Transcription Is Required to Establish Maternal Imprinting at the Prader-Willi Syndrome and Angelman Syndrome Locus
Figure 8
A working model for the establishment of the maternal imprint at the PWS-IC.
Schematic diagrams of the locus around Snrpn at various stages of development. The U exons are indicated by red boxes and the PWS-IC is depicted as an orange oval overlying Snrpn exon 1. Imprints are erased in fetal germ cells and the Snrpn upstream exons are not expressed. In the neonatal period, transcription is initiated from the Snrpn upstream exons prior to the appearance of the DNA methylation imprint in growing oocytes. These transcripts proceed through the PWS-IC, triggering repressive epigenetic modification of this element, indicated by black lollipops. The PWS-IC on the future maternal allele is thereby inactivated, rendering the paternally expressed genes silent.