gamma 2-COP, a novel imprinted gene on chromosome 7q32, defines a new imprinting cluster in the human genome

We describe a novel imprinted gene, gamma 2-COP (nonclathrin coat protein), identified in a search for expressed sequences in human chromosome 7q32 wh ere the paternally expressed MEST gene is located. gamma 2-COP contains 24 exons and spans >50 kb of genomic DNA, Like MEST, gamma 2-COP is ubiquitous ly transcribed in fetal and adult tissues, In fetal tissues, including skel etal muscle, skin, kidney, adrenal, placenta, intestine, lung, chorionic pl ate and amnion, gamma 2-COP is imprinted and expressed from the paternal al lele, In contrast to the monoallelic expression observed in these fetal tis sues, biallelic expression was evident in fetal brain and liver and in adul t peripheral blood, Biallelic expression in blood is supported by the demon stration of gamma 2-COP transcripts in lymphoblastoid cell lines with mater nal uniparental disomy 7, Absence of paternal gamma 2-COP transcripts durin g embryonic development may contribute to Silver-Russell syndrome, However, on mutation scanning the only gamma 2-COP mutation detected was maternally derived. Amino acid comparison of gamma 2-COP protein revealed close relat ion to gamma-COP, a subunit of the coatomer complex COPI, suggesting a role of gamma 2-COP in cellular vesicle traffic. The existence of distinct coat omer complexes could be the basis for the functional heterogeneity of COPI vesicles in retrograde and anterograde transport and/or in cargo selection. Together, gamma 2-COP and MEST constitute a novel imprinting cluster in th e human genome that may contain other, as yet unknown, imprinted genes.