complete biallelic insulation at the h19igf2 imprinting control region position results in fetal growth retardation and perinatal lethality完成biallelic绝缘在h19igf2印记控制区域位置导致胎儿生长迟缓和围产儿死亡率.pdf

Complete Biallelic Insulation at the H19/Igf2 Imprinting Control Region Position Results in Fetal Growth Retardation and Perinatal Lethality 1 1 2 ´ 1 Dong-Hoon Lee , Purnima Singh , Walter M. K. Tsark , Piroska E. Szabo * 1 Department of Molecular and Cellular Biology, City of Hope National Medical Center, Duarte, California, United States of America, 2 Transgenic Mouse Facility, City of Hope National Medical Center, Duarte, California, United States of America Abstract Background: The H19/Igf2 imprinting control region (ICR) functions as an insulator exclusively in the unmethylated maternal allele, where enhancer-blocking by CTCF protein prevents the interaction between the Igf2 promoter and the distant enhancers. DNA methylation inhibits CTCF binding in the paternal ICR allele. Two copies of the chicken b-globin insulator (ChbGI)2 are capable of substituting for the enhancer blocking function of the ICR. Insulation, however, now also occurs upon paternal inheritance, because unlike the H19 ICR, the (ChbGI)2 does not become methylated in fetal male germ cells. The (ChbGI)2 is a composite insulator, exhibiting enhancer blocking by CTCF and chromatin barrier functions by USF1 and VEZF1. We asked the question whether these barrier proteins protected the (ChbGI)2 sequences from methylation in the male germ line. Methodology/Principal Findings: We genetically dissected the ChbGI in the mouse by deleting the binding sites USF1 and VEZF1. The methylation of the mutant versus normal (Ch bGI)2 significantly increased from 11% to 32% in perinatal male germ cells, suggesting that the barrier proteins did have a role in protecting the (ChbGI)2 from methylation in the male germ line. Contrary to the H19 ICR, however, the mutant (mChbGI)2 lacked the potential to attain full de novo me