RESUMO
The imprinted gene cluster at the telomeric end of mouse chromosome 7 contains a differentially methylated CpG island, KvDMR, that is required for the imprinting of multiple genes, including the genes encoding the maternally expressed placental-specific transcription factor ASCL2, the cyclin-dependent kinase CDKN1C, and the potassium channel KCNQ1. The KvDMR, which maps within intron 10 of Kcnq1, contains the promoter for a paternally expressed, noncoding, antisense transcript, Kcnq1ot1. A 244-base-pair deletion of the promoter on the paternal allele leads to the derepression of all silent genes tested. To distinguish between the loss of silencing as the consequence of the absence of transcription or the transcript itself, we prematurely truncated the Kcnq1ot1 transcript by inserting a transcriptional stop signal downstream of the promoter. We show that the lack of a full-length Kcnq1ot1 transcript on the paternal chromosome leads to the expression of genes that are normally paternally repressed. Finally, we demonstrate that five highly conserved repeats residing at the 5' end of the Kcnq1ot1 transcript are not required for imprinting at this locus.
Assuntos
Ilhas de CpG , Metilação de DNA , Impressão Genômica/genética , RNA Antissenso/genética , RNA Mensageiro Estocado/genética , RNA não Traduzido/genética , Regiões Terminadoras Genéticas , Animais , Inibidor de Quinase Dependente de Ciclina p57/genética , Metiltransferases/genética , Camundongos , Regiões Promotoras Genéticas/genética , RNA Mensageiro Estocado/metabolismo , Deleção de Sequência , Transcrição GênicaRESUMO
The imprinted gene cluster on mouse distal chromosome 7 contains a differentially methylated CpG island that maps within the Kcnq1 gene that has been shown to be required for the imprinting of multiple genes. To evaluate models for how this imprinting control region (ICR) regulates imprinting, we have characterized it structurally and functionally. We show that the region contains a promoter for a paternally expressed anti-sense transcript, Kcnq1ot1, and we define the extent of the minimal promoter. We describe three paternal-specific nuclease hypersensitive sites immediately upstream from the start site and show that they are required for full promoter activity. The expression of Kcnq1ot1 during pre- and postnatal development is compared to that of other imprinted genes in its vicinity, Cdnkn1c and Kcnq1. The lack of coordination in their expression tends to rule out an enhancer competition model for the action of the ICR in imprinting control. Using a stable transfection assay we show that the region contains a position-independent and orientation-independent silencer. We propose, on the basis of these findings, that the Kcnq1 ICR functions as a silencer on the paternal chromosome to effect the repression of neighboring genes.
