009), that transcription is a prerequisite for the establishment of methylation at four maternal gDMRs (Chotalia et al, 2009, Singh, Sribenja et al, 2017, Smith, Futtner et al, 2011, Veselovska et al, 2015, and regarding the characteristics of the methylome and transcriptome in growing oocytes (Smallwood, Tomizawa et al, 2011, Veselovska et al, 2015. Analyses of the methylome revealed that most methylation in the oocyte genome occurs within actively transcribed regions, and that maternal gDMRs are not specifically targeted for methylation, but are instead methylated along with other parts of the transcribed regions where the gDMRs reside.…”

“…Methylation failed at the gDMRs in the Gnas locus and the KvDMR in the Kcnq1 locus when a poly(A) signal-truncation cassette was inserted into these loci to prevent transcription from elongation through the gDMRs (Chotalia et al, 2009, Singh et al, 2017. Failure of methylation was also reported at PWS-IC and the Zac1-DMR when the promoter regions from which transcription originated and then proceeded through the maternal gDMRs were deleted (Smith et al, 2011, Veselovska et al, 2015.…”

Changes in DNA methylation and imprinting disorders in E9.5 mouse fetuses and placentas derived from vitrified eight‐cell embryos

“…The establishment and maintenance of imprinting depend mostly on DNA methylation in these regions of genes, specifically in CpG islands (CGIs: regions with a high frequency of CpG sites). The maternally methylated KvDMR1 ICR includes the promoter of the IncRNA KCNQIOT1 and thereby regulates the expression of KCNQIOT1 and a cluster of maternally expressed genes (Singh et al, 2017). Absence of methylation at KvDMR1 promotes the expression of KCNQIOT1.…”