Final Report Summary - KCNK9 IMPRINTING (The role of Kcnk9 imprinting in development and disease)
Genomic imprinting is a form of epigenetic gene regulation in mammals in which genes are marked differently in male and female gametes, resulting in complete silencing of expression of one gene copy (allele) in a strict parent-of-origin manner. Although it affects a small subset of our genes, imprinting has profound implications for our development and health. Because imprinted genes are expressed only from one allele, they are particularly vulnerable to mutation or other disruption: disease phenotypes can arise because of inactivation of the single active allele or because of loss of normal imprinted silencing and ensuing over-expression. This suggests that the active gene dosage of imprinted genes is particularly important: altered environmental/nutritional conditions are thought to cause sustained imbalance in imprinted gene expression and contribute to the risk of chronic disease; in addition, there is evidence that the incidence of imprinted gene syndromes is elevated by assisted reproduction technologies, possibly because of altered epigenetic marking during embryo manipulation, although these conditions are very rare. For these reasons, it is important to understand the function of imprinted genes and how their imprinting is established and controlled.
In this project, I aimed to characterise the imprinted gene Kcnk9 in detail. The Kcnk9 gene is imprinted such that expression of the paternal allele is silenced. Kcnk9 encodes the two-pore domain potassium channel protein TASK3. Genetic analysis implicates altered Kcnk9 expression in some tumours and mutations of Kcnk9 have been linked to a form of epilepsy in rats and mental retardation in human. In addition, I sought to understand how imprinting of Kcnk9 was regulated.
Some of the original objectives of the project were superseded because another research group generated a knock-out of Kcnk9 and investigated its impact on brain function. Although the work demonstrated a role of TASK3 in sleep behaviour and anaesthetic sensitivity, the full impact of Kcnk9 gene imprinting remains to be established, in particular, why it is imprinted and what impact loss of imprinted over-expression could have. The work I undertook on the epigenetic regulation of Kcnk9, and on establishment of imprinting in general, is important for designing future strategies to abrogate imprinting of this gene and to ascertain the impact of loss-of-imprinted over-expression.
My project succeeded in further characterising the dynamics of expression and the imprinting of the Kcnk9 gene, identifying previously unrecognised sites of expression (glycogen cells of the placenta), which might contribute to the growth phenotype of mice deficient in Kcnk9. I obtained an initial characterisation of the epigenetic properties of Kcnk9, which revealed that imprinted expression is more likely attributed to allelic histone modifications than to differential DNA methylation directly. Imprinting mediated by histone modifications may explain the incomplete monoallelic expression of Kcnk9 and suggest that imprinted expression of this gene is not hard-wired. In an extension of my original objectives towards elucidating fundamental mechanisms of gametic imprinting establishment, I established genome-wide histone modification assays in mouse oocytes. This last accomplishment, which represents the first description of genome-wide and gene-specific histone modification analysis in oocytes, is likely to be the most far-reaching outcome of my project. It demonstrates the feasibility of epigenomic profiling of maturing oocytes, which will be very important in studies of reproductive biology and fertility. Histone modification profiling of low cell numbers could also become a very important method for epigenomic analysis of other key cell-types that are only available in small numbers, e.g. defined neuronal populations involved in metabolic control, and how epigenomic profiles differ in health and disease.
In this project, I aimed to characterise the imprinted gene Kcnk9 in detail. The Kcnk9 gene is imprinted such that expression of the paternal allele is silenced. Kcnk9 encodes the two-pore domain potassium channel protein TASK3. Genetic analysis implicates altered Kcnk9 expression in some tumours and mutations of Kcnk9 have been linked to a form of epilepsy in rats and mental retardation in human. In addition, I sought to understand how imprinting of Kcnk9 was regulated.
Some of the original objectives of the project were superseded because another research group generated a knock-out of Kcnk9 and investigated its impact on brain function. Although the work demonstrated a role of TASK3 in sleep behaviour and anaesthetic sensitivity, the full impact of Kcnk9 gene imprinting remains to be established, in particular, why it is imprinted and what impact loss of imprinted over-expression could have. The work I undertook on the epigenetic regulation of Kcnk9, and on establishment of imprinting in general, is important for designing future strategies to abrogate imprinting of this gene and to ascertain the impact of loss-of-imprinted over-expression.
My project succeeded in further characterising the dynamics of expression and the imprinting of the Kcnk9 gene, identifying previously unrecognised sites of expression (glycogen cells of the placenta), which might contribute to the growth phenotype of mice deficient in Kcnk9. I obtained an initial characterisation of the epigenetic properties of Kcnk9, which revealed that imprinted expression is more likely attributed to allelic histone modifications than to differential DNA methylation directly. Imprinting mediated by histone modifications may explain the incomplete monoallelic expression of Kcnk9 and suggest that imprinted expression of this gene is not hard-wired. In an extension of my original objectives towards elucidating fundamental mechanisms of gametic imprinting establishment, I established genome-wide histone modification assays in mouse oocytes. This last accomplishment, which represents the first description of genome-wide and gene-specific histone modification analysis in oocytes, is likely to be the most far-reaching outcome of my project. It demonstrates the feasibility of epigenomic profiling of maturing oocytes, which will be very important in studies of reproductive biology and fertility. Histone modification profiling of low cell numbers could also become a very important method for epigenomic analysis of other key cell-types that are only available in small numbers, e.g. defined neuronal populations involved in metabolic control, and how epigenomic profiles differ in health and disease.