Fig. 1

Biallelic expression of placenta-specific imprinted genes in specimens of biparental placental mesenchymal dysplasia (PMD). Using single-nucleotide polymorphisms (SNPs), we screened the genotypes of imprinted genes via polymerase chain reaction with genomic DNAs (gPCR) and examined their allelic expression via reverse-transcription PCR (RT-PCR). Two biparental-PMD specimens (PMD-002 and PMD-020) showed biallelic expression. Specimen PMD-024 was a biparental-PMD specimen in which the cystic region had shrunk during pregnancy; this specimen showed biallelic expression of one gene and monoallelic expression of two genes. Specimen PMD-028 was a biparental-normal specimen in which the cystic region had also shrunk during pregnancy; in this specimen, one gene exhibited biallelic expression, two exhibited monoallelic expression, and one was indeterminate (*) because of very low expression of the maternal allele in some of the normal placental samples we used as controls (Additional file 3: Fig. S5). Arrows indicate the positions of the SNPs. bi: biallelic expression; mono: monoallelic expression. Differences in DNA methylation levels between the normal specimens and the PMD specimens are indicated in parentheses. Since the analyses were performed on additional specimens excised from placental tissues, the methylation levels differ from those shown in Table 2, which refer to the original specimens