The gene MEST (or PEG1) on chromosome 7q32 is paternally expressed in human fetal tissues as a result of genomic imprinting. Since some imprinted genes are clustered, we speculated that an imprinted gene cluster might exist at 7q32. We have sought to isolate additional human genes close to MEST and to characterize their allelic expression patterns. Here, we report the biallelic expression of the gene, gamma2-COP (coatomer protein complex, subunit gamma 2, HUGO-approved symbol COPG2), and monoallelic expression of the transcript, CIT1, which is located in intron 20 of gamma2-COP. Recently, gamma2-COP was reported to be a novel imprinted gene that overlaps the 3'-untranslated region (3'-UTR) of MEST in a tail-to-tail orientation. However, our results revealed biallelic expression in all fetal tissues and adult blood lymphocytes. On the other hand, CIT1 was an antisense transcript of gamma2-COP intron 20 and was expressed from the paternal allele in all fetal tissues examined. Adult blood lymphocytes showed biallelic expression. We identified additional MEST 3'-UTR sequence, which overlaps the last four exons and introns of gamma2-COP. This additional MEST 3'-UTR may complicate analysis of gamma2-COP imprinting. Our data indicate that the region containing MEST at 7q32 is an imprinted domain, but gamma2-COP adjacent to MEST escapes genomic imprinting.
Copyright 2000 Academic Press.