An Imprinted Antisense RNA, LIT1 (2)

Toshiro Hayashida
Department of Molecular and Cell Genetics; Tottori University

LIT1 (Long QT Intronic Transcript 1) was identified by screening for differentially expressed transcripts in the 11p15 region using monochromosomal hybrids with a paternal or maternal human chromosome 11. This gene without the open reading frame is expressed from paternal chromosome as the antisense transcript within the KvLQT1 locus. The CpG island located between exons 10 and 11 of KvLQT1 is specifically methylated on the silent maternal allele from which KvLQT1 is expressed. Furthermore, the targeted replacement of this CpG island with the puromycin resistant gene abolished the imprinted expression of KvLQT1 and other imprinted genes surrounded KvLQT1 locus. These results suggest that this CpG island is not only a possible promoter region but also an important region to regulate the expressions of genes in the imprinted domain including KvLQT1. To clarify the role of this CpG island, the luciferase assay was performed. The result showed that a part of this CpG island includes a promoter activity but not an enhancer activity. Now, we are trying to determine the transcription start site of LIT1 by primer extension method and Rnase protection assay. In the future, we wish to isolate the factor that regulates the expression of LIT1 and to clarify the mechanism to regulate the expression of imprinted genes in this domain.