Role of promoter strength in gene regulation in Kcnq1 imprinted domain

Sammanfattning: Genomic imprinting is a genetic phenomenon by which some of the genes go through several processes that restrict them from biallelic expression. To date, many investigations have been focused on mechanism of genomic imprinting in gene clusters. Though, there have been several attempts to uncover the mechanisms behind this complex phenomenon, but it is not fully yet understood. Kcnq1 is a genomic imprinting domain in mammalian genomes that is located on chromosome 7 in mouse and on chromosome 11p15.5 in human; consists of 8-10 paternally imprinted genes and a maternally imprinted non-coding gene known as Kcnq1ot1 that encodes for a long non-coding RNA. Additionally, a number of non-imprinted genes are also localized between these genes in this locus. These imprinted genes are classified into two distinct groups including placenta specific genes, which are expressed only from embryonic tissue and ubiquitously imprinted genes, which expression is repressed in both placenta and embryo’s tissues. A growing body of evidence indicates several roles for long non-coding RNA Kcnq1ot1 in imprinting of these genes in a tissue and cell type specific manner. It has been shown that this long non-coding RNA regulates the imprinting via DNA and chromatin modification at the Kcnq1 domain. This thesis aimed to investigate the effect of promoter strength on imprinting. The Promoter strength differences among these genes could be one of the possible factors involving differential patterns of imprinting within Kcnq1 locus. The promoter activities of five genes including two ubiquitously (Kcnq1 and Slc22a18), two placenta specific (Ascl2 and Tssc4) and a non-imprinted genes (Nap1l4 were assayed. We showed that the non-imprinted gene and placenta specific imprinted genes have higher promoter activities than ubiquitously imprinted genes. Our data indicate that degree of promoter strength is involved in imprinting of these genes in the locus and those genes with stronger promoter can escape silencing. However, further investigations are needed to be done to define the role for promoter strength in tissue-specific imprinting.