PEG1 EXPRESSION IN MATERNAL UNIPARENTAL DISOMY-7

PEG1/MEST is an imprinted gene mapping to human chromosome 7q32. In hu man embryos and placenta, PEG1 is expressed from the paternally derive d allele only, while maternal and paternal alleles are transcribed in adult blood lymphocytes, We aimed at investigating the origin of the m aternal PEG1 transcript by studying PEG1 mRNA in two maternal uniparen tal disomy 7 patients suffering from severe pre-and post-natal growth restriction, PEG1 expression has been characterised by RT-PCR from leu kocytes RNA using several primer pairs. The distal coding region in PE G1 mRNA could be repeatedly amplified from mUPD patients blood cells, but no amplification could be performed from the first exon, suggestin g that the first exon was not a component of the maternal PEG1 transcr ipt. As six independent database sequences showed that exon 2 was exac tly joined to a novel sequence unrelated to exon 1 but identical in th e common region of the six sequences, we hypothesized that our observa tion of PEG1 expression in the two maternal uniparental disomy 7 patie nts could be explained by transcription of the maternal allele from an alternate maternal upstream promoter.