Three duplicons form a novel chimeric transcription unit in the pericentromeric region of chromosome 22q11

Pericentromeric regions of human chromosomes are preferential sites for the integration of duplicated DNA, or "duplicons", which often contain gene fragments. Although pericentromeric regions appear to be genomic junkyards, they could also be the birthplace of new genes with novel functions. We have characterized a chimeric transcription unit (cat eye syndrome critical region gene 7, CECR7) formed from three duplicons in the pericentromeric region of chromosome 22q. CECR7 exons show similarity to sequences on chromosomes 2, 5, 7, 10, 11, 12, 13, 14, 15, 16, 18, 19, 21, and elsewhere on 22. Based on polymerase chain reaction (PCR) analysis of CECR7 duplicon boundaries in various primate species, and the sequence divergence between the human duplicons and their putative ancestral human loci, CECR7 was probably formed before the separation of macaque and is therefore older than most previously reported pericentromeric duplicons. Expression of CECR7 was detected by RT-PCR in humans and gorilla fibroblasts, but not orangutan, suggesting that expression did not result immediately from the formation of this novel transcription unit, or that expression was silenced in orangutan following its formation.